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REFEREED PUBLICATIONS


(in press)
 
Prey consumption by cetaceans reveals the importance of energy-rich food webs in the Bay of Biscay.
Spitz, J., V. Ridoux, A. W. Trites, S. Laran and M. Authiera. (in press).
Progress in Oceanography
abstract
Ecosystem-based management requires a clear understanding of marine ecosystem functioning, particularly the transfer of energy (consumption) to higher trophic levels. However, robust estimates of consumption are generally hampered by a dearth of data for predators (diet and abundance), and by methodological weaknesses. We undertook a comprehensive assessment of energy requirements and prey consumption for the 10 most abundant cetacean species in the Bay of Biscay (northeastern Atlantic Ocean, France) by combining recent data on their abundances from aerial surveys, and diets from stomach content analyses. We also incorporated functional considerations to group prey and address interspecific differences in the cost of living of cetaceans that are independent of body size. Species considered included harbour porpoise, common dolphins, striped dolphins, bottlenose dolphins, long-finned pilot whales, Risso's dolphins, sperm whales, Cuvier's beaked whales, minke whales and fin w hales. We used Monte Carlo resampling methods to estimate annual and seasonal (winter and summer) consumption over the continental shelf and slope

keywords     food webs, consumption, cetaceans, continental shelf, toothed whales, baleen whales
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2018
 
Reference ranges and age-related and diving exercise effects on hematology and serum chemistry of female Steller sea lions (Eumetopias jubatus).
Gerlinsky, C. D., M. Haulena, A. W. Trites and D. A. S. Rosen. 2018.
Journal of Zoo and Wildlife Medicine 49(1):18-29.
abstract
Decreased health may have lowered the birth and survival rates of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands over the past 30 yr. Reference ranges for clinical hematology and serum chemistry parameters needed to assess the health of wild sea lion populations are limited. Here, blood parameters were serially measured in 12 captive female Steller sea lions ranging in age from 3 wk to 16 yr to establish baseline values and investigate age-related changes. Whether diving activity affects hematology parameters in animals swimming in the ocean compared with animals in a traditional aquarium setting was also examined. Almost all blood parameters measured exhibited significant changes with age. Many of the age-related changes reflected developmental life history changes, including a change in diet during weaning, an improvement of diving capacity, and the maturity of the immune system. Mean corpuscular hemoglobin and mean corpuscular volume were also higher in the ocean diving group compared with the aquarium group, likely reflecting responses to increased exercise regimes. These data provide ranges of hematology and serum chemistry values needed to evaluate and compare the health and nutritional status of captive and wild Steller sea lions.

keywords     Diving, Eumetopias jubatus, hematology, marine mammal, serum chemistry, Steller sea lion
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Telemetry tags increase the costs of swimming in northern fur seals, Callorhinus ursinus.
Rosen, D. A. S., C. D. Gerlinsky and A. W. Trites. 2018.
Marine Mammal Science 34 (2):385-402. doi:10.1111/mms.12460
abstract
Animal-borne instruments have become a standard tool for collecting important data from marine mammals. However, few studies have examined whether placement of these data loggers affects the behavior and energetics of individual animals, potentially leading to biasing data. We measured the effect of two types of relatively small data loggers (<1% of animals

keywords     northern fur seals, Callorhinus ursinus, telemetry, bioenergetics, biologging, diving, swimming, marine mammal
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2017
 
Lesser devil rays Mobula cf. hypostoma from Venezuela are almost twice their previously reported maximum size and may be a new sub-species.
Ehemann, N. R., L. V. Gonzalez-Gonzalez and A. W. Trites. 2017.
Journal of Fish Biology 90:1142-1148.
abstract
Three rays opportunistically obtained near Margarita Island, Venezuela, were identified as lesser devil rays Mobula cf. hypostoma, but their disc widths were between 207 and 230 cm, which is almost double the reported maximum disc width of 120 cm for this species. These morphometric data suggest that lesser devil rays are either larger than previously recognized or that these specimens belong to an unknown sub-species of Mobula in the Caribbean Sea. Better data are needed to describe the distribution, phenotypic variation and population structure of this poorly known species.
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Evidence of molting and the function of rock-nosing behavior in bowhead whales in the eastern Canadian Arctic.
Fortune, S. M. E., W. R. Koski, J. W. Higdon, A. W. Trites, M. F. Baumgartner and S. H. Ferguson. 2017.
PLoS ONE, pages: e0186156 Vol 12(1)
abstract
Bowhead whales (Balaena mysticetus) have a nearly circumpolar distribution, and occasionally occupy warmer shallow coastal areas during summertime that may facilitate molting. However, relatively little is known about the occurrence of molting and associated behaviors in bowhead whales. We opportunistically observed whales in Cumberland Sound, Nunavut, Canada with skin irregularities consistent with molting during August 2014, and collected a skin sample from a biopsied whale that revealed loose epidermis and sloughing. During August 2016, we flew a small unmanned aerial system (sUAS) over whales to take video and still images to: 1) determine unique individuals; 2) estimate the proportion of the body of unique individuals that exhibited sloughing skin; 3) determine the presence or absence of superficial lines representative of rock-rubbing behavior; and 4) measure body lengths to infer age-class. The still images revealed that all individuals (n = 81 whales) were sloughing skin, and that nearly 40% of them had mottled skin over more than two-thirds of their bodies. The video images captured bowhead whales rubbing on large rocks in shallow, coastal areas --likely to facilitate molting. Molting and rock rubbing appears to be pervasive during late summer for whales in the eastern Canadian Arctic.
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Accelerometers can measure total and activity-specific energy expenditure in free-ranging marine mammals only if linked to time-activity budgets.
Jeanniard du Dot, T., C. Guinet, J. P. Y. Arnould, J. R. Speakman and A. W. Trites. 2017.
Functional Ecology 31:377-386.
abstract
1-Energy expenditure is an important component of foraging ecology, but is extremely difficult to estimate in free-ranging animals and depends on how animals partition their time between different activities during foraging. Acceleration data has emerged as a new way to determine energy expenditure at a fine scale but needs to be tested and validated in wild animals. 2-This study investigated whether vectorial dynamic body acceleration (VeDBA) could accurately predict the energy expended by marine predators during a full foraging trip. We also aimed to determine whether the accuracy of predictions of energy expenditure derived from acceleration increased when partitioned by different types of at-sea activities (i.e., diving, transiting, resting and surface activities) vs calculated activity-specific metabolic rates. 3-To do so, we equipped 20 lactating northern (Callorhinus ursinus) and 20 Antarctic fur seals (Arctocephalus gazella) with GPS, time-depth recorders and tri-axial accelerometers, and obtained estimates of field metabolic rates using the doubly-labelled water (DLW) method. VeDBA was derived from tri-axial acceleration, and at-sea activities (diving, transiting, resting and surface activities) were determined using dive depth, tri-axial acceleration and traveling speed. 4-We found that VeDBA did not accurately predict the total energy expended by fur seals during their full foraging trips (R2 = 0.36). However, the accuracy of VeDBA as a predictor of total energy expenditure increased significantly when foraging trips were partitioned by activity and used activity-specific VeDBA paired with time activity budgets (R2 = 0.70). Activity-specific VeDBA also accurately predicted the energy expenditures of each activity independent of each other (R2 > 0.85). 5-Our study confirms that acceleration is a promising way to estimate energy expenditures of free-ranging marine mammals at a fine scale never attained before. However, it shows that it needs to be based on the time-activity budget that make up foraging trips rather than being derived as a single measure of VeDBA applied to entire foraging trips. Our activity-based method provides a cost-effective means to accurately calculate energy expenditures of fur seals using acceleration and time-activity budgets, a stepping stone for numerous other research fields.

keywords     Antarctic fur seal, Arctocephalus gazella, Callorhinus ursinus, diving, energy expenditure, foraging, metabolic rate, northern fur seal, time-activity budget
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Reproductive success is energetically linked to foraging efficiency in Antarctic fur seals.
Jeanniard-du-Dot, T., A.W. Trites, J.P. Arnould, and C. Guinet. 2017.
PLoS ONE. 12:e0174001
abstract
The efficiency with which individuals extract energy from their environment defines their survival and reproductive success, and thus their selective contribution to the population. Individuals that forage more efficiently (i.e., when energy gained exceeds energy expended) are likely to be more successful at raising viable offspring than individuals that forage less efficiently. Our goal was to test this prediction in large long-lived mammals under free-ranging conditions. To do so, we equipped 20 lactating Antarctic fur seals (Arctocephalus gazella) breeding on Kerguelen Island in the Southern Ocean with tags that recorded GPS locations, depth and tri-axial acceleration to determine at-sea behaviours and detailed time-activity budgets during their foraging trips. We also simultaneously measured energy spent at sea using the doubly-labeled water (DLW) method, and estimated the energy acquired while foraging from 1) type and energy content of prey species present in scat remains, and 2) numbers of prey capture attempts determined from head acceleration. Finally, we followed the growth of 36 pups from birth until weaning (of which 20 were the offspring of our 20 tracked mothers), and used the relative differences in body mass of pups at weaning as an index of first year survival and thus the reproductive success of their mothers. Our results show that females with greater foraging efficiencies produced relatively bigger pups at weaning. These mothers achieved greater foraging efficiency by extracting more energy per minute of diving rather than by reducing energy expenditure. This strategy also resulted in the females spending less time diving and less time overall at sea, which allowed them to deliver higher quality milk to their pups, or allowed their pups to suckle more frequently, or both. The linkage we demonstrate between reproductive success and the quality of individuals as foragers provides an individual-based quantitative framework to investigate how changes in the availability and accessibility of prey can affect fitness of animals.

keywords     foraging, energetics, pups, growth, biologging, doubly-labeled water, Antarctic fur seal, Arctocephalus gazella
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Activity-specific metabolic rates for diving, transiting and resting at sea can be estimated from time-activity budgets in free-ranging marine mammals.
Jeanniard-du-Dot, T., A.W. Trites, J.P.Y. Arnould, and C. Guinet. 2017.
Ecology and Evolution 2017:1-8.
abstract
Time and energy are the two most important currencies in animal bioenergetics. How much time animals spend engaged in different activities with specific energetic costs ultimately defines their likelihood of surviving and successfully reproducing. However, it is extremely difficult to determine the energetic costs of independent activities for free-ranging animals. In this study, we developed a new method to calculate activity-specific metabolic rates, and applied it to female fur seals. We attached biologgers (that recorded GPS locations, depth profiles, and triaxial acceleration) to 12 northern (Callorhinus ursinus) and 13 Antarctic fur seals (Arctocephalus gazella), and used a hierarchical decision tree algorithm to determine time allocation between diving, transiting, resting, and performing slow movements at the surface (grooming, etc.). We concomitantly measured the total energy expenditure using the doubly-labelled water method. We used a general least-square model to establish the relationship between time-activity budgets and the total energy spent by each individual during their foraging trip to predict activity-specific metabolic rates. Results show that both species allocated similar time to diving (~29%), transiting to and from their foraging grounds (~26-30%), and resting (~8-11%). However, Antarctic fur seals spent significantly more time grooming and moving slowly at the surface than northern fur seals (36% vs. 29%). Diving was the most expensive activity (~30 MJ/day if done non-stop for 24 hr), followed by transiting at the surface (~21 MJ/day). Interestingly, metabolic rates were similar between species while on land or while slowly moving at the surface (~13 MJ/day). Overall, the average field metabolic rate was ~20 MJ/day (for all activities combined). The method we developed to calculate activity-specific metabolic rates can be applied to terrestrial and marine species to determine the energetic costs of daily activities, as well as to predict the energetic consequences for animals forced to change their time allocations in response to environmental shifts.

keywords     Antarctic fur seal, Arctocephalus gazella, Callorhinus ursinus, diving, energy expenditure, foraging, metabolic rate, northern fur seal, time-activity budget
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Combining hard-part and DNA analyses in scats with biologging and stable isotopes can reveal different diet compositions and feeding strategies within a population.
Jeanniard-du-Dot, T., A. C. Thomas, Y. Cherel, A. W. Trites and C. Guinet. 2017.
Marine Ecology Progress Series 584:1-16.
abstract
Accurately estimating predators' diets at relevant spatial and temporal scales is key to understanding animals' energetics and fitness, particularly in populations whose decline might be related to their diet such as northern fur seals Callorhinus ursinus. Our goals were to improve the accuracy of diet estimates and extend understanding of feeding ecology by combining 2 scat-based methods of diet determination (hard-part identification and DNA-metabarcoding) with stable isotope measurements and individual behavioural data. We collected 98 scats on a northern fur seal breeding colony. We also tracked 20 females with biologgers, and took blood samples to determine δ13C and δ15N values as proxies for seal foraging habitat and diet. Results show that diet composition from hard-parts analysis corresponded well with DNA results, with DNA yielding a greater diversity of prey species at a finer taxonomic level. Overall, scat-based methods showed that seals mostly fed on neritic shelf-associated prey. Cluster analyses of combined hard-parts and DNA results however identified 2 diet groups, one mostly neritic and the other mostly pelagic. Stable isotopes and behavioural data revealed that 40% of seals fed in oceanic waters on pelagic prey. This is more than indicated by scat-based analyses, which are likely biased towards animals foraging closest to the colony and underestimate some dietary specializations within the population. Consequently, the combination of multiple methods for diet identification with at-sea tracking of individuals can help identify and quantify specialist groups within a population and provide a wider spatial and temporal ecological context for dietary analysis.
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Proxies of energy expenditure for marine mammals: an experimental test of the time trap.
Ladds, M. A., D. A. S. Rosen, D. J. Slip and R. G. Harcourt. 2017.
Scientific Reports 7:11815
abstract
Direct measures of energy expenditure are difficult to obtain in marine mammals, and accelerometry may be a useful proxy. Recently its utility has been questioned as some analyses derived their measure of activity level by calculating the sum of accelerometry-based values and then comparing this summation to summed (total) energy expenditure (the so-called 'time trap'). To test this hypothesis, we measured oxygen consumption of captive fur seals and sea lions wearing accelerometers during submerged swimming and calculated total and rate of energy expenditure. We compared these values with two potential proxies of energy expenditure derived from accelerometry data: flipper strokes and dynamic body acceleration (DBA). Total number of strokes, total DBA, and submergence time all predicted total oxygen consumption (sVO2 ml kg−1). However, both total DBA and total number of strokes were correlated with submergence time. Neither stroke rate nor mean DBA could predict the rate of oxygen consumption (sV.O2 ml min−1 kg−1). The relationship of total DBA and total strokes with total oxygen consumption is apparently a result of introducing a constant (time) into both sides of the relationship. This experimental evidence supports the conclusion that proxies derived from accelerometers cannot estimate the energy expenditure of marine mammals.

keywords     energy expenditure, accelerometers, Steller sea lions
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On the utility of accelerometers to predict stroke rate using captive fur seals and sea lions.
Ladds, M. A., D. A. S. Rosen, D. J. Slip and R. G. Harcourt. 2017.
Biology Open 6:1396-1400.
abstract
Energy expenditure of free-living fur seals and sea lions is difficult to measure directly, but may be indirectly derived from flipper stroke rate. We filmed 10 captive otariids swimming with accelerometers either attached to a harness (Daily Diary: sampling frequency 32Hz, N = 4) or taped to the fur (G6a+: 25Hz, N = 6). We used down sampling to derive four recording rates from each accelerometer (Daily Diary: 32, 16, 8, 4Hz; G6a+: 25, 20, 10, 5Hz). For each of these sampling frequencies we derived 20 combinations of two parameters (RMW - the window size used to calculate the running mean, and m – the minimum number of points smaller than the local maxima used to detect a peak), from the dynamic acceleration of x, z and x+z, to estimate stroke rate from the accelerometers. These estimates differed by up to ~20% in comparison to the actual number of foreflipper strokes counted from videos. RMW had little effect on the overall differences, nor did the choice of axis used to make the calculations (x, z or x+z), though the variability was reduced when using x+z. The best m varied depending on the axis used and the sampling frequency, where a larger m was needed for higher sampling frequencies. This study demonstrates that when parameters are appropriately tuned, accelerometers are a simple yet valid tool for estimating the stroke rates of swimming otariids.

keywords     otariid, swim mechanics, stroke rate, accelerometer, energetics, biologger
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Physiological constraints and energetic costs of diving behaviour in marine mammals: a review of studies using trained Steller sea lions diving in the open ocean.
Rosen, D.A.S., A.G. Hindle, C. Gerlinsky, E. Goundie, G.D. Hastie and A.W. Trites. 2017.
Journal of Comparative Physiology B 187:29-50.
abstract
Marine mammals are characterized as having physiological specializations that maximize the use of oxygen stores to prolong time spent under water. However, it has been difficult to undertake the requisite controlled studies to determine the physiological limitations and trade-offs that marine mammals face while diving in the wild under varying environmental and nutritional conditions. For the past decade, Steller sea lions (Eumetopias jubatus) trained to swim and dive in the open ocean away from the physical confines of pools participated in studies that investigated the interactions between diving behaviour, energetic costs, physiological constraints, and prey availability. Many of these studies measured the cost of diving to understand how it varies with behaviour and environmental and physiological conditions. Collectively, these studies show that the type of diving (dive bouts or single dives), the level of underwater activity, the depth and duration of dives, and the n utritional status and physical condition of the animal affect the cost of diving and foraging. They show that dive depth, dive and surface duration, and the type of dive result in physiological adjustments (heart rate, gas exchange) that may be independent of energy expenditure. They also demonstrate that changes in prey abundance and nutritional status cause sea lions to alter the balance between time spent at the surface acquiring oxygen (and offloading CO2 and other metabolic by-products) and time spent at depth acquiring prey. These new insights into the physiological basis of diving behaviour further our understanding of the potential scope for behavioural responses of marine mammals to environmental changes, the energetic significance of these adjustments, and the consequences of approaching physiological limits.
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Marine mammals exploring the oceans pole to pole: a review of the MEOP consortium.
Treasure, A. M., F. Roquet, I. J. Ansorge, M. N. Bester, L. Boehme, H. Bornemann, J.-B. Charrassin, D. Chevallier, D. P. Costa, M. A. Fedak, C. Guinet, M. O. Hammill, R. G. Harcourt, M. A. Hindell, K. M. Kovacs, M.-A. Lea, P. Lovell, A. D. Lowther, C. Lydersen, T. McIntyre, C. R. McMahon, M. M. C. Muelbert, K. Nicholls, B. Picard, G. Reverdin, A. W. Trites, G. D. Williams and P.J. Nico de Bruyn. 2017.
Oceanography 30:132-138.
abstract
Polar oceans are poorly monitored despite the important role they play in regulating Earth's climate system. Marine mammals equipped with biologging devices are now being used to fill the data gaps in these logistically difficult to sample regions. Since 2002, instrumented animals have been generating exceptionally large data sets of oceanographic CTD casts (>500,000 profiles), which are now freely available to the scientific community through the MEOP data portal (http://meop.net). MEOP (Marine Mammals Exploring the Oceans Pole to Pole) is a consortium of international researchers dedicated to sharing animal-derived data and knowledge about the polar oceans. Collectively, MEOP demonstrates the power and cost-effectiveness of using marine mammals as data-collection platforms that can dramatically improve the ocean observing system for biological and physical oceanographers. Here, we review the MEOP program and database to bring it to the attention of the international community.
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Fine-scale foraging movements by fish-eating killer whales (Orcinus orca) relate to the vertical distributions and escape responses of salmonid prey (Oncorhynchus spp.).
Wright, B. M., J. K. B. Ford, G. M. Ellis, V. B. Deecke, A. D. Shapiro, B. C. Battaile and A. W. Trites. 2017.
Movement Ecology 5:1-18.
abstract
Background: We sought to quantitatively describe the fine-scale foraging behavior of northern resident killer whales (Orcinus orcas), a population of fish-eating killer whales that feeds almost exclusively on Pacific salmon (Oncorhynchus spp.). To reconstruct the underwater movements of these specialist predators, we deployed 34 biologging Dtags on 32 individuals and collected high-resolution, three-dimensional accelerometry and acoustic data. We used the resulting dive paths to compare killer whale foraging behavior to the distributions of different salmonid prey species. Understanding the foraging movements of these threatened predators is important from a conservation standpoint, since prey availability has been identified as a limiting factor in their population dynamics and recovery. Results: Three-dimensional dive tracks indicated that foraging (N = 701) and non-foraging dives (N = 10,618) were kinematically distinct (Wilks

keywords     Foraging, Movement, Diving behavior, Biologging, Dtag, Accelerometry, Killer whale, Orcinus orca, Pacific salmon
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2016
 
Protozoal-related mortalities in endangered Hawaiian monk seals Neomonachus schauinslandi.
Barbieri, M. M., L. Kashinsky, D. S. Rotstein, K. M. Colegrove, K. H. Haman, S. L. Magargal, A. R. Sweeny, A. C. Kaufman, M. E. Grigg and C. L. Littnan. 2016.
Diseases of Aquatic Organisms 121:85-95.
abstract
Protozoal infections have been widely documented in marine mammals and may cause morbidity and mortality at levels that result in population level effects. The presence and potential impact on the recovery of endangered Hawaiian monk seals Neomonachus schauinslandi by protozoal pathogens was first identified in the carcass of a stranded adult male with disseminated toxoplasmosis and a captive monk seal with hepatitis. We report 7 additional cases and 2 suspect cases of protozoal-related mortality in Hawaiian monk seals between 2001 and 2015, including the first record of vertical transmission in this species. This study establishes case definitions for classification of protozoal infections in Hawaiian monk seals. Histopathology and immunohistochemistry were the primary diagnostic modalities used to define cases, given that these analyses establish a direct link between disease and pathogen presence. Findings were supported by serology and molecular data when available. Tox oplasma gondii was the predominant apicomplexan parasite identified and was associated with 100% of mortalities (n = 8) and 50% of suspect cases (n = 2). Incidental identification of sarcocysts in the skeletal muscle without tissue inflammation occurred in 4 seals, including one co-infected with T. gondii. In 2015, 2 cases of toxo-plasmosis were identified ante-mortem and shared similar clinical findings, including hematological abnormalities and histopathology. Protozoal-related mortalities, specifically due to toxoplasmosis, are emerging as a threat to the recovery of this endangered pinniped and other native Hawaiian taxa. By establishing case definitions, this study provides a foundation for measuring the impact of these diseases on Hawaiian monk seals.

keywords     Protozoa, Mortality, Pathology, Immunohistochemistry, Toxoplasma gondii, Sarcocystis, Pinniped
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Net energy gained by northern fur seals (Callorhinus ursinus) is impacted more by diet quality than by diet diversity.
Diaz Gomez, M, D.A.S. Rosen and A.W. Trites. 2016.
Canadian Journal of Zoology 94:123-135.
abstract
Understanding whether northern fur seals (Callorhinus ursinus (L., 1758)) are negatively affected by changes in prey quality or diversity could provide insights into their on-going population decline in the central Bering Sea. We investigated how six captive female fur seals assimilated energy from eight different diets consisting of four prey species (walleye pollock (Gadus chalcogrammus Pallas, 1814, formerly Theragra chalcogrammus (Pallas, 1814)), Pacific herring (Clupea pallasii Valenciennes in Cuvier and Valenciennes, 1847), capelin (Mallotus villosus (Muller, 1776)), and magister armhook squid (Berryteuthis magister (Berry, 1913))) fed alone or in combination. Net energy was quantified by measuring fecal energy loss, urinary energy loss, and heat increment of feeding. Digestible energy (95.9%-96.7%) was high (reflecting low fecal energy loss) and was negatively affected by ingested mass and dietary protein content. Urinary energy loss (9.3%-26.7%) increased significantly for high-protein diets. Heat increment of feeding (4.3%-12.4%) was significantly lower for high-lipid diets. Overall, net energy gain (57.9%-83.0%) was affected by lipid content and varied significantly across diets. Mixed-species diets did not provide any energetic benefit over single-species diets. Our study demonstrates that diet quality was more important in terms of energy gain than diet diversity. These findings suggest that fur seals consuming low-quality prey in the Bering Sea would be more challenged to obtain sufficient energy to satisfy energetic and metabolic demands, independent of high prey abundance.

keywords     northern fur seal, Callorhinus ursinus, net energy, mixed-species diets, diet quality
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Dive, food, and exercise effects on blood microparticles in Steller sea lions (Eumetopias jubatus): exploring a biomarker for decompression sickness.
Fahlman, A., M.J. Moore, A.W. Trites, D.A. Rosen, M. Haulena, N. Waller, T. Neale, M. Yang and S.R. Thom. 2016.
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 310:R596-R601.
abstract
Recent studies of stranded marine mammals indicate that exposure to underwater military sonar may induce pathophysiological responses consistent with decompression sickness (DCS). However, DCS has been difficult to diagnose in marine mammals. We investigated whether blood microparticles (MPs, measured as number/l plasma), which increase in response to decompression stress in terrestrial mammals, are a suitable biomarker for DCS in marine mammals. We obtained blood samples from trained Steller sea lions (Eumetopias jubatus, 4 adult females) wearing time-depth recorders that dove to predetermined depths (either 5 or 50 meters). We hypothesized that MPs would be positively related to decompression stress (depth and duration underwater). We also tested the effect of feeding and exercise in isolation on MPs using the same blood sampling protocol. We found that feeding and exercise had no effect on blood MP levels, but that diving caused MPs to increase. However, blood MP levels did not correlate with diving depth, relative time underwater, and presumed decompression stress, possibly indicating acclimation following repeated exposure to depth.
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Flipper strokes can predict energy expenditure and locomotion costs in free-ranging northern and Antarctic fur seals.
Jeanniard du Dot, T., A.W. Trites J.P.Y. Arnould, and C. Guinet. 2016.
Scientific Reports. 6:33912
abstract
Flipper strokes have been proposed as proxies to estimate the energy expended by marine vertebrates while foraging at sea, but this has not been validated on free-ranging otariids (fur seals and sea lions). Our goal was to investigate how well flipper strokes correlate with energy expenditure in 33 foraging northern and Antarctic fur seals equipped with accelerometers, GPS, and time-depth recorders. We concomitantly measured field metabolic rates with the doubly-labeled water method and derived activity-specific energy expenditures using fine-scale time-activity budgets for each seal. Flipper strokes were detected while diving or surface transiting using dynamic acceleration. Despite some inter-species differences in flipper stroke dynamics or frequencies, both species of fur seals spent 3.79 ± 0.39 J/kg per stroke and had a cost of transport of ~1.6-1.9 J/kg/m while diving. Also, flipper stroke counts were good predictors of energy spent while diving (R2 = 0.76) and to a lesser extent while transiting (R2 = 0.63). However, flipper stroke count was a poor predictor overall of total energy spent during a full foraging trip (R2 = 0.50). Amplitude of flipper strokes (i.e., acceleration amplitude x number of strokes) predicted total energy expenditure (R2 = 0.63) better than flipper stroke counts, but was not as accurate as other acceleration-based proxies, i.e. Overall Dynamic Body Acceleration.

keywords     accelerometer, energy expenditure, field metabolic rate, doubly-labelled-water, flipper strokes, cost of transport, ODBA, VeDBA, northern fur seal, Antarctic fur seal
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Bayesian data fusion approaches to predicting spatial tracks: application to marine mammals.
Liu, Y., J. V. Zidek, A. W. Trites and B. C. Battaile. 2016.
Annals of Applied Statistics 10:1517-1546.
abstract
Bayesian Melding (BM) and downscaling are two Bayesian approaches commonly used to combine data from different sources for statistical inference. We extend these two approaches to combine accurate but sparse direct observations with another set of high-resolution but biased calculated observations. We use our methods to estimate the path of a moving or evolving object and apply them in a case study of tracking northern fur seals. To make the BM approach computationally feasible for high dimensional (big) data, we exploit the properties of the processes along with approximations to the likelihood to break the high dimensional problem into a series of lower dimensional problems. To implement the alternative, downscaling approach, we use R-INLA to connect the two sources of observations via a linear mixed effect model. We compare the predictions of the two approaches by cross-validation as well as simulations. Our results show that both approaches yield similar results— both provide accurate, high resolution estimates of the atea locations of the northern fur seals, as well as Bayesian credible intervals to characterize the uncertainty about the estimated movement paths.

keywords     Bayesian Melding, Downscaling, Bio-logging, Conditional independence, INLA, Dead-Reckoning, Tracking, Marine mammals
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Behavioral responses affect distribution analyses of bowhead whales in the vicinity of seismic operations.
Robertson, F.C., W.R. Koski and A.W. Trites. 2016.
Mar Ecol Prog Ser 549:243-262.
abstract
Aerial surveys are sometimes used to assess the densities of wide-ranging whales, as well as changes in their distributions in response to human activity. Such surveys also provide data used to estimate numbers of animals exposed to different received levels of seismic sound, as required by regulators. However, estimates of abundance are often biased because they fail to account for the effects of seismic operations on the surfacing and diving behavior of whales. Our objective was to determine the extent to which analyses of the distribution of bowhead whales Balaena mysticetus are affected by changes in visual 'availability' caused by seismic operations. We used aerial survey data collected during seismic operations in the Alaskan Beaufort Sea from late August to early October 2008 and fit spatial density surface models to bowhead sighting data to predict whale density in an ensonified area. We also incorporated availability correction factors to determine the sensitivity of density estimates to changes in surfacing and diving behavior caused by seismic operations. The influence of altered whale behavior was then evaluated by comparing a series of realistic simulated scenarios in which models incorporated undisturbed or seismic disturbance-related correction factors. Results suggest that the numbers of bowhead whales present in the vicinity of seismic operations during the bowhead autumn migration are underestimated if the behavioral effects of seismic operations on whales are ignored. Our study highlights the importance of accounting for changes in whale behavior that can affect sightability when estimating numbers and distribution of whales in the vicinity of industrial activity.

keywords     Bowhead whale, Seismic survey, Distance sampling, Beaufort Sea, Availability, g(0), Alaska, Spatial models, Behavior, Generalized additive model
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Quantitative DNA metabarcoding: improved estimates of species proportional biomass using correction factors derived from control material.
Thomas, A. C., B. E. Deagle, P. J. Eveson, C. H. Harsch and A. W. Trites. 2016.
Molecular Ecology Resources 16:714-726.
abstract
DNA metabarcoding is a powerful new tool allowing characterization of species assemblages using high-throughput amplicon sequencing. The utility of DNA metabarcoding for quantifying relative species abundances is currently limited by both biological and technical biases which influence sequence read counts. We tested the idea of sequencing 50/50 mixtures of target species and a control species in order to generate relative correction factors (RCFs) that account for multiple sources of bias and are applicable to field studies. RCFs will be most effective if they are not affected by input mass ratio or co-occurring species. In a model experiment involving three target fish species and a fixed control, we found RCFs did vary with input ratio but in a consistent fashion, and that 50/50 RCFs applied to DNA sequence counts from various mixtures of the target species still greatly improved relative abundance estimates (e.g., average per species error of 19 ± 8% for uncorrected versu s 3 ± 1% for corrected estimates). To demonstrate the use of correction factors in a field setting, we calculated 50/50 RCFs for 18 harbour seal (Phoca vitulina) prey species (RCFs ranging from 0.68 to 3.68). Applying these corrections to field-collected seal scats affected species percentages from individual samples (Δ 6.7 ± 6.6%) more than population level species estimates (Δ 1.7 ± 1.2%). Our results indicate that the 50/50 RCF approach is an effective tool for evaluating and correcting biases in DNA metabarcoding studies. The decision to apply correction factors will be influenced by the feasibility of creating tissue mixtures for the target species, and the level of accuracy needed to meet research objectives.

keywords     DNA metabarcoding, high-throughput amplicon sequencing, harbor seal, Phoca vitulina, diets, prey consumption, diet reconstruction, scats, fecal samples
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One-two punches to eliminate depredation by marine mammals on fish caught or raised for human consumption.
Trites, A. W. and J. Spitz. 2016.
Animal Conservation 19:222-224.
abstract
The ultimate solution to protecting fish farms and fishing gear from marine mammals is not yet at hand - and there is unlikely to be a one-size-fits-all solution. Protecting fish raised in open-ocean meshed pens will likely prove to be a two-stepped process that begins with using physical barriers around pens to prevent predators from obtaining the fish (such as predator exclusion nets) - and turning to sound (such as acoustic deterrence) as the second step to quickly push back any individuals that breach the protective perimeter. Some capture fisheries may be able to protect their catches using barriers (such as traps instead of hooks) or using smart fishing techniques (such as shorter soak times, or modified hauling techniques), while others might find electrified nets and acoustic deterrence are effective in scaring predators in the short-term. Unfortunately, all technologically-based deterrence methods are likely to fail in the long-term as animals adapt to prolonged stimulus and find the rewards they receive to be greater than the price they pay to obtain them. New technologies often also equate to new problems and conflicts - it is just that no one knows yet what they are until the technology has been fully implemented. Thus, simple (but perhaps initially expensive) options that prevent predators from seeing or accessing the fish intended for human consumption are likely to be the most successful, while the technologically based solutions are likely to be most successful when used sparingly. Using one-two punch solutions that combine the two methods would seem to have the greatest likelihood of successfully reducing or removing conflicts between fisheries and marine mammals. They may also ultimately yield the peace of mind that society and those whose livelihoods depend on harvesting marine species seek to ensure t hat humans can co-exist with marine mammals with minimal conflict.

keywords     depredation, marine mammals, fisheries, fish farms, acoustic deterrence, harbor seal, harbor porpoise
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Bottom time does not always predict prey encounter rate in Antarctic fur seals.
Viviant, M., T. Jeanniard du Dot, P. Monestiez, M. Authier and C. Guinet. 2016.
Functional Ecology 30:1834-1844.
abstract
1. Optimal foraging models applied to breath-holding divers predict that diving predators should optimize the time spent foraging at the bottom of dives depending on prey encounter rate, distance to prey patch (depth) and physiological constraints. 2. We tested this hypothesis on a free-ranging diving marine predator, the Antarctic fur seal Arctocephalus gazella, equipped with accelerometers or Hall sensors (n=11) that recorded mouth-opening events, a proxy for prey capture attempts and thus feeding events. Over the 5896 dives analyzed (>15m depth), the mean number of mouth-opening events per dive was 1.21 ą 1.69 (mean ą sd). Overall, 82% of mouth-openings occurred at the bottom of dives. 3. As predicted, fur seals increased their inferred foraging time at the bottom of dives with increasing patch distance (depth), irrespective of the number of mouth-openings. 4. For dives shallower than 55m, the mean bottom duration of dives without mouth-openings was shorter than for dives with mouth-opening events. However, this difference was only due to the occurrence of V-shaped dives with short bottom durations (0 or 1s). When removing those V-shaped dives, bottom duration was not related to the presence of mouth openings anymore. Thus, the decision to abandon foraging is likely related to other information about prey availability than prey capture attempts (i.e. sensory cues) that seals collect during the descent phase. We did not observe V-shaped dives for dives deeper than 55m, threshold beyond which the mean dive duration exceeded the apparent aerobic dive limit. For dives deeper than 55m seals kept on foraging at bottom irrespective of the number of mouth-openings performed. 5. Most dives occurred at shallower depths (30-55m) than the 60m depth of highest foraging efficiency (i.e. of greatest number of mouth-opening events per dive). This is likely related to physiological constraints during deeper dives. 6. We suggest that foraging decisions are more complex than predicted by current theory and highlight the importance of the information collected by the predator during the descent as well as its physiological constraints. Ultimately, this will help establishing reliable predictive foraging models for marine predators based on diving patterns only.

keywords     aerobic diving limit, diving behaviour, foraging strategies, foraging depth, Antarctic fur seals
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Transiting to depth disrupts the relationship between overall dynamic body acceleration and oxygen consumption in freely diving Steller sea lions.
Volpov, B.L., E.T. Goundie, D.A.S. Rosen, A.W. Trites and J.P.Y. Arnould. 2016.
Marine Ecology Progress Series 562:221-236.
abstract
Previous research has presented contradictory evidence on the ability of overall dynamic body acceleration (ODBA) to predict oxygen consumption (sV̇O2) in air-breathing diving vertebrates. We investigated a potential source of these discrepancies by partitioning the ODBA: sV̇O2 relationship over 3 phases of the dive cycle (transiting to and from depth, bottom time, and post-dive surface interval). Trained Steller sea lions (Eumetopias jubatus) executed 4 types of dives to 40 m (single dives, long-duration dive bouts of 4-6 dives, short-duration dive bouts of 10 or 12 dives, and transit dives with minimal bottom duration). Partitioning single dives by dive phase showed differing patterns in the ODBA: sV̇O2 relationship among dive phases, but no significant linear relationships were observed. The proportion of the dive cycle spent transiting to and from the surface was a significant predictive factor in the ODBA: sV̇O2 relationship, while bottom duration or post-dive surface interval had no effect. ODBA only predicted sV̇O2 for dives when the proportion of time spent transiting was small. The apparent inability of ODBA to reliably predict sV̇O2 reflects differences in the inherent relationships between ODBA and sV̇O2 during different phases of the dive. These results support the growing body of evidence that ODBA on its own is not a reliable field predictor of energy expenditure at the level of the single dive or dive bout in air-breathing diving vertebrates likely because ODBA (a physical measure) cannot account for physiological changes in sV̇O2 that occur during the different phases of a dive cycle.

keywords     diving behaviour, metabolic rate, ODBA, dive phase, pinniped
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Dive characteristics can predict foraging success in Australian fur seals (Arctocephalus pusillus doriferus) as validated by animal-borne video.
Volpov, B.L.V., D.A.S. Rosen, A.J. Hoskins, H.J. Lourie, N. Dorville, A.M.M. Baylis, K.W. Wheatley, G. Marshall, K. Abernathy, J. Semmens, M.A. Hindell and J.P.Y. Arnould. 2016.
Biology Open 5:262-271.
abstract
Dive characteristics and dive shape are often used to infer foraging success in pinnipeds. However, these inferences have not been directly validated in the field with video, and it remains unclear if this method can be applied to benthic foraging animals. This study assessed the ability of dive characteristics from time-depth recorders (TDR) to predict attempted prey capture events (APC) that were directly observed on animal-borne video in Australian fur seals (Arctocephalus pusillus doriferus, n=11). The most parsimonious model predicting the probability of a dive with ≥1 APC on video included only descent rate as a predictor variable. The majority (94%) of the 389 total APC were successful, and the majority of the dives (68%) contained at least one successful APC. The best model predicting these successful dives included descent rate as a predictor. Comparisons of the TDR model predictions to video yielded a maximum accuracy of 77.5% in classifying dives as either APC or non-APC or 77.1% in classifying dives as successful verses unsuccessful. Foraging intensity, measured as either total APC per dive or total successful APC per dive, was best predicted by bottom duration and ascent rate. The accuracy in predicting total APC per dive varied based on the number of APC per dive with maximum accuracy occurring at 1 APC for both total (54%) and only successful APC (52%). Results from this study linking verified foraging dives to dive characteristics potentially opens the door to decades of historical TDR datasets across several otariid species.

keywords     Crittercam, Foraging behaviour, Animal-borne video, Dive profile analysis
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Averaged propulsive body acceleration (APBA) can be calculated from biologging tags that incorporate gyroscopes and accelerometers to estimate swimming speed, hydrodynamic drag and energy expenditure for Steller sea lions.
Ware, C., A. W. Trites, D. A. S. Rosen and J. Potvin. 2016.
PLoS ONE 11(6): e0157326
abstract
Forces due to propulsion should approximate forces due to hydrodynamic drag for animals horizontally swimming at a constant speed with negligible buoyancy forces. Propulsive forces should also correlate with energy expenditures associated with locomotion預n important cost of foraging. As such, biologging tags containing accelerometers are being used to generate proxies for animal energy expenditures despite being unable to distinguish rotational movements from linear movements. However, recent miniaturizations of gyroscopes offer the possibility of resolving this shortcoming and obtaining better estimates of body accelerations of swimming animals. We derived accelerations using gyroscope data for swimming Steller sea lions (Eumetopias jubatus), and determined how well the measured accelerations correlated with actual swimming speeds and with theoretical drag. We also compared dive averaged dynamic body acceleration estimates that incorporate gyroscope data, with the widely used Overa ll Dynamic Body Acceleration (ODBA) metric, which does not use gyroscope data. Four Steller sea lions equipped with biologging tags were trained to swim alongside a boat cruising at steady speeds in the range of 4 to 10 kph. At each speed, and for each dive, we computed a measure called Gyro-Informed Dynamic Acceleration (GIDA) using a method incorporating gyroscope data with accelerometer data. We derived a new metric輸veraged Propulsive Body Acceleration (APBA), which is the average gain in speed per flipper stroke divided by mean stroke cycle duration. Our results show that the gyro-based measure (APBA) is a better predictor of speed than ODBA. We also found that APBA can estimate average thrust production during a single stroke-glide cycle, and can be used to estimate energy expended during swimming. The gyroscope-derived methods we describe should be generally applicable in swimming animals where propulsive accelerations can be clearly identified in the signal預nd they should also prove useful for dead-reckoning and improving estimates of energy expenditures from locomotion.

keywords     biologging, ODBA, accelerometer, gyroscope, swimming, speed, energy expenditure, drag, stroke
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2015
 
Foraging a new trail with northern fur seals (Callorhinus ursinus): Lactating seals from islands with contrasting population dynamics have different foraging strategies, and forage at scales previously unrecognized by GPS interpolated dive data.
Battaile, B.C., C.A. Nordstrom, N. Liebsch and A.W. Trites. 2015.
Marine Mammal Science 31:1494-1520.
abstract
We reconstructed the foraging tracks of lactating northern fur seals (Callorhinus ursinus) from two eastern Bering Sea islands (St. Paul Island and Bogoslof Island) using linear interpolation between GPS locations recorded at a maximum of four times per hour and compared it to tri-axial accelerometer and magnetometer data collected at 16 Hz to reconstruct pseudotracks between the GPS fixes. The high-resolution data revealed distances swum per foraging trip were much greater than the distances calculated using linearly interpolated GPS tracks (1.5 times further for St. Paul fur seals and 1.9 times further for Bogoslof fur seals). First passage time metrics calculated from the high resolution data revealed that the optimal scale at which the seals searched for prey was 500 m (radius of circle searched) for fur seals from St. Paul Island that went off-shelf, and 50 m for fur seals from Bogoslof Island and surprisingly, 50 m for fur seals from St. Paul that foraged on-s helf. These area-restricted search scales were significantly smaller than those calculated from GPS data alone (12 km for St. Paul and 6 km for Bogoslof) indicating that higher resolution movement data can reveal novel information about foraging behaviors that have important ecological implications.

keywords     foraging ecology, biologging, northern fur seal, Callorhinus ursinus, marine mammal, Bering Sea, magnetometer, accelerometer, spatial analysis, area restricted search
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Accelerometers identify new behaviors and show little difference in the activity budgets of lactating northern fur seals (Callorhinus ursinus) between breeding islands and foraging habitats in the eastern Bering Sea.
Battaile, B.C., K.Q. Sakamoto, C.A. Nordstrom, D.A.S. Rosen and A.W. Trites. 2015.
PLoS ONE Vol 10(3):e0118761
abstract
We tagged 82 lactating northern fur seals (Callorhinus ursinus) with tri-axial accelerometers and magnetometers on two eastern Bering Sea islands (Bogoslof and St. Paul) with contrasting population trajectories. Using depth data, accelerometer data and spectral analysis we classified time spent diving (30%), resting (~7%), shaking and grooming their pelage (9%), swimming in the prone position (~10%) and two types of previously undocumented rolling behavior (29%), with the remaining time (~15%) unspecified. The reason for the extensive rolling behavior is not known. We ground-truthed the accelerometry signals for shaking and grooming and rolling behaviors—and identified the acceleration signal for porpoising—by filming tagged northern fur seals in captivity. Speeds from GPS interpolated data indicated that animals traveled fastest while in the prone position, suggesting that this behavior is indicative of destination-based swimming. Very little difference was found in the percentages of time spent in the categorical behaviors with respect to breeding islands (Bogoslof or St. Paul Island), forager type (cathemeral or nocturnal), and the region where the animals foraged (primarily on-shelf <200m, or off-shelf > 200m). The lack of significant differences between islands, regions and forager type may indicate that behaviors summarized over a trip are somewhat hardwired even though foraging trip length and when and where animals dive are known to vary with island, forager type and region.

keywords     seals, accelerometers, animal behavior, foraging, biological locomotion, sine wave, fur seal
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Resting metabolic rate and activity: Key components of seasonal variation in daily energy expenditure for the northern fur seal (Callorhinus ursinus).
Dalton, A. J. M., D. A. S. Rosen and A.W Trites. 2015.
Canadian Journal of Zoology 93(8):635-644.
abstract
Seasonal changes in daily energy expenditure (DEE) and its key underlying components (costs of resting metabolic rate (RMR), thermoregulation, activity, and growth) were measured to determine seasonal energy requirements, bioenergetic priorities, and potential times of year when unpredicted episodes of nutritional stress would have their greatest effect on female northern fur seals (Callorhinus ursinus L., 1758). The DEE of 6 captive juvenile female fur seals averaged 527.8 Ä… 65.7 kJ kg-1 d-1 (Ä… SD) and fluctuated seasonally (lower during summer and winter, and up to 20% greater in spring and fall). RMR also changed significantly with season, and was higher in the fall (potentially due to moulting or anticipated migratory activity). However, changes in RMR did not follow the same seasonal trend as those of DEE. The largest component of DEE was RMR (~ 80% on average), followed by the cost of activity (which may have driven some of the seasonal variations in DEE). In contrast, the energetic costs associated with growth and thermoregulation appeared negligible within the scope of overall energy expenditures. Elevated innate costs of RMR and higher growth rates in the fall and summer, respectively, suggest that inadequate nutrition could comparatively have greater negative effects on female fur seals during these seasons

keywords     northern fur seal, Callorhinus ursinus, daily energy expenditure,resting metabolic rate, activity, growth, thermoregulation
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Low prey abundance leads to less efficient foraging behaviour in Steller sea lions.
Goundie, E.T., D. A. S. Rosen and A.W. Trites. 2015.
Journal of Experimental Marine Biology and Ecology 470:70-77.
abstract
Breath-hold divers should adjust their dive behaviors to maximize the benefits and minimize the costs of foraging on prey patches of different densities at different depths. However, few studies have quantified how animals respond to changes in prey availability (depth and density), and how this affects their foraging efficiency. We tested the effects of changes in prey availability on the foraging behavior and efficiency of Steller sea lions (Eumetopias jubatus) by measuring diving metabolic rate, dive durations, and food intake of 4 trained sea lions diving in the open ocean on controlled prey patches of different densities at different depths. Sea lions completed bouts of 5 consecutive dives on high- or low-density prey patches at two depths (10m and 40m). We found that the rate of energy expenditure did not change under any of the imposed foraging conditions (meanąSD: 0.22ą0.02 kJ min−1 kg−1), but that the proportion of time spent consuming prey increased with prey patch density due to changes in diving patterns. At both depths, sea lions spent a greater proportion of the dive bout foraging on prey patches with high prey density, which led to high rates of energy gain (4.3 ą 0.96 kJ min−1 kg−1) and high foraging efficiency (cost:benefit was 1:20). In contrast, the sea lions spent a smaller proportion of their dive bout actively feeding on prey patches with low prey density, and consequently had a lower energetic gain (0.91 ą 0.29 kJ min−1 kg−1) and foraging efficiency (1:4). The 5-fold differences in foraging efficiency between the two types of prey patches were greater than the 3-fold differences that we expected based on differences in food availability. Our results suggest that sea lions faced with reduced prey availability forage less efficiently and therefore would have greater difficulty obtaining their daily energy requirements.

keywords     Dive behavior, Diving energetics, Foraging efficiency, Optimal foraging, Steller sea lion
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Assessment of competition between fisheries and Steller sea lions in Alaska based on estimated prey biomass, fisheries removals and predator foraging behaviour.
Hui, T.C.Y., R. Gryba, E.J. Gregr and A.W. Trites. 2015.
PLoS ONE Vol 10(5): e0123786
abstract
A leading hypothesis to explain the dramatic decline of Steller sea lions (Eumetopias jubatus) in western Alaska during the latter part of the 20th century is a change in prey availability due to commercial fisheries. We tested this hypothesis by exploring the relationships between sea lion population trends, fishery catches, and the prey biomass accessible to sea lions around 33 rookeries between 2000 and 2008. We focused on three commercially important species that have dominated the sea lion diet during the population decline: walleye pollock, Pacific cod and Atka mackerel. We estimated available prey biomass by removing fishery catches from predicted prey biomass distributions in the Aleutian Islands, Bering Sea and Gulf of Alaska; and modelled the likelihood of sea lions foraging at different distances from rookeries (accessibility) using satellite telemetry locations of tracked animals. We combined this accessibility model with the prey distributions to estima te the prey biomass accessible to sea lions by rookery. For each rookery, we compared sea lion population change to accessible prey biomass. Of 304 comparisons, we found 3 statistically significant relationships, all suggesting that sea lion populations increased with increasing prey accessibility. Given that the majority of comparisons showed no significant effect, it seems unlikely that the availability of pollock, cod or Atka mackerel was limiting sea lion populations in the 2000s.

keywords     Eumetopias jubatus, walleye pollock, Pacific cod, Atka mackerel, accessibility, prey distribution, CPUE, linear mixed-effects models
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Linking northern fur seal dive behaviour to environmental variables in the eastern Bering Sea.
Joy, R., M.G. Dowd, B.C. Battaile, P.M. Lestenkof, J. T. Sterling, A.W. Trites and R.D. Routledge. 2015.
Ecosphere Vol 6(5) pp. 75
abstract
Northern fur seals (Callorhinus ursinus) breeding on the Pribilof Islands, Alaska have declined dramatically over the past 40 years. Effective conservation of northern fur seals depends on understanding the foraging behaviour of adult females whose foraging success is linked to pup survival. We determined the foraging behaviour for 11 tagged lactating female northern seals from the Pribilof Islands using a state-space modelling approach with an autoregressive movement model. To interpret at-sea behaviour in the context of oceanic habitat, we matched high-resolution reconstructed tracks spatially and temporally to a set of environmental covariates that included: commercial groundfish catch, sea surface temperature, primary productivity, wind speed, depth and time of day. We used a Bayesian hierarchical framework to implement a multinomial regression model to link behaviour to environmental covariates; and account for the mismatch of scale between fur seal behaviour and the environmental variables by incorporating an error-in-covariates approach into the hierarchical model. The Bayesian framework allowed us to build a single model to synthesize the information from all the northern fur seal foraging tracks and the available information about the underlying environmental conditions. Application of the approach indicated that the behavioural states for the northern fur seal were significantly related to the Alaska commercial groundfish catch, particularly walleye pollock (Gadus chalogramma).

keywords     northern fur seal, Bayesian hierarchical model, error-in-covariates, diel pattern, juvenile walleye pollock
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Bias correction and uncertainty characterization of dead-reckoned paths of marine mammals.
Liu, Y., B.C. Battaile, A.W. Trites and J.V. Zidek. 2015.
Animal Biotelemetry 3(51):1-11.
abstract
Biologgers incorporating triaxial magnetometers and accelerometers can record animal movements at infra-second frequencies. Such data allow the Dead-Reckoned (DR) path of an animal to be reconstructed at high-resolution. However, poor measures of speed,undocumented movements caused by ocean currents, confounding between movement and gravitational acceleration and measurement error in the sensors, limits the accuracy and precision of DR paths. The conventional method for calculating DR paths attempts to reduce random errors and systematic biases using GPS observations without rigorous statistical justification or quantification of uncertainty in the derived swimming paths. Methods: We developed a Bayesian Melding (BM) approach to characterize uncertainty and correct for bias of DR paths. Our method used a Brownian Bridge process to combine the fine-resolution (but seriously biased) DR path and the sparse (but precise and accurate) GPS measurements in a statistically rigorous way. We also exploited the properties of underlying processes and some approximations to the likelihood to dramatically reduce the computational burden of handling large, high-resolution data sets. We implemented this approach in an R package "BayesianAnimalTracker", and applied it to biologging data obtained from northern fur seals (Callorhinus ursinus) foraging in the Bering Sea. We also tested the accuracy of our method using cross-validation analysis and compared it to the conventional bias correction of DR and linear interpolation between GPS observations (connecting two consecutive GPS observations by a straight line). Results: Our BM approach yielded accurate, high-resolution estimated paths with uncertainty quantified as credible intervals. Cross-validation analysis demonstrated the greater prediction accuracy of the BM method to reconstruct movements versus the conventional and linear interpolation methods. Moreover, the credible intervals covered the true path points albeit with probabilities somewhat higher than 95%. The GPS corrected high-resolution path also revealed that the total distance traveled by the northern fur seals we tracked was 40% - 50% further than that calculated by linear interpolation of the GPS observations.

keywords     Biologging; Dead-Reckoning; High-resolution animal tracking; Bayesian melding; energy expenditure; Global Positioning System; uncertainty statement; Brownian Bridge
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Extrapolating cetacean densities beyond surveyed regions: habitat-based predictions in the circumtropical belt.
Mannocci, L., P. Monestiez, J. Spitz and V. Ridoux. 2015.
Journal of Biogeography 42(7):1267-1280.
abstract
Our knowledge of cetacean distributions is impeded by large data-gaps worldwide, particularly at tropical latitudes. This study aims to (1) understannd generic relationships between cetaceans and their habitats in a range of tropical waters, and (2) extrapolate cetacean densities in a circumtropical belt extending far beyond surveyed regions. Aerial surveys were conducted over three regions in the tropical Atlantic (132,000 km2), Indian (1.4 million km2) and Pacific (1.4 million km2)oceans. Three cetacean guilds were studied (Delphininae, Globicephalinae andsperm and beaked whales). For each guild, a generalized additive model was submitted using sightings recorded in all three regions and 14 candidate environmental predictors. Cetacean densities were tentatively extrapolated over a circumtropical belt, excluding waters where environmental characteristics departed from those encountered in the surveyed regions. Each cetacean guild exhibited a relationship with the primary production and depth of the minimum dissolved oxygen concentration. Delphininae also showed a relationship with the dominant phytoplankton group. The prediction envelopes were primarily constrained by water temperature. Circumtropical extrapolations of Delphininae and Globicephalinae were contrasted between ocean basins, with high densities predicted in the equatorial waters of the three ocean basins. The predicted densities of sperm and beaked whales were lower and more uniform across the circumtropical belt than for the other two guilds. Our modelling approach represents a good analytical solution to predicting cetacean population densities in poorly documented tropical waters. Future data collection should concentrate on areas where environmental characteristics were not encountered in our survey regions and where the predicted densities were the most uncertain. By highlighting cetacean hotspots far beyond waters under national jurisdiction, this study can provide guidance for the delimitation of Ecologically and Biologically Significant Marine Areas.

keywords     Cetaceans, circumtropical, conservation biogeography, density, extrapolation, generalized additive models, pelagic waters
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Feeding kinematics and performance of basal otariid pinnipeds, Steller sea lions and northern fur seals: implications for the evolution of mammalian feeding.
Marshall, C. D., D. A. S. Rosen and A. W. Trites. 2015.
Journal of Experimental Biology 218:3229-3240.
abstract
Feeding performance studies can address questions relevant to feeding ecology and evolution. Our current understanding of feeding mechanisms for aquatic mammals is poor. Therefore, we characterized the feeding kinematics and performance of five Steller sea lions (Eumetopias jubatus) and six northern fur seals (Callorhinus ursinus). We tested the hypotheses that both species use suction as their primary feeding mode, and that rapid jaw opening was related to suction generation. Steller sea lions used suction as their primary feeding mode, but also used a biting feeding mode. In contrast, northern fur seals only used a biting feeding mode. Kinematic profiles of Steller sea lions were all indicative of suction feeding (i.e. a small gape, small gape angle, large depression of the hyolingual apparatus and lip pursing). However, jaw opening as measured by gape angle opening velocity (GAOV) was relatively slow in Steller sea lions. In contrast to Steller sea lions, the GAOV of northern fur seals was extremely fast, but their kinematic profiles indicated a biting feeding mode (i.e. northern fur seals exhibited a greater gape, a greater gape angle and minimal depression of the hyolingual apparatus compared with Steller sea lions). Steller sea lions produced both subambient and suprambient pressures at 45 kPa. In contrast, northern fur seals produced no detectable pressure measurements. Steller sea lions have a broader feeding repertoire than northern fur seals, which likely enables them to feed on a greater variety of prey, in more diverse habitats. Based on the basal phylogenetic position of northern fur seals, craniodental morphological data of the Callorhinus lineage, and the performance data provided in this study, we suggest that northern fur seals may be exhibiting their ancestral feeding mode.

keywords     Otariidae, Callorhinus ursinus, Eumetopias jubatus,suction, biting, fossil pinnipeds
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Correction factors account for the availability of bowhead whales exposed to seismic operations in the Beaufort Sea.
Robertson, F.C., W.R. Koski, J.R. Brandon, T.A. Thomas, and A.W. Trites. 2015.
Journal of Cetacean Research and Management 15:35-44.
abstract
The accuracy of estimates of cetacean density from line-transect survey data depends in large part on how visible the target species is to the observer. Behavioural data (i.e. surface and dive times) from government- and industry-funded aerial observation programs (1980-2000) were used to calculate availability correction factors needed to estimate the number of bowhead whales (Balaena mysticetus) from aerial survey sighting data. Correction factors were calculated for bowheads exposed and not exposed to seismic operations. Travelling non-calf whales were found to be less likely to be available for detection than other whales, and their availability further declined in the presence of seismic operations. Non-calves were also less available to observers during autumn when exposed to seismic operations than when not exposed, regardless of activity (travelling or otherwise). Such differences in availability appear to reflect behavioural responses to the sound of seismi cooperations that alters the surfacing and diving patterns of bowhead whales. Localised abundance estimated from aerial surveys may range from 3% to as much as 63% higher in areas ensonified by seismic operations if correction factors are applied to account for differences in availability associated with the presence of seismic operations, compared to abundance estimates derived from assessments that only account for changes in availability of undisturbed whales. These results provide the first empirical estimates of availability for bowhead whales exposed to seismic operations and highlight the implications of not correcting for disturbance-related availability in density assessments in the vicinity of seismic operations.
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Evidence of partial deferment of digestion during diving in Steller sea lions (Eumetopias jubatus).
Rosen, D.A.S., C.D. Gerlinsky and A.W. Trites. 2015.
Journal of Experimental Marine Biology and Ecology 469:93-97.
abstract
Past foraging success of diving air-breathing vertebrates can adversely affect future foraging capabilities and costs through changes in circulation or increased metabolic costs associated with digestion that are incompatible with efficient diving. This study tested the physiological interaction between digestion and diving by comparing the cost of diving in fasted and pre-fed trained Steller sea lions foraging under controlled conditions in the open ocean. Pre-dive and post-dive surface metabolism and diving metabolic rate were all higher in the pre-fed animals than the fasted animals, indicating an effect of digestion on metabolism. However, the sea lions displayed a significant reduction in the apparent additive effect of digestion during diving. The increase in rate of oxygen consumption associated with digestion was reduced by 54% during diving compared to the increase observed in pre-dive metabolism. This truncation of the additional cost of digestion rapidly disappeared following cessation of diving. The results suggest that Steller sea lions diving to depth demonstrate a partial deferment of digestion while actively foraging and that the classically held view that digestion and diving are incompatible processes may be much more variable and adaptable to specific diving conditions and behaviors than previously thought.
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A nutrigenomic approach to detect nutritional stress from gene expression in blood samples drawn from Steller sea lions.
Spitz, J., V. Becquet, D.A.S. Rosen and A.W. Trites. 2015.
Comparative Biochemistry and Physiology: Part A 187:214-223.
abstract
Gene expression profiles are increasingly being used as biomarkers to detect the physiological responses of a number of species to disease, nutrition, and other stressors. However, little attention has been given to using gene expression to assess the stressors and physiological status of marine mammals. We sought to develop and validate a nutrigenomics approach to quantify nutritional stress in Steller sea lions (Eumetopias jubatus). We subjected 4 female Steller sea lions to 3 feeding regimes over 70-day trials (unrestricted food intake, acute nutritional stress, and chronic nutritional stress), and drew blood samples from each animal at the end of each feeding regime. We then extracted the RNA of white blood cells and measured the response of 8 genes known to react to diet restriction in terrestrial mammals. Overall, we found that the genomic response of Steller sea lions experiencing nutritional stress was consistent with diet restriction regulation in terrestrial mammals. Our nutritionally stressed sea lions down-regulated some cellular processes involved in immune response and oxidative stress, and up-regulated pro-inflammatory responses and metabolic processes. Nutrigenomics appears to be a promising means to monitor nutritional status and contribute to mitigation measures needed to assist in the recovery of Steller sea lions and other at-risk species of marine mammals.

keywords     Genomics, Expression profile, q-PCR, Diet, restriction, Biomarker, Monitoring
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Diet of Harbour seals Phoca vitulina: implication for the flatfish nursery in the Bay of Somme (English Channel, France).
Spitz, J., L. Dupuis, V. Becquet, B. Dubief and A.W. Trites. 2015.
Aquatic Living Resources 28:11-19.
abstract
Changes in marine species abundance can impact ecosystems’ stability and sustainability of fisheries. In the eastern Atlantic Ocean, harbour seals (Phoca vitulina) are top predator occupying highest trophic level in coastal marine food webs. Although, the overall European population decline, harbour seals have increased dramatically since the 1990Â’s at the southern limit of their European distribution along the French coast of the English Channel. However, little is known about the feeding habits of the expanding peripheral populations limiting the assessment of the role and the impact of this predator in these coastal ecosystems. Here, we investigated the sex-specific diet of harbour seals during summer in the Bay of Somme, the largest colony in the English Channel. We collected 91 faecal samples from haul-out sites mainly used by harbour seal but also by few grey seals. Molecular methods have been used to discard grey seal samples and differentiate gender. Collectively, the 86 faecal samples of harbour seals contained the remains of 3327 prey belonging to at least 13 fish species, and represented ~109 kg of consumed fish (of which 85% were soles and plaices). Most of the fish consumed were juvenile and small flatfish (Buglossidium luteum, Microchirus variegatus, Solea vulgaris, Pegusa lascaris, Pleuronectes platessa and Platichthys flesus). Hard-part identification further showed a similar diet between the sexes in terms of primary prey consumed, but a greater diversity of preys in the male diet. The dependence of harbour seals on flatfish has not been reported elsewhere and has significant implications for the sustainability of the important flatfish nursery in the Bay of Somme. Consumption estimation and ecosystem modelling are now required to provide robust assessment of the effect of harbour seal predation on population dynamics of the flatfish nursery, on ecosystem of the Bay of Biscay at- large, and finally on interactions with fisheries.
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Stable carbon and nitrogen isotope trophic enrichment factors for Steller sea lion vibrissae relative to milk and fish/invertebrate diets.
Stricker, C.A., A.M. Christ, M.B. Wunder, A.C. Doll, S.D. Farley, L.D. Rea, D.A.S. Rosen, R.D. Scherer and D.J. Tollit. 2015.
Marine Ecology Progress Series. 523:255-266.
abstract
Nutritional constraints have been proposed as a contributor to population declines in the endangered Steller sea lion Eumetopias jubatus in some regions of the North Pacific. Isotopic analysis of vibrissae (whiskers) is a potentially useful approach to resolving the nutritional ecology of this species because long-term (up to 8 yr) dietary information is sequentially recorded and metabolically inert once formed. Additionally, vibrissae are grown in utero, potentially offering indirect inference on maternal diet. However, diet reconstruction using isotopic techniques requires a priori knowledge of trophic enrichment factors (TEFs), which can vary relative to diet quality and among animal species. In this study, we provide new TEF estimates for (1) maternal relative to pup vibrissae during both gestation and nursing and (2) adult vibrissae relative to a complex diet. Further, we refine vibrissa−milk TEFs based on an additional 76 animals with an age distribution ranging from 1 to 20 mo. Mother−pup vibrissae TEF values during gestation and nursing were near zero for δ13C and averaged 0.8 and 1.6‰, respectively, for δ15N. In contrast, vibrissa− fish/invertebrate TEFs averaged 3.3 (± 0.3 SD) and 3.7‰ (±0.3) for lipid-free δ13C and δ15N, respectively. Average lipid-free δ13C and δ15N vibrissa−milk TEFs were 2.5 (±0.9) and 1.8‰ (±0.8), respectively, and did not differ among metapopulations. Empirically determined TEFs are critical for accurate retrospective diet modeling, particularly for evaluating the hypothesis of nutritional deficiency contributing to the lack of Steller sea lion population recovery in some regions of Alaska.
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Diet of Steller sea lions (Eumetopias jubatus) in Frederick Sound, southeast Alaska: a comparison of quantification methods using scats to describe temporal and spatial variability.
Tollit, D. J., M. A. Wong and A. W. Trites. 2015.
Canadian Journal of Zoology 93:361-376.
abstract
We compared eight dietary indices used to describe the diet of Steller sea lions (Eumetopias jubatus (Schreber, 1776)) from 2001-2004 in Frederick Sound, Southeast Alaska. Remains (n=9 666 items) from 59+ species categories were identified from 1 693 fecal samples (scats) from 14 collection periods. The most frequently occurring prey were walleye pollock (Theragra chalcogramma (Pallas, 1814), 95%), Pacific herring (Clupea harengus (Cuvier and Valenciennes, 1847), 30%), Pacific hake (Merluccius productus (Ayres, 1855), 29%), and arrowtooth flounder (Atheresthes stomias (Jordan and Gilbert 1880), 21%). These species, along with salmon (Oncorhynchus spp.) and skate (Raja spp.), accounted for 80-90% of the reconstructed biomass and energy contribution, with pollock contributing 37-60%. Overall, 80% of fish were 14-42cm long and mainly pelagic, though 40% of scats contained benthic-associated prey. Steller sea lions switched from adult pollock to strong cohorts of juvenile pollock, and took advantage of spawning concentrations of salmon in autumn and herring in late-spring and summer, as well as a climate-driven increase in hake availability. Observed temporal and site differences in diet confirm the need for robust long-term scat sampling protocols. All major indices similarly tracked key temporal changes, despite differences in occurrence and biomass-energy based diet estimates linked to prey size and energy density effects and the application of correction factors.

keywords     Diet, scat, biomass reconstruction, hard remains, otoliths, Steller sea lion, dietary index
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Identification of prey captures in Australian fur seals (Arctocephalus pusillus doriferus) using head-mounted accelerometers: Field validation with animal-borne video cameras.
Volpov, B.L., A.J. Hoskins, B. Battaile, M. Viviant, K.E. Wheatley, G.J. Marshall, K. Abernathy and J.P.Y. Arnould. 2015.
PloS One Vol 10(6): e0128789
abstract
This study investigated prey captures in free-ranging adult female Australian fur seals (Arctocephalus pusillus doriferus) using head-mounted 3-axis accelerometers and animal-borne video cameras. Acceleration data was used to identify individual attempted prey captures (APC), and video data were used to independently verify APC and prey types. Results demonstrated that head-mounted accelerometers could detect individual APC but were unable to distinguish among prey types (fish, cephalopod, stingray) or between successful captures and unsuccessful capture attempts. Mean detection rate (true positive rate) on individual animals in the testing subset ranged from 67-100%, and mean detection on the testing subset averaged across 4 animals ranged from 82-97%. Mean False positive (FP) rate ranged from 15-67% individually in the testing subset, and 26-59% averaged across 4 animals. Surge and sway had significantly greater detection rates, but also conversely greater FP rates compared to heave. Video data also indicated that some head movements recorded by the accelerometers were unrelated to APC and that a peak in acceleration variance did not always equate to an individual prey item. The results of the present study indicate that head-mounted accelerometers provide a complementary tool for investigating foraging behaviour in pinnipeds, but that detection and FP correction factors need to be applied for reliable field application.

keywords     Arctocephalus pusillus doriferus, accelerometer, prey capture success, foraging behavior, foraging success, pinniped
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Validating the relationship between 3-dimensional body acceleration and oxygen consumption in trained Steller sea lions.
Volpov, B.L., D.A.S. Rosen, A.W. Trites and J.P.Y. Arnould. 2015.
Journal of Comparative Physiology B 185:695-708.
abstract
We tested the ability of overall dynamic body acceleration (ODBA) to predict the rate of oxygen consumption (sVO2) in freely diving Steller sea lions ( Eumetopias jubatus/) while resting at the surface and diving. The trained sea lions executed three dive types―single dives, bouts of multiple long dives with 4-6 dives per bout, or bouts of multiple short dives with 10-12 dives per bout葉o depths of 40 m, resulting in a range of activity and oxygen consumption levels. Average metabolic rate (AMR) over the dive cycle or dive bout calculated was calculated from sVO2. We found that ODBA could statistically predict AMR when data from all dive types were combined, but that dive type was a significant model factor. However, there were no significant linear relationships between AMR and ODBA when data for each dive type was analyzed separately. The potential relationships between AMR and ODBA were not improved by including dive duration, food consumed, proportion of dive cycle spent submerged or number of dives per bout. It is not clear whether the lack of predictive power within dive type was due to low statistical power, or whether it reflected a true absence of a relationship between ODBA and AMR. The average percent error for predicting AMR from ODBA was 7-11%, and standard error of the estimated AMR was 5-32%. Overall, the extensive range of dive behaviours and physiological conditions we tested indicated that ODBA was not suitable for estimating AMR in the field due to considerable error and the inconclusive effects of dive type.

keywords     Steller sea lion, oxygen consumption, overall dynamic body acceleration, activity, oxygen depletion, diving physiology
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2014
 
Energetic linkages between short-term and long-term effects of whale watching disturbance on cetaceans: an example drawn from northeast Pacific resident killer whales.
Bain, D.E., R. Williams, and A.W. Trites. 2014.
In L. Bejder and R. Williams J. E. S. Higham (eds), Whale-watching, sustainable tourism and ecological management. Cambridge University Press, United Kingdom. pp. 206-228.
abstract
The core objective of efforts to understand and mitigate the effects of whale-watching has been to ensure the survival of populations. The first rigorous studies in the 1980s simply demonstrated that short-term behavioural responses existed. Managers, both in the private sector (whale-watch operators) and public sector responded with simple guidelines. Later studies showed some practices elicited stronger responses than others, and managers again responded with more effective guidelines to preclude activities that elicited strong evasive responses from killer whales. Recent work has shown that these guidelines are insufficient to prevent effects likely to be directly related to fitness (e.g. a reduction in foraging activity and increases in energy expenditure). As managers contemplate how to respond to such results, models such as ours can be constructed to address how short-term effects might relate to population dynamics, and whether data support a correlation between the quantity of exposure and shifts in population growth and decline. As better parameter estimates become available to inform these simple bioenergetics and population dynamics models, they should provide sufficient accuracy and precision to determine whether the effects of vessel traffic are sufficient to reduce the probability that the populations will survive in the long term (i.e. do they exceed potential biological removal (PBR)), or do the cumulative effects of whale watching and other human activities put the population in jeopardy of imminent extinction? The resident killer whales of the northeast Pacific represent an exceedingly data-rich case study of behavior and population biology, but they also represent an interesting study in management. The degree to which management is or is not precautionary determines how much evidence of population-level effects is needed before management actions are imposed. And as some of the science that has been done on this population is applied to other cetaceans, it is important to spell out another lesson learned— namely, that it is essential to specify quantitative management objectives that identify how much of an effect managers are willing to tolerate (limits of acceptable change, PBR and uncertainty:. Otherwise, the science can and will continue without serving any practical purpose as long as the whales persist.
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Species-and size-related patterns in stable isotopes and mercury concentrations in fish help refine marine ecosystem indicators and provide evidence for distinct management units for hake in the Northeast Atlantic.
Chouvelon T., Cherel, Y., B. Simon-Bouhet, J. Spitz and P. Bustamante. 2014.
ICES Journal of Marine Science. 71:1073-1087.
abstract
Recent European environmental policies argue for the development of indicators of the ecological status of ecosystems that are easy to implement and powerful enough to detect changes quickly. For instance, some indicators that are currently proposed for monitoring foodweb structure and functioning are based on the size of organisms, using size as a proxy for trophic level. However, these indicators do not necessarily accurately reflect the underlying trophic structure and dynamics to follow. Ecological tracers (i.e. chemical parameters measured in consumer tissues to infer the trophic ecology of organisms) may serve as complementary indicators of trophic level, and may also help distinguish different populations of a species when more commonly used methods (e.g. genetic, age determination) present their own limitations. Here, we analysed the potential of muscle δ13C and δ15N values and of muscle mercury (Hg) concentrations to depict size-related trophic ha bits of different fish species. We expected that intra- and interspecific variation in these ecological tracers could be helpful in refining currently proposed indicators of marine ecosystems, and also help in discriminating management unitsfor some species. Four fish species were selected for their economical and/or ecological importance in the Bay of Biscay (Northeast Atlantic): whiting Merlangius merlangus, European hake Merluccius merluccius, Atlantic horse mackerel Trachurus trachurus and anglerfish Lophius piscatorius. Muscle δ13C and δ15N values segregated the species and enabled us to discriminate species-specific feeding strategies with increasing size of individuals. Fish body size was not always linearly correlated with δ15N or trophic level. In contrast, Hg concentrations and size-related Hg patterns were more similar from species to species. Interestingly, muscle δ15N values together with Hg concentrations segregated the two putative stocks of Europe an hake within the Bay of Biscay. Hence, we propose the combined use of ecological tracers as a promising method for accurately assigning a consumer to a trophic guild, investigating Hg trophodynamics in foodwebs, and helping discriminate distinct ecological populations within a species when defining management units.
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Broad thermal capacity facilitates the primarily pelagic existence of northern fur seals (Callorhinus ursinus).
Dalton, A.J.M., D.A.S. Rosen and A.W. Trites. 2014.
Marine Mammal Science 30:994-1013.
abstract
Thermoregulatory capacity may constrain the distribution of marine mammals despite having anatomical and physiological adaptations to compensate for the thermal challenges of an aquatic lifestyle. We tested whether subadult female northern fur seals (Callorhinus ursinus) experience increased thermoregulatory costs in water temperatures potentially encountered during their annual migration in the Bering Sea and North Pacific Ocean. Metabolic rates were measured seasonally in 6 captive female northern fur seals (2.75 to 3.5 yr old) in ambient air and controlled water temperatures of 2, 10, and 18 °C. Rates of oxygen consumption in ambient air (1 – 18 °C) were not related to environmental temperature except below 2.5 °C (winter only). However, metabolism was significantly higher during the fall seasonal trials (Sept – Oct) compared to other times of year, perhaps due to the costs of molting. The fur seals appeared thermally neutral in all seasons for all water temperat ures tested (2 – 18 °C) except during the summer when metabolic rates were higher in the 2 °C water. Comparing this broad thermal neutral zone to the average sea surface temperatures potentially encountered during annual migrations indicates wild fur seals can likely exploit a large geographic area without added thermal metabolic costs.
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Season and time of day affect the ability of accelerometry and the doubly labeled water methods to measure energy expenditure in northern fur seals (Callorhinus ursinus).
Dalton, A.J.M., D.A.S. Rosen and A.W. Trites. 2014.
Journal of Experimental Marine Biology and Ecology 452:125-136.
abstract
Estimates of energy expenditure for free-ranging animals are essential to answering a range of fundamental questions in animal biology, but are challenging to obtain and difficult to validate. We simultaneously employed three methods to measure the energy expenditure of 6 captive female northern fur seals (Callorhinus ursinus) during 5-day trials across 4 seasons: respirometry (oxygen consumption), doubly labeled water (DLW), and accelerometry. The DLW method estimated that the fur seals expended 13.1 ? 16.5% more energy than indicated by the more direct measures of oxygen consumption. Accelerometry failed to predict the average mass specific rate of oxygen consumption (VË™ O2DEE) within the individual seasons over entire 5- day trials. However, on a finer time scale (15 or 60 min) and adjusted for time of day, accelerometry estimated energy expenditure within an average difference of 5.4 ? 29.3% (60 min intervals) and 13.8 ? 39.5% (15 min intervals) of respirometry measured values. Our findings suggest that accelerometers have the potential to be more effective than the DLW method for measuring energy expenditure of free-ranging animals. However, rates of oxygen consumption varied with season, independent of overall activity. Seasonal effects (and time of day for accelerometry) must therefore be accounted for when estimating energy expenditure from measures of DLW and acceleration of free-swimming northern fur seals. Such corrections required for estimating energy expenditures in northern fur seals have implications for using accelerometers and DLW to estimate the energy expenditure of other species.

keywords     accelerometry, Callorhinus ursinus, daily energy expenditure, doubly labeled water, northern fur seal, respirometry
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Inflation and deflation pressure-volume loops in anesthetized pinnipeds confirms compliant chest and lungs.
Fahlman, A., S.H. Loring, S.P. Johnson, M. Haulena, A.W. Trites, V.A. Fravel and W.G. Van Bonn. 2014.
Frontiers in Physiology Vol 5(433)
abstract
We examined structural properties of the marine mammal respiratory system, and tested Scholander's hypothesis that the chest is highly compliant by measuring the mechanical properties of the respiratory system in five species of pinniped under anesthesia (Pacific harbor seal, Phoca vitulina; northern elephant seal, Mirounga angustirostris; northern fur seal Callorhinus ursinus; California sea lion, Zalophus californianus; and Steller sea lion, Eumetopias jubatus). We found that the chest wall compliance (CCW) of all five species was greater than lung compliance (airways and alveoli, CL) as predicted by Scholander, which suggests that the chest provides little protection against alveolar collapse or lung squeeze. We also found that specific respiratory compliance was significantly greater in wild animals than in animals raised in an aquatic facility. While differences in ages between the two groups may affect this incidental finding, it is also possible that lung conditioning in free-living animals may increase pulmonary compliance and reduce the risk of lung squeeze during diving. Overall, our data indicate that compliance of excised pinniped lungs provide a good estimate of total respiratory compliance.
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Sensitivity to hypercapnia and elimination of CO2 following diving in Steller sea lions (Eumetopias jubatus).
Gerlinsky, C.D., D.A.S. Rosen and A.W. Trites. 2014.
Journal of Comparative Physiology B. 184:535-544.
abstract
Marine mammal foraging behaviour inherently depends on diving ability. Declining populations of Steller sea lions may be facing nutritional stress that could affect their diving ability through changes in body composition or metabolism. Our objective was to determine whether nutritional stress (restricted food intake resulting in a 10% decrease in body mass) altered the calculated aerobic dive limit (cADL) of four captive sea lions diving in the open ocean, and how this related to changes in observed dive behaviour. We measured diving metabolic rate (DMR), blood O2 stores, body composition and dive behaviour prior to and while under nutritional restriction. We found that nutritionally stressed sea lions increased the duration of their single long dives, and the proportion of time they spent at the surface during a cycle of four dives. Nutritionally stressed sea lions lost both lipid and lean mass, resulting in potentially lower muscle O2 stores. However, total body O2 stores increased due to rises in blood O2 stores associated with having higher blood volumes. Nutritionally stressed sea lions also had higher mass-specific metabolic rates. The greater rise in O2 stores relative to the increase in mass-specific DMR resulted in the sea lions having a longer cADL when nutritionally stressed. We conclude that there was no negative effect of nutritional stress on the diving ability of sea lions. However, nutritional stress did lower foraging efficiency and require more foraging time to meet energy requirements due to increases in diving metabolic rates and surface recovery times.
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Steller sea lions (Eumetopias jubatus) have greater blood volumes, higher diving metabolic rates and a longer aerobic dive limit when nutritionally stressed.
Gerlinsky, C.D., A.W. Trites and D.A.S. Rosen. 2014.
Journal of Experimental Biology 217:769-778.
abstract
Marine mammal foraging behavior inherently depends on diving ability. Declining populations of Steller sea lions may be facing nutritional stress that could affect their diving ability through changes in body composition or metabolism. Our objective was to determine whether nutritional stress (restricted food intake resulting in a 10% decrease in body mass) altered the calculated aerobic dive limit (cADL) of four captive sea lions diving in the open ocean, and how this related to changes in observed dive behaviour. We measured diving metabolic rate (DMR), blood O2 stores, body composition and dive behaviour prior to and while under nutritional restriction. We found that nutritionally stressed sea lions increased the duration of their single long dives, and the proportion of time they spent at the surface during a cycle of four dives. Nutritionally stressed sea lions lost both lipid and lean mass, resulting in potentially lower muscle O2 stores. However, total body O2 stores increased due to rises in blood O2 stores associated with having higher blood volumes. Nutritionally stressed sea lions also had higher mass-specific metabolic rates. The greater rise in O2 stores relative to the increase in mass-specific DMR resulted in the sea lions having a longer cADL when nutritionally stressed. We conclude that there was no negative effect of nutritional stress on the diving ability of sea lions. However, nutritional stress did lower foraging efficiency and require more foraging time to meet energy requirements due to increases in diving metabolic rates and surface recovery times.

keywords     Steller sea lion, blood volume, nutritional stress, diving metabolism, oxygen stores, dive behavior
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Bayesian melding of the dead-reckoned path and GPS measurements for an accurate and high-resolution path of marine mammals.
Liu, Y., B.C. Battaile, J. V. Zidek and A.W. Trites. 2014.
arXiv Vol 14116683v2
abstract
With the recent advances in electrical engineering, devices attached to free-ranging marine mammals today can collect oceanographic data in remarkable high spatial-temporal resolution. However, those data cannot be fully utilized without a matching high-resolution and accurate path of the animal, which is currently missing in this field. In this paper, we develop a Bayesian melding approach based on a Brownian Bridge process to combine the fine-resolution but seriously biased Dead-Reckoned path and the precise but sparse GPS measurements, which results in an accurate and high-resolution estimated path together with credible bands as quantified uncertainty statements. We also exploit the properties of underlying processes and some approximations to the likelihood to dramatically reduce the computational burden of handling those big high resolution data sets.

keywords     Dead reckoning, swimming path, northern fur seal, Bayesian melding, Brownian Bridge
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The decline of Steller sea lions (Eumetopias jubatus) in the North Pacific: insights from indigenous people, ethnohistoric records and archaeological data.
Maschner, H. D. G., A. W. Trites, K. L. Reedy-Maschner and M. Betts. 2014.
Fish and Fisheries 15:634-660.
abstract
A number of hypotheses have been proposed to explain the most recent decline (1977-2012) of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands. We examined hypotheses about fisheries competition, environmental change, predation, anthropogenic effects, and disease using observations of modern Aleut and archaeological, ethnohistoric, and ethnographic data from the western Gulf of Alaska and Aleutian Islands. These data indicate that Steller sea lion numbers have declined and recovered repeatedly over the past 4,500 years and were last at critically low numbers during the 1870s-1930s. Steller sea lions appear to have been more abundant during the cool periods—and lower during the warmer periods. Observations by local peoples, explorers, early government surveyors, and biologists since the late 1800s suggest that low populations of Steller sea lions have been associated with high populations of Gadidae fishes (Pacific cod – Gadus macrocephalus and walleye pollock – Theragra chalcogramma), and are consistent with the ocean climate hypothesis to explain the decline of sea lions. They suggest that removals by people and killer whales (Orcinus orca) did not cause the sea lion declines, but could have compounded the magnitude of the decline as sea lion numbers approached low densities. Archaeological, anthropological and ethnohistorical analyses demonstrate that fluctuations have occurred in the North Pacific over hundreds to thousands of years, and provide context for understanding the changes that occur today and the changes that will continue to occur in the future.
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An assessment of contaminant concentrations in toothed whale species of the NW Iberian Peninsula : Part II. Trace element concentrations.
Méndez-Fernandez, P., L. Webster, T. Chouvelon, P. Bustamante, M. Ferreira, A. González, A. López, C.F. Moffat, G.J. Pierce, F. Read, M. Russell, M.B. Santos, J. Spitz, J.V. Vingada and F. Caurant. 2014.
Science of The Total Environment. 484:206-216.
abstract
Concentrations of Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V and Zn were investigated in the liver and kidney of the five most common toothed whales off the Northwest Iberian Peninsula (NWIP), specifically common dolphin, long-finned pilot whale, harbour porpoise, striped dolphin and bottlenose dolphin. Differences were observed in the bioaccumulation of the above elements between the five species. The differences are probably related to biological factors such as age and sex and/or to ecological factors specific to each species such as feeding habits or bioavailability of the various elements. However, no significant relationship was observed between element accumulation and sex. Pilot whale and striped dolphin showed the highest concentrations of renal Cd and the highest concentrations of hepatic Hg and Se, while bottlenose dolphin showed the highest concentrations of Hg in kidneys. An analysis of inter-elemental relationships showed strong positive correla tions be tween Hg and Se in the five species, however most individuals have Hg:Se molar ratio less than 1:1 indicating an excess of Se compare to Hg. This result, probably reflect the high proportion of young animals in the sample available for this study and/or that these animals had a good health status. We also observed a positive correlation in striped dolphins between Cd and Cu and between Cd and Zn in kidneys. In addition, comparing with other studies world-wide, the element concentrations (Hg and Cd) found in Iberian toothed whales indicate that these populations are not specially threatened by Hg and Cd exposure in the area.

keywords     Trace elements; Bioaccumulation; Toothed whales; Northwest Iberian Peninsula
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An assessment of contaminant concentrations in toothed whale species of the NW Iberian Peninsula : Part I. Persistent organic pollutants.
Méndez-Fernandez, P., L. Webster, T. Chouvelon, P. Bustamante, M. Ferreira, A. González, A. López, C.F. Moffat, G.J. Pierce, F. Read, M. Russell, M.B. Santos, J. Spitz, J.V. Vingada and F. Caurant. 2014.
Science of The Total Environment. 484:196-205.
abstract
Concentrations and patterns of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the blubber of the five most common toothed whales off the Northwest Iberian Peninsula (NWIP), specifically common dolphin, long-finned pilot whale, harbour porpoise, striped dolphin and bottlenose dolphin, were investigated. The study revealed that differences in PCB and PBDE concentrations among the species are highly dependent on age and sex but also on ecological factors such as trophic level, prey type and habitat. Of the five species studied, bottlenose dolphin and harbour porpoise showed the greatest concentrations of PCBs. Both species exceed the toxic threshold of 17 μg g− 1 lipid weight (PCB Aroclor equivalent) for health effects on marine mammals, for 100% and 75% of the individuals tested, respectively. Overall, the PCB and PBDE levels observed in the NWIP toothed whales were of the same order of magnitude or lower than those reported by previ ous studies in areas of the NE Atlantic. However, they are often higher than those for toothed whales from the southern Atlantic and Pacific Ocean.

keywords     PCBs; PBDEs; Bioaccumulation; Patterns; Toothed whales; Northwest Iberian Peninsula
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Rare sightings of white-beaked dolphins (Lagenorhynchus albirostris) off south-eastern Baffin Island, Canada.
Reinhart, N.R., S.M.E. Fortune, P.R. Richard and C.J.D. Matthews. 2014.
Marine Biodiversity Records. e121
abstract
We report two opportunistic and unusual observations of white-beaked dolphins (Lagenorhynchus albirostris) in the Canadian Arctic that are outside the known range of this species. Sightings occurred off the south-east coast of Baffin Island (Nunavut, Canada) in Frobisher Bay (September 2004) and Cumberland Sound (August 2013). Despite dedicated, multi-year marine mammal surveys in the region (boat-based and aerial), white-beaked dolphins have not previously been reported in the eastern Davis Strait. Our sightings suggest that white-beaked dolphins may infrequently inhabit coastal waters off south-eastern Baffin Island, and furthermore, that their habitat use may correspond with recent changes in prey distribution and availability.

keywords     distribution; western North Atlantic; white-beaked dolphins
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Short-term episodes of imposed fasting have a greater effect on young northern fur seals (Callorhinus ursinus) in summer than in winter.
Rosen, D. A. S., B. L. Volpov and A. W. Trites. 2014.
Conservation Physiology 2:1-9.
abstract
Unexpected shortages of food may affect wildlife differently depending on the time of year it occurs. We imposed 48-hr fasts on six female northern fur seals (Callorhinus ursinus; ages 6 ? 24 months) to identify times of year when they might be particularly sensitive to interruptions in food supply. We monitored changes in their resting metabolic rates and their metabolic response to thermal challenges, and also examined potential bioenergetic causes for seasonal differences in body mass loss. Pre-fast metabolism of the fur seals while in ambient air or submerged in 4 ?C water was higher during summer (Jun-Sep) than winter (Nov-Mar), and submergence did not significantly increase metabolism indicating a lack of additional thermoregulatory costs. There was no evidence of metabolic depression following the fasting periods, nor did metabolism increase during the post-fast thermal challenge, suggesting that mass loss did not negatively impact thermoregulatory capacity. However, the fur seals lost mass at greater rates while fasting during the summer months when metabolism is normally high to facilitate faster growth rates (which would ordinarily have been supported by higher food intake levels). Our findings suggest that summer is a more critical time of year than winter for young northern fur seals to obtain adequate nutrition.
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Thermal limits in young northern fur seals, Callorhinus ursinus.
Rosen, D.A.S. and A.W. Trites. 2014.
Marine Mammal Science 30(3):1014-1028.
abstract
The thermoregulatory abilities of northern fur seals (Callorhinus ursinus) during their first two years in the frigid waters of the North Pacific Ocean may limit their geographic distribution and alter the costs for exploiting different species of prey. We determined the thermoneutral zone of 6 young northern fur seals by measuring their metabolism in ambient air and controlled water temperatures (0-12 °C) from ages 8 to 24 mo. We found that the ambient air temperatures within our study (overall 1.5-23.9 °C) did not affect resting metabolic rates. Calculated lower critical temperatures in water varied between 3.9 and 8.0 °C, while an upper critical temperature in water was only discernible during a single set of trials. These thermal responses provide insight into the possible physiological constraints on foraging ecology in young northern fur seals, as well as the potential energetic consequences of ocean climate change and altered prey distributions.

keywords     Northern fur seal, Callorhinus ursinus, thermoregulation, metabolism, bioenergetics
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Lets go beyond taxonomy in diet description: testing a trait-based approach to prey-predator relationships.
Spitz, J., V. Ridoux and A. Brind'Amour. 2014.
Journal of Animal Ecology 83:1137-1148.
abstract
Understanding ‘Why a prey is a prey for a given predator?’ can be facilitated through trait-based approaches that identify linkages between prey and predator morphological and ecological characteristics and highlight key functions involved in prey selection.' Enhanced understanding of the functional relationships between predators and their prey is now essential to go beyond the traditional taxonomic framework of dietary studies and to improve our knowledge of ecosystem functioning for wildlife conservation and management. We test the relevance of a three-matrix approach in foraging ecology among a marine mammal community in the northeast Atlantic to identify the key functional traits shaping prey selection processes regardless of the taxonomy of both the predators and prey. Our study reveals that prey found in the diet of marine mammals possess functional traits which are directly and significantly linked to predator characteristics, allowing the establishment of a functional typology of marine mammal–prey relationships. We found prey selection of marine mammals was primarily shaped by physiological and morphological traits of both predators and prey, confirming that energetic costs of foraging strategies and muscular performance are major drivers of prey selection in marine mammals. We demonstrate that trait-based approaches can provide a new definition of the resource needs of predators. This framework can be used to anticipate bottom-up effects on marine predator population dynamics and to identify predators which are sensitive to the loss of key prey functional traits when prey availability is reduced.
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Drag, but not buoyancy, affects swim speed in captive Steller sea lions.
Suzuki, I., K. Sato, A. Fahlman, Y. Naito, N. Miyazaki and A. W. Trites. 2014.
Biology Open 3:379-386.
abstract
Swimming at an optimal speed is critical for breath-hold divers seeking to maximize the time they can spend foraging underwater. Theoretical studies have predicted that the optimal swim speed for an animal while transiting to and from depth is independent of buoyancy, but is dependent on drag and metabolic rate. However, this prediction has never been experimentally tested. Our study assessed the effects of buoyancy and drag on the swim speed of three captive Steller sea lions (Eumetopias jubatus) that made 186 dives. Our study animals were trained to dive to feed at fixed depths (10–50 m) under artificially controlled buoyancy and drag conditions. Buoyancy and drag were manipulated using a pair of polyvinyl chloride (PVC) tubes attached to harnesses worn by the sea lions, and buoyancy conditions were designed to fall within the natural range of wild animals (,12–26% subcutaneous fat). Drag conditions were changed with and without the PVC tubes, and swim speeds were recorded and compared during descent and ascent phases using an accelerometer attached to the harnesses. Generalized linear mixed-effect models with the animal as the random variable and five explanatory variables (body mass, buoyancy, dive depth, dive phase, and drag) showed that swim speed was best predicted by two variables, drag and dive phase (AIC=-139). Consistent with a previous theoretical prediction, the results of our study suggest that the optimal swim speed of Steller sea lions is a function of drag, and is independent of dive depth and buoyancy.
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Improving accuracy of DNA diet estimates using food tissue control materials and an evaluation of proxies for digestion bias.
Thomas, A.C., S.N. Jarman, K.H. Haman, A.W. Trites and B.E. Deagle. 2014.
Molecular Ecology 23:3706-3718.
abstract
Ecologists are increasingly interested in quantifying consumer diets based on food DNA in dietary samples and high-throughput sequencing of marker genes. It is tempting to assume that food DNA sequence proportions recovered from diet samples are representative of consumer's diet proportions, despite the fact that captive feeding studies do not support that assumption. Here, we examine the idea of sequencing control materials of known composition along with dietary samples in order to correct for technical biases introduced during amplicon sequencing, and biological biases such as variable gene copy number. Using the Ion Torrent PGM©, we sequenced prey DNA amplified from scats of captive harbour seals (Phoca vitulina) fed a constant diet including three fish species in known proportions. Alongside, we sequenced a prey tissue mix matching the seals’ diet to generate Tissue Correction Factors (TCFs). TCFs improved the diet estimates (based on sequence proportions) for all species and reduced the average estimate error from 28 ± 15% (uncorrected), to 14 ± 9% (TCF corrected). The experimental design also allowed us to infer the magnitude of prey-specific digestion biases and calculate Digestion Correction Factors (DCFs). The DCFs were compared to possible proxies for differential digestion (e.g., fish% protein,% lipid,% moisture) revealing a strong relationship between the DCFs and percent lipid of the fish prey, suggesting prey-specific corrections based on lipid content would produce accurate diet estimates in this study system. These findings demonstrate the value of parallel sequencing of food tissue mixtures in diet studies and offer new directions for future research in quantitative DNA diet analysis.

keywords     next-generation sequencing; diet analysis; pinniped; correction factors
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2013
 
Linking survival and reproductive can improve model estimates of vital rates derived from limited time-series counts of pinnipeds and other species.
Battaile, B.C. and A.W. Trites. 2013.
PLoS ONE. Vol 8(11):e77389
abstract
We propose a method to model the physiological link between somatic survival and reproductive output that reduces the number of parameters that need to be estimated by models designed to determine combinations of birth and death rates that produce historic counts of animal populations. We applied our Reproduction and Somatic Survival Linked (RSSL) method to the population counts of three species of North Pacific pinnipeds (harbor seals, Phoca vitulina richardii (Gray, 1864); northern fur seals, Callorhinus ursinus (L., 1758); and Steller sea lions, Eumetopias jubatus (Schreber, 1776))—and found our model outperformed traditional models when fitting vital rates to common types of limited datasets, such as those from counts of pups and adults. However, our model did not perform as well when these basic counts of animals were augmented with additional observations of ratios of juveniles to total non-pups. In this case, the failure of the ratios to improve model performance may indicate that the relationship between survival and reproduction is redefined or disassociated as populations change over time or that the ratio of juveniles to total non-pups is not a meaningful index of vital rates. Overall, our RSSL models show advantages to linking survival and reproduction within models to estimate the vital rates of pinnipeds and other species that have limited time-series of counts.

keywords     Callorhinus ursinus, Eumetopias jubatus, harbor seal, model parameterization, northern fur seal, Phoca vitulina richardii, pinniped, population dynamics, reproduction, senescence, survival, vital rates
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Prey patch patterns predict habitat use by top marine predators with diverse foraging strategies.
Benoit-Bird, K. J., B. C. Battaile, S. A. Heppell, B. Hoover, D. Irons, N. Jones, K. J. Kuletz, C. A. Nordstrom, R. Paredes, R. M. Suryan, C. M. Waluk and A. W. Trites. 2013.
PLoS ONE Vol 8(1):e53348.
abstract
Spatial coherence between predators and prey has rarely been observed in pelagic marine ecosystems. We used measures of the environment, prey abundance, prey quality, and prey distribution to explain the observed distributions of three cooccurring predator species breeding on islands in the southeastern Bering Sea: black-legged kittiwakes (Rissa tridactyla), thick-billed murres (Uria lomvia), and northern fur seals (Callorhinus ursinus). Predictions of statistical models were tested using movement patterns obtained from satellite-tracked individual animals. With the most commonly used measures to quantify prey distributions - areal biomass, density, and numerical abundance - we were unable to find a spatial relationship between predators and their prey. We instead found that habitat use by all three predators was predicted most strongly by prey patch characteristics such as depth and local density within spatial aggregations. Additional prey patch characteristics and physic al habitat also contributed significantly to characterizing predator patterns. Our results indicate that the smallscale prey patch characteristics are critical to how predators perceive the quality of their food supply and the mechanisms they use to exploit it, regardless of time of day, sampling year, or source colony. The three focal predator species had different constraints and employed different foraging strategies – a shallow diver that makes trips of moderate distance (kittiwakes), a deep diver that makes trip of short distances (murres), and a deep diver that makes extensive trips (fur seals). However, all three were similarly linked by patchiness of prey rather than by the distribution of overall biomass. This supports the hypothesis that patchiness may be critical for understanding predator-prey relationships in pelagic marine systems more generally.
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Foraging behavior of northern fur seals closely matches the hierarchical patch scales of prey.
Benoit-Bird, K. J., B. C. Battaile, C. A. Nordstrom and A. W. Trites. 2013.
Marine Ecology Progress Series 479:283-302.
abstract
Marine prey often occur in hierarchical mosaics whereby small, high-density patches are nested inside of larger, lower density aggregations. We tested the extent to which the foraging behavior of a marine predator (northern fur seal Callorhinus ursinus) could be explained by the hierarchical patch structure of a dominant prey species (juvenile walleye pollock Theragra chalcogramma) in the eastern Bering Sea. Comparing the movements of satellite-tracked fur seals with ship-based acoustic surveys of prey revealed that fur seals did not randomly search for prey, but instead showed deviations in the distribution of step-lengths (distances between their foraging patches) corresponding to the distances between aggregations of prey. Scales of prey distribution varied between Bering Sea shelf and deep-water slope habitats, while spatial scale distributions of fur seals showed corresponding changes, indicating that their search strategies were not innate patterns decoupled from the environment. Fur seals tended to avoid the smallest prey patches in both shelf and slope habitats. They also avoided prey patches that were separated by large distances. Fur seals responded to several levels of prey patchiness simultaneously, resulting in strong correlations between predator and prey over the entire range of aggregation scales observed in juvenile pollock. Our results indicate that, despite having a varied diet, fur seal foraging paths were defined by juvenile pollock aggregations. The presence of hierarchical, scale-dependent aggregation in both predator and prey provides new insights into fur seal behavior and a means to predict the dynamics of their interactions with prey.

keywords     Patchiness, Spatial scale, Predator–prey, Foraging behavior, Hierarchical, Northern fur seal, Juvenile walleye pollock
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Faecal DNA amplification in Pacific walruses (Odobenus rosmarus divergens).
Bowles, E. and A.W. Trites. 2013.
Polar Biology. 36:755-759.
abstract
Dietary information is critical for assessing the population status of seals, sea lions and walruses—and is determined for most species of pinnipeds using non-invasive methods. However, diets of walruses continue to be described from the stomach contents of dead individuals. Our goal was to assess whether DNA could be extracted from the faeces of Pacific walruses (O. rosmarus divergens) collected at haulout sites, and whether potential prey species or taxa could be amplified from that DNA. We extracted DNA from 70 faecal samples collected from ice pans in the Bering Sea during the spring of 2008 and 2009 (with between 4.6 and 308.9 ng/µl of DNA in every sample). We also extracted DNA from 12 potential prey species or taxa collected by bottom grabs in 2009 to identify positive controls for primers, and to test the ability of previously published taxon-specific and species-specific primers to correctly identify the prey using conventional PCR. We tested primers that successfu lly amplified DNA from the tissue of at least one potential prey species or taxon on all 70 walrus faecal samples. We found that two sets of primers successfully amplified many of the potential prey species or taxa using DNA from their tissue, and that one of these primer sets produced positive amplification in 4 of the 70 faecal samples. The band size that was produced for prey organisms and in the faecal samples was consistent with expectations, although prey identities were not verified with sequencing. Our pilot study demonstrates that DNA can be successfully extracted and amplified from walrus faeces, providing a stepping stone towards describing the diets of walruses from faecal DNA.
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Quantifying sequence proportions in a DNA-based diet study using Ion Torrent amplicon sequencing: which counts count?
Deagle, B.E., A.C. Thomas, A. K. Shaffer, A.W. Trites, and S.N. Jarman. 2013.
Molecular Ecology Resources
abstract
A goal of many environmental DNA barcoding studies is to infer quantitative information about relative abundances of different taxa based on sequence read proportions generated by high-throughput sequencing. However, potential biases associated with this approach are only beginning to be examined. We sequenced DNA amplified from faeces (scats) of captive harbour seals (Phoca vitulina) to investigate whether sequence counts could be used to quantify the seals’ diet. Seals were fed fish in fixed proportions, a chordate- specific mitochondrial 16S marker was amplified from scat DNA and amplicons sequenced using an Ion Torrent PGM™. For a given set of bioinformatic parameters, there was generally low variability between scat samples in proportions of prey species sequences recovered. However, proportions varied substantially depending on sequencing direction, level of quality filtering (due to differences in sequence quality between species) and minimum read length considered. Short primer tags used to identify individual samples also influenced species proportions. In addition, there were complex interactions between factors; for example, the effect of quality filtering was influenced by the primer tag and sequencing direction. Resequencing of a subset of samples revealed some, but not all, biases were consistent between runs. Less stringent data filtering (based on quality scores or read length) generally produced more consistent proportional data, but overall proportions of sequences were very different than dietary mass proportions, indicating additional technical or biological biases are present. Our findings highlight that quantitative interpretations of sequence proportions generated via high- throughput sequencing will require careful experimental design and thoughtful data analysis.

keywords     DNA barcoding, Ion Torrent, metabarcoding, next-generation sequencing, pinniped diet
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Activity as a proxy to estimate metabolic rate and to partition the metabolic cost of diving vs. breathing in pre- and post-fasted Steller sea lions.
Fahlman, A., C. Svärd, D. A. S. Rosen, R. Wilson and A. W. Trites. 2013.
Aquatic Biology 18:175-184.
abstract
Three Steller sea lions (Eumetopias jubatus), trained to dive voluntarily to depths ranging from 10 to 50 m, were used to determine whether the relationship between activity and metabolic rate during a diving interval (MRDI, dive + surface interval) was affected by fasting (9-days) during the breeding season (spring through summer). We subsequently used the relationship between activity and MRDI to partition the metabolic costs between underwater breath-holding activity and surface breathing activities. We estimated activity from Overall Dynamic Body Acceleration (ODBA) measured using a 3-axis accelerometer, and measured MRDI using flow-through respirometry. The relationship between ODBA-based activity and MRDI was not affected by fasting period, suggesting ODBA can be used to predict energy expenditure regardless of nutritional state in the spring and summer. However, the relationship between ODBA and dive metabolic rate differs from the relationship between ODBA and the s urface metabolic rate before diving (MRSp). Partitioning MRDI into the metabolic cost of remaining at the surface (MRs) versus swimming underwater (MRUS) suggests that the metabolic cost of diving for Steller sea lions is approximately 29% lower than when breathing at the surface. ODBA appears to be a reasonable proxy to estimate metabolic rate in marine mammals, but more detailed behavioral data may be required to accurately apply the method in the field.
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Energetic requirements of North Atlantic right whales and the implications for species recovery.
Fortune, S.M.E., A.W. Trites, C.A. Mayo, D.A.S. Rosen and P.K. Hamilton. 2013.
Marine Ecology Progress Series. 478:253-272.
abstract
Management plans for North Atlantic right whales Eubalaena glacialis focus on preventing mortality from ship strikes and fishing gear entanglement. However, recovery may also be limited because individuals are under nutritional stress. We quantified the food requirements of North Atlantic right whales by age, sex and reproductive state and compared their predicted needs with field estimates of prey consumption to assess whether any demographic group of right whales might be nutritionally stressed. Energy requirements were estimated using a bioenergetics model that accounted for uncertainty in energy inputs and outputs. Consumption was estimated with prey samples taken near feeding whales in Cape Cod Bay (n = 28 net collections) and the Bay of Fundy (n = 19 optical plankton recordings). We found that calves required the least energy (~1767 MJ d-1) and that lactating females required the most (~4120 MJ d-1). Juveniles required considerably more energy than adult males and non-reproductive females. Our estimates of energy requirements for juveniles (~1906 MJ d-1), adult males (~1793 MJ d-1), and non-reproductive females (~2104 MJ d-1) compared favorably with estimates of actual consumption in Cape Cod Bay and the Bay of Fundy (i.e. they differed by ≤15%), suggesting that our model was reliable. However, lactating females appear to have obtained considerably less than their predicted energy requirements in both habitats. These findings suggest that lactating females may be experiencing an energy deficit, which may affect reproductive rates and slow population recovery. Nutritional stress may thus be limiting the recovery of North Atlantic right whales.

keywords     Bioenergetic model, Eubalaena glacialis, nutritional stress, energetic consumption, energetic requirements
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High diving metabolism results in a short aerobic dive limit for Steller sea lions (Eumetopias jubatus).
Gerlinsky, C. D., D. A. S. Rosen and A. W. Trites. 2013.
Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology. 186:699-708.
abstract
The diving capacity of marine mammals is typically defined by the aerobic dive limit (ADL) which, in lieu of direct measurements, can be calculated (cADL) from total body oxygen stores (TBO) and diving metabolic rate (DMR). To estimate cADL, we measured blood oxygen stores, and combined this with diving oxygen consumption rates (VO(2) recorded from 4 trained Steller sea lions diving in the open ocean to depths of 10 or 40 m. We also examined the effect of diving exercise on O(2) stores by comparing blood O(2) stores of our diving animals to non-diving individuals at an aquarium. Mass-specific blood volume of the non-diving individuals was higher in the winter than in summer, but there was no overall difference in blood O(2) stores between the diving and non-diving groups. Estimated TBO (35.9 ml O(2) kg(-1) )was slightly lower than previously reported for Steller sea lions and other Otariids. Calculated ADL was 3.0 min (based on an average DMR of 2.24 L O(2) min(-1)) and was signific antly shorter than the average 4.4 min dives our study animals performed when making single long dives-but was similar to the times recorded during diving bouts (a series of 4 dives followed by a recovery period on the surface), as well as the dive times of wild animals. Our study is the first to estimate cADL based on direct measures of VO(2) and blood oxygen stores for an Otariid and indicates they have a much shorter ADL than previously thought.
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Inter-population movements of Steller sea lions in Alaska with implications for population separation.
Jemison, L.A., G.W. Pendleton, L.W. Fritz, K.K. Hastings, J.M. Maniscalco, A.W Trites and T.S. Gelatt. 2013.
PLoS ONE. Vol 8(8):e70167.
abstract
Genetic studies and differing population trends support the separation of Steller sea lions (Eumetopias jubatus) into a western distinct population segment (WDPS) and an eastern DPS (EDPS) with the dividing line between populations at 144° W. Despite little exchange for thousands of years, the gap between the breeding ranges narrowed during the past 15–30 years with the formation of new rookeries near the DPS boundary. We analyzed >22,000 sightings of 4,172 sea lions branded as pups in each DPS from 2000–2010 to estimate probabilities of a sea lion born in one DPS being seen within the range of the other DPS (either ‘West’ or ‘East’). Males from both populations regularly traveled across the DPS boundary; probabilities were highest at ages 2–5 and for males born in Prince William Sound and southern Southeast Alaska. The probability of WDPS females being in the East at age 5 was 0.067 but 0 for EDPS females which rarely traveled to the West. Prince William Sound-born females had high probabilities of being in the East during breeding and non-breeding seasons. We present strong evidence that WDPS females have permanently emigrated to the East, reproducing at two ‘mixing zone’ rookeries. We documented breeding bulls that traveled 6,500 km round trip from their natal rookery in southern Alaska to the northern Bering Sea and central Aleutian Islands and back within one year. WDPS animals began moving East in the 1990s, following steep population declines in the central Gulf of Alaska. Results of our study, and others documenting high survival and rapid population growth in northern Southeast Alaska suggest that conditions in this mixing zone region have been optimal for sea lions. It is unclear whether eastward movement across the DPS boundary is due to less-optimal conditions in the West or a reflection of favorable conditions in the East.

keywords     branding, resights, distribution, migration, movements, colonization
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Ecological niche segregation among five toothed whale species off the NW Iberian Peninsula using ecological tracers as multi-approach.
Méndez-Fernandez, P., Pierce, G.J., Bustamante, P., Chouvelon, T., Ferreira, M., Gonzales, A., López, A., Read, F., Santos, M.B., Spitz, J., Vingada, J.V., Caurant, F. 2013.
Marine Biology 160:2825-2840.
abstract
This study aims to assess niche segregation among the five main toothed whales that frequent the NW Iberian Peninsula waters: the common dolphin, the harbour porpoise, the bottlenose dolphin, the striped dolphin and the long-finned pilot whale. We used cadmium (Cd) and stable isotope ratios (d 13C and d15N) as ecological tracers to assess degree of segregation in diet/trophic level and in foraging habitat, over various time-scales. d13C values highlighted different habitats, while Cd concentrations highlighted feeding differences between oceanic and neritic species. Moreover, d15N values suggest different trophic levels of prey targeted within oceanic and neritic species. Hence, results revealed long-term ecological segregation among five toothed whales that coexist in the NWIP and demonstrated the ability of ecological tracers to discriminate ecological niches among closely related species.
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Foraging habitats of lactating northern fur seals are structured by thermocline depths and submesoscale fronts in the eastern Bering Sea.
Nordstrom, C. A., B.C. Battaile, C. Cotté and A. W. Trites. 2013.
In Deep-Sea Research II: Topical Studies in Oceanography.  88-89:78-96.
abstract
The relationships between fine-scale oceanographic features, prey aggregations, and the foraging behavior of top predators are poorly understood. We investigated whether foraging patterns of lactating northern fur seals (Callorhinus ursinus) from two breeding colonies located in different oceanographic domains of the eastern Bering Sea (St. Paul Island˜shelf; Bogoslof Island˜oceanic) were a function of submesoscale oceanographic features. We tested this by tracking 87 lactating fur seals instrumented with bio-logging tags (44 St. Paul Island, 43 Bogoslof Island) during JulyˆSeptember, 2009. We identified probable foraging hotspots using first-passage time analysis and statistically linked individual areas of high-use to fine-scale oceanographic features using mixed-effects Cox-proportional hazard models. We found no overlap in foraging areas used by fur seals from the two islands, but a difference in the duration of their foraging trips˜trips from St. Paul Island were twice as long (7.9 d average) and covered 3-times the distance (600 km average) compared to trips from Bogoslof Island. St. Paul fur seals also foraged at twice the scale (mean radius = 12 km) of Bogoslof fur seals (6 km), which suggests that prey were more diffuse near St. Paul Island than prey near Bogoslof Island. Comparing first passage times with oceanographic covariates revealed that foraging hotspots were linked to thermocline depth and occurred near submesoscale surface fronts (eddies and filaments). St. Paul fur seals that mixed epipelagic (night) and benthic (day) dives primarily foraged on-shelf in areas with deeper thermoclines that may have concentrated prey closer to the ocean floor, while strictly epipelagic (night) foragers tended to use waters with shallower thermoclines that may have aggregated prey closer to the surface. Fur seals from Bogoslof Island foraged almost exclusively over the Bering Sea basin and appeared to hunt intensively along submesoscale fronts that may have converged prey within narrow bands near the surface. Bogoslof fur seals also foraged closer to their island which was surrounded by strong surface fronts, while fur seals from St. Paul Island traveled4100 km and extended some trips off-shelf to the basin to forage at similar oceanographic features. The relative distribution and accessibility of prey-concentrating oceano- graphic features can account for the observed inter-island foraging patterns, which may in turn have population level consequences for the two fur seal colonies.

keywords     Habitat selection, First-passage time, Submesoscale features, Finite-size Lyapunov exponent,Cox proportional hazard model, Alaska, Eastern Bering Sea
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Northern fur seals augment ship-derived ocean temperatures with higher temporal and spatial resolution data in the eastern Bering Sea.
Nordstrom, C.A., K. J. Benoit-Bird, B.C. Battaile and A.W. Trites. 2013.
Deep Sea Research II 94:257-273.
abstract
Oceanographic data collected by marine vertebrates are increasingly being used in biological and physical studies under the assumption that data recorded by free-ranging animals are comparable to those from traditional vertical sampling. We tested this premise by comparing the water temperatures measured during a 2009 oceanographic cruise with those measured during 82 foraging trips by instrumented northern fur seals (Callorhinus ursinus) in the eastern Bering Sea. The animal-borne data loggers were equipped with a fast-response temperature sensor and recorded 6,492 vertical profiles to depths ≥ 50 m during long distance (up to 600 km) foraging trips. Concurrent sampling during the oceanographic cruise collected 247 CTD casts in the same 5-week period. Average temperature differences between ship casts and seal dives (0.60 ± 0.61 °C), when the two were within 1 day and 10 km of each other (n = 32 stations), were comparable to mean differences between adjacent 10 km ship casts (0.46 ± 0.44 °C). Isosurfaces were evaluated at region wide scales at depths of 1 m and 50 m while the entire upper 100 m of the water column was analyzed at finer-scales in highly sampled areas. Similar trends were noted in the temperature fields produced by ships or seals despite the differences in sampling frequency and distribution. However, the fur seal dataset was of higher temporal and spatial resolution and was thereby able to visualize finer-detail with less error than ship-derived data, particularly in dynamic areas. Integrating the ship and seal datasets provided temperature maps with an unprecedented combination of resolution and coverage allowing fine-scale processes on-shelf and over the basin to be described simultaneously. Fur seals (n = 65 trips) also collected 4,700 additional profiles post ship cruise which allowed ≥1 °C warming of the upper 100 m to be documented through mid-September, including regions where ship sampling has traditionally been sparse. Our data show that hydrographic information collected by wide-ranging, diving animals such as fur seals can contribute physical data comparable to, or exceeding those, of traditional sampling methods at regional or finer scales when the questions of interest coincide with the ecology of the species.
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Seasonal changes in the food intake of captive Pacific white-sided dolphins (Lagenorhynchus obliquidens).
Piercey, R.S., E.U. Rechsteiner, B.C. Battaile and A.W. Trites. 2013.
Aquatic Mammals. 39:211-220.
abstract
The Pacific white-sided dolphin (Lagenorhynchus obliquidens) is one of the most abundant apex predators in the North Pacific Ocean, but little is known about how much food they consume and whether their food requirements vary seasonally. We attempted to address these two issues using the feeding records of five Pacific white-sided dolphins housed at the Vancouver Aquarium. These individuals consumed an average of 7.9 kg ± 0.35 (± SE) of fish and squid per day (~11,000 kcal day-1), which equated to ~7% of their body mass and an annual mean intake of 2,880 kg ± 131.8 (± SE) per dolphin (N = 5). Patterns of food consumption and seasonal changes were assessed using long-term feeding records (1977 to 2001) from a single adult female, and were found to be highest in terms of biomass and calories in late December, and about 15% less in late May and early June. Seasonal pool temperatures (range 6.5 to 21.5 C) were inversely related to food intake and accounted for part of the variation, suggesting that seasonal cues other than temperature triggered the changes in food consumption. Amounts of prey consumed by Pacific white-sided dolphins are undoubtedly higher in the wild than in captivity due to relative differences in their respective behaviors in the two environments. However, relative seasonal changes in energy requirements are likely to be independent of living conditions and have implications for estimating the energy requirements of Pacific white-sided dolphins in the wild.
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Energy requirements of Pacific white-sided dolphins (Lagenorhynchus obliquidens) as predicted by a bioenergetic model.
Rechsteiner, E. U., D. A. S. Rosen and A. W. Trites. 2013.
Journal of Mammalogy 94:820-832.
abstract
Apex predators such as Pacific white-sided dolphins (Lagenorhynchus obliquidens) have the potential to impact prey populations and to be affected by changes in prey abundance. As an abundant predator that ranges widely across the North Pacific Ocean, their interactions with prey populations may have conservation implications. We estimated the energy required by individual Pacific white-sided dolphins using a bioenergetic model that accounted for different age classes and reproductive stages (calf, juvenile, adult, pregnant and lactating). Monte Carlo simulations incorporating variability in model parameters (body mass, growth rate, costs of gestation and lactation, metabolic rate, cost of activity, and assimilation efficiencies) were used to predict ranges in energetic requirements. Mean (±SD) total energy requirements in MJ day-1 were 40.3 ± 6.2 for calves, 70.8 ± 8.2 for juveniles, 69.0 ± 3.6 for adults, 70.3 ± 3.6 for pregnant females, and 98.4 ± 20.0 for lactating femal es. Estimates of energy requirements were most sensitive to uncertainty in values used for resting metabolic rates and energetic costs of activity. Estimated mass-specific energy requirements in MJ kg-1 day-1 were elevated in calves (1.55 ± 0.23), juveniles (0.97 ± 0.11) and lactating females (1.01 ± 0.21) when compared with non-reproductive adults and pregnant females (~0.71 ± 0.04). Based on a high-energy density diet, an average sized dolphin (78 kg) would consume approximately 12.5 - 15.8 kg of fish or 15-20% of its body weight per day. These high energetic requirements may indicate a reliance of dolphins on energy rich prey, which has implications for fisheries management and conservation of marine mammals.
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Seasonal resting metabolic rate and food intake of captive Pacific white-sided dolphins (Lagenorhynchus obliquidens).
Rechsteiner, E.U., D.A.S. Rosen and A.W. Trites. 2013.
Aquatic Mammals. 39:241-252.
abstract
Like many marine mammals, Pacific white-sided dolphins (Lagenorhynchus obliquidens) consume prey that change seasonally in numbers, distribution, and energy density. However, it is not known whether these ecological factors are associated with underlying seasonal changes in energy requirements. We investigated these potential seasonal shifts in physiology by measuring resting metabolic rate (a conserved physiological trait) and recording associated daily food energy intake of three captive adult Pacific white-sided dolphins over 12 consecutive months. Two dolphins that met the criteria for measuring resting metabolism had a mean (± SE) mass-specific rate of 0.31 ± 0.0047 MJ kg-1 day- 1 (~34 MJ day-1), which was higher than that of other species of small cetaceans. Resting metabolic rates of Pacific white-sided dolphins did not vary seasonally and, hence, were not related to observed seasonal changes in water or air temperature, total energy intake, or body mass. Overall, resting metabolism accounted for ~70% of total energy intake. However, total food energy intake changed seasonally and was highest during the fall (October to December). While levels of food intake were not predicted by resting metabolic rate, body mass, or water and air temperatures, the increased intake in the fall resulted in the seasonal increase in body mass exhibited by all three dolphins. Our estimates of resting metabolic rates and relative changes in total energy intake can be used to parameterize bioenergetic models needed to estimate the ecological impacts and energetic requirements of Pacific white-sided dolphins in the wild, which will have conservation implications.

keywords     energetics, oxygen consumption, Pacific white-sided dolphins, season, food intake, metabolic rate
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Seismic operations have variable effects on dive-cycle behavior of bowhead whales in the Beaufort Sea.
Robertson, F.C., W.R. Koski, T.A. Thomas, W.J. Richardson, B. Würsig, and A.W. Trites. 2013.
Endangered Species Research 21:143-160.
abstract
The surfacing, respiration and diving (SRD) behavior of bowhead whales Balaena mysticetus changes upon exposure to seismic operations. However, it is unknown whether these changes differ by season, reproductive status (calves, mothers, and non-calves), and whale activity (traveling, foraging, or socializing). Such SRD behavioral responses to seismic operations might influence the detectability of whales during aerial surveys. We addressed these questions by applying non-parametric univariate tests and linear mixed models to behavioral data collected by aerial observation of bowheads in the Beaufort Sea from 1980 to 2000. Durations of surfacings decreased upon exposure to seismic operations, especially for traveling or socializing non-calf whales. The mixed models also indicated that dive durations were affected by the presence of seismic operations, but the effects depended on other variables such as season and whale activity. Overall, our results suggest that changes in the behavior exhibited by bowhead whales exposed to seismic operations are context-dependent (i.e. responses to seismic operations depend on both the circumstance and activity of the whale). The level of perceived threat may also be important based on similarities with behavioral changes observed in other air-breathing aquatic foragers facing dangers. We conclude that seismic-induced changes in bowhead SRD behaviors may affect the availability of bowhead whales for visual detection in some circumstances. This in turn means that estimates of abundance and distribution of bowhead whales near seismic surveys should be context-sensitive and incorporate correction factors that account for sound exposure, season, reproductive status, and whale activity.

keywords     Bowhead whale, Behavior, Disturbance, Seismic operations,Beaufort Sea,Aerial surveys, Sightability
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Resting metabolic rate of a mature male Beluga whale (Delphinapterus leucas).
Rosen, D.A.S. and A.W. Trites. 2013.
Aquatic Mammals 39:85-88.
abstract
We conducted repeated measurements of rates of oxygen consumption on a mature (~17 yrs) male beluga whale held at the Vancouver Aquarium, and trained to rest quietly at the surface of his holding pool underneath a specially designed floating dome that completely contained the portion of his body above the water line. Each trial lasted ~20 minutes prior to the morning feed, and rates of oxygen consumption were calculated over the last 10 minutes of each trial. The average metabolic rate over 11 trials was 73,050 ± 2290 kJ d-1 (Mean ± S.E.). This translated into approximately 54.48 ± 1.71 kJ kg-1 d-1, which was approximately 1.13 ± .035 times the predicted value for a similarly-sized terrestrial mammal. This was statistically greater than 1.0, but did not approach the much higher values reported for many other small cetacean species.
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Prey preferences of adult sea bass Dicentrarchus labrax in the northeastern Atlantic: implications for bycatch of common dolphin Delphinus delphis.
Spitz, J., T. Chouvelon, M. Cardinaud, C. Kostecki and P. Lorance. 2013.
ICES Journal of Marine Science 70:452-461.
abstract
In the northeastern Atlantic, adult sea bass (Dicentrarchus labrax) is one of largest fish living on the shelf, and this species has important commercial value. However, pelagic trawl fisheries that target sea bass have negative operational interactions with common dolphins (Delphinus delphis). Our goal was to determine the diet of adult sea bass in the Bay of Biscay from stomachcontent and stable-isotope analyses, and explore the dietary overlap between sea bass and common dolphins. We found that sea bass primarily target small pelagic fish, most notably mackerel (Scomber scombrus), scads (Trachurus spp.), anchovy (Engraulis encrasicolus), and sardine (Sardina pilchardus). These four species also dominated the diets of common dolphins. This overlap in feeding preferences could increase the risk of dolphins being caught by trawl fisheries while feeding among sea bass, and may be an underlying mechanism to explain the high rate of common dolphin bycatch observed in the pelagic trawl fishery for sea bass in the Bay of Biscay. Understanding the foraging ecology and trophic interactions of predator species is an essential step for identifying and resolving management issues in the northeastern Atlantic and other marine ecosystems.

keywords     Chesson’s index, marine top predator, prey selection, SIAR, stable isotope, stomach content
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Variability in energy density of forage fish from the Bay of Biscay (NE Atlantic): reliability of functional grouping based on prey quality.
Spitz, J. and J. Jouma. 2013.
Journal of Fish Biology 82(6):2147-2152.
abstract
Energy densities of 670 individual fish from nine different species were measured to evaluate intraspecific variability. Functional groups based on energy density appeared to be sufficiently robust to individual variability to provide a classification of forage fish quality applicable in a variety of ecological fields including ecosystem modelling.

keywords     calorific value, prey quality, ecological grouping, functional ecology
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2012
 
Distribution and relative abundance of humpback whales in relation to environmental variables in coastal British Columbia and adjacent waters.
Dalla Rosa, L., J.K. Ford and A.W. Trites. 2012.
Continental Shelf Research 36:89-104.
abstract
Humpback whales are common in feeding areas off British Columbia (BC) from spring to fall, and are widely distributed along the coast. Climate change and the increase in population size of North Pacific humpback whales may lead to increased anthropogenic impact and require a better understanding of species-habitat relationships. We investigated the distribution and relative abundance of humpback whales in relation to environmental variables and processes in BC waters using GIS and generalized additive models (GAMs). Six non-systematic cetacean surveys were conducted between 2004 and 2006. Whale encounter rates and environmental variables (oceanographic and remote sensing data) were recorded along transects divided into 4 km segments. A combined 3-year model and individual year models (two surveys each) were fitted with the mgcv R package. Model selection was based primarily on GCV scores. The explained deviance of our models ranged from 39% for the 3-year model to 76% for the 2004 model. Humpback whales were strongly associated with latitude and bathymetric features, including depth, slope and distance to the 100-m isobath. Distance to sea-surface-temperature fronts and salinity (climatology) were also constantly selected by the models. The shapes of smooth functions estimated for variables based on chlorophyll concentration or net primary productivity with different temporal resolutions and time lags were not consistent, even though higher numbers of whales seemed to be associated with higher primary productivity for some models. These and other selected explanatory variables may reflect areas of higher biological productivity that favor top predators. Our study confirms the presence of at least three important regions for humpback whales along the BC coast: south Dixon Entrance, middle and southwestern Hecate Strait, and the area between La Perouse Bank and the southern edge of Juan de Fuca Canyon.
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Growth and rapid early development of North Atlantic right whales (Eubalaena glacialis).
Fortune, S.M.E., A.W. Trites, W.L. Perryman, M.J. Moore, H.M. Pettis and M.S. Lynn. 2012.
Journal of Mammalogy 93:1342-1354.
abstract
Body growth of North Atlantic right whales (Eubalaena glacialis) was described from measurements of known- age live and dead individuals to gain insights into the nutritional needs and life-history strategies of this endangered species. Body lengths from 154 individuals revealed that calves more than doubled in size and attained three-fourths of asymptotic adult size by the time they had weaned at 12 months. Calves gained on average ~1.7 cm and ~34 kg per day while nursing during this extremely rapid growth phase. Mean predicted lengths and weights were 4.2 m and 1.1 metric tons (mt) at birth, 10.3 m and 13.5 mt at weaning, and 13.6 m and 29.6 mt when fully grown. Growth of right whales was best described using a 2-phased Gompertz growth model and could not be fit using any of the single continuous growth models commonly used for other mammals. Rapid growth during dependency may minimize the risk of predation and maximize calf survival. Rapid calf growth also may maximize development of the mouth and baleen to optimize foraging efficiency of juveniles at the time of weaning, as well as improve reproductive fitness by reducing the age at which sexual maturity is attained. However, transferring the amount of energy needed to support the rapid postnatal growth of North Atlantic right whales may ultimately affect the intervals between pregnancies (.3 years) of mature females.

keywords     Eubalaena glacialis, growth models, length, mass, reproductive costs, right whale
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Mechanical reliability of devices subdermally implanted into the young of long lived and endangered wildlife.
Hori, B., R.J. Petrell, G. Fernlund and A.W. Trites. 2012.
Journal of Materials Engineering and Performance. 21:1924-1931.
abstract
Service data does not exist for the strength of enclosures for subdermally implanted biotelemetry devices intended for young wild animals. Developing adequate tests especially for implants intended for endangered species is difficult due to the very limited availability of live animals and cadaverous tissue, ethical concerns about using them, and high enclosure costs. In this research, these limitations were overcome by taking a conservative approach to design and testing. Reliability tests were developed and performed to establish the likelihood that a thin subdermally and cranially implanted alumina enclosure would fail due to typical external forces related to diving, fights, and falls over the expected 30-year life time of sea lions. Cyclic fatigue tests indicative of deep dives performed out of tissue and at the 90% reliability level indicated no failure after 70,000 stress cycles at stresses of approximately 15 MPa; dynamic fatigue tests indicated a 5% probability of failure at 250 MPa; and puncture tests indicative of fight bites showed a 5% probability of failure at 1500 N. These values were far outside of what the animals might expect to encounter in real life. On the other hand, the response of the enclosure to impact outside of the tissue was failure at a mean energy level of 6.7 J. Modeling results predict that head impacts due to trampling by fighting sea lion males and falls over 1 m onto a rocky ledge typical of haul out environments would likely fracture an infant‚s head as well as the implant. The device can be implanted under an impact absorbing 1 cm blubber layer for extra protection. More service data for enclosures can be made more available despite limited availability of test animals if a conservative approach to testing is taken.

keywords     alumina, biomaterials, biotelemetry, mechanical testing, Sea Lion, structural ceramics
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Effect of phylogeny and prey type on fatty acid calibration coefficients in three species of pinnipeds - implications for the QFASA dietary quantification technique.
Rosen, D. A. S. and D.J. Tollit. 2012.
Marine Ecology Progress Series 467:263-276.
abstract
Quantitative fatty acid signature analysis (QFASA) has been proposed as a technique for determining the long-term diet of animals. The method compares the fatty acid (FA) profiles of predators and potential prey items to estimate relative prey intake. We tested the assumptions of a key step in QFASA, the correction of predator FA signatures for metabolic processes through sets of calibration coefficients (CCs). We conducted long-term controlled feeding studies with captive Steller sea lions consuming herring and eulachon and northern fur seals consuming herring. We compared the results with data from harbour seals eating herring to evaluate the effects of phylogeny and prey type on individual CCs. Even within the limited extended dietary FA subset recommended for use by other researchers, we found that at least 41% of the CCs differed by family (otariid vs. phocid seals) and 58% differed by predator species (sea lion vs. fur seal), suggesting that CCs may be highly species- specific. We also found that 64% of the CCs differed by prey type (sea lions consuming herring vs. eulachon), which raises some fundamental implementation issues. We also found significant differences in diet predictions when the herring- and eulachon-derived sets of CCs were applied to an actual multi-species diet. CCs are presently used as a simple mathematical attempt to describe potentially complex biochemistry. The results of this study raise questions regarding the validity of using CCs derived from an alternative predator species, and highlight some fundamental issues regarding QFASA methodology that need to be addressed through further controlled studies.
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Rates of maximum food intake in young northern fur seals (Callorhinus ursinus) and the seasonal effects of food intake on body growth.
Rosen, D., B.L. Young and A.W. Trites. 2012.
Canadian Journal of Zoology 90:61-91.
abstract
Accurate estimates of food intake and its subsequent affect on growth are required to understand the interaction between an animals‚ physiology and its biotic environment. We determined how food intake and growth of 6 young northern fur seals (Callorhinus ursinus L., 1758) responded seasonally to changes in food availability. Animals were given unrestricted access to prey for 8 hr per day on either consecutive days or on alternate days only. We found animals offered ad libitum food on consecutive days substantially increased their food intake over normal Œtraining‚ levels. However, animals that fasted on alternative days were unable to compensate by further increasing their levels of consumption on subsequent feeding days. Absolute levels of food intake were highly consistent during winter and summer trials (2.7 ˆ 2.9 kg d-1), but seasonal differences in body mass meant that fur seals consumed more food relative to their body mass in summer (~27%) than in winter (~20%). Despite significant increases in absolute food intake during both seasons, the fur seals did not appear to efficiently convert this additional energy into mass growth, particularly in the winter. These seasonal differences in conversion efficiencies and estimates of maximum intake rates can be used to generate physiologically realistic predictions about the effect of changes in food availability on an individual fur as well as the consequences for an entire population.
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Cost of living dictates what whales, dolphins and porpoises eat: the importance of prey quality on predator foraging strategies.
Spitz, J., A.W. Trites, V. Becquet, A. Brind'Amour, Y. Cherel, R. Galois and V. Ridoux. 2012.
PLoS ONE. Vol 7(11):e50096.
abstract
Understanding the mechanisms that drive prey selection is a major challenge in foraging ecology. Most studies of foraging strategies have focused on behavioural costs, and have generally failed to recognize that differences in the quality of prey may be as important to predators as the costs of acquisition. Here, we tested whether there is a relationship between the quality of diets (kJ g-1) consumed by cetaceans in the North Atlantic and their metabolic costs of living as estimated by indicators of muscle performance (mitochondrial density, n = 60, and lipid content, n = 37). We found that the cost of living of 11 cetacean species is tightly coupled with the quality of prey they consume. This relationship between diet quality and cost of living appears to be independent of phylogeny and body size, and runs counter to predictions that stem from the well-known scaling relationships between mass and metabolic rates. Our finding suggests that the quality of prey rather than th e sheer quantity of food is a major determinant of foraging strategies employed by predators to meet their specific energy requirements. This predator-specific dependence on food quality appears to reflect the evolution of ecological strategies at a species level, and has implications for risk assessment associated with the consequences of changing the quality and quantities of prey available to top predators in marine ecosystems.
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A review of the effects of different marking and tagging techniques on marine mammals.
Walker, K. A., A. W. Trites, M. Haulena and D. M. Weary. 2012.
Wildlife Research 59:15-30.
abstract
Wildlife research often requires marking and tagging animals to collect data on survival, reproduction, movement, behaviour and physiology. Identification of individual marine mammals can be carried out using tags, brands, paint, dye, photogrammetry, telemetry and other techniques. An analysis of peer-reviewed articles published from January 1980 to April 2011 addressing the effects of marking revealed a preponderance of studies focussed on short-term effects such as injuries and behavioural changes. Some marking techniques were reported to cause pain and to change swimming and haul-out behaviour, maternal attendance, and duration of foraging trips. However,marking has typically not been found to affect survival. No published research has addressed other possible long-term effects of marking related to injuries or pain responses. Studies of the more immediate effects of marking (mostly related to externally attached devices such as radio-transmitters) have shown a variety of different types and magnitudes of responses. It is important to note that studies failing to find treament differences are less likely to be published, meaning that the present and any other reviews based on published literaturemay be a biased sample of all research conducted on the topic. Publishing results that found no or low impacts (i.e. best practices) as well as those that found significant impacts on animals should both be encouraged. Future research under more controlled conditions is required to document acute effects of marking, including injury and pain, and to better understand longer-term effects on health, reproduction and survival. We recommend that studies using marked animals standardise their reports, with added detail on methodology, monitoring and sampling design, and address practices used to minimise the impact of marking on marine mammals.
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2011
 
An independent, scientific review of the Biological Opinion (2010) of the National Marine Fisheries Service Fisheries Management Plan for the Bering Sea/Aleutian Islands management areas.
Bernard, D.R., S.J. Jeffries, G. Knapp, and A.W. Trites. 2011.
Alaska Department of Fish and Game Special Publication 11-16. pp. 136
abstract
This special publication contains the final report of an independent scientific and economic review of a Biological Opinion (BiOp) issued 24 November, 2010 by the National Marine Fisheries Service (NMFS) on the Fisheries Management Plan (FMP) for the Bering Sea and Aleutian Islands (BSAI) Management Area under a section 7 consultation required by the Endangered Species Act. The BiOp involved the western distinct population segment (WDPS) of Steller sea lions Eumetopias jubatus, the conclusion of which is a finding that fisheries in the western and central Aleutian Islands placed the WDPS in jeopardy of recovery through adverse modification of habitat. The review panel evaluated the scientific evidence and argument given in support of this finding against the scientific requirements of the Endangered Species Act based on consistency, validity, and biologic relevance. The review panel also evaluated the economic analyses that formed the basis for the reasonable and prudent actions arising from the finding. The review panel followed only the terms of reference as published in this final report, and in their deliberations, considered written testimony and testimony provided at two public meetings, one in Seattle on June 2, 2011, and the other in Anchorage on August 22, 2011. The conclusions of the review panel can be found in total in the executive summary and in part at the end of each chapter of the special publication.
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Proportion of prey consumed can be determined from faecal DNA using real-time PCR.
Bowles, E., P.M. Schulte, D.J. Tollit, B.E. Deagle and A.W. Trites. 2011.
Molecular Ecology Resources 11:530-540.
abstract
Reconstructing the diets of pinnipeds by visually identifying prey remains recovered in faecal samples is challenging because of differences in digestion and passage rates of hard parts. Analyzing the soft-matrix of faecal material using DNA-based techniques is an alternative means to identify prey species consumed, but published techniques are largely non-quantitative, which limits their usefulness for some studies. We further developed and validated a real-time PCR technique using species-specific mitochondrial DNA primers to quantify the proportion of prey in the diets of Steller sea lions (Eumetopias jubatus), a pinniped species thought to be facing significant diet related challenges in the North Pacific. We first demonstrated that the proportions of prey tissue DNA in mixtures of DNA isolated from four prey species could be estimated within a margin of ~12% of the percent in the mix. These prey species included herring Clupea palasii, eulachon Thaleichthyes pacificus, squid Loligo opalescens and rosethorn rockfish Sebastes helvomaculatus. We then applied real-time PCR to DNA extracted from faecal samples obtained from Steller sea lions in captivity that were fed 11 different combinations of herring, eulachon, squid and Pacific ocean perch rockfish (Sebastes alutus), ranging from 7-75% contributions per meal (by wet weight). The difference between the average percentage estimated by real-time PCR and the percentage of prey consumed was generally less than 12% for all diets fed. Our findings indicate that real-time PCR of faecal DNA can detect the approximate relative quantity of prey consumed for complex diets and prey species, including cephalopods and fish.
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Predation on Fraser River sockeye salmon.
Christensen, V. and A.W. Trites. 2011.
In Cohen Commission Technical Report. www.cohencommission.ca. Vancouver, B.C. pp. 129
abstract
A review of the available scientific literature reveals a wide range of species holding the remains of sockeye salmon in their stomachs, but only a few of these predators have specialized in targeting sockeye, and there are no studies showing that a predator has consumed sufficient numbers over the past three decades to pose a population threat to sockeye salmon. There is no sign of a smoking gun among the long list of potential predators of Fraser River sockeye salmon. In the open ocean, sockeye salmon appear to draw the predatory attention of salmon sharks, blue sharks, and an obscure species fittingly called daggertooth. All three species likely increased in recent decades (after the 1992 UN ban on driftnet fisheries) ˜ and two of them (salmon sharks and daggertooth) may favor sockeye. Unfortunately, data for these species is also too sparse to draw conclusions about their otential role in the poor return of Fraser River sockeye in 2009, but their life histories suggest relatively stable numbers that should not have exerted greater predation upon sockeye in any single year relative to others. In addition to the daggertooth and sharks, marine mammals also consume adult sockeye salmon. However, sockeye are not an important part of marine mammal diets compared to the other species of salmon. No studies have reported marine mammals consuming sockeye salmon in the open ocean. However, small amounts of sockeye have been found in the stomachs or fecal samples collected from Steller sea lions, northern fur seals, harbour seals, killer whales, and white-sided dolphins feeding over the continental shelf and inside waters of British Columbia. Seal and sea lion populations have increased significantly in British Columbia and southeast Alaska since the late 1970s. However, the available data indicate that sockeye salmon is not a preferred prey species among marine mammals.
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Estimating behavioral parameters in animal movement models using a state-augmented particle filter.
Dowd, M. and R. Joy. 2011.
Ecology 92:568-575.
abstract
Data on fine-scale animal movement are being collected worldwide, with the number of species being tagged and the resolution of data rapidly increasing. In this study, a general methodology is proposed to understand the patterns in these high-resolution movement time series that relate to marine animal behavior. The approach is illustrated with dive data from a northern fur seal (Callorhinus ursinus) tagged on the Pribilof Islands, Alaska, USA. We apply a state-space model composed of a movement model and corresponding high-resolution vertical movement data. The central goal is to estimate parameters of this movement model, particularly their variation on appropriate time scales, thereby providing a direct link to behavior. A particle filter with state augmentation is used to jointly estimate the movement parameters and the state. A multiple iterated filter using overlapping data segments is implemented to match the parameter time scale with the behavioral inference. The time variation in the auto-covariance function facilitates identification of a movement model, allows separation of observation and process noise, and provides for validation of results. The analysis yields fitted parameters that show distinct time-evolving changes in fur seal behavior over time, matching well what is observed in the original data set.
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Convergent evolution in locomotory patterns of flying and swimming animals.
Gleiss, A.C., S.J. Jorgensen, N. Liebsch, J.E. Sala, B. Norman, G.C. Hays, F. Quintana, E. Grundy, C. Campagna, A.W. Trites, B.A. Block and R.P. Wilson. 2011.
Nature Communications Vol 2:352
abstract
Locomotion is one of the major energetic costs faced by animals and various strategies have evolved to reduce its cost. Birds use interspersed periods of flapping and gliding to reduce the mechanical requirements of level flight while undergoing cyclical changes in flight altitude, known as undulating flight. Here we equipped free-ranging marine vertebrates with accelerometers and demonstrate that gait patterns resembling undulating flight occur in four marine vertebrate species comprising sharks and pinnipeds. Both sharks and pinnipeds display intermittent gliding interspersed with powered locomotion. We suggest, that the convergent use of similar gait patterns by distinct groups of animals points to universal physical and physiological principles that operate beyond taxonomic limits and shape common solutions to increase energetic efficiency. Energetically expensive large-scale migrations performed by many vertebrates provide common selection pressure for efficient locomotion, with potential for the convergence of locomotory strategies by a wide variety of species.
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Cohort effects and spatial variation in age-specific survival of Steller sea lions from southeastern Alaska.
Hastings, K.K., L.A. Jemison, T.S Gelatt, J.L. Laake, G. Pendelton, J.C. King, A.W. Trites and K.W. Pitcher. 2011.
Ecosphere 2 Vol 111
abstract
Information concerning mechanistic processes underlying changes in vital rates and ultimately population growth rate is required to monitor impacts of environmental change on wildlife. We estimated age-specific survival and examined factors influencing survival for a threatened population of Steller sea lions (Eumetopias jubatus) in southeastern Alaska. We used mark-recapture models and data from 1,995 individuals marked at approximately one month of age at four of five rookeries in southeastern Alaska, and resighted from Oregon to the Bering Sea. Average annual survival probability for females was .64 for pups and 0.77 for yearlings, and increased from 0.91 to 0.96 from age 3ˆ7 yrs. Annual survival probability of males averaged 0.60 for pups and 0.88 by 7 yrs, resulting in probability of survival to age 7, 33% lower for males compared to females. Pups from northern southeastern Alaska (including an area of low summer population size but rapid growth) were twice as likely to survive to age 7 compared to pups from southern rookeries (including a large, historical, stable rookery). Effects of early conditions on future fitness were observed as (1) environmental conditions in the birth year equally affected first- and second year survival, and (2) effects of body mass at approximately one month of age were still apparent at 7 yrs. Survival from 0ˆ2 yrs varied among five cohorts by a maximum absolute difference of 0.12. We observed survival costs for long-distance dispersal for males, particularly as juveniles. However, survival was higher for non-pups that dispersed to northern southeastern Alaska, suggesting that moving to an area with greater productivity, greater safety, or lower population size may alleviate a poor start and provide a mechanism for spatial structure for sea lion populations.
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Aerial audiograms of several California sea lions (Zalophus californianus) and Steller sea lions (Eumetopias jubatus) measured using single and multiple simultaneous auditory steady-state response methods.
Mulsow, J., C. Reichmuth, F.M.D. Gulland, D.A.S. Rosen and J.J. Finneran. 2011.
Journal of Experimental Biology 214:1138-1147.
abstract
Measurements of the electrophysiological auditory steady-state response (ASSR) have proven to be efficient for evaluating hearing sensitivity in odontocete cetaceans. In an effort to expand these methods to pinnipeds, ASSRs elicited by single and multiple simultaneous tones were used to measure aerial hearing thresholds in several California sea lions (Zalophus californianus) and Steller sea lions (Eumetopias jubatus). There were no significant differences between thresholds measured using the single and multiple ASSR methods, despite the more rapid nature of data collection using the multiple ASSR method. There was a high degree of variability in ASSR thresholds among subjects; thresholds covered a range of ~40dB at each tested frequency. As expected, ASSR thresholds were elevated relative to previously reported psychophysical thresholds for California and Steller sea lions. The features of high-frequency hearing limit and relative sensitivity of most ASSR audiograms were, however, similar to those of psychophysical audiograms, suggesting that ASSR methods can be used to improve understanding of hearing demographics in sea lions, especially with respect to high-frequency hearing. Thresholds for one Steller sea lion were substantially elevated relative to all other subjects, demonstrating that ASSR methods can be used to detect hearing loss in sea lions.
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Whistle communication in mammal-eating killer whales (Orcinus orca): further evidence for acoustic divergence between ecotypes.
Riesch, R. and V.B. Deecke. 2011.
Behavioral Ecology and Sociobiology 65:1377-1387.
abstract
Public signaling plays an important role in territorial and sexual displays in animals; however, in certain situations, it is advantageous to keep signaling private to prevent eavesdropping by unintended receivers. In the northeastern Pacific, two populations of killer whales (Orcinus orca), fish-eating resident killer whales and mammal-eating transient killer whales, share the same habitat. Previous studies have shown that residents use whistles as private signals during close-range communication, where they probably serve to coordinate behavioral interactions. Here, we investigated the whistling behavior of mammal-eating killer whales, and, based on divergent social structures and social behaviors between residents and transients, we predicted to find differences in both whistle usage and whistle parameters. Our results show that, like resident killer whales, transients produce both variable and stereotyped whistles. However, clear differences in whistle parameters between ecotypes show that the whistle repertoire of mammal-eating killer whales is clearly distinct from and less complex than that of fish-eating killer whales. Furthermore, mammal-eating killer whales only produce whistles during milling after kill and surface-active behaviors, but are almost completely silent during all other activities. Nonetheless, whistles of transient killer whales may still serve a role similar to that of resident killer whales. Mammal-eating killer whales seem to be under strong selection to keep their communication private from potential prey (whose hearing ranges overlap with that of killer whales), and they appear to accomplish this mainly by restricting vocal activity rather than by changes in whistle parameters.
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South American sea lions in Peru have a lek-like breeding system.
Soto, K.H. and A.W. Trites. 2011.
Marine Mammal Science 307:306-333.
abstract
Five years of behavioral observations revealed significant effects of high air temperatures and breeding site topography on the mating system of South American sea lions in Peru. Unlike most polygynous mammals that defend females or fixed territories, male sea lions in Peru maintained positions along the shoreline where females passed each day to thermoregulate, and where most copulations occurred. Sex ratios (1 male per 17 females) and male mating success were extremely skewed (14% of males achieved 50% of the copulations, and 25% of them did not copulate at all). The mass daily movements of females toward the water and cool substrate of the shoreline, along with a highly skewed sex ratio, accentuated the difficulty for males to monopolize and restrict female movements. Femalesmoved freely and chose their mates, unlike in temperate regions of their range where male South American sea lions control groups of females or access to tide pools. Our observations indicate that the South American sea lion in Peru has a lek-like breeding system. This is a rare alternative to the common male strategies of defending females and resources, and is likely an evolutionary product of their highly skewed sex ratio, protracted breeding season, and the extreme subtropical climate where they breed.
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Harbor seal foraging response to a seasonal resource pulse, spawning Pacific herring.
Thomas, A. C., M. M. Lance, S. J. Jeffries, B. G. Miner and A. Acevedo-Gutiérrez. 2011.
Marine Ecology Progress Series 441:225-239.
abstract
Evidence suggests that Pacific harbor seals Phoca vitulina are likely to alter their foraging behavior in response to seasonal prey pulses. We hypothesized that spawning herring Clupea pallasii aggregations are seasonally important prey for harbor seals, predicting that (1) harbor seal consumption of adult herring would peak during the spawning season, (2) harbor seals would seasonally change their foraging areas to take advantage of spawning herring aggregations, and (3) seal diving behavior would reflect the vertical distribution of herring during the spawning season. The predictions were tested using an analysis of harbor seal prey remains, GPS telemetry, and satellite-linked time/depth recorder data. Contrary to predictions, herring in harbor seal diet was comprised of 74% juveniles and 26% adults in the spawn season, versus 37% juveniles and 63% adults in the post-spawn season. Harbor seal use of documented herring areas was highest during the season when herring did not spawn, and seal diving behavior did not reflect the vertical distribution of herring. The lack of response by harbor seals to spawning herring pulses is likely explained by the low energy density of adult herring during the spawn season, and the availability of profitable alternative prey such as juvenile herring. This study highlights the influence of relative prey profitability on the foraging behavior of harbor seals, and may help to explain why predators do not always respond as predicted to resource pulses.
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Competing Conservation Objectives for Predators and Prey: Estimating Killer Whale Prey Requirements for Chinook Salmon.
Williams, R., M. KrkoÅ¡ek, E. Ashe, T.A. Branch, S. Clark, P.S. Hammond, E. Hoyt, D.P. Noren, D.A.S. Rosen and A. Winship. 2011.
PloS One Vol 6:e26738.
abstract
Ecosystem-based management (EBM) of marine resources attempts to conserve interacting species. In contrast to single-species fisheries management, EBM aims to identify and resolve conflicting objectives for different species. Such a conflict may be emerging in the northeastern Pacific for southern resident killer whales (Orcinus orca) and their primary prey, Chinook salmon (Oncorhynchus tshawytscha). Both species have at-risk conservation status and transboundary (CanadaˆUS) ranges. We modeled individual killer whale prey requirements from feeding and growth records of captive killer whales and morphometric data from historic live-capture fishery and whaling records worldwide. The models, combined with caloric value of salmon, and demographic and diet data for wild killer whales, allow us to predict salmon quantities needed to maintain and recover this killer whale population, which numbered 87 individuals in 2009. Our analyses provide new information on cost of lactation and new parameter estimates for other killer whale populations globally. Prey requirements of southern resident killer whales are difficult to reconcile with fisheries and conservation objectives for Chinook salmon, because the number of fish required is large relative to annual returns and fishery catches. For instance, a U.S. recovery goal (2.3% annual population growth of killer whales over 28 years) implies a 75% increase in energetic requirements. Reducing salmon fisheries may serve as a temporary mitigation measure to allow time for management actions to improve salmon productivity to take effect. As ecosystem-based fishery management becomes more prevalent, trade-offs between conservation objectives for predators and prey will become increasingly necessary. Our approach offers scenarios to compare relative influence of various sources of uncertainty on the resulting consumption estimates to prioritise future research efforts, and a general approach for assessing the extent of conflict between conservation objectives for threatened or protected wildlife where the interaction between affected species can be quantified.
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Dive behaviour impacts the ability of heart rate to predict oxygen consumption in Steller sea lions (Eumetopias jubatus) foraging at depth.
Young, B. L., D. A. S. Rosen, A. G. Hindle, M. Haulena and A. W. Trites. 2011.
Journal of Experimental Biology 214:2267-2275.
abstract
The predictive relationship between heart rate (fH) and oxygen consumption (VO2) has been derived for several species of marine mammals swimming horizontally or diving in tanks to shallow depths. However, it is unclear how dive activity affects the fH:VO2 relationship and whether the existing equations apply to animals diving to deeper depths. We investigated these questions by simultaneously measuring the fH and VO2 of Steller sea lions (Eumetopias jubatus) under different activity states (surface resting or diving), types of dives (single dives or dive bouts), and depths (10 or 40m). We examined the relationship over dives only and also over dive cycles (dive + surface interval). We found that fH could only predict VO2 over a complete single dive cycle or dive bout cycle (i.e. surface intervals had to be included). The predictive equation derived for sea lions resting on the surface did not differ from that for single dive cycles. However, the equation derived over dive bout cycles multiple dives + surface intervals) differed from those for single dive cycles or surface resting, with similar fH for multiple dive bout equations yielding higher predicted VO2 than that for single dive bout cycles (or resting). The fH:VO2 relationships were not significantly affected by dive duration, dive depth, water temperature or cumulative food consumed under the conditions tested. Ultimately, our results demonstrate that fH can be used to predict activity-specific metabolic rates of diving Steller sea lions, but only over complete dive cycles that include a post-dive surface recovery period.
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Environment and feeding change the ability of heart rate to predict metabolism in resting Steller sea lions (Eumetopias jubatus).
Young, B. L., D.A.S. Rosen, M. Haulena, A. G. Hindle and A.W. Trites. 2011.
Journal of Comparative Physiology-B 118:105-116.
abstract
The ability to use heart rate (fh) to predict oxygen consumption rates (VO2) in Steller sea lions and other pinnipeds has been investigated in fasting animals. However, it is unknown whether established fh:VO2 relationships hold under more complex physiological situations, such as when animals are feeding or digesting. We assessed whether fh could accurately predict VO2 in trained Steller sea lions while fasting and after being fed. Using linear mixed-effects models, we derived unique equations to describe the fh:VO2 relationship for fasted sea lions resting on land and in water. Feeding did not significantly change the fh:VO2 relationship on land. However, Steller sea lions in water displayed a different fh:VO2 relationship after consuming a 4 kg meal compared to the fasting condition. Incorporating comparable published fh:VO2 data from Steller sea lions showed a distinct effect of feeding after a 6 kg meal. Ultimately, our study illustrated that both feeding and physical environment are statistically relevant when deriving VO2 from telemetered fh, but that only environment affects the practical ability to predict metabolism from fh. Updating current bioenergetic models with data gathered using these predictive fh:VO2 equations will yield more accurate estimates of metabolic rates of free-ranging Steller sea lions under a variety of physiological, behavioral, and environmental states.
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2010
 
Animal behaviour and marine protected areas: incorporating behavioural data into the selection of marine protected areas for an endangered killer whale population.
Ashe, E., D.P. Noren, and R. Williams. 2010.
Animal Conservation 13:196-203.
abstract
Like many endangered wildlife populations, the viability and conservation status of ‘southern resident’ killer whales Orcinus orca in the north-east Pacific may be affected by prey limitation and repeated disturbance by human activities. Marine protected areas (MPAs) present an attractive option to mitigate impacts of anthropogenic activities, but they run the risk of tokenism if placed arbitrarily. Notwithstanding recreational and industrial marine traffic, the number of commercial vessels in the local whalewatching fleet is approaching the number of killer whales to be watched. Resident killer whales have been shown to be more vulnerable to vessel disturbance while feeding than during resting, travelling or socializing activities, therefore protected-areas management strategies that target feeding ‘hotspots’ should confer greater conservation benefit than those that protect habitat generically. Classification trees and spatially explicit generalized additive models were used to model killer whale habitat use and whale behaviour in inshore waters of Washington State (USA) and British Columbia (BC, Canada). Here we propose a candidate MPA that is small (i.e. a few square miles), but seemingly important. Killer whales were predicted to be 2.7 times as likely to be engaged in feeding activity in this site than they were in adjacent waters. A recurring challenge for cetacean MPAs is the need to identify areas that are large enough to be biologically meaningful while being small enough to allow effective management of human activities within those boundaries. Our approach prioritizes habitat that animals use primarily for the activity in which they are most responsive to anthropogenic disturbance.
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Changes in the foraging dive behaviour and energetics of king penguins through summer and autumn: a month by month analysis.
Halsey, L.G., P.J. Butler, A. Fahlman, C.A. Bost, and Y. Handrich. 2010.
Marine Ecology Progress Series 401:279-289.
abstract
King penguins Aptenodytes patagonicus are known to change their diving behaviour in response to changes in both prey location and their breeding status through the early stages of the breeding cycle (austral summer and autumn). However, little information exists on whether and how these changes affect the energy expenditure of such behaviour. By deploying heart rate and hydrostatic pressure data loggers, we investigated detailed changes in the dive time budgeting of king penguins during foraging dives across the breeding season, in the same individuals, and the associated changes in estimated oxygen consumption during those dives. Maximum dive depth, duration, bottom duration, feeding events (indicated by wiggles) per dive and post-dive duration increased through the study period. While a foraging dive later in the breeding season was energetically more costly than a dive earlier in the season, the overall rate of energy expenditure did not change, nor did energy cost per unit prey capture. These findings indicate an ability of king penguins to adjust their foraging dive behaviours through the summer and autumn without affecting the energetic costs of diving to capture prey. Such plasticity may be necessary to compensate for changes both in prey location and abundance, and in the energy requirements of the chick over time.
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Swimming depth and ocean currents affect transiting costs in Steller sea lions (Eumetopias jubatus).
Hindle, A.G., D.A.S. Rosen and A.W. Trites. 2010.
Aquatic Biology 10:139-148.
abstract
Transit costs associated with commuting between resting sites ashore and foraging areas at sea are an appreciable portion of foraging expenditures in pinnipeds. We examined transit swimming in three Steller sea lions (Eumetopias jubatus) trained to follow a moving boat at different speeds and depths. We measured dive behavior (duration) and focused specifically on activity measures (fore-flipper stroking and ODBA, an overall measure of body motion), which may be proxies for metabolic expenditure. Sea lions appeared to increase efficiency while transiting at depths that approached three times their body diameters (mean depth = 151 ± 1 cm SEM, n = 87). Although the response was not uniform for all tested scenarios, all of the significant adjustments we observed to dive behavior and swimming mechanics supported an increased efficiency at this depth. An increase in transit speed (4.5 versus 3.5 knots surface speed) was associated with elevated flipper stroke frequencies (+5%) and stroke output (ODBA•stroke-1, +48%). Sea lions transiting against the flow of a tidal current had reduced dive durations (-10%), while total ODBA was consistently elevated (+8% overall). This response to tidal flow was accompanied either by elevated ODBA•stroke-1 (3.5 knots) or a parallel increase in stroking (4.5 knots). Our data demonstrate that small changes in the physical environment affect transiting in Steller sea lions, and imply that altered prey fields or changing ocean conditions can carry energetic consequences.
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Dive response differs between shallow- and deep-diving Steller sea lions (Eumetopias jubatus).
Hindle, A.G., B.L. Young, D.A.S. Rosen, M. Haulena and A.W. Trites. 2010.
Journal of Experimental Marine Biology and Ecology 394:141-148.
abstract
Muscle exercise correlates with oxygen use, tissue perfusion and heart rate (fH) in terrestrial animals, but the relationship between these physiological processes is less clear in diving animals. We found the mean heart rate of Steller sea lions trained to voluntarily dive to depths up to 40m dropped by 40% while diving, and noted that mean bradycardia was 9% greater during shallow (10m) compared to deep (40m) dives. Longer dives resulted in lower heart rates, but only when they were shallow; on the other hand, minimum instantaneous fH decreased consistently with dive duration. In general, instantaneous fH did not reflect activity over short timescales. Our data suggest that our sea lions invoked a different dive response depending on whether they dove to shallow or deep depths. During shallow (10m) dives only, the correlation between activity and fH was indicative of vascular compromise between diving and exercise. However, during deep dives (40m), there was no such correlation, suggesting that locomotory activity was uncoupled from dive bradycardia, which was possibly mediated by an absence of blood flow to active muscle. For both diving scenarios, surface fH correlated with dive activity, suggesting that some underwater locomotory costs were deferred to the post-dive surface interval. Ultimately, our data support the speculation that Steller sea lion locomotory muscles become hypoxic during diving, regardless of dive depth.
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Fecal triiodothyronine and thyroxine concentrations change in response to thyroid stimulation in Steller sea lions (Eumetopias jubatus).
Keech, A.L., D.A.S. Rosen, R.K. Nelson Booth, A.W. Trites and S.K. Wasser. 2010.
General and Comparative Endocrinology 166:180-185.
abstract
Variation in concentrations of thyroid hormones shed in feces may help to identify physiological states of animals, but the efficacy of the technique needs to be validated for each species. We determined whether a known physiological alteration to thyroid hormone production was reflected in hormone concentrations in the feces of Steller sea lions (Eumetopias jubatus). We quantified variation of triiodothyronine (T3) and thyroxine (T4) concentrations in feces following two intramuscular injections of thyrotropin (thyroid-stimulating hormone, TSH) at 24 h intervals in four captive female sea lions. We found fecal T3 concentrations increased 18-57% over concentrations measured in the baseline sample collected closest to the time of the first TSH injection (p=0.03) and 1-75% over the mean baseline concentration (p=0.12) for each animal of all samples collected prior to injections. The peak T3 response occurred 48 h post injection in three animals and 71 h in the fourth. Post-injection T4 concentrations did not differ between the baseline sample collected closest to the time of the first TSH injection (p=0.29) or the mean baseline concentration (p=0.23) for each animal. These results indicate that induced physiological alterations to circulating thyroid hormone concentrations can be adequately detected through analyses of fecal T3 concentrations and that the technique may provide a means of non-invasively detecting metabolic changes in Steller sea lions.
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Confronting the costs and conflicts associated with biodiversity.
Linnell, J.D.C., D. Rondeau, D.H. Reed, R. Williams, R. Altwegg, C.J. Raxworthy, J.D. Austin, N. Hanley, H. Fritz, and D.M. Evans. 2010.
 13:429-431.
abstract
Capturing the global benefits of biodiversity requires sacrifice from us all, not only in financial terms (e.g. higher taxes and foregone profits) but also in terms of personal risk, material losses, freedom of action or convenience. Our common task should not only be to focus on research, but also on communicating to non-scientists both the merits and challenges of maintaining biodiversity and presenting the practical measures that can be deployed to achieve this goal. Open dialogue of the trade-offs involved in biodiversity conservation actions leads to the types of democratic decision making, increased sense of community and social justice, and respect for indigenous, rural and local ways of life that are hallmarks of successful conservation programs.
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The diving behaviour of mammal-eating killer whales (Orcinus orca): variations with ecological not physiological factors. Canadian.
Miller, P. J. O., A. D. Shapiro and V. B. Deecke. 2010.
Journal of Zoology 88:1103-1112.
abstract
Mammal-eating killer whales (Orcinus orca(L., 1758)) are a rare example of social predators that hunt together in groups of sexually dimorphic adults and juveniles with diverse physiological diving capacities. Dayˆnight ecological differences should also affect diving as their prey show diel variation in activity and mammal-eating killer whales do not rely on echolocation for prey detection. Our objective was to explore the extent to which physiological aerobic capacities versus ecological factors shape the diving behaviour of this breath-hold diver. We used suction-cup-attached depth recorders (Dtags) to record 7608 dives of 11 animals in southeast Alaska. Analysis of dive sequences revealed a strong bout structure in both dive depth and duration. Dayˆnight comparisons revealed reduced rates of deep dives, longer shallow dives, and shallower long-duration dives at night. In contrast, dive variables did not differ by ageˆsex class. Estimates of the aerobic dive limit (cADL) suggest that juveniles exceeded their cADL during as much as 15% of long dives, whereas adult males and females never exceeded their cADL. Mammal-eating killer whales in this area appear to employ a strategy of physiological compromise, with smaller group members diving nearer their physiological limits and large-bodied males scaling down their physiological performance.
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Growth rates and differential investment in male and female Juan Fernández fur seal pups.
Osman, L.P., C.A. Moreno and A.W. Trites. 2010.
Journal of Mammalogy 91:1188-1196.
abstract
Male Juan Fernández fur seals (Arctocephalus philippii) are significantly larger than females at birth and show extreme dimorphism as adults. We investigated morphological differences among male and female pups using a cross-sectional sampling design to evaluate whether pup growth rates during the breeding season were sex-specific. We characterized growth rates using mass, length, and girth and found that length was the least variable measure of body growth (based on the coefficients of variation for the three measures of body size). Male pups were heavier on average than female pups on any given day of sampling but did not grow faster than females. No significant differences were noted in the body conditions of male and female pups. These findings suggest that the sexual differences among A. philippii pups originate before birth and are not accentuated while suckling during the breeding season.
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Seasonal influence on the response of the somatotropic axis to nutrient restriction and re-alimentation in captive Steller sea lions (Eumetopias jubatus).
Richmond, J.P., T. Jeanniard du Dot, D.A.S. Rosen and S.A. Zinn. 2010.
Journal of Experimental Zoology 311A:144-156.
abstract
Fluctuations in availability of prey resources can impede acquisition of sufficient energy for maintenance and growth. By investigating the hormonal mechanisms of the somatotropic axis that link nutrition, fat metabolism, and lean tissue accretion, we can assess the physiological impact of decreased nutrient intake on growth. Further, species that undergo seasonal periods of reduced intake as a part of their normal life history may have a differential seasonal response to nutrient restriction. This experiment evaluated the influence of season and age on the response of the somatotropic axis, including growth hormone (GH), insulin-like growth factor (IGF)-I, and IGF-binding proteins (BP), to reduced nutrient intake and re-alimentation in Steller sea lions. Eight captive females (five juveniles, three sub-adults) were subject to 28-day periods of food restriction, controlled re-feeding, and ad libitum recovery in summer (long-day photoperiod) and winter (short-day photoperiod). Hormone concentrations were insensitive to type of fish fed (low fat pollock vs. high fat herring), but sensitive to energy intake. Body mass, fat, and IGF-I declined, whereas GH and IGFBP-2 increased during feed restriction. Reduced IGF-I and IGFBP with increased GH during controlled re-feeding suggest that animals did not reach positive energy balance until fed ad libitum. Increased IGF-I, IGFBP-2, IGFBP-3, and reduced GH observed in summer reflected seasonal differences in energy partitioning. There was a strong season and age effect in the response to restriction and re-alimentation, indicating that older, larger animals are better able to cope with stress associated with energy deficit, regardless of season.
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Stable isotope signal homogeneity and differences between and within pinniped muscle and skin.
Todd, S.K., B. Holm, D.A.S. Rosen and D.J. Tollit. 2010.
Marine Mammal Science 26:176-185.
abstract
Stable isotope analysis is often used to examine diet choice and tropic relationships in marine mammals. However, the technique makes a number of largely untested assumptions. For example, researchers often assume localized biopsies to be representative of the whole animal—that is, that the isotopic signal is homogenous within a tissue. Further, isotopic composition may differ across the body within the same tissue type due to differential assimilation or catabolization rates. We investigated the homogeneity of 13C and 15N values in skin and muscle across the body per individual in three pinniped species: Steller sea lions (Eumetopias jubatus, n = 5), California sea lions (Zalophus californianus, n = 6), and harbor seals (Phoca vitulina, n = 7). We also assessed if there are consistent carbon and nitrogen isotope differences between these two commonly sampled tissues. Our results show that skin tissue was significantly 13C enriched when compared to muscle tissue, and more difficult to properly process. Despite expected differences across the body in physiological processes and biochemical composition, our data indicate stable isotope signal homogeneity across the body within both muscle and skin, for both carbon and nitrogen isotopes, in all three species. These results indicate that sufficient homogeneity exists within skin and muscle tissues to suggest that point sampling can be considered representative of entire tissues, and is thus a valid technique in stable isotope studies of marine mammals.
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Prey capture attempts can be detected in Steller sea lions and other marine predators using accelerometers.
Viviant, M., A.W. Trites, D.A.S. Rosen, P. Monestiez and C. Guinet. 2010.
Polar Biology 33:713-719.
abstract
We attached accelerometers to the head and jaw of a Steller sea lion (Eumetopias jubatus) to determine whether feeding attempts in a controlled setting could be quantified by acceleration features characteristic of head and jaw movements. Most of the 19 experimental feeding events that occurred during the 51 dives recorded resulted in specific acceleration patterns that were clearly distinguishable from swimming accelerations. The differential acceleration between the head-mounted and jaw-mounted accelerometers detected 84% of prey captures on the vertical axis and 89% on the horizontal axis. However, the jaw-mounted accelerometer alone proved to be equally effective at detecting prey capture attempts. Acceleration along the horizontal (surge)-axis appeared to be particularly efficient in detecting prey captures, and suggests that a single accelerometer placed under the jaw of a pinniped is a promising and easily implemented means of recording prey capture attempts.
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Shark aggregation in coastal waters of British Columbia.
Williams, R., T.A. Okey, S.S. Wallace, and V.F. Gallucci. 2010.
Marine Ecology Progress Series 414:249-256.
abstract
A concentration of pelagic sharks was observed in an area of western Queen Charlotte Sound, British Columbia, during systematic shipboard line-transect surveys conducted (2004 to 2006) for marine mammals throughout coastal waters of British Columbia. Surveys allowed only brief observations of sharks at the surface, providing limited opportunity to confirm species identity. Observers agreed, however, that salmon sharks Lamna ditropis (Lamnidae) were most common, followed by blue sharks Prionace glauca (Carcharhinidae). Both conventional and model-based distance sampling statistical methods produced large abundance estimates (~20000 sharks of all species combined) concentrated within a hotspot encompassing ~10% of the survey region. Neither statistical method accounted for submerged animals, thereby underestimating abundance. Sightings were made in summer, corresponding with southern movement of pregnant salmon sharks from Alaska. The previously undocumented high density of these pelagic sharks in this location has implications for understanding at-sea mortality of returning Pacific salmon Oncorhynchus spp. (Salmonidae) and for assessing conservation status of sharks in Canada and beyond. We recommend that a dedicated Canada-US sightings and biological sampling programme be considered, perhaps under the UN Transboundary Species Fishery programme.
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2009
 
Lamination for subdermal implant fixation.
Hori, B.D., R.J. Petrell, A.W. Trites, and T. Godbey. 2009.
Journal of Biomedical Materials Research: Part B - Applied Biomaterials 91B:17-25.
abstract
hirty-six aluminum oxide laminated discs were implanted into 12 young rabbits (18 with a 0.5 mm porous layer and 18 with 1 mm) to determine whether implants that are porous only on one side could fixate to subcutaneous tissue. After 3 months, discs were encased within thin pouches (0.02-0.14 mm) of fibrous connective tissue, as would have been expected of a completely porous implant. Solid sides showed no while the porous sides showed little attachment to pouches. 47% (17) of the discs had moved 1.4±0.8 cm beyond the 4.7 + 1 cm they had moved due to normal skin growth, while two others had moved between 6.2 and 6.5 cm beyond this measure. The proportion of 1 mm porous layer discs migrating within subcutaneous tissue was no greater than the proportion of 0.5 mm layer discs migrating (p=0.15). Porous layer height and disc migration did not affect the attachment strength of pouch to surrounding tissues (68 ±23 N, p=0.34). Pouch thickness, which has been associated to the level of applied forces in other studies, increased with migration distance (p=0.054). Results indicate that one sided porous disks are likely easier to retrieve than completely porous ones, but cannot be prevented from migrating in loose tissue of young animals. Data is being used to design subdermal radio frequency devices for endangered marine animals.
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Changes in glucocorticoids, IGF-I and thyroid hormones as indicators of nutritional stress and subsequent refeeding in Steller sea lions (Eumetopias jubatus).
Jeanniard du Dot, T., D.A.S. Rosen, J.P. Richmond, A.S. Kitaysky, S.A. Zinn and A.W Trites. 2009.
Comparative Biochemistry and Physiology, Part A 152:524-534.
abstract
Physiological responses to changes in energy balance are tightly regulated by the endocrine system through glucocorticoids, IGF-I and thyroid hormones. Changes in these hormones were studied in eight captive female Steller sea lions that experienced changes in food intake, body mass, body composition, and blood metabolites during summer and winter. During a period of energy restriction, one group of sea lions was fed reduced amounts of Pacific herring and another was fed an isocaloric diet of walleye pollock, after which both groups returned to their pre-experimental diets of herring. Cortisol was negatively and IGF-I was positively associated with changes in body mass during periods of energy restriction (mass loss associated with increase in cortisol and decrease in IGF-I) and refeeding (body mass maintenance associated with stable hormone concentrations in summer and compensatory growth linked to decrease in cortisol and increase in IGF-I in winter). Cortisol and IGF-I were also correlated with changes in lipid and lean mass, respectively. Consequently, these two hormones likely make adequate biomarkers for nutritional stress in sea lions, and when combined provide indication of the energetic strategy (lipid vs lean mass catabolism) animals adopt to cope with changes in nutrient intake. Unlike type of diet fed to the sea lions, age of the animals also impacted hormonal responses, with younger animals showing more intense hormonal changes to nutritional stress. Thyroid hormones, however, were not linked to any physiological changes observed in this study.
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Energy reallocation during and after periods of nutritional stress in Steller sea lions: low-quality diet reduces capacity for physiological adjustments.
Jeanniard du Dot, T., D.A.S Rosen and A.W. Trites. 2009.
Physiological and Biochemical Zoology 89:516-530.
abstract
Two groups of female Steller sea lions (Groups H and P) were subjected to periods of energy restriction and subsequent re-feeding during winter and summer to determine changes in energy partition among principal physiological functions and the potential consequences to their fitness. Both sea lion groups consumed high-quality fish (herring) before and after the energy restrictions. During restrictions, Group H was fed a lower quantity of herring and Group P a caloric equivalent of low-quality fish (pollock). Quantitative estimates of maintenance and production energies and qualitative estimates of thermoregulation, activity and basal metabolic rate were measured. During summer, all animals compensated for the imposed energy deficit by releasing stored energy (production energy). Group H also optimized the energy allocation to seasonal conditions by increasing activity during summer when fish are naturally abundant (foraging effort) and by decreasing thermoregulation capacity when waters are warmer. During winter, both groups decreased the energy allocated to overall maintenance functions (basal metabolic rate, thermoregulation and activity together) in addition to releasing stored energy, but preserved thermoregulatory capacity. Group H also decreased activity levels in winter when foraging in the wild is less efficient, unlike Group P. Overall, sea lions fed pollock did not change energy allocation to suit environmental conditions as readily as those fed herring. This implies that low energy density diet may further reduce fitness of animals in the wild during periods of nutritional stress.
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Vessel traffic disrupts the foraging behavior of southern resident killer whales Orcinus orca.
Lusseau, D., D.E. Bain, R. Williams, and J.C. Smith. 2009.
Endangered Species Research 6:211-221.
abstract
Vessel traffic may have contributed to southern resident killer whales Orcinus orca becoming endangered. To determine the importance of this threat, we measured the behavior of southern residents in the presence and absence of vessels from 2003 to 2005 at 2 different sites along San Juan Island, Washington, USA. We observed activity states of killer whale schools using scan sampling and collected information on the number of vessels present at various distances from those. We use first-order, time-discrete Markov chains to estimate state-transition probability matrices under varying boat exposure conditions. Transition probabilities between activity states were significantly affected by vessel traffic. In addition, there was a reduction in time spent foraging, as estimated from the stationary state budget from the Markov chains, confirming an effect also previously observed in northern resident killer whales. If reduced foraging effort results in reduced prey capture, this would result in decreased energy acquisition. Each school was within 400 m of a vessel most of the time during daylight hours from May through September. The high proportion of time southern resident killer whales spend in proximity to vessels raises the possibility that the short-term behavioral changes reported here can lead to biologically significant consequences.
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Seasonal differences in biochemical adaptation to fasting in juvenile and subadult Steller sea lions (Eumetopias jubatus).
Rea, L.D., M. Berman-Kowalewski, D.A.S. Rosen, and A. W.Trites. 2009.
Physiological and Biochemical Zoology 82:236-247.
abstract
Nine Steller sea lions (Eumetopias jubatus) aged 1.756 yr were experimentally fasted for 714 d during the breeding and nonbreeding seasons to identify changes in plasma metabolites that are indicative of fasting and to determine whether the ability of sea lions to fast varies seasonally or with age. Although some animals approached the limit of their protein-sparing ability by the end of our fasting experiments, there was no sign of irreversible starvation biochemistry. Plasma blood urea nitrogen (BUN) concentrations decreased in all animals within the first week of fasting, reflecting a shift to a fasting-adapted state; however, significant increases in plasma BUN concentration at the end of the nonbreeding season fasts suggest that subadult Steller sea lions were not able to maintain a protein-sparing metabolism for a full 14 d during the nonbreeding season. In contrast, juveniles were able to enter protein sparing sooner during the nonbreeding season when they had slightly higher initial percent total body lipid stores than during the breeding season. Subadult and juvenile sea lions had low circulating ketone body concentrations compared with young sea lion pups, suggesting an age-related difference in how body reserves are utilized during fasting or how the resulting metabolites are circulated and catabolized. Our data suggest that metabolite concentrations from a single blood sample cannot be used to accurately predict the duration of fast; however, threshold metabolite concentrations may still be useful for assessing whether periods of fasting in the wild are unusually long compared with those normally experienced.
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Steller sea lions Eumetopias jubatus and nutritional stress: evidence from captive studies.
Rosen, D.A.S. 2009.
Mammal Review 39:284-306.
abstract
1. Numbers of Steller sea lions Eumetopias jubatus in the North Pacific have declined. According to the Nutritional Stress Hypothesis, this decline is due to reduced food availability. Data from studies conducted on pinnipeds in the laboratory are used here to test whether the Nutritional Stress Hypothesis can explain the decline of Steller sea lions. 2. Overall, there is strong evidence for biologically meaningful differences in the nutritional quality of major prey species. Steller sea lions can partly compensate for low-quality prey by increasing their food consumption. 3. There appear to be no detrimental effects of low-lipid prey on sea lion growth or body composition when sea lions can consume sufficient quantities of prey. However, the ability to increase consumption is physiologically limited, particularly in young animals. Overall, it is more difficult to maintain energy intake on a diet of low-quality prey than on a normal diet. 4. Under conditions of inadequate food intake (either due to decreased prey availability or quality, or increased energy requirements) the overall impacts of nutritional stress are complex, and are dependent upon season, prey quality, age, and the duration and intensity of the nutritional stress event. 5. Studies on pinnipeds in the laboratory have been instrumental in identifying the conditions under which changes in sea lion prey can result in nutritional stress, and the nature of the physiological impacts of nutritional stress events.
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Steller sea lion foraging response to seasonal changes in prey availability.
Sigler, M.F., D.J. Tollit, J.J. Vollenweider, J.F. Thedinga, D.J. Csepp, J.N. Womble, M.A. Wong, M.J. Rehberg and A.W. Trites. 2009.
Marine Ecology Progress Series 388:243-261.
abstract
We hypothesized that: (1) Steller sea lion Eumetopias jubatus diet choice is a function of prey availability, (2) sea lions move to take advantage of times and locations of seasonal prey concentrations and (3) the number present depends on the amount of prey available (numerical response). Over 3 yr, typically on a quarterly basis, in Frederick Sound, SE Alaska, multiple measurements were taken of Steller sea lion abundance (aerial surveys), diet (scats), dive behavior (satellite telemetry)and prey availability and caloric density (nearshore, pelagic and demersal fish surveys). We found that Steller sea lions shifted diet composition in response to changes in prey availability of pollock Theragra chalcogramma, hake Merluccius productus, herring Clupea pallasi and salmon Oncorhynchus spp. They selected intermediate-sized fish and avoided small (<10 cm) and large (>60 cm) fish, and moved between areas as prey became available seasonally. The number of sea lions present depended on the amount of prey available; a standing biomass of 500 to 1700 t of prey in a nonbreeding area such as Frederick Sound, depending on species composition, can attract and sustain about 500 sea lions. Pollock was more frequent in sea lion diet in inside waters of SE Alaska including Frederick Sound, Stephens Passage and Lynn Canal than anywhere else in Alaska and contributed about one-third of the dietary energy in Frederick Sound. This finding implies that a diet with substantial year-round contributions from less nutritious, but abundant prey such as pollock can form part of a healthy diet as long as more nutritious prey such as herring, salmon or eulachon Thaleichthys pacificus also are consumed. Our study supports the conclusion that the Steller sea lion is an opportunistic marine predator with a flexible foraging strategy that selects abundant, accessible prey and shifts among seasonally available species.
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Fasting affects the surface and diving metabolic rates of Steller sea lions (Eumetopias jubatus).
Svärd, C., A. Fahlman, D.A.S. Rosen, R. Joy and A.W. and Trites. 2009.
Aquatic Biology 8:71-82.
abstract
Changes in metabolic rates were measured in 3 captive female Steller sea lions (Eumetopias jubatus) that experienced fasts during summer and winter. Metabolic rates were measured (via O2 consumption) before (MRs, surface) and after (DMR, dive + surface interval) the sea lions dove to 10–50 m depths. Measurements were obtained prior to 9-10 day fasts, and following a 14 day recovery period. The sea lions lost significantly more body mass (Mb) during the winter fast (10.6%), compared with the summer (9.5%). Mass-corrected dive metabolic rate (cDMR = DMR • Mb-0.714) was not affected by dive depth or duration, but increased significantly following the winter fasts (13.5 ± 8.1%), unlike the decrease during summer (-1.1 ± 3.2%). However, mass-corrected surface metabolic rate (cMRs) decreased significantly after both the summer (-16.4 ± 4.7%) and winter (-8.0 ± 9.0%) fasts. Consequently, the ratio between cDMR and cMRc was significantly higher in winter, suggestive of an increased thermal challenge and convective heat loss while diving. Increased cDMs following the fast indicated that digestion began during foraging and was not deferred, implying that access to ingested energy was of higher priority than optimizing diving ability. cDMR was elevated throughout the recovery period, independent of season, resulting in a 12% increase in foraging cost in winter and a 3% increase in summer. Our data suggest that Steller sea lions are more sensitive to changes in body condition due to food shortages in the winter compared with the summer.
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Development and application of DNA techniques for validating and improving pinniped diet estimates.
Tollit, D.J., A.D. Schulze, A.W. Trites, P.F. Olesiuk, S.J. Crockford, R.R. Ream T.S. Gelatt and K.M. Miller. 2009.
Ecological Applications 19:889-905.
abstract
Polymerase chain reaction techniques were developed and applied to identify DNA from >40 species of prey contained in fecal (scat) soft part matrix collected at terrestrial sites used by Steller sea lions (Eumetopias jubatus) in British Columbia and the Eastern Aleutian Islands, Alaska. Sixty percent more fish and cephalopod prey were identified by morphological analyses of hard parts compared with DNA analysis of soft parts (hard parts identified higher relative proportions of Ammodytes sp., Cottidae and certain Gadidae). DNA identified 213 prey occurrences of which 75 (35%) were undetected by hard parts (mainly Salmonidae, Pleuronectidae, Elasmobranchii and Cephalopoda), and thereby increased species occurrences by 22% overall and species richness in 44% of cases (when comparing 110 scats that amplified prey DNA). Prey composition was identical within only 20% of scats. Overall, diet composition derived from both identification techniques combined did not differ significantly from hard part identification alone, suggesting that past scat-based diet studies have not missed major dietary components. However, significant differences in relative diet contributions across scats (as identified using the two techniques separately) reflect passage rate differences between hard and soft digesta material and highlight certain hypothesized limitations in conventional morphological-based methods (e.g., differences in resistance to digestion, hard part regurgitation, partial and secondary prey consumption), as well as potential technical issues (e.g., resolution of primer efficiency and sensitivity, and scat subsampling protocols). DNA analysis of salmon occurrence (from scat soft part matrix and 238 archived salmon hard parts) provided species-level taxonomic resolution that could not be obtained by morphological identification, and showed that Steller sea lions were primarily consuming pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. Notably, DNA from Atlantic salmon (Salmo salar) that likely originated from a distant fish farm was also detected in two scats from one site in the Eastern Aleutian Islands. Overall, molecular techniques are valuable for identifying prey in the fecal remains of marine predators. Combining DNA and hard part identification will effectively alleviate certain predicted biases, and will ultimately enhance measures of diet richness, fisheries interactions (especially salmon related ones) and the ecological role of pinnipeds and other marine predators, to the benefit of marine wildlife conservationist and fisheries managers.
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Phenotypic plasticity in age at first reproduction of female northern sea otters (Enhydra lutris kenyoni).
von Biela, V.R., V.A. Gill, J.L. Bodkin, and J.M. Burns. 2009.
Journal of Mammalogy 90:1224-1231.
abstract
Life-history theory predicts that within a species, reproduction and survival rates will differ among populations that differ in resource availability or predation rates through phenotypic plasticity. When populations are near carrying capacity (K) or when they are declining due to reduced prey resources, the average age at 1st reproduction (average AFR) is predicted to be older than in populations below K. Differences between the trajectories of northern sea otter (Enhydra lutris kenyoni) populations in Alaska provides an opportunity to examine phenotypic plasticity. Using premolar teeth or reproductive tracts, we estimated average AFR from demographically distinct populations of sea otters in Alaska. We obtained samples from 2 populations near K, Prince William Sound (PWS) and the Aleutian Archipelago (archived samples), and from 2 populations below K, the Kodiak Archipelago and Sitka. The average AFR was lower in populations below K (3.60 years ± 0.16 SD) compared to those near K (4.21 ± 0.13 years, P < 0.001), and differed among all populations, with the Aleutian population possessing the oldest average AFR (4.29 ± 0.09 years) followed by PWS (4.05 ± 0.24 years), Sitka (3.80 ± 0.21 years), and Kodiak (3.19 ± 0.37 years). The difference in average AFR among populations supports life-history theory and provides evidence of phenotypic plasticity in sea otters. Our findings highlight the value of using average AFR as a tool for monitoring mammalian populations.
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The role of social aggregations and protected areas in killer whale conservation: the mixed blessing of critical habitat.
Williams, R., D. Lusseau, and P.S. Hammond. 2009.
Biological Conservation 142:709-719.
abstract
Protected areas are often proposed as tools for conserving endangered populations of marine megafauna. Our study area includes a voluntary no-entry reserve embedded within wider critical habitat for Threatened ‘northern resident’ killer whales under Canada’s Species at Risk Act. Our study quantified the reserve’s importance to whales by assessing habitat preference in a behavioural context, and population-level implications of that preference given threats from human activities, such as oil spills resulting from shipping traffic. We recorded summertime activities of whales from 1995 to 2002. Whales were observed on 397 of 530 (74.9%) days. Whales showed strong preference for the reserve over adjacent waters, and used it preferentially for feeding and beach-rubbing. While the area comprises 0.001% of the whales’ range, an overall average of 6.5% of the population was present each day. Frequently, >50% of this small population was aggregated in the restricted and heavily trafficked waterway of Johnstone Strait. Using the Potential Biological Removal equation, we calculated potential annual mortality limits (ML) of 2.2 animals. Mean group size in the area exceeded ML on 55.8% of days overall, and 98.8% of days when conditioning on whale presence. The whales’ high reliance on a trivial fraction of their range means that opportunities are routine for one stochastic, catastrophic event to cause population decline. On 20 August 2007, a barge loaded with 10,000 L of diesel sank in the area, exposing 25% of the population. This underscores the importance of identifying critical habitat for threatened populations, and ensuring meaningful protection.
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Swimming speed, respiration rate, and estimated cost of transport in adult killer whales.
Williams, R., and D.P. Noren. 2009.
Marine Mammal Science 25:327-350.
abstract
The physiology of free-ranging cetaceans is difficult to study and as a consequence, data on the energetics of these animals are limited. To better understand the energetic cost of swimming in killer whales, total cost of transport (COT) was estimated from swimming speeds and respiration rates from wild adult northern resident killer whales (Orcinus orca) and reported values of oxygen consumption in captive whales. Respiration rate (breaths per minute) was positively correlated with swimming speed (meters per second), while mass-specific COT (Joules per kilogram per meter) decreased with speed. Lack of data on very fast-swimming animals hindered assessment of the exact speed at which COT was minimal. However, minimum mass-specific COT for killer whales in the present study approached those predicted by a previously published allometric equation for marine mammals, and corresponded to “optimal” swimming speeds of 2.6–3 m/s. Interestingly, the observed average swimming speed (1.6 m/s) was lower than predicted optimal swimming speed. Finally, females with dependent calves had higher respiration rates than females without calves. These findings could be due to synchronous breathing with calves or could result from increased costs of lactation and swimming with a calf in echelon formation. Consequently, females with calves may have much greater COT at optimal swimming speeds than females without calves.
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Cost-effective abundance estimation of rare animals: Testing performance of small-boat surveys for killer whales in British Columbia.
Williams, R., and L. Thomas. 2009.
Biological Conservation 142:1542-1547.
abstract
Top predators are often rare, subject to anthropogenic mortality, and possess life-history traits that make them inherently vulnerable to extinction. IUCN criteria recognise populations as Critically Endangered when abundance is <250 mature individuals, but estimating abundance of rare species can be more challenging than for common ones. Cost-effective methods are needed to provide robust abundance estimates. In marine environments, small boats are more widely accessible than large ships for researchers conducting sightings surveys with limited funds, but studies are needed into efficacy of small-boat surveys. This study compares line transect and mark-recapture estimates from small-boat surveys in summer 2004 and 2005 for ‘northern resident’ killer whales in British Columbia to true population size, known from censuses conducted by Fisheries and Oceans Canada. The line transect estimate of 195 animals (95% CI 27–559) used model averaging to incorporate uncertainty in the detection function, while the mark-recapture estimate of 239 animals (CI 154–370) used a simple two-sample Chapman estimator. Both methods produced estimates close to the true population size, which numbered 219 animals in 2004 and 235 in 2006, but both suffered from the small sample sizes and violations of some model assumptions that will vex most pilot studies of rare species. Initial abundance estimates from relatively low-cost surveys can be thought of as hypotheses to be tested as new data are collected. For species of conservation concern, any cost-effective attempt to estimate absolute abundance will assist status assessments, as long as estimates are presented with appropriate caveats.
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2008
 
Movements of satellite-monitored humpback whales on their feeding ground along the Antarctic Peninsula.
Dalla Rosa, L., Secchi, E.R., Maia, Y.G., Zerbini, A.N. and Heide-Jørgensen. 2008.
Polar Biology 31(7):771-781.
abstract
Humpback whales were instrumented with satellite transmitters off the western Antarctic Peninsula in January of 2004-2006 to examine their movement patterns and habitat use. Whales were tracked from 4 to 80 days (mean = 36.5 days). Distance and travel rate estimates for nine individuals ranged from to 223 to 4,356 km and from 17 to 75 km/day, respectively. Considerable individual variation was observed in direction, speed and range of movements. The overall pattern was characterized by short- and long-distance movements between presumed foraging areas with relatively short residency times. Travel rates were lower at these sites, characterized by erratic movements, than during traveling between them. Area usage for six individuals based on the 95% fixed kernel home range with least squares cross-validation ranged from 2,771 to 172,356 km2. The management boundary between the feeding grounds associated with Breeding Stocks G and A needs revision, as current available data suggest it should be located to the east of 50oW. This study is the first to present detailed information on the movements of humpback whales in the Southern Ocean.
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Mitochondrial DNA diversity of the Southwestern Atlantic humpback whale (Megaptera novaeangliae) breeding area off Brazil, and the potential connections to Antarctic feeding areas.
Engel, M.H., N.J.R. Fagundes, H.C. Rosenbaum, P.H. Ott, R. Schmitt, E. Secchi, L. Dalla Rosa and S.L. Bonatto. 2008.
Conservation Genetics 9:1253-1262.
abstract
In the Southwestern Atlantic Ocean, humpback whales migrate every winter to the Brazilian coast for breeding and calving in the Abrolhos Bank. This breeding stock represents the remnants of a larger population heavily exploited during the beginning of the 20th century. Despite its relevance to conservation efforts, the degree of current genetic variation and the migratory relationship with Antarctic feeding areas for this population are still largely unknown. To examine these questions, we sequenced *400 bp of the mitochondrial DNA control region from samples taken off the Brazilian coast (n = 171) and near the Antarctic Peninsula (n = 77). The genetic variability of the Brazilian humpback whale breeding population was high and similar to that found in other Southern Hemisphere breeding grounds. Phylogenetic analysis suggested the existence of a new mitochondrial clade that exists at low frequency among Southern Hemisphere populations. Direct comparison between the Brazilian and the Colombian breeding populations and the Antarctic Peninsula feeding population showed no genetic differentiation between this feeding region and the Colombian breeding area or between feeding Areas I and II near the Antarctic Peninsula. In contrast, these populations were genetically distinct from the Brazilian population. Two humpback whales sampled off South Georgia Islands, in the Scotia Sea, shared identical haplotypes to whales from Brazil. Our results, supported by photo-identification and satellite telemetry data, suggest that the main feeding area of the Southern Hemisphere humpback whale population is likely to be located near the South Georgia/South Sandwich Islands area and not in the Antarctic Peninsula.
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Metabolic costs of foraging and the management of O2 and CO2 stores in Steller sea lions.
Fahlman, A., Svärd, C., Rosen, D.A.S., Jones, D.R. and Trites, A.W. 2008.
Journal of Experimental Biology 211:3573-3580.
abstract
The metabolic costs of foraging and the management of O2 stores during breath-hold diving was investigated in three female Steller sea lions (Eumetopias jubatus) trained to dive between 10 and 50 m (n=1142 dives). Each trial consisted of 2 to 8 dives separated by surface intervals (SI) that were determined by the sea lion (spontaneous trials) or by the researcher (conditioned trials). During conditioned trials, SI was long enough for O2 to return to pre-dive levels between each dive. The metabolic cost of each dive event (DMR = dive + surface interval) was measured using flow-through respirometry. The respiratory exchange ratio (VCO2 ·VCO2 -1) was significantly lower during spontaneous trials compared with conditioned trials. DMR was significantly higher during spontaneous trials and decreased exponentially with dive duration. A similar decrease in DMR was not as evident during conditioned trials. DMR could not be accurately estimated from the SI following individual dives that had short surface intervals (SI < 50 sec), but could be estimated on a dive by dive basis for longer SIs (SI > 50 sec). DMR decreased by 15%, but did not differ significantly from surface metabolic rates (MRS) when dive duration increased from 1 to 7 min. Overall, these data suggest that DMR is almost the same as MRS, and that Steller sea lions incur an O2 debt during spontaneous diving that is not repaid until the end of the dive bout. This has important consequences in differentiating between the actual and ‘apparent’ metabolic rate during diving, and may explain some of the metabolic differences reported between pinniped species.
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Buoyancy does not affect diving metabolism during shallow dives in Steller sea lions Eumetopias jubatus.
Fahlman, A., G.D. Hastie, D.A.S. Rosen, Y. Naito and A.W. Trites. 2008.
Aquatic Biology 3:147-154.
abstract
hanges in buoyancy due to seasonal or abnormal changes in body composition are thought to significantly affect the energy budget of marine mammals through changes in diving costs. We assessed how changes in body composition might alter the foraging efficiency of Steller sea lions Eumetopias jubatus by artificially adjusting the buoyancy of trained individuals. PVC tubes were attached to harnesses worn by Steller sea lions that had been trained to feed at fixed depths (10 to 30 m) and to resurface inside a metabolic dome. Buoyancy was altered to simulate the naturally occurring differences in body composition reported in adult females (~12 to 26% subcutaneous fat). Diving characteristics (transit times and time at depth) and aerobic energy expenditure (gas exchange) were measured. We found that foraging cost decreased with the duration of the dive and increased with dive depth. However, changes in body composition did not affect the diving metabolic rate of Steller sea lions for dives between 10 and 30 m. We propose that Steller sea lions may adjust their diving lung volume to compensate for changes in buoyancy to avoid additional metabolic costs.
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Activity and diving metabolism correlate in Steller sea lion Eumetopias jubatus.
Fahlman, A., R. Wilson, C. Svärd, D.A.S. Rosen and A.W. Trites. 2008.
Aquatic Biology 2:75-84.
abstract
Three Steller sea lions Eumetopias jubatus were trained to participate in free-swimming, open-ocean experiments designed to determine if activity can be used to estimate the energetic cost of finding prey at depth. Sea lions were trained to dive to fixed depths of 10 to 50 m, and to re-surface inside a floating dome to measure energy expenditure via gas exchange. A 3-axis accelerometer was attached to the sea lions during foraging. Acceleration data were used to determine the overall dynamic body acceleration (ODBA), a proxy for activity. Results showed that ODBA correlated well with the diving metabolic rate (dive + surface interval) and that the variability in the relationship (r2 = 0.47, linear regression including Sea lion as a random factor) was similar to that reported for other studies that used heart rate to estimate metabolic rate for sea lions swimming underwater in a 2 m deep water channel. A multivariate analysis suggested that both ODBA and dive duration were important for predicting diving metabolic cost, but ODBA alone predicted foraging cost to within 7% between animals. Consequently,collecting 3-dimensional acceleration data is a simple technique to estimate field metabolic rate of wild Steller sea lions and other diving mammals and birds.
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A novel presence-only validation technique for improved Steller sea lion Eumetopias jubatus critical habitat descriptions.
Gregr, E.J. and A.W. Trites. 2008.
Marine Ecology Progress Series 365:247-261.
abstract
We used published information about foraging behaviour, terrestrial resting sites, bathymetry, and seasonal ocean climate to develop hypotheses relating life history traits and physical variables to the at-sea habitat of a wide-ranging marine predator, the Steller sea lion (Eumetopias jubatus). We used the hypotheses to develop a series of habitat models that predicted the probability of sea lions occurring within 3 x 3 km2 grids overlaid on the Gulf of Alaska and Bering Sea; and compared these deductive model predictions with opportunistic at-sea observations of sea lions (presence-only data) using 1) a likelihood approach in a small area where effort was assumed to be uniformly distributed, and 2) an adjusted skewness (Skadj) test that evaluated the distribution of the predicted values associated with true presence observations. We found the Skadj statistic was comparable to the likelihood test when using pseudo-absence data, but it was more powerful for assessing the relative performance of the different predictive spatial models. We also found that the habitat maps we produced for adult female sea lions using the deductive modelling approach captured a higher proportion of presence observations than the current habitat model (Critical Habitat) used by fisheries managers since 1993 to manage Steller sea lions. Such improved predictions of habitat are necessary to effectively design, implement, and evaluate fishery mitigation measures. The deductive approach we propose is suitable for modelling the habitat use of other age- and sex- classes, and for integrating these age/sex class specific models into a revised definition of Critical Habitat for Steller sea lions. It can also be readily used to identify the at-sea habitat of other central place foragers.
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Steller sea lions show diet-dependent changes in body composition during nutritional stress and recover more easily from mass loss in winter than in summer.
Jeanniard du Dot, T., Rosen, D. A. S. , Trites, A. W. 2008.
Journal of Experimental Marine Biology and Ecology 367(1):1-10.
abstract
Controlled feeding experiments were undertaken with captive Steller sea lions (Eumetopias jubatus) to assess seasonal (winter vs. summer) physiological responses of individual animals to reduced quantities and qualities of food that are hypothesised to occur in the wild. Eight animals were randomly divided into two experimental groups fed isocaloric diets: Group H ate Pacific herring (Clupea pallasi) throughout the experiment while Group P was switched to walleye pollock (Theragra chalcogramma) during a 28-day food restriction (after a 28-day baseline) and back to herring during a 28-day controlled re-feeding. Diet type did not impact the rates of body mass lost when food was restricted, but did influence the type of internal energy reserve (protein vs lipids) the sea lions predominantly used. In both summer and winter, Group H lost significantly more lipids and less lean mass than Group P that was fed pollock during the restriction phase. The response of Group H was consistent with the predicted pattern of nutritional stress physiology (i.e. protein sparing and utilization of lipid reserves). Group P lost a surprisingly high proportion of body protein while consuming restricted levels of pollock, which could lead to muscle impairment and vital organ failure on a long-term basis. When given increased amounts of herring during the controlled re-feeding phase, the capacity of both groups to compensate for the previous mass loss was found to depend on season and was independent of previous diet. All of the sea lions increased their rates of mass gain and returned to their pre-experimental weight during winter, but not during summer. Some intrinsic energetic plasticity related to seasonal adaptation to the environment may render winter an easier period than summer to recover from nutritional stress.
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A 4500-year time series of Pacific cod (Gadus macrocephalus) size and abundance: archaeology, regime shifts, and sustainable fisheries.
Maschner, H. D. G., M. W. Betts, K. L. Reedy-Maschner and A. W. Trites. 2008.
Fishery Bulletin 106:386-394.
abstract
4500-year archaeological record of Pacific cod (Gadus macrocephalus) bones from Sanak Island, Alaska, was used to assess the sustainability of the modern fishery and the effects of this fishery on the size of fish caught. Allometric reconstructions of cod length for eight prehistoric time periods indicated that the current size of the near shore, commercially fished cod stocks is statistically unchanged from that of fish caught during 4500 years of subsistence harvesting. This finding indicates that the current Pacific cod fishery that uses selective harvesting technologies is a sustainable commercial fishery. Variation in relative cod abundances provides further insights into the response to punctuated changes in ocean climate (regime shifts) and suggests that Pacific cod stocks can recover from major environmental perturbations. Such palaeofisheries data can extend the short time-series of fisheries data (<50 y) that form the basis for fisheries management in the Gulf of Alaska and place current trends within the context of centennial- or millennial-scale patterns.
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Evaluating Quantitative Fatty Acid Signature Analysis (QFASA) using harbour seals (Phoca vitulina richardsi) in captive feeding studies.
Nordstrom, C.A., L.J. Wilson, S.J. Iverson and D.J. Tollit. 2008.
Marine Ecology Progress Series 360:245-263.
abstract
Quantitative fatty acid (FA) signature analysis (QFASA) has recently been developed to estimate the species composition of predator diets by statistically comparing FA signatures of predator adipose tissue with that of their potential prey. Captive feeding trials were used to test the technique with newly-weaned harbour seals (Phoca vitulina richardsi, N = 21). Two groups of seals were fed monotypic diets of either Pacific herring (Clupea pallasii) or surf smelt (Hypomesus pretiosus) for 42 days while a third group was fed smelt (21 days) followed by herring (21 days). Blubber biopsies were taken dorsally at day 0, 21 and 42. Specific calibration coefficients (CC) required by QFASA were developed from 4 juvenile harbour seals and in some cases differed by two-fold with previously reported phocid CC. QFASA diet estimates were evaluated using 2 CC sets, 15 FA subsets and a library of 3 – 11 potential prey species. Diet switches were best tracked using the harbour seal CC and a new FA subset. Overall prey misclassifications were apparent (mean = 12%, range = 4 – 25%) when modeled with 8 additional prey not fed, often consistent with overlapping prey FA signatures. Blubber FA turnover rates were not strictly linear and in the order of 1.5 – 3 months in newly-weaned animals. Following model parameter optimization, QFASA estimates reflected major diet trends in the feeding study, but were sensitive to the CC and FA subsets used as well as to prey species with similar FA signatures. Our results have important implications in the application of QFASA to study pinniped diets in more complex conditions.
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Hormone changes indicate that winter is a critical period for food shortages in Steller sea lions.
Rosen, D.A.S., Kumagai, S. 2008.
Journal of Comparative Physiology B 178:573-583.
abstract
Given that many marine mammals display seasonal energetic priorities, it is important to investigate whether the impact of unexpected food restriction differs during the year. Steller sea lions (Eumetopias jubatus) fed restricted diets for up to 9 days during spring, summer, fall, and winter lost an average of 10% of their initial body mass. We tracked changes in the levels of three hormones (cortisol, total thyroxine—TT4, total triiodothyronine—TT3) and one blood metabolite (blood urea nitrogen—BUN) following a food restriction in relation to season, body mass, body composition, and metabolism. Degree of changes in cortisol, TT3, and BUN after food restriction was significantly affected by season. The greatest changes in cortisol (+231%), BUN (+11.4%), TT4 (-23.3%), and TT3 (-35.6%) occurred in the winter (November/December) when rates of body mass loss were also greatest. Changes in cortisol levels were positively related to total body mass loss, while changes in TT3 levels were negatively related. While greater increases in BUN were related to greater rates of mass loss, the use of BUN levels as an indicator of metabolic state is complicated by the type and level of food intake. The observed changes in hormone levels support morphological data suggesting Steller sea lions may be more strongly impacted by short-term, reduced energy intake during winter than at other times of the year.
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Diets of mature male and female Steller sea lions differ and cannot be used as proxies for each other.
Trites, A.W., and D.G. Calkins. 2008.
Aquatic Mammals 34:25-34.
abstract
Disturbance of otariid breeding sites (rookeries) to determine diet from fecal remains (scats) could be eliminated if the diets of males using adjoining bachelor haulouts could be used as a proxy for diets of breeding females. We collected scats from sexually mature Steller sea lions (Eumetopias jubatus) at one male resting site (haulout) and three female dominated breeding sites (rookeries) at Forrester Island, Southeast Alaska (June-July, 1994–1999) to test whether the diets of bachelor bulls differed from that of breeding females. Female diets were fairly evenly distributed between gadids, salmon and small oily fishes (forage fish), and contained lesser amounts of rockfish, flatfish, cephalopods and other fishes. Female diet did not differ significantly between the 3 rookeries, but did differ significantly from that of males. Males consumed significantly fewer salmon, and more pollock, flatfish and rockfish compared to females. The males also consumed larger pollock compared to females. These dietary differences may reflect a sex-specific difference in foraging areas or differences in hunting abilities related to the disparity in physical sizes of males and females. The similarity of the female diets between rookeries suggests that female diets can be determined from samples collected at a single site within a rookery complex. Unfortunately, summer diets of breeding females cannot be ascertained from hard parts contained in the scats of mature male Steller sea lions.
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Evaluating cementum to determine past reproduction in northern sea otters.
von Biela, V.R., J.W. Testa, V.A. Gill and J.M. Burns. 2008.
Journal of Wildlife Management 72:618-624.
abstract
Age at first reproduction (AFR) has been difficult to quantify in mammals, as the most commonly used methods require reproductive tracts or direct observations. However, work in several large mammal species suggests that the width of cementum light bands in teeth decline once females begin to reproduce, suggesting that teeth structures might provide a new tool to examine AFR. To determine if changes in cementum light band width could be used to calculate AFR for the northern sea otter (Enhydra lutris kenyoni), we measured cementum light band widths on sectioned premolar teeth and compared them to reproductive tracts. We classified otters as parous if any single light band was narrower than a threshold value, selected as the value that minimized error rates. At a threshold value of 0.32, we correctly identified otters as parous or nulliparous in 83% of cases (n = 92) as compared to reproductive tracts, and the AFR estimated from teeth samples (3.52 ± 0.032 yr) was not different from that determined by reproductive tract analysis (3.45 ± 0.031 yr; t-test, P > 0.05). These data support the use of cementum as an indicator of past reproduction in individual female otters, which can then be used to estimate average AFR. Given that declines in cementum width have been described for other mammal species, the same quantitative approach used here could be applied to other species.
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Potential limits to anthropogenic mortality of small cetaceans in coastal waters of British Columbia.
Williams, R., A. Hall, and A. Winship. 2008.
Canadian Journal of Fisheries and Aquatic Sciences 65:1867-1878.
abstract
Small cetaceans are by-caught in salmon gillnet fisheries in British Columbia (BC) waters. In Canada, there is currently no generic calculation to identify when management action is necessary to reduce cetacean bycatch below sustainable limits. We estimated potential anthropogenic mortality limits for harbour (Phocoena phocoena) and Dall's (Phocoenoides dalli) porpoises and Pacific white-sided dolphins (Lagenorhynchus obliquidens) using quantitative objectives from two well-established frameworks for conservation and management (the United States' Marine Mammal Protection Act and the Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas), which are similar to some management objectives developed for marine mammal stocks elsewhere in Canada. Limits were calculated as functions of (i) a minimum abundance estimate (2004-2005); (ii) maximum rate of population increase; and (iii) uncertainty factors to account for bias in abundance estimates and uncertainty in mortality estimates. Best estimates of bycatch mortality in 2004 and 2005 exceeded only the most precautionary limits and only for porpoise species. Future research priority should be given to determining small cetacean stock structure in BC and refining species-specific entanglement rates in these and other fisheries. The approach offers a quantitative framework for Canada to meet its stated objectives to maintain favourable conservation status of cetacean populations.
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2007
 
Migratory destinations of humpback whales from the Magellan Strait feeding ground, Southeast Pacific.
Acevedo, J., K. Rasmussen, F. Felix, C. Castro, M. Llano, E. Secchi, M. T. Saborio, A. Aguayo-Lobo, B. Haase, M. Scheidat, L. Dalla Rosa, C. Olavarria, P. Forestell, P. Acuna, G. Kaufman and L. A. Pastene. 2007.
Marine Mammal Science 23:453-463.
abstract
Historical summer feeding and winter breeding grounds of humpback whales in the southeast Pacific humpback whales have been recorded in the west of the Antarctic Peninsula during the austral summer and off Ecuador and Colombia during the austral winter. In recent years, southeast Pacific humpback whales have been found further north, off Panama and Costa Rica during the austral winter, in areas also frequented by northeast Pacific humpback whales during the boreal winter. Photographs were taken from research and whale-watching vessels between 1991 and 2004 in wintering areas and Antarctica, and between 2003 and 2005 in the Magellan Strait. Whales identified in the Magellan Strait (n=62) were not resighted in the Antarctic Peninsula (n = 508). The absence of matches between these humpback whale aggregations suggests that these represent two discrete feeding populations. Humpback whales from Magellan Strait show a higher exchange rate (measured as the Interchange Index) with the Panama/Costa Rica regions (0.87) than with the Ecuador (0.09) and north of Colombia (0.24), although a goodness-of-fit test showed the observations were not significantly different from the expectation ratio. We hypothesize that southeast Pacific humpback whales migrate from their northernmost feeding area (Magellan Strait) primarily to the northernmost wintering areas (northern Colombia, Panama, and Costa Rica), whereas those from the southern feeding area near the Antarctic Peninsula winter mainly off Ecuador and southern Colombia. Such a possible sub structure within the southeast Pacific population has important implications for the management and assessment of population trends
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Characteristics of whistles from resident bottlenose dolphins (Tursiops truncatus) in southern Brazil.
Azevedo, A. F., A. M. Oliveira, L. Dalla Rosa and J. Lailson-Brito. 2007.
Journal of the Acoustical Society of America 121:2978-2983.
abstract
Little is known of the whistles produced by bottlenose dolphins in the South Atlantic Ocean. A total of 788 whistles were recorded from free-ranging bottlenose dolphins in Patos Lagoon estuary, southern Brazil. The mean number of whistles emitted per minute per animal was 0.8. Bottlenose dolphins emitted a varied repertoire of whistles, in which those with more than one inflection point were the most frequent and there was no predominance of ascending or descending whistles. Whistles recorded had a great frequency range, between 1.2 and 22.3 kHz. Whistle duration was 553.3 (+/- 393.9 ms) and 66.6% of the whistles lasted <800 ms. Differences in the mean values of the whistles' characters were found between this study and other values previously reported for Tursiops. Bottlenose dolphins in the Patos Lagoon estuary emitted repeated whistle contours and individuals may be sharing some whistle types, as it has been suggested for Tursiops. (C) 2007 Acoustical Society of America.
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Quantification of terrestrial haul-out and rookery characteristics of Steller sea lions.
Ban, S. and A.W. Trites. 2007.
Marine Mammal Science 23:496-507.
abstract
Steller sea lions (Eumetopias jubatus)are known to have occupied the same terrestrial haul-out and rookery sites across the North Pacific rim for centuries, but it is not known why they choose and stay at these locations, or what defines their preferred habitat. Classifying and comparing the shoreline type of haulouts and rookeries against sites not used by Steller sea lions showed that they preferentially locate their haulouts and rookeries on exposed rocky shorelines and wave-cut platforms. However, no preference was found for selecting rookeries on sheltered shore-types. Shoreline types used less frequently by sea lions included fine-to-medium-grained sand beaches, mixed sand and gravel beaches, gravel beaches, and sheltered rocky shores. Quantifying the shoreline types used by sea lions confirms anecdotal reports of habitat preferences and may prove useful in identifying and protecting sea lion terrestrial habitat, or in forecasting how climate change might affect the distribution of sea lions.
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Turning maneuvers in Steller sea lions (Eumatopias jubatus).
Cheneval, O., R. W. Blake, A. W. Trites and K. H. S. Chan. 2007.
Marine Mammal Science 23:94-109.
abstract
Steller sea lions are highly maneuverable marine mammals (expressed as minimum turning radius). Video recordings of turns (n=195) are analyzed from kinematic measurements for three captive animals. Speed-time plots of 180° turns have a typical ?V-shape?. The sea lions decelerated during the first half of the turn, reached a minimum speed in the middle of the curved trajectory and re-accelerated by adduction of the pectoral flippers. The initial deceleration was greater than that for passive gliding due to pectoral flipper braking and/or change in body contour from a stiff, straight streamlined form. Centripetal force and thrust were determined from the body acceleration. Most thrust was produced during the power phase of the pectoral flipper stroke cycle. Contrary to previous findings on otariids, little or no thrust was generated during initial abduction of the pectoral flippers and during the final drag-based paddling phase of the stroke cycle. Peak thrust force! at the center of gravity occurs halfway through the power phase while the centripetal force is maximal at the beginning of the power stroke. Performance is modulated by changes in the duration and intensity of movements without changing their sequence. Turning radius, maximum velocity, maximum acceleration and turning duration were 0.3 body lengths, 3.5 m/s, 5 m/s2 and 1.6 s respectively. The relative maneuverability based on velocity and length specific minimum turning radius is comparable to other otariids, superior to cetaceans but inferior to many fish.
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Killer whale (Orcinus orca) interactions with the tuna and swordfish longline fishery off southern and south-eastern Brazil: a comparison with shark interactions.
Dalla Rosa, L. and E.R. Secchi. 2007.
Journal of the Marine Biological Association of the United Kingdom 87:135-140.
abstract
Depredation by cetaceans and sharks on longline fisheries is a global issue that can have negative impacts on both animals and fisheries and has concerned researchers, managers and the fishing industry. Nevertheless, detailed information on depredation is only available for a few regions where the problem exists. With the purpose of evaluating killer whale depredation on longline-caught tuna (Thunnus spp.) and swordfish (Xiphias gladius) in the waters off southern and south-eastern Brazil and comparing it to shark depredation, data sheets were distributed to the captains of tuna vessels in Santos, south-eastern Brazil, between 1993 and 1995. Data on the catch per unit effort (CPUE) of tuna and swordfish and some records of interactions were also obtained from fishing vessel logbooks. Dockside interviews with fishermen and with researchers on board tuna vessels provided additional information. Killer whale and shark interactions were analysed per longline set and per trip. Killer whale interactions occurred from June to February, mainly between June and October, while shark interactions occurred year round. The number of sets and trips involving shark interactions was significantly higher than the number of sets and trips involving killer whale interactions. However, when depredation occurred, the proportion of fish damaged by killer whales was significantly higher than by sharks. Furthermore, killer whales removed or damaged significantly more hooked swordfish than hooked tuna, whereas sharks damaged significantly more hooked tuna than swordfish. This study also shows that cetacean by-catch is experienced by the tuna and swordfish longline fishery in Brazilian waters.
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Quantitative analysis of prey DNA in pinniped faeces: potential to estimate diet composition?
Deagle, B.E. and D.J. Tollit. 2007.
Conservation Genetics 8:743-747.
abstract
Recent studies have shown prey DNA can be consistently recovered from faeces and effectively used to provide dietary information. We investigate the possibility of using the relative amounts of DNA recovered from different prey in faeces to obtain quantitative diet composition data. Faecal samples were obtained from captive Steller seas lions (Eumetopias jubatus) being fed a fish diet consisting of 50% Pacific herring (Clupea pallasii), 36% surf smelt (Hypomesus pretiosus) and 14% sockeye salmon (Oncorhynchus nerka) by mass. Quantitative real-time PCR was used to measure the amount of mtDNA from the three fish species in: (i) a blended tissue mix representative of the sea lion diet and (ii) the sea lion faecal samples. The percent composition of fish mtDNA extracted from the undigested tissue samples corresponded reasonably well to the mass of fish in the mixture. In the faecal samples (n = 23) the absolute amount of fish mtDNA recovered varied 100-fold, but the percent composition of the three fish was relatively consistent (57.5 ± 9.3% for herring, 19.3 ± 6.6% for smelt and 23.2 ± 12.2% for salmon). Differences between the mtDNA proportions in the tissue samples compared to the faecal samples indicate there are prey-specific biases in DNA survival during digestion. These biases may be less than those commonly observed in the conventional analysis of prey hard remains. Further investigation of this approach is warranted.
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Adaptive classification of marine ecosystems: identifying biologically meaningful regions in the marine environment.
Gregr, E.J. and K. Bodtker. 2007.
Deep-Sea Research Part 1 54:385-402.
abstract
The move to ecosystem-based management of marine fisheries and endangered species would be greatly facilitated by a quantitative method for identifying marine ecosystems that capture temporal dynamics at meso-scale (10?s or 100?s of kilometers) resolutions. Understanding the dynamics of ecosystem boundaries, which may differ according to the species of interest or the management objectives, is a fundamental challenge of ecosystem-based management. We present an adaptive ecosystem classification that can accommodate these different needs. To demonstrate the approach, we quantitatively bounded distinct, biologically meaningful marine regions in the North Pacific Ocean based on physical oceanography. We identified the regions by applying image classification algorithms to a comprehensive description of the ocean?s surface, derived from an oceanographic circulation model. Our resulting maps illustrate 15 distinct marine regions. We investigated seasonal and long-term c! hanges in the pattern of regions and their boundaries by dividing the oceanographic data into four seasons and two 10-year time periods, one on either side of the 1976 ? 1977 North Pacific Ocean climate regime shift. The size and location of our mapped regions related well to previously described water masses in the North Pacific. We compared our results for each season across the regime shift and for sequential seasons within regimes using the Kappa Index of Agreement and the index of Average Mutual Information. Seasonal patterns were more similar between regimes than from one season to the next within a regime. The magnitude of seasonal transitions also appeared to differ before and after the regime shift. We assessed the biological relevance of the identified regions using seasonal maps derived from remotely sensed chlorophyll-a concentrations ([chl-a]). We used Kruskal-Wallis and Wilcoxon rank sum tests to evaluate the correspondence between the [chl-a] maps and our pos! t-regime shift regions. There was a significant difference in ! [chl-a] among the regions in all seasons. We found that the number of regions with distinct chlorophyll signatures, and the associations between different regions, varied by season. The overall pattern of association between the regions was suggestive of observed, broad-scale patterns in the seasonal development and distribution of primary production in the North Pacific. This demonstrated that regions with different biological properties can be delineated using only physical variables. The flexibility of our approach will enable researchers to visualize the geographic extents of regions with similar physical conditions, providing insight into ocean dynamics and changes in marine ecosystems. It will also provide resource managers with a powerful tool for broad application in ecosystem-based management and conservation of marine resources.
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Reductions in oxygen consumption during dives and estimated submergence limitations of Steller sea lions (Eumetopias jubatus).
Hastie, G.D., D.A.S. Rosen and A.W. Trites. 2007.
Marine Mammal Science 23:272-286.
abstract
Accurate estimates of diving metabolic rate are central to assessing the energy needs of marine mammals. To circumvent some of the limitations inherent with conducting energy studies in both the wild and captivity, we measured diving oxygen consumption of two trained Steller sea lions (Eumetopias jubatus) in the open ocean. The animals dived to predetermined depths (5–30 m) for controlled periods of time (50–200 s). Rates of oxygen consumption were measured using open-circuit respirometry before and after each dive. Mean resting rates of oxygen consumption prior to the dives were 1.34 (±0.18) and 1.95 (±0.19) liter/min for individual sea lions. Mean rates of oxygen consumption during the dives were 0.71 (±0.24) and 1.10 (±0.39) liter/min, respectively. Overall, rates of oxygen consumption during dives were significantly lower (45% and 41%) than the corresponding rates measured before dives. These results provide the first estimates of diving oxygen consumption rate for Steller sea lions and show that this species can exhibit a marked decrease in oxygen consumption relative to surface rates while submerged. This has important consequences in the evaluation of physiological limitations associated with diving such as dive duration and subsequent interpretations of diving behavior in the wild.
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Evaluating network analysis indicators of ecosystem status in the Gulf of Alaska.
Heymans, S.J.J., S. Guenette and V. Christensen. 2007.
Ecosystems 10:488-502.
abstract
This is the first study on the emergent properties for empirical ecosystem models that have been validated by time series information. Ecosystem models of the western and central Aleutian Islands and Southeast Alaska were used to examine indices of ecosystem status generated from network analysis and incorporated into Ecopath with Ecosim. Dynamic simulations of the two ecosystems over the past 40 years were employed to examine if these indices reflect the dissimilar changes that occurred in the ecosystems. The results showed that the total systems throughput (TST) and ascendency (A) followed the climate change signature (Pacific decadal oscillation, PDO) in both ecosystems, while the redundancy (R) followed the inverse trend. The different trajectories for important species such as Steller sea lions (Eumetopias jubatus), Atka mackerel (Pleurogrammus monopterygius), pollock (Theragra chalcograma), herring (Clupea pallasii), Pacific cod (Gadus macrocephalus) and halibut (Hippoglossus stenolepis) were noticeable in the Finn cycling index (FCI), entropy (H) and average mutual information (AMI): not showing large change during the time that the Stellers sea lions, herring, Pacific cod, halibut and arrowtooth flounder (Atheresthes stomias) increased in Southeast Alaska, but showing large declines during the decline of Steller sea lions, sharks, Atka mackerel and arrowtooth flounder in the Aleutians. On the whole, there was a change in the emergent properties of the Aleutians around 1976 that was not seen in Southeast Alaska. Conversely, the emergent properties of both systems showed a change around 1988, which indicated that both systems were unstable after 1988.
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Comparison of fatty acid profiles of spawning and non-spawning Pacific herring, Clupea harengus pallasi.
Huynh, M.D., D.D. Kitts, C. Hu and A.W. Trites. 2007.
Journal of Comparative Biochemistry and Physiology, Part B 146:504-511.
abstract
Crude lipid and fatty acid composition from liver, intestine, roe, milt and flesh of spawning and non-spawning Pacific herring Clupea harengus pallasi were examined to determine the relative effects of spawning on the nutritional value of herring. Depletion of lipid due to spawning condition was significant (Pb0.01) in all organ tissues and flesh of spawning herring. The lipid content ranged from an average of 1.9 to 3.4% (wet weight basis) in different organ tissues of spawning herring, to 10.5 to 16% in non-spawning fish. The fatty acid profile exhibited many differences in the relative distribution of individual fatty acids among organ tissues and between the two fish groups. Oleic acid (C18:1n-9), a major monounsaturated fatty acid (MUFA) found in all tissue lipids, decreased significantly (Pb0.01) in spawning fish. The two monoenes, C20:1n-9 and C22:1n-11, occurred at high concentrations in the flesh but at only minor proportion in the digestive organs and gonads. Spawning herring also had significantly (Pb0.01) higher polyunsaturated fatty acids (PUFA) content in the organ tissues, particularly in the milt and ovary, with docosahexaenoic acid (C22:6n-3, DHA) having the greatest proportion. Among the n-6 fatty acids, only C18:2n-6 and C20:4n-6 occurred at notable amounts and were present in higher proportions in spawning fish. We concluded that although relatively higher n-3 fatty acid content was found in the organ lipids of spawning herring, they are not an energy-dense prey food source due to the fact that both flesh and gonads contain a very low amount of lipid.
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Ecotypic variation and predatory behavior among killer whales (Orcinus orca) off the eastern Aleutian Islands, Alaska.
Matkin, C., L.G. Barrett-Lennard, H.Yurk, D. Ellifrit, and A.W. Trites. 2007.
Fishery Bulletin 105:74-87.
abstract
From 2001 to 2004 in the eastern Aleutian Islands, Alaska, killer whales (Orcinus orca) were encountered 250 times during 421 days of surveys that covered a total of 22,491 miles. Three killer whale lineages (resident, transient, and offshore) were identified acoustically and genetically. Resident killer whales were found 12 times more frequently than transient killer whales, while offshore killer whales were only encountered once. A minimum of 901 photographically-identified resident whales used the region during our study. A total of 165 mammal-eating transient killer whales were identified, with the majority (70%) encountered during spring (May and June). The diet of transient killer whales in spring was primarily gray whales (Eschrichtius robustus), while northern fur seals (Callorhinus ursinus) were primary prey in summer. Steller sea lions (Eumetopias jubatus) did not appear to be a preferred prey or major prey item during spring and summer. The majority of killer whales in the eastern Aleutian Islands are the resident ecotype, which do not consume marine mammals.
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Southern Hemisphere humpback whales wintering off Central America: insights from water temperature into the longest mammalian migration.
Rasmussen, K., D. M. Palacios, J. Calambokidis, M. T. Saborio, L. Dalla Rosa, E. R. Secchi, G. H. Steiger, J. M. Allen and G. S. Stone. 2007.
Biology Letters 3:302-305.
abstract
We report on a wintering area off the Pacific coast of Central America for humpback whales (Megaptera novaeangliae) migrating from feeding areas off Antarctica. We document seven individuals, including a mother/calf pair, that made this migration (approx. 8300 kin), the longest movement undertaken by any mammal. Whales were observed as far north as 11 degrees N off Costa Rica, in an area also used by a boreal population during the opposite winter season, resulting in unique spatial overlap between Northern and Southern Hemisphere populations. The occurrence of such a northerly wintering area is coincident with the development of an equatorial tongue of cold water in the eastern South Pacific, a pattern that is repeated in the eastern South Atlantic. A survey of location and water temperature at the wintering areas worldwide indicates that they are found in warm waters (21.1-28.3 degrees C), irrespective of latitude. We contend that while availability of suitable reproductive habitat in the wintering areas is important at the fine scale, water temperature influences whale distribution at the basin scale. Calf development in warm water may lead to larger adult size and increased reproductive success, a strategy that supports the energy conservation hypothesis as a reason for migration.
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Utilization of stored energy reserves during fasting varies by age and season in Steller sea lions.
Rea, L.D., D.A.S. Rosen and A.W Trites. 2007.
Canadian Journal of Zoology 85:190-200.
abstract
Nine captive Steller sea lions (Eumetopias jubatus (Schreber, 1776), 1.75–6 years of age) were fasted for 7–14 d to test the effect of short-term fasting on changes in body mass and body condition. Trials were repeated during both the summer breeding season and the nonbreeding season in seven animals to elucidate whether there was a seasonal component to the ability of Steller sea lions to adapt to limited food resources. Mean percent mass loss per day was higher during the breeding season in juveniles (1.8% ± 0.2%·d–1) than in subadults (1.2% ± 0.1%·d–1), but there were no significant age-related differences during the nonbreeding season (juveniles, 1.5% ± 0.3%·d–1; subadults, 1.7% ± 0.3%·d–1). A decrease in the rate of mass loss occurred after the first 3 d of fasting only in subadults during the breeding season. Percent total body lipid ranged from 11% to 28% of total body mass at the initiation of fasting trials. Animals with lower initial percent total body lipid exhibited higher subsequent rates of mass loss and a lower percentage of tissue catabolism derived from lipid reserves. There was no evidence of metabolic adaptation to fasting in juveniles, which suggests that juvenile sea lions would be more negatively impacted by food limitation during the breeding season than would subadults.
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Thermal and digestive constraints to foraging behavior in marine mammals.
Rosen, D.A.S., A.J. Winship, and L.A. Hoopes. 2007.
Philosophical Transactions, Royal Society of London B 362:2151-2168.
abstract
While foraging models of terrestrial mammals are concerned primarily with optimizing time/energy budgets, models of foraging behavior in marine mammals have been primarily concerned with physiological constraints. This has historically centered on calculations of aerobic dive limits. However, other physiological limits are key to forming foraging behavior, including digestive limitations to food intake and thermoregulation. The ability of an animal to consume sufficient prey to meet its energy requirements is partly determined by its ability to acquire prey (limited by available foraging time, diving capabilities and thermoregulatory costs) and to process that prey (limited by maximum digestion capacity and the time devoted to digestion). Failure to consume sufficient prey will have feedback effects on foraging, thermoregulation, and digestive capacity through several interacting avenues. Energy deficits will be met through catabolism of tissues, principally the hypodermal lipid layer. Depletion of this blubber layer can affect both buoyancy and gait, increasing the costs and decreasing the efficiency of subsequent foraging attempts. Depletion of the insulative blubber layer may also increase thermoregulatory costs, which will decrease foraging abilities through higher metabolic overheads. Thus, an energy deficit may lead to a downward spiral of increased tissue catabolism to pay for increased energy costs. Conversely, the heat generated through digestion and foraging activity may help to offset thermoregulatory costs. Finally, the circulatory demands of diving, thermoregulation, and digestion may be mutually incompatible. This may force animals to alter time budgets to balance these exclusive demands. Analysis of these interacting processes will lead to a greater understanding of the physiological constraints within which foraging behavior must operate.
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Impact of diet index selection and the digestion of prey hard remains on determining the diet of the Steller sea lion (Eumetopias jubatus).
Tollit, D.J., S.G. Heaslip, R.L. Barrick and A.W. Trites. 2007.
Canadian Journal of Zoology 85:1-15.
abstract
Abstract: Nine prey species (n = 7,431) were fed to four captive female Steller sea lions (Eumetopias jubatus (Schreber, 1776)) in eleven feeding trials over 75 days to investigate the effectiveness of different methods used to determine diet from prey hard remains. Trials aimed to replicate short (1-2 day) and long feeding bouts and consisted of single species and mixed daily diets. Overall, an average of 25.2% ± 22.2% (mean ± SD, range 0-83%) of otoliths were recovered, but recovery rates varied by species (ANOVA, P = 0.01) and were linearly related to otolith robustness (R2 = 0.88). Squid beaks were recovered at higher frequencies (mean = 96%) than the otoliths of all species. Enumerating both non-otolith skeletal structures and otoliths (together termed ?bones?) increased species recovery rates by twofold on average (P < 0.001), with increases up to 2.5 times for herring and 3-4 times for salmonids. Using bones reduced inter-specific differences (P = 0.08), but recovery ! varied among sea lions. Bones were distributed over more scats per meal (mean = 2.9 scats, range = 0-5) than otoliths (mean = 1.9 scats, range = 0-4). In three different 15-day mixed diet trials, biomass reconstruction (BR) indices performed better than frequency of occurrence indices in predicting diet fed. Applying our experimentally derived numerical correction factors (to account for species differences in complete prey digestion) further improved BR estimates, resulting in all twelve unweighted comparisons within 5% (for otoliths) and 12% (for bones) of the actual diet fed.
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Bottom-up forcing and the decline of Steller sea lions (Eumetopias jubatus) in Alaska: assessing the ocean climate hypothesis.
Trites, A. W., A. J. Miller, H. D. G. Maschner, M. A. Alexander, S. J. Bograd, J. A. Calder, A. Capotondi, K. O. Coyle, E. D. Lorenzo, B. P. Finney, E. J. Gregr, C. E. Grosch, S. R. Hare, G. L. Hunt, J. Jahncke, N. B. Kachel, H.-J. Kim, C. Ladd, N. J. Mantua, C. Marzban, W. Maslowski, R. Mendelssohn, D. J. Neilson, S. R. Okkonen, J. E. Overland, K. L. Reedy-Maschner, T. C. Royer, F. B. Schwing, J. X. L. Wang and A. J. Winship. 2007.
Fisheries Oceanography 16:46-67.
abstract
Declines of Steller sea lion (Eumetopias jubatus) populations in the Aleutian Islands and Gulf of Alaska could be a consequence of physical oceanographic changes associated with the 1976-77 climate regime shift. Changes in ocean climate are hypothesized to have affected the quantity, quality and accessibility of prey, which in turn may have affected the rates of birth and death of sea lions. Recent studies of the spatial and temporal variations in the ocean climate system of the North Pacific support this hypothesis. Ocean climate changes appear to have created adaptive opportunities for various species that are preyed upon by Steller sea lions at mid-trophic levels. The east-west asymmetry of the oceanic response to climate forcing after 1976-77 is consistent with both the temporal aspect (populations decreased after the late 1970's) and the spatial aspect of the decline (western, but not eastern, sea lion populations decreased). These broad-scale climate variations appear to be modulated by regionally sensitive biogeographic structures along the Aleutian Islands and Gulf of Alaska, which include a transition point from coastal to open-ocean conditions at Samalga Pass westward along the Aleutian Islands. These transition points delineate distinct clusterings of different combinations of prey species, which are in turn correlated with differential population sizes and trajectories of Steller sea lions. Archaeological records spanning 4000 years further indicate that sea lion populations have experienced major shifts in abundance in the past. Shifts in ocean climate are the most parsimonious underlying explanation for the broad suite of ecosystem changes that have been observed in the North Pacific Ocean in recent decades.
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Killer whales, whaling and sequential megafaunal collapse in the North Pacific: a comparative analysis of the dynamics of marine mammals in Alaska and British Columbia following commercial whaling.
Trites, A. W., V. B. Deecke, E. J. Gregr, J. K. B. Ford, and P. F. Olesiuk. 2007.
Marine Mammal Science 23:751-765.
abstract
The hypothesis that commercial whaling caused a sequential megafaunal collapse in the North Pacific Ocean by forcing killer whales to eat progressively smaller species of marine mammals is not supported by what is known about the biology of large whales, the ecology of killer whales and the patterns of ecosystem change that took place in Alaska, British Columbia, and elsewhere in the world following whaling. A comparative analysis shows that populations of seals, sea lions and sea otters increased in British Columbia following commercial whaling, unlike the declines noted in the Gulf of Alaska and Aleutian Islands. The declines of seals and sea lions that began in western Alaska around 1977 were mirrored by increases in numbers of these species in British Columbia. A more likely explanation is the seal and sea lion declines and other ecosystem changes in Alaska stems from a major oceanic regime shift that occurred in 1977. Killer whales are unquestionably a significant predator of seals, sea lions and sea otters but not because of commercial whaling.
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Diets of Steller sea lions (Eumetopias jubatus) in Southeast Alaska from 1993-1999.
Trites, A.W., D.G Calkins and A.J. Winship. 2007.
Fishery Bulletin 105:234-248.
abstract
Diet of Steller sea lions (Eumetopias jubatus) was determined from 1494 scats (feces) collected at breeding (rookeries) and non-breeding (haulout) sites in Southeast Alaska from 1993 to 1999. The most common prey of 61 species identified were walleye pollock (Theragra chalcogramma), Pacific herring (Clupea pallasii), Pacific sand lance (Ammodytes hexapterus), Pacific salmon (Salmonidae), arrowtooth flounder (Atheresthes stomias), rockfish (Sebastes spp.), skates (Rajidae), and cephalopods (squid and octopus). Sea lion diets at the three Southeast Alaska rookeries differed significantly from one another. Steller sea lions consumed the most diverse range of prey categories during summer, and the least diverse during fall. Diet was more diverse in Southeast Alaska during the 1990s than in any other region of Alaska (Gulf of Alaska and Aleutian Islands). Dietary differences between increasing and declining populations of sea lions in Alaska correlate with rates of population change, and add credence to the view that diet may have played a role in the decline of sea lions in the Gulf of Alaska and Aleutian Islands.
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2006
 
Relationship between Steller sea lion diets and fish distributions in the eastern North Pacific.
Bredesen, E.L., A.P. Coombs, and A.W. Trites. 2006.
In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 131-139.
abstract
Distributions of fish species were compared with diet information for Steller sea lions (Eumetopias jubatus) to assess the level of correspondence between potential prey availability and sea lion feeding habits. Fish distributions were compiled as part of the Sea Around Us Project at the UBC Fisheries Centre, and were based on published distributions and habitat preferences (e.g., latitude, depth). Sea lion scat samples were collected during the 1990s from seven geographic regions from Oregon to the western and central Aleutian Islands. The frequencies of occurrence of four prevalent species (walleye pollock, Theragra chalcogramma ; Pacific herring, Clupea pallasii ; Pacific cod, Gadus macrocephalus ; and North Pacific hake, Merluccius productus ) in the Steller sea lion diet were compared to their distributions in the North Pacific Ocean. The data suggest that Steller sea lion diets broadly reflect the distributions of these major prey species. However, some of the fish species that were regionally predicted to be present in high abundance were not proportionally reflected in the Steller sea lion diet, suggesting that other factors in addition to fish abundance influence their diets.
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Studying marine mammal cognition in the wild - a review of four decades of playback experiments.
Deecke, V.B. 2006.
Aquatic Mammals 32(4):461-482.
abstract
The playback of sounds to animals to assess their behavioural responses presents a powerful tool to study animal cognition in the wild. While playbacks are commonly used to study acoustic responses in birds and other terrestrial animals, their application to the study of marine mammal cognition so far has been limited. A survey of the published literature on field playback experiments with marine mammals identified 46 studies, with a trend towards increased use of playback approaches in recent years. Field playbacks to marine mammals have been used to address questions of wildlife management, the impact of anthropogenic noise, acoustic interactions between predators and prey, individual and kin recognition, as well as the function of communicative sounds. This paper summarizes the major findings of marine mammal playbacks to date and reviews recent advances in the design and execution of playback experiments, with special reference to marine mammals. Issues concer! ning appropriate presentation of acoustic stimuli, appropriate quantification of behavioural responses, as well as appropriate control and replication of treatments are discussed. An analysis of replication in marine mammal playbacks showed that the use of a small number of playback stimuli to conduct multiple playback trials (pseudoreplication) was common. This overview of playback experiments in the study of marine mammal cognition in the wild showed that such approaches contribute significantly to the field; however, in many cases there appears to be substantial room for improvement of playback procedure and experimental design
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The Sequential Megafaunal Collapse Hypothesis: Testing with Existing Data.
DeMaster, D.P., A.W. Trites, P. Clapham, S. Mizroch, P. Wade, R.J. Small, and J. Ver Hoef. 2006.
Progress in Oceanography 68:329-342.
abstract
Springer et al. [Springer, A.M., Estes, J.A., van Vliet, G.B., Williams, T.M., Doak, D.F., Danner, E.M., Forney, K.A., Pfister, B., 2003. Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling? Proceedings of the National Academy of Sciences 100 (21), 12,223–12,228] hypothesized that great whales were an important prey resource for killer whales, and that the removal of fin and sperm whales by commercial whaling in the region of the Bering Sea/Aleutian Islands (BSAI) in the late 1960s and 1970s led to cascading trophic interactions that caused the sequential decline of populations of harbor seal, northern fur seal, Steller sea lion and northern sea otter. This hypothesis, referred to as the Sequential Megafaunal Collapse (SMC), has stirred considerable interest because of its implication for ecosystem-based management. The SMC has the following assumptions: (1) fin whales and sperm whales were important as prey species in the Bering Sea; (2) the biomass of all large whale species (i.e., North Pacific right, fin, humpback, gray, sperm, minke and bowhead whales) was in decline in the Bering Sea in the 1960s and early 1970s; and (3) pinniped declines in the 1970s and 1980s were sequential. We concluded that the available data are not consistent with the first two assumptions of the SMC. Statistical tests of the timing of the declines do not support the assumption that pinniped declines were sequential. We propose two alternative hypotheses for the declines that are more consistent with the available data. While it is plausible, from energetic arguments, for predation by killer whales to have been an important factor in the declines of one or more of the three populations of pinnipeds and the sea otter population in the BSAI region over the last 30 years, we hypothesize that the declines in pinniped populations in the BSAI can best be understood by invoking a multiple factor hypothesis that includes both bottom–up forcing (as indicated by evidence of nutritional stress in the western Steller sea lion population) and top–down forcing (e.g., predation by killer whales, mortality incidental to commercial fishing, directed harvests). Our second hypothesis is a modification of the top–down forcing mechanism (i.e., killer whale predation on one or more of the pinniped populations and the sea otter population is mediated via the recovery of the eastern North Pacific population of the gray whale). We remain skeptical about the proposed link between commercial whaling on fin and sperm whales, which ended in the mid-1960s, and the observed decline of populations of northern fur seal, harbor seal, and Steller sea lion some 15 years later.
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Ecosystem models show combined effects of fishing, predation, competition, and ocean productivity on Steller sea lions (Eumetopias jubatus) in Alaska.
Guénette, S., S.J.J. Heymans, V. Christensen, and A.W. Trites. 2006.
Canadian Journal of Fisheries and Aquatic Sciences 63:2495-2517.
abstract
Steller sea lions (Eumetopias jubatus) increased in the eastern portion of their range while declining in the Gulf of Alaska and Aleutian Islands from the late 1970s to late 1990s. We constructed ecosystem models of the central and western Aleutians and of Southeast Alaska to simultaneously evaluate four hypotheses explaining sea lion dynamics: killer whale (Orcinus orca) predation, ocean productivity, fisheries, and competition with other species. Comparisons of model predictions to historical time series data indicate that all four factors likely contributed to the trends observed in sea lion numbers in both ecosystems. Changes in ocean productivity conveyed by the Pacific Decadal Oscillation influenced the abundance trajectory of several species. Fishing could have affected the ecosystem structure by influencing the abundance of Atka mackerel (Pleurogrammus monopterygius) in the Aleutians, and herring (Clupea pallasii) in Southeast Alaska. Halibut (Hypoglossus stenolepis) in the Aleutians and arrowtooth flounder (Reinhardtius stomias) in Southeast Alaska appear to impede sea lion population growth through competitive interactions. Predation by killer whales was important when sea lions were less abundant in the 1990s in the Aleutians and in the 1960s in Southeast Alaska, but appear to have little effect when sea lion numbers were high.
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Studying trained Steller sea lions in the open ocean.
Hastie, G, D.A.S. Rosen, and A.W. Trites. 2006.
In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 193-204.
abstract
The costs associated with diving are a central component of a sea lions? energy budget. Accurate estimates of diving costs are needed to assess energetic and physiological constraints on foraging behavior, including the potential effects of changes in prey distribution or density. However, information on sea lion diving physiology is limited to relatively few species of pinnipeds, and there is currently no information for Steller sea lions. Information on diving energetics of pinnipeds has traditionally been gathered using either wild or captive animals. However, studies with wild animals are logistically challenging and are limited by the opportunistic nature of data collection, whilst studies in captivity have been constrained by the physical restrictions of the holding facility. To circumvent some of these limitations, we combined the best aspects of both techniques by conducting diving metabolism studies with trained Steller sea lions in an open ocean environment. Two captive-reared Steller sea lions were housed in a holding pen and transported by boat to a diving trial area. The animals were trained to dive to predetermined depths for controlled periods of time using an underwater light targeting system and a video system to monitor behavior. At the end of each dive the sea lions returned to a respirometry dome on the surface where oxygen consumption was measured to estimate diving metabolism. This paper describes the experimental setup used to evaluate diving metabolism, discusses the logistical challenges of the study and the advantages of using such an approach to carry out physiological experiments with sea lions, and provides preliminary data on the diving energetics of Steller sea lions.
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The influence of depth on a breath-hold diver: predicting the diving metabolism of Steller sea lions (Eumetopias jubatus).
Hastie, G.D, D.A.S. Rosen, A.W. Trites. 2006.
Journal of Experimental Marine Biology and Ecology 336:163-170.
abstract
Diving animals must endeavor to increase their dive depths and prolong the time they spend exploiting resources at depth. Results from captive and wild studies suggest that many diving animals extend their foraging bouts by decreasing their metabolisms while submerged. We measured metabolic rates of Steller sea lions (Eumetopias jubatus) trained to dive to depth in the open ocean to investigate the relationships between diving behaviour and the energetic costs of diving. We also constructed a general linear model to predict the oxygen consumption of sea lions diving in the wild. The resultant model suggests that mean swimming distance and depth of dives significantly influence the oxygen consumption of diving Steller sea lions. The predictive power of the model was tested using a cross-validation approach, whereby models reconstructed using data from pairs of sea lions were found to accurately predict the oxygen consumption of the third diving animal. Predict! ed oxygen consumption during dives to depth ranged from 3.37 L min-1 at 10 meters, to 1.40 L min-1 at 300 meters over a standardized swimming distance of 600 meters. This equated to an estimated metabolic rate of 97.54 and 40.52 MJ day-1, and an estimated daily feeding requirement of 18.92 and 7.96 kg day-1 for dives between 10 and 300 meters, respectively. The model thereby provides information on the potential energetic consequences that alterations in foraging strategies due to changes in prey availability could have on wild populations of sea lions.
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Using simulations to evaluate reconstructions of sea lion diet from scat.
Joy, R., D.J. Tollit, J.L. Laake, and A.W. Trites. 2006.
In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 205-222.
abstract
Models used to describe pinniped diet can provide very different composition estimates. Occurrence indices as well as biomass reconstruction models (which use estimates of the number and sizes of prey consumed) are commonly used and increasingly utilize a variety of fish hard remains (bones) found in scats. However, the importance of any single fish can be overestimated if its bones are deposited in a succession of scats assumed to be from different fish. Similarly, the importance of a species will be underestimated relative to other species if the bones of one species are more fragile and are completely digested or if bones from different fish of the same species are contained in a single scat and assumed to be from a single fish. Species differences in the proportion of fish bones that survive digestion can be assessed from captive feeding studies where the number and species of prey consumed is known. Numerical correction factors can be calculated to take into account the levels of complete digestion. We performed computer simulations using data from captive feeding studies to investigate levels and sources of error in reconstructing simulated mixed species diets. Our simulations used different combinations of hard remains, were conducted both with and without the application of numerical correction factors, and compared four different diet indices (1. Modified frequency of occurrence, 2. Split sample frequency of occurrence, 3. Variable biomass reconstruction, 4. Fixed biomass reconstruction). Simulations indicated that levels of error were related to the MNI method of inferring fish numbers from prey remains, prey size, the number of identifiable prey structures used, and the robustness of the remains to digestive processes (recovery rate). The fewer fish fed, the higher the relative probability of counting the fish, particularly when a multiple element structure or all structure techniques are used. If recovery rates were assumed to be consistent across species, then large fish (particularly when fed in small amounts) were overestimated relative to smaller sized prey in all models, but particularly biomass reconstruction models and when using more than one paired structure. When recovery rates of a paired structure (otoliths) were varied across species (as observed in captive feeding studies) then biomass models tended to overestimate the species with high recovery rates. In contrast, frequency of occurrence models overestimated the contribution of smaller prey (particularly when fed in small amounts). Simulations also indicated correction factors can reduce levels of error in biomass reconstruction models, but cannot solve problems related to counting fish using MNI. Our work shows simulations can form a valuable component in assessing diet indices and the level (and direction) of associated errors in each.
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Mapping world-wide distributions of marine mammal species using a relative environmental suitability (RES) model.
Kaschner, K., R. Watson, A. W. Trites and D. Pauly. 2006.
Marine Ecology Progress Series 316:285-310.
abstract
The lack of comprehensive sighting data sets precludes the application of standard habitat suitability modeling approaches to predict distributions of the majority of marine mammal species on very large scales. As an alternative, we developed an ecological niche model to map global distributions of 115 cetacean and pinniped species living in the marine environment using more readily available expert knowledge about habitat usage. We started by assigning each species to broad-scale niche categories with respect to depth, sea-surface temperature, and ice edge association based on synopses of published information. Within a global information system framework and a global grid of 0.5° latitude/longitude cell dimensions, we then generated an index of the relative environmental suitability(RES) of each cell for a given species by relating known habitat usage to local environmental conditions. RES predictions closely matched published maximum ranges for most species, thu! s representing useful, more objective alternatives to existing sketched distributional outlines. In addition, raster-based predictions provided detailed information about heterogeneous patterns of potentially suitable habitat for species throughout their range. We tested RES model outputs for 11 species (northern fur seal, harbor porpoise, sperm whale, killer whale, hourglass dolphin, fin whale, humpback whale, blue whale, Antarctic minke, and dwarf minke whales) from a broad taxonomic and geographic range, using data from dedicated surveys. Observed encounter rates and species-specific predicted environmental suitability were significantly and positively correlated for all but 1 species. In comparison, encounter rates were correlated with <1% of 1000 simulated random data sets for all but 2 species. Mapping of large-scale marine mammal distributions using this environmental envelope model is helpful for evaluating current assumptions and knowledge about species? occurrence! s, especially for data-poor species. Moreover, RES modeling can help to focus research efforts on smaller geographic scales and usefully supplement other, statistical, habitat suitability models.
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A review of the potential effects of disturbance on sea lions: assessing response and recovery.
Kucey, L., and A.W. Trites. 2006.
In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 581-589.
abstract
Human intrusion within areas of sea lion habitat is increasing worldwide, leading to concerns about disruption of distribution and daily activities of sea lions. Sea lion responses to disturbance can be quantified by recording changes in behavioural patterns, documenting numbers of animals on shore before, during and after the disturbance, or by measuring physiological stress of individual animals. However, assessing recovery is not so straightforward, as highlighted by an example from a study of the short-term effects of disturbance on Steller sea lions. Recovery is generally recognized as a return to an original state or normal condition, but is often operationally defined as a percent-return to pre-disturbance numbers or behaviours. Simple interpretation of disturbance effects can be easily confounded by concurrent natural seasonal changes in behaviours or haulout patterns, or by daily variability in numbers that can be attributed to weather, tidal cycle stage and other factors. Overall, a range of recovery criteria needs to be simultaneously applied when assessing the effects of human disturbance on sea lion populations. Insights gained from research on the effects of disturbance on Steller sea lions may help guide the development of studies undertaken on other species of sea lions.
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Body mass and composition responses to short-term low energy intake are seasonally dependent in Steller sea lions (Eumetopias jubatus).
Kumagai, S., D.A.S Rosen and A.W. Trites. 2006.
Comparative Biochemistry and Physiology 179:589-598.
abstract
Steller sea lions (Eumetopias jubatus) were fed restricted iso-caloric amounts of Pacific herring (Clupea pallasi) or walleye pollock (Theragra chalcogramma) for 8-9 days, four times over the course of a year to investigate effects of season and prey composition on sea lion physiology. At these levels, the sea lions lost body mass at a significantly higher rate during winter (1.6 ± 0.14 kg d-1), and at a lower rate during summer (1.2 ± 0.32 kg d-1). Decreases in body fat mass and standard metabolic rates during the trials were similar throughout the seasons and for both diet types. The majority of the body mass that was lost when eating pollock derived from decreases in lipid mass, while a greater proportion of the mass lost when eating herring derived from decreases in lean tissue, except in the summer when the pattern was reversed. Metabolic depression was not observed during all trials despite the constant loss of body mass. Our study supports the hypothesis that restricted energy intake may be more critical to Steller sea lions in the winter months, and that the type of prey consumed (e.g., herring or pollock) may have seasonally-specific effects on body mass and composition.
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Techniques for real-time, active tracking of sea lions.
Lea, M.A., and B. Wilson. 2006.
In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 235-253.
abstract
The movements of otariids at sea are generally studied by satellite telemetry. At fine scales (1-20km), however, the level of precision provided by this technique (+- mean 1.5-19 km) may be insufficient to accurately reconstruct the track of an individual and/or integrate such movement data with habitat and environmental features. An alternative technique is the boat-based active tracking of individuals by very high frequency (VHF) or acoustic telemetry. By following an individual equipped with transmitters, detailed observations of habitat use, predator occurrence, social context, behavioral state, and prey availability may be integrated to provide a real-time context in which to place the animals? movements. For species such as the Steller sea lion (Eumetopias jubatus), which are difficult to recapture, such techniques enable the collection of much needed contextual information. Here we describe the methods we applied to actively track Steller sea lions. Twenty-o! ne juveniles were captured in southeast Alaska during October 2003 and February 2004. They were fitted with a variety of VHF, satellite, and/or acoustic tags and were tracked through the winter and spring of 2003-2004. The use of ship-based VHF telemetry in conjunction with real time navigation plotting software was highly successful and provided 37 fine-scale tracks of coastal and pelagic sea lion movements covering a total distance of 482 km. Acoustic telemetry techniques were less successful because of the suspected overlap in tag transmission frequency and sea lion hearing. The study represents the first active tracking of a sea lion species, highlighting the high-resolution tracks and contextual behavioral and habitat information that can be obtained using VHF telemetry at sea.
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Potential effects of short-term prey changes on sea lion physiology.
Rosen, D.A., D.J. Tollit, A.J. Winship, and A.W. Trites. 2006.
In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 103-116.
abstract
hanges in the proximate composition of prey can result in a nutritional imbalance in individual animals, regardless of total energy intake. This mechanism has been hypothesized to have contributed to the decline of Steller sea lions (Eumetopias jubatus). Yet little is known about how otariids react physiologically to short-term changes in prey quality and availability. A series of studies with young captive Steller sea lions tested several potential links between prey quality and sea lion health. Body composition (fat to total mass ratio) of animals fed constant, maintenance-level, isocaloric diets of high- or low-lipid prey changed with season, but overall was not aff ected by prey composition. The sea lions appeared to prioritize maintaining core growth rates even when energy was limited, electing to deplete lipid reserves to fulfi ll energy defi cits, resulting in changes in relative body condition. In contrast, sea lions subject to short- term, sub-maintenance diets of high- or low-lipid prey utilized a greater portion of their lipid reserves when losing body mass on low lipid prey. Experiments with diff erent ad libitum feeding regimes indicated that sea lions are readily able to alter food intake levels to compensate for diff erences in prey energy content and, to a lesser degree, prey availability. However, the results also suggest that decreases in prey quality and/or foraging opportunities can readily combine to require food intake levels that are greater than the digestive capacity of the individual. This is particularly true for young animals that may already be living ?on the edge? energetically.
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Changes in diet and maternal attendance of a South American sea lions indicate changes in the marine environment and the abundance of prey.
Soto, K., A.W. Trites, and M. Arias-Schreiber. 2006.
Marine Ecology Progress Series 312:277-290.
abstract
Behavioural observations were made of South American sea lions Otaria flavescens in Peru to determine whether changes in their diet and maternal attendance patterns reflected physical changes in the marine environment and alterations in the abundance and distribution of prey. The study was conducted during the breeding season between 1998 and 2002, which was a period that encompassed a strong El Niño (1997–1998) and a moderate La Niña (1999–2001). Observations revealed strong linkages between maternal attendance patterns and the abundance of prey and oceanographic features close to the rookeries. Acute prey shortage during El Niño resulted in females increasing the length of their foraging trips and decreasing the time they spent onshore with their pups. In contrast, shorter times at sea and longer times onshore were observed during the favourable conditions of La Niña when preferred prey (anchovy and squat lobster) were more abundant near the rookeries. Pup mortalities increased when females spent more time at sea searching for prey and did not return frequently enough to nurse their pups. A larger diversity of prey species (particularly of demersal fishes) was consumed during El Niño when anchovy and lobster were less available. Females appeared to adjust their diets and maternal attendance patterns in response to annual changes in the abundance and distribution of prey. These observations suggested that diet and maternal responses reflect interannual fluctuations of the unpredictable Peruvian upwelling ecosystem, and implied that South American sea lions may be good indicators of relative changes in the distribution and abundance of marine resources.
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Estimating diet composition in sea lions: which technique to choose?
Tollit, D.J., S.G. Heaslip, B.E. Deagle, S.J. Iverson, R. Joy, D.A.S. Rosen and A.W. Trites. 2006.
In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 293-307.
abstract
Accurate estimates of diets are vital to monitor impacts of sea lion populations on their ecosystems, their interactions with fisheries and to understand the role of food to animal nutrition and health. Approaches include using: (1) prey remnants in stomach contents, spews and scats, (2) prey DNA in scats (3) fatty acid signatures in blubber and (4) stable isotope ratios in predator's tissue. Each methodology has particular advantages and limitations, many of which can be assessed and improved through controlled captive feeding trials. Analysis of prey remnants from captive sea lion scats have shown significant variability in digestion between and within prey species, which coupled with preferential regurgitation and enumeration biases, can confound accurate diet quantification, but does not prevent spatial or temporal comparisons. Correction for partial digestion and use of additional structures besides otoliths can provide accurate prey size estimates. Prey DNA can be reliably isolated from soft remains in scats from captive sea lions and with further development this approach may allow quantification of diet. Genetic methods can be expensive and representative of only one to two days foraging (like prey remnant analysis), but may be less affected by differential digestion and can identify prey in scats that could not be identified through structural remnants. Validation of fatty acid signature analysis to quantify diet at longer temporal scales in sea lions is ongoing, but this new technique promises to be particularly useful to assess biases in traditional methods, identify the onset of weaning and to highlight what prey most contribute to lipid reserves. Stable isotope analysis of predator tissues gives only trophic level data, but can provide data on diet changes on many temporal scales. Remote video monitoring of foraging events and lavage/enema techniques can provide valuable diet information, but, like many newer techniques, animal capture is required. Ideally a suite of techniques should be used to study diet. While methods and correction factors developed for Steller sea lions can likely be applied to the other five sea lion species, they should be verified experimentally.
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Insights into the Timing of Weaning and the Attendance Patterns of Lactating Steller Sea Lions (Eumetopias jubatus) in Alaska During Winter, Spring and Summer.
Trites, A.W., B.P. Porter, V.B. Deecke, A.P. Coombs, M.L. Marcotte and D.A.S. Rosen. 2006.
Aquatic Mammals 32:85-97.
abstract
Behavioral observations of lactating Steller sea lions (Eumetopias jubatus) and their offspring were recorded at 4 haulout sites in Alaska to determine: 1) whether sea lions wean during winter while they are 7-9 months old, and 2) whether sea lions using sites in the Gulf of Alaska (the declining endangered population) made longer foraging trips than sea lions in Southeast Alaska (where the population appeared larger and healthier). Longer foraging trips are commonly thought to be an indicator of nutritional stress. Eight sets of behavioral observations were made using focal and scan sampling techniques at haulouts over 4 years (1995-1998) during 3 seasons (winter, spring and summer). Counter to expectations, we found no significant differences between haulout populations in the time that lactating Steller sea lions spent at sea or on shore. This suggests that sea lions did not have more difficulty capturing prey from winter through summer in the area of decline compared to where sea lion numbers increased. However, lactating Steller sea lions in both regions made longer foraging trips in winter than they did in spring and summer. These changes in foraging patterns between seasons were consistent among all years and sites. The proportion of time that immature Steller sea lions suckled declined through the spring to early summer, suggesting that sea lions began supplementing their milk diet with solid food in the spring. We did not observe any sea lions weaning during winter. Rather, most appeared to wean at the start of the breeding season when they were 1 or 2 y old. Sea lions observed in Southeast Alaska during the late 1990s while population growth was slowing suggest that most males weaned at 2 y, and that about 50% of females weaned at 1 y and the remainder at 2 y.
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Sea Lions of the World.
Trites, A.W., S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea, and K. Wynne (eds). 2006.
Alaska Sea Grant Alaska College Program, University of Alaska, Fairbanks. 664 pages
abstract
The goal of the symposium was to bring together scientists and resource managers to address knowledge of world sea lion populations in order to compare them with Steller sea lions, and to identify research needs. managers to address knowledge of world sea lion populations in order to compare them with Steller sea lions, and to identify research needs.

Changes in the worldwide abundance of sea lions is of growing concern to fisheries and conservation groups, because fisheries are feared to threaten sea lions, and/or because sea lions are feared to threaten fisheries. Over the past few decades, major changes have been noted in the abundance of all five species of sea lions around the world. In the North Pacific, the Steller sea lion has been declared endangered in parts of its range and is considered threatened with extinction in others. This is in contrast to the rapid increase in populations of California sea lions in Mexico and California. Elsewhere, the Japanese subspecies of the California sea lion is probably extinct and the Galapagos subspecies is in low numbers. Numbers of New Zealand sea lions and Australian sea lions are also extremely low, with major declines recently reported in Australia. Relatively little is known about the South American sea lion.

This symposium brought the world community of sea lion researchers and policy makers together to share their experiences and knowledge with each other. Interspecies comparisons can shed light on why some populations might decline while others increase. Insights might also be gained on whether trends in the abundance of sea lions are related to fishing activities through food dependencies or more directly through control or conservation measures. A better understanding of the biology of sea lions is urgently needed. The symposium significantly contributed to the understanding of fluctuating sea lion populations, especially as they compare to the Steller sea lion, by synthesizing current knowledge and forging new directions.

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Effects of fisheries on ecosystems: just another top predator?
Trites, A.W., V. Christensen and D. Pauly. 2006.
In I.L. Boyd, K. Camphuysen and S. Wanless (eds), Top predators in marine ecosystems: their role in monitoring and management. Cambridge University Press, Cambridge. pp. 11-27.
abstract
Apex predators such as pinnipeds, cetaceans, seabirds and sharks, are constrained by the sizes of prey they can consume and thus typically feed within a narrow range of trophic levels. Having co-evolved with their prey, they have influenced the behaviors, physiologies, morphologies and life history strategies of the species they target. In contrast, humans can consume prey of any size from all trophic levels using methods that can rapidly deplete populations. On an ecological time scale, fisheries, like apex predators, can directly affect the abundance of other species by consuming, or out-competing them; or they can indirectly affect the abundance of non-targeted species by removing other predators. However, there is growing evidence that the effects of fisheries go well beyond those imposed by apex predators. Theory and recent observations confirm that the continued development and expansion of fisheries over the past half century has led to a decrease in the! size and life spans of targeted species, with reproduction of fish occurring at earlier ages and at smaller sizes. Also, high levels of fishing have altered the makeup of many ecosystems, depressing the average trophic level of heavily fished ecosystems and speeding up the rate of nutrient turnover within them. An inevitable consequence of fishing down the food web is increased ecosystem instability, unsustainable fisheries and an inability for the ecosystem to support healthy abundant populations of apex predators.
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Food consumption by sea lions: existing data and techniques.
Winship, A.J., A.M.J. Hunter, D.A.S. Rosen, and A.W. Trites. 2006.
In A.W. Trites, S. Atkinson, D.P. DeMaster, L.W. Fritz, T.S. Gelatt, L.D. Rea and K. Wynne (eds), Sea Lions of the World. Alaska Sea Grant College Program, University of Alaska, Fairbanks. pp. 177-191.
abstract
Knowing the quantity of prey that sea lions consume is a prerequisite for assessing the role of sea lions in aquatic ecosystems and the potential for competition to occur with fisheries. We reviewed the different approaches that have been used to estimate the food requirements for the six species of sea lions. We reviewed data on the quantity of food consumed by sea lions in captivity, and examined how consumption varied by species, body size, and season. We also reviewed and quantified available information on the energetics of sea lions and assessed the potential application of these data to parameterize an existing bioenergetic model that was developed to estimate the food requirements of Steller sea lions. Our study provided ranges of estimates of food consumption for sea lions that can be used in various modeling strategies to assess the impact of sea lions on prey populations, including commercially exploited fish species. The approaches reviewed in our study shared common difficulties arising from the quantity and quality of data, and the integration of data across scales and species. Our modeling exercise, in particular, identified the major uncertainties involved in estimating the food requirements of each sea lion species using an energetics approach. Our results provide direction for future research aimed at improving the accuracy and comparability of estimates of food consumption for sea lions.
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Risk of extirpation of Steller sea lions in the Gulf of Alaska and Aleutian Islands: a population viability analysis based on alternative hypotheses for why sea lions declined in western Alaska.
Winship, A.J., and A.W. Trites. 2006.
Marine Mammal Science 22(1):124-155.
abstract
We estimated the risk that the Steller sea lion will be extirpated in western Alaska using a population viability analysis (PVA) that combined simulations with statistically fitted models of historical population dynamics. Our analysis considered the roles that density-dependent and density-independent factors may have played in the past, and how they might influence future population dynamics. It also established functional relationships between population size, population growth rate and the risk of extinction under alternative hypotheses about population regulation and environmental variability. These functional relationships can be used to develop recovery criteria and guide research and management decisions. Life table parameters (e.g., birth and survival rates) operating during the population decline (1978?2002) were estimated by fitting simple age-structured models to time-series of pup and non-pup counts from 33 rookeries (subpopulations). The PVA was carried out by projecting all 33 subpopulations into the future using these estimated site-specific life tables (with associated uncertainties) and different assumptions about carrying capacities and the presence or absence of density-dependent population regulation. Results suggest that the overall predicted risk of extirpation of Stelsler sea lions as a species in western Alaska was low in the next 100 yr under all scenarios explored. However, most subpopulations of Steller sea lions had high probabilities of going extinct within the next 100 yr if trends observed during the 1990s were to continue. Two clusters of contiguous subpopulations occurring in the Unimak Pass area in the western Gulf of Alaska/eastern Aleutian Islands and the Seguam?Adak region in the central Aleutian Islands had relatively lower risks of extinction. Risks of extinction for a number of subpopulations in the Gulf of Alaska were reduced if the increases observed since the late 1990s continue into the fu ture. The risks of subpopulations going extinct were small whe n densit ydependent compensation in birth and survival rates were assumed, even when random stochasticity in these vital rates was introduced.
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2005
 
Infectious disease and the decline of Steller sea lions (Eumetopias jubatus) in Alaska: insights from serology data.
Burek, K.A., F.M.D. Gulland, G. Sheffield, K.B. Beckman, E. Keyes, T.R. Spraker, A.W. Smith, D.E. Skilling, J.E. Evermann, J.L. Stott, J.T. Saliki and A.W. Trites. 2005.
Journal of Wildlife Diseases 41(3):512-524.
abstract
Serology data were examined to determine whether infectious disease may have played a role in the decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands. Available published data, historical unpublished data, and recent collections (1997-2000) were compared and reviewed. Data was stratified by geography in order to compare the declining western Alaska population in the Aleutian Islands regions through eastern Prince William Sound to the increasing population in Southeast Alaska. Prevalences of antibodies from the 1970s to early 1990s were noted for Leptospira interrogans, Chlamydophila psittaci, Brucella spp., phocid herpesvirus 1, and canine parvovirus. Serum samples collected and analyzed from 1997?2000 were tested for antibodies to these agents as well as to caliciviruses, marine mammal morbilliviruses, and canine adenoviruses 1 and 2. Conclusions could not be drawn about changes in the prevalence of exposure to disease agents during the decline of Steller sea lions because data were not comparable either because of inconsistencies in test techniques, or because the samples were either not collected in all decades from all regions or were not tested for antibodies to the same disease agents in different decades. Despite these shortcomings, the available data contained no convincing evidence of significant exposure of Steller sea lions to morbilliviruses, B. spp., canine parvovirus or L. interrogans. Steller sea lions have been exposed to a phocid herpesvirus, caliciviruses, canine adenovirus, and C. psittaci or to cross reactive organisms in regions of both increasing and decreasing sea lion abundance. These disease agents are not likely to have been the primary cause of the decline because they are found at comparable levels in both the increasing and the decreasing populations. However they may have contributed to the decline or impeded recovery of the Steller sea lion population due to undetected mortality and morbidity, or reduction of fecundity and body condition in animals under other stresses. Systematic monitoring for disease agents and their effects is needed to determine whether infectious disease is currently playing a role in the decline and lack of recovery of Steller sea lions.
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Molecular scatology as a tool to study diet: analysis of prey DNA in scats from captive Steller sea lions.
Deagle, B.E., D.J. Tollit, S.N. Jarman, M.A. Hindell, A.W. Trites and N.J. Gales. 2005.
Molecular Ecology 14:1831-1842.
abstract
The DNA of prey present in animal scats may provide a valuable source of information for dietary studies. We conducted a captive feeding trial to test whether prey DNA could be reliably detected in scat samples from Steller sea lions (Eumetopias jubatus). Two sea lions were fed a diet of fish (five species) and squid (one species), and DNA was extracted from the soft component of collected scats. Most of the DNA obtained came from the predator, but prey DNA could be amplified using prey-specific primers. The four prey species fed in consistent daily proportions throughout the trial were detected in more than 90% of the scat DNA extractions. Squid and sockeye salmon, which were fed as a relatively small percentage of the daily diet, were detected as reliably as the more abundant diet items. Prey detection was erratic in scats collected when the daily diet was fed in two meals that differed in prey composition, suggesting that prey DNA is passed in meal specific puls! es. Prey items that were removed from the diet following one day of feeding were only detected in scats collected within 48 hours of ingestion. Proportions of fish DNA present in eight scat samples (evaluated through the screening of clone libraries) was roughly proportional to the mass of prey items consumed, raising the possibility that DNA quantification methods could provide semi-quantitative diet composition data. This study should be of broad interest to researchers studying diet since it highlights an approach that can accurately identify prey species and is not dependent on prey hard parts surviving digestion.
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The vocal behaviour of mammal-eating killer whales (Orcinus orca): Communicating with costly calls.
Deecke, V.B., Ford, J.K.B., Slater, P.J.B. 2005.
Animal Behaviour 69:395-405.
abstract
The cost of vocal behaviour is usually expressed in energetic terms; however, many animals pay additional costs arising from predators or potential prey eavesdropping on their vocal communication. The northeastern Pacific is home to two distinct ecotypes of killer whales (Orcinus orca): resident killer whales feed on fish, a prey with poor hearing abilities, whereas transient killer whales hunt marine mammals, which 5 have sensitive underwater hearing at the frequencies of killer whale vocal communication. In this study, we investigated how the superior hearing ability of their prey has shaped the vocal behaviour of the transient ecotype. We recorded pulsed calls and the associated behavioural context of groups of transient and resident killer whales in British Columbia and southeastern Alaska. Transient killer whales emitted pulsed calls significantly less frequently than residents. Transient killer whales only exhibited significant amounts of vocal 10 behaviour after a marine mammal kill or when the whales where displaying surface-active behaviour. Vocal activity of transients increased after a successful attack on a marine mammal. Since marine mammals are able to detect killer whale pulsed calls and respond with anti-predator behaviour, the reduced vocal activity of transients is probably due to a greater cost for calling in this ecotype resulting from eavesdropping by potential prey. The increase in vocal behaviour after a successful attack may represent food calling (informing other animals in the area about the presence of food), but is more likely to reflect an increase in social interactions during feeding and/or the fact that the cost for vocal behaviour is comparatively low after a successful attack.
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The dielectric properties of the cranial skin of five young captive Stellar sea sea lions (Eumetopias jubatus) and a similar number of young domestic pigs (Sus scrofa) and sheep (Ovis aries) between 0.1 and 10 GHz.
Olawale, K.O., R.J. Petrell, D.G. Michelson and A.W. Trites. 2005.
Physiological Measurement 26:626-637.
abstract
To aid in the development of a long-range subcutaneous radio frequency identification tag to monitor the fate sea lion pups, the dielectric properties of the cranial skin of young female otariids, and possible test subjects of similar size and age, or pigs (Sus scrofa) and sheep (Ovis aries)were obtained over a frequency range of 0.1 to 10 GHz at the base of their heads where the tag will be implanted. The resulting curves were similar in shape to adult human skin data, but the values were generally lower. Between ubjects, variations were noted in all the species. Circuitry for the RF-ID tag is being designed to account for antenna detuning as a result of the lossy media or skin and he variation in dielectric properties.

keywords     Keywords: dielectric constant, dielectric loss, skin thickness,
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Examining the potential for nutritional stress in young Steller sea lions: physiological effects of prey composition.
Rosen, D.A.S. and A.W. Trites. 2005.
Journal of Comparative Physiology 175:265-273.
abstract
The effects of high- and low-lipid prey on the body mass, body condition, and metabolic rates of young captive Steller sea lions (Eumetopias jubatus) were examined to better understand how changes in prey composition might impact the physiology and health of wild sea lions and contribute to their population decline. Results of three feeding experiments suggest that prey lipid content did not significantly affect body mass or relative body condition (lipid mass as a percent of total mass) when sea lions could consume sufficient prey to meet their energy needs. However, when energy intake was insufficient to meet daily requirements, sea lions lost more lipid mass (9.16±1.80 kg±SE) consuming low-lipid prey compared with eating high-lipid prey (6.52±1.65 kg). Similarly, the sea lions lost 2.7±0.9 kg of lipid mass while consuming oil-supplemented pollock at maintenance energy levels but gained 5.2±2.7 kg lipid mass while consuming identical energetic levels of herring. Contrary to expectations, there was a 9.7±1.8% increase in metabolism during mass loss on submaintenance diets. Relative body condition decreased only 3.7±3.8% during periods of imposed nutritional stress, despite a 10.4±4.8% decrease in body mass. These findings raise questions regarding the efficacy of measures of relative body condition to detect such changes in nutritional status among wild animals. The results of these three experiments suggest that prey composition can have additional effects on sea lion energy stores beyond the direct effects of insufficient energy intake.
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Dietary analysis from fecal samples: how many scats are enough?
Trites, A.W. and Joy, R. 2005.
Journal of Mammalogy 86(4):704-712.
abstract
Diets of mammals are increasingly being inferred from identification of hard parts from prey eaten and recovered in fecal remains (scats). Frequencies with which particular prey species occur among collections of scats are easily compiled to describe the average diet, and can be used to compare diets between and within geographic regions, and across years and seasons. Important to these analyses is the question of statistical power. In other words, how many scats should be collected to compare the diet among and between species? We addressed this problem using Monte Carlo simulations to analytically determine the consequence of sample size on the dietary analysis of scats using frequency of occurrence methods. We considered two questions: 1) how is the statistical power affected by sample size; and 2) what is the likelihood of not identifying a prey species? We randomly sampled predetermined numbers of scats (n=10–200) from computer-generated populations of scats containing prey of known species and frequencies of occurrences. We also randomly sampled a large database of field-collected scats from Steller sea lions (Eumetopias jubatus). We then used standard contingency table tests such as chi-square and Fisher’s exact test to determine whether differences between our samples and populations were statistically significant. We found a minimum size of 59 scats is necessary to identify principal prey remains occurring in >5% of scats. However, 94 samples are required when comparing diets to distinguish moderate effect sizes over time or between areas. These findings have significant implications for the interpretation of published dietary data, as well as for the design of future scat-based dietary studies for pinnipeds and other species.
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2004
 
Validation of a fecal glucocorticoid assay for Steller sea lions (Eumetopias jubatus).
Hunt, K.E., A.W. Trites, and S.K. Wasser. 2004.
Physiology and Behavior 80:595-601.
abstract
The Steller sea lion (Eumetopias jubatus) is listed as endangered in parts of its range and is suspected of suffering from ecological stressors that may be reflected by fecal glucocorticoid hormones. We validated a fecal glucocorticoid assay for this species with an adrenocorticotropic hormone (ACTH) challenge. Feces were collected from captive Steller sea lions (two males and two females) for 2 days before injection with ACTH, and for 4 or more days postinjection. Feces were freeze-dried, extracted with a methanol vortex method, and assayed for glucocorticoids. The assay demonstrated good parallelism and accuracy. All animals showed the expected peak of fecal glucocorticoid excretion after ACTH injection. However, the two males had higher baselines, higher peaks, and more delayed peaks than the females. Peak glucocorticoid excretion occurred at 5 and 28 h postinjection for the two females, and at 71 and 98 h for the two males. Correction for recoveries by the addition of tritiated hormones produced ACTH profiles that were virtually identical in pattern to uncorrected data, but with higher within-sample coefficients of variation. Based on these results, we conclude that this fecal glucocorticoid assay accurately reflects endogenous adrenal activity of Steller sea lions, and that recovery corrections are not necessary for this species when using the methanol vortex extraction method. More research is needed to address possible sex differences and other possible influences on fecal glucocorticoid concentrations.
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Season variation in nutrient composition of Alaskan walleye pollock.
Kitts, D. D., Huynhl,M. D., Hu, C. and Trites, A.W. 2004.
Canadian Journal of Zoology 82:1408-1415.
abstract
A popular hypothesis for the noted steady decline in the population of Steller sea lions in the regions from Prince William Sound through the Aleutian Islands relates to their nutritional status. Sea lion diets appear to have shifted from primarily small schooling fatty fishes to low fat fish such as walleye pollock (Theragra chalcogramma). We examined the seasonal changes in proximate nutrients of pollock collected in the Bering Sea. Mean energy density (dry-weight) of pollock peaked in October then declined and remained low throughout winter. Energy recovery occurred in the summer months with strong recovery observed in female fish caught in July. Contrary to whole fish carcass energy contents, both total protein and moisture contents were at their highest levels in winter (January) when total crude lipid content was at its lowest (p<0.05). This trend gradually declined to its lowest levels in the fall, when lipid content was high. The decline in total lipi! ds during winter seasons appeared to parallel gonad development during the pre-spawning period. Sex differences in energy densities were not found. Nor did proximate analysis data for moisture, protein, ash and lipid content show any significant variation between males and females. Protein digestibility of pollock was higher (p<0.05) in the summer than in the spring, but not different for winter or fall seasons. We conclude that the nutrient content of pollock may have some impact on the Steller sea lions that feed on them, particularly the energetic value that appears to be low during important feeding periods for this marine mammal.
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Parallel influence of climate on the behaviour of Pacific killer whales and Atlantic bottlenose dolphins.
Lusseau, D., R. Williams, B. Wilson, K. Grellier, T.R. Barton, P.S. Hammond and P.M. Thompson. 2004.
Ecology Letters 7:1068-1076.
abstract
The grouping behaviour of animals is governed by intrinsic and extrinsic factors which play an important role in shaping their social organization. We investigated the influence of ocean climate variation on the grouping behaviour of two widely separated populations of cetaceans, inhabiting north Atlantic and north Pacific coastal waters. The group size of both bottlenose dolphins in the Moray Firth, UK, and killer whales in Johnstone Strait, Canada, varied from year to year in relation to large-scale ocean climate variation. Local indices of prey abundance were also related both to climate indices and predator group sizes. The cetaceans tended to live in smaller groups when there was less salmon available in both areas which seem to occur 2 years after a lower phase of the North Atlantic and Pacific Decadal Oscillations. These findings suggest that, even in highly social mammals, climate variation may influence social organization through changes in prey availability.
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Suckling attempts during winter by two non-filial Steller sea lion pups (Eumetopias jubatus).
Porter, B.T. and Trites, A.W. 2004.
Mammalia 63:23-26.
abstract
Milk stealing and fostering care is rare among mammals. Among pinnipeds, the nursing of offspring that are not their own has been noted for some species of seals, but rarely for sea lions or fur seals. Thousands of hours have been spent observing Steller sea lions in the wild, but only a few successful suckling attempts have been noted. From January to March 1996, we observed two non-filial pups repeatedly suckling lactating females at a winter haulout site at Timbered Island in southeast Alaska. These two observations are noteworthy because of their rarity and the bearing they have on the poorly understood process of weaning in Steller sea lions. The timing of weaning in Steller sea lions has been speculated to occur sometime during winter or spring when pups are 6 months or older. Both mothers and pups we observed were aggressive toward intruding conspecifics and were very protective of their mother’s teats. However, there was a range of individual variation in the tolerance of both mature females and their offspring to the distance they would allow strange pups near the teats. It is undoubtedly advantageous for nutritionally stressed pups to attempt to steal milk, compared with the alternative — starvation. However the potential for injury likely out-weighs any gain in resources and probably deters most young from attempting to approach strange females. The pups we observed stealing milk did not supplement their intake with fish despite the apparent ability of this age group to capture prey. The fact that they did not suggests that they may not have been behaviourally or physiologically capable of consuming fish. Compared with milk, they may also not be physically capable of consuming enough prey to meet their daily energy needs during this period of rapid growth and development. This further suggests that weaning of Steller sea lions pups may occur much later in spring or early summer than many have previously thought.
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The effects of prey availability on pup mortality and the timing of birth of South American sea lions (Otaria flavescens) in Peru.
Soto, K., A.W. Trites, and M. Arias-Schreiber. 2004.
Journal of Zoology 264:419-428.
abstract
Pup mortality and the timing of birth of South American sea lions Otaria flavescens were investigated to determine the possible relationship between fluctuations in prey availability in the Peruvian upwelling ecosystem and current and future reproductive success of sea lions during six consecutive breeding seasons. Our study from 1997 to 2002 encompassed the strongest El Nino on record and one La Nina event. Pup mortality ranged from 13% before El Nino to 100% during El Nino, and was negatively correlated with prey availability. Abortions were also more frequent when prey availability was low. However, pup mortality remained high following El Ni~no due to the punctuated short-term effects it had on population dynamics and subsequent maternal behaviour. Births occurred later in the season after years of low food availability and earlier following years of high food availability. The peak of pupping coincided with the peak of mortality in all years, and may have ! been the product of intensive competition between bulls at the peak of the breeding season. The stronger and more frequent El Ninos that appear to be occurring along the Peruvian coast may produce significant stochastic changes in future births and pup mortality, which may place the vulnerable South American sea lion population in Peru at greater risk.
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Sizes of walleye pollock (Theragra chalcogramma) consumed by the eastern stock of Steller sea lions (Eumetopias jubatus) in Southeast Alaska from 1994-1999.
Tollit, D.J., Heaslip, S.G. and Trites, A.W. 2004.
Fishery Bulletin 102(3):522-532.
abstract
Lengths of walleye pollock (Theragra chalcogramma) consumed by Steller sea lions (Eumetopias jubatus) were estimated using allometric regressions applied to seven diagnostic cranial structures recovered from 531 scats collected in Southeast Alaska between 1994-1999. Selected structural measurements were corrected for loss of size due to erosion using experimentally derived condition-specific digestion correction factors. Correcting for digestion increased the estimated length of fish consumed by 23%, and the average mass of fish consumed by 88%. Mean corrected fork length (FL) of pollock consumed was 42.4 11.6 cm (range=10.0-78.1 cm, n=909). Adult pollock (>45.0 cm FL) occurred more frequently in scats collected from rookeries along the open ocean coastline of Southeast Alaska during June and July (74% adults, mean FL=48.4 cm) than they did in scats from haulouts located in inside waters between October and May (51% adults, mean FL=38.4 cm). Overall, the contribution of juvenile pollock (20 cm) to the sea lion diet was insignificant, while adults contributed 44% to the diet by number and 74% by mass. On average, larger pollock were eaten in summer at rookeries throughout Southeast Alaska than at rookeries in the Gulf of Alaska or the Bering Sea. Overall it appears that Steller sea lions are capable of consuming a wide size range of pollock, with the bulk of fish falling between 20-60 cm. The use of cranial hard parts other than otoliths and the application of digestion correction factors are fundamental to correctly estimating the sizes of prey consumed by sea lions and for determining their overlap with commercial fisheries.
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A method to improve size estimates of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius) consumed by pinnipeds: digestion correction factors applied to bones and otoliths recovered in scats.
Tollit, D.J., Heaslip, S.G., Zeppelin, T.K., Joy, R., Call, K.A. and Trites, A.W. 2004.
Fishery Bulletin 102(3):498-508.
abstract
The lengths of otoliths and other skeletal structures recovered from the scats of pinnipeds, such as Steller sea lions (Eumetopias jubatus), correlate with body size and can be used to estimate the length of prey consumed. Unfortunately, otoliths are often found in too few numbers or are too digested to usefully estimate prey size. Techniques are therefore required to account for the degree of digestion of alternative diagnostic bones prior to estimating prey size. We developed a method (using defined criteria and photo-reference material) to assign the degree of digestion for key cranial structures of two prey species (walleye pollock, Theragra chalcogramma and Atka mackerel, Pleurogrammus monopterygius). The method grades each structure into one of three condition categories; good, fair or poor. We also conducted captive feeding trials to determine the extent of erosion and derive condition-specific digestion correction factors to reconstruct the original sizes of the structures consumed. In general, larger structures were relatively more digested than smaller ones. Mean size reduction varied between different types of structures (3.3-26.3%), but was not influenced by the size of the prey consumed. Results from the observations and experiments were combined to reconstruct the size of prey consumed by sea lions and other pinnipeds. The proposed method has four steps: 1) measure the recovered structures and grade the extent of digestion using defined criteria and photo-reference collection; 2) exclude structures graded in poor condition; 3) multiply measurements of structures in good and fair condition by their appropriate digestion correction factors to derive their original size; and 4) calculate the size of prey from allometric regressions relating corrected structure measurements to body lengths. This technique can be readily applied to piscivore dietary studies that use fish hard remains.
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Sizes of walleye pollock and Atka mackerel consumed by the Western stock of Steller sea lions (Eumetopias jubatus) in Alaska from 1998-2000.
Zeppelin, T. K., Tollit, D.J., Call, K.A., Orchard, T. J. and Gudmundson, C. J. 2004.
Fishery Bulletin 102(3):509-521.
abstract
Prey size selectivity by Steller sea lions (Eumetopias jubatus) is relevant for understanding the foraging ecology of this declining predator, but studies have been problematic due to the erosion or absence of prey skeletal structures and otoliths usually used to estimate fish length. We developed regression formulae to estimate fish length from seven diagnostic cranial structures of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius). For both species, all structure measurements were related with fork length of prey (r squared range: 0.78 - 0.99). Fork length of walleye pollock and Atka mackerel consumed by Steller sea lions was estimated by applying these regression models to cranial structures recovered from scats (feces) collected between 1998 and 2000 across the range of the Alaskan western stock of Steller sea lions. Experimentally derived digestion correction factors were applied to take into account loss of size due to digestion. Fork lengths (FL) of walleye pollock consumed by Steller sea lions ranged from 3.7 to 70.8 cm FL (mean = 1 39.3 cm, SD = 14.3 cm, n = 1 666) and Atka mackerel ranged from 15.3 to 49.6 cm FL (mean = 1 32.3 cm, SD = 5.9 cm, n = 1,685). Although sample sizes were limited, a greater proportion of juvenile (less than to 20 cm) walleye pollock were found in samples collected on summer (June - September) haul-out sites (64% juveniles, n = 1 11 scats) than on summer rookeries (9% juveniles, n = 1 132 scats) or winter (February - March) haul-out sites (3% juveniles, n = 1 69 scats). Annual changes in the size of Atka mackerel consumed by Steller sea lions corresponded to changes in the length distribution of Atka mackerel resulting from exceptionally strong year classes. Considerable overlap (> 51%) in the size composition of walleye pollock and Atka mackerel taken by Steller sea lions and the commercial trawl fishery was demonstrated.
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2003
 
Possible effects of pollock and herring on the growth and reproductive success of Steller sea lions: insights from feeding experiments using an alternative animal model, Rattus novegicus.
Donnelly, C.P., A.W. Trites and D.D. Kitts. 2003.
British Journal of Nutrition 89:71-82.
abstract
The decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska appears to have been associated with a switch of diet from one dominated by fatty forage fishes (such as her-ring; Clupea pallasi ) to one dominated by low-fat fish (such as pollock; Theragra chalco-gramma). Observations made during the decline include reduced body size of sea lions, low pregnancy rates, and high mortality. We used the general mammalian model, the laboratory rat (Rattus norvegicus ), to test whether changing the quality of prey consumed could cause changes in size and reproductive performance. Five groups of twelve fiale, weanling rats were fed diets composed of herring (H), pollock (P), pollock suppliented with herring oil (PH), pollock suppliented with pollock oil (PP), or a sii-purified diet (ICN). Mean body weights were greatest for H, followed by PH, P, PP and finally ICN, although ICN was the only group significantly different from the others (P 0·05). Food intakes before mating were 10 % higher for groups on the lower-fat diets (P and ICN), resulting in similar energy intakes in all groups. The protein efficiency ratio was highest for the H diet, slightly lower for all pollock diets, and significantly lower for ICN (P 0·05). The fetal weights for mothers fed P were significantly reduced (P 0·05). The present study shows that the energy content was a major limiting factor in the nutritional quality of pollock. When food intake was adjusted to meet energetic requirients, there were no detrimental consequences from eating pollock. However, supplientation of pollock meal with additional pollock oil may reduce growth and reproductive performance, although the reasons for this were not apparent.
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Maternal attendance patterns of lactating Steller sea lions (Eumetopias jubatus) from a stable and a declining population in Alaska.
Milette, L.L. and A.W. Trites. 2003.
Canadian Journal of Zoology 81:340-348.
abstract
Maternal attendance patterns of Alaskan Steller sea lions (Eumetopias jubatus) were compared during the summer breeding seasons in 1994 and 1995 at Sugarloaf Island (a declining population) and Lowrie Island (a stable population). Our goal was to determine whether there were differences in maternal attendance between the two populations that were consistent with the hypothesis that lactating Steller sea lions in the area of decline were food-limited during summer. Our a priori expectations were based on well-documented behavioural responses of otariids to reduced prey availability. We found that foraging trips were significantly shorter in the area of population decline, counter to initial predictions. The mean length of foraging trips in the declining area was 19.5 h compared with 24.9 h in the stable area. In contrast, the mean perinatal period (time between parturition and first feeding trip) was significantly longer in the area of decline (9.9 versus 7.9 days), again countering initial predictions. The mean length of shore visits for the declining population was also significantly longer (27.0 h compared with 22.6 h where the population was stable). For both populations, the mean time that mothers foraged increased as pups grew older, whereas the time that they spent on shore with their pups became shorter. Behavioural observations of maternal attendance patterns are inconsistent with the hypothesis that lactating Steller sea lions from the declining population had difficulty obtaining prey during summer.
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No evidence for bioenergetic interaction between digestion and thermoregulation in Steller sea lions, Eumetopias jubatus.
Rosen, D.A.S. and A.W. Trites. 2003.
Physiological and Biochemical Zoology 76(6):899-906.
abstract
The increase in metabolism during digestion—the heat increment of feeding—is often regarded as an energetic waste product. However, it has been suggested that this energy could offset thermoregulatory costs in cold environments. We investigated this possibility by measuring the rate of oxygen consumption of four juvenile Steller sea lions (Eumetopias jubatus) before and after they ingested a meal in water temperatures of 2-8 degrees C. Rates of oxygen consumption of fasted and fed animals increased in parallel with decreasing water temperature, such that the apparent heat increment of feeding did not change with water temperature. These results suggest that Steller sea lions did not use the heat released during digestion to offset thermoregulatory costs.
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Quantifying errors associated with using prey skeletal structures from fecal samples to determine the diet of the Steller sea lion (Eumetopias jubatus).
Tollit, D.J., M. Wong, A.J. Winship, D.A.S. Rosen and A.W. Trites. 2003.
Marine Mammal Science pp. 724-744.
abstract
We examined the digestion and passage times of bones and other hard parts from pollock, herring, salmon, and sandlance recovered from two juvenile captive Steller's sea lions (Eumetopias jubatus) subjected to varying activity levels. Key bones that could be identified to species were distributed over an average of 3.2 scats (range 1–6) following a single meal, with pollock remains occurring in significantly more scats than other species. Relying on otoliths alone to determine the presence of prey resulted in significantly fewer prey being identified than if other structures were also used (such as vertebrae, jaw bones, and teeth), particularly for salmon. Using either technique, there were significant differences in the likelihood that bones would be recovered from the series of scats produced following a meal, with pollock recovery exceeding herring (by three-fold) and sandlance (by eight-fold). Differences between species were reduced when recovery was calculated on a per scat basis rather than over multiple scats. Active animals passed greater numbers of bones, but the overall effect on prey recovery estimates was not significant. Defecation times of prey structures from a meal were variable and ranged from an initial 2–56 h to a final 28–148 h. The time interval to pass 95% of recovered structures varied by a factor of two among prey species, and was highest for pollock due to retention beyond 65 h.
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Food webs in the ocean: who eats whom, and how much?
Trites, A.W. 2003.
In M. Sinclair and G. Valdimarsson (eds), Responsible Fisheries in the Marine Ecosystem. FAO, Rome and CABI Publishing, Wallingford. pp. 125-143.
abstract
Over 100 food webs have been published for marine cosystems to describe the transfer of food energy from its source in plants,through herbivores,to carnivores and higher order predators.The webs suggest that the lengths of the chains that form food webs are typically short (3 –4 links),and that ecosystems with long food chains may be less stable than those with shorter food chains.

Stomach contents have been the primary means for determining what marine organisms eat.More recently developed techniques include faecal analysis and fatty acid signatures from blood or fat samples. Consumption has been estimated from the volume of food found in stomachs,from the feeding rates of captive individuals and from bioenergetic modelling.Consumption of marine organisms,expressed as a percentage of an individual ’s body weight per day,ranges from about 4 –15% or zooplankton,to 1 –4% for cephalopods,1 –2%for fish,3 –5% or marine mammals and 15 –20%for sea birds.Immature age classes consume about twice as much (per unit of body weight)as do mature individuals. Furthermore,consumption is not constant throughout the year,but varies with seasonal periods of growth and reproduction.Most groups of species consume 3 –10 times more than they produce,and export or pass up the food web about 70 –95%of their production. Marine organisms tend to be larger at successive trophic levels and are limited in the sizes of food they can consume. Humans are one of the few species that can prey uponalmost any level of the food chain and any size of prey.

Food web analysis and estimates of consumption are essential for understanding which ecosystems can support additional species,and which may be less stable and susceptible to species loss through the synergistic effects of fishing or culling.They are also critical tools for understanding changes in ecosystem dynamics as highlighted by a case study from the eastern Bering Sea.

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The decline of Steller sea lions in Alaska: A review of the nutritional stress hypothesis.
Trites, A.W. and C.P. Donnelly. 2003.
Mammal Review 33:3-28.
abstract

1. The decline of Steller sea lions Eumetopias jubatus in the Gulf of Alaska and Aleutian Islands between the late 1970s and 1990s may have been related to reduced availability of suitable prey. Many studies have shown that pinnipeds and other mammals suffering from nutritional stress typically exhibit reduced body size, reduced productivity, high mortality of pups and juveniles, altered blood chemistry and specific behavioural modifications.

2. Morphometric measurements of Steller sea lions through the 1970s and 1980s in Alaska indicate reduced body size. Reduced numbers of pups born and an apparent increase in juvenile mortality rates also appear to be nutritionally based. Blood chemistry analyses have further shown that Steller sea lions in the Gulf of Alaska and Aleutian Islands area exhibited signs of an acute phase reaction, or immune reaction, in response to unidentified physical and/or environmental stress. Behavioural studies during the 1990s have not noted any changes that are indicative of an overall shortage in the quantity of prey available to lactating female sea lions.

3. The data collected in Alaska are consistent with the hypothesis that Steller sea lions in the declining regions were nutritionally compromised because of the relative quality of prey available to them (chronic nutritional stress), rather than because of the overall quantity of fish per se (acute nutritional stress). This is further supported by captive studies that indicate the overall quality of prey that has been available to Steller sea lions in the declining popu-lation could compromise the health of Steller sea lions and hinder their recovery.


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Prey consumption of Steller sea lions (Eumetopias jubatus) off Alaska: how much prey do they require?
Winship, A.J. and A.W. Trites. 2003.
Fishery Bulletin 101:147-163.
abstract
The effects of seasonal and regional differences in diet composition on the food requirements of Steller sea lions (Eumetopias jubatus)were estimated by using a bioenergetic model. The model considered differences in the energy density of the prey, and differences in digestive effciency and the heat increment of feeding of different diets. The model predicted that Steller sea lions in southeast Alaska required 45–60% more food per day in early spring (March) than after the breeding season in late summer (August) because of seasonal changes in the energy density of the diets (along with seasonal changes in energy require ments).The southeast Alaska population,at 23,000 (±1660 SD)animals (all ages), consumed an estimated 140,000 (±27,800) of prey in 1998. In contrast, we estimated that the 51,000 (±3680) animals making up the western Alaska population in the Gulf of Alaska and Aleutian Islands consumed just over twice this amount (303,000 [±57,500 ] t). In terms of biomass removed in 1998 from Alaskan waters,we estimated that Steller sea lions accounted for about 5% of the natural mortality of gadids (pollock and cod) and up to 75% of the natural mortality of hexagram mids (adult Atka mackerel).These two groups of species were consumed in higher amounts than any other.The predicted average daily food require ment per individual ranged from 16 (±2.8)to 20 (±3.6)kg (all ages com bined). Per capita food requirements differed by as much as 24% between regions of Alaska depending on the rel ative amounts of low–energy-density prey (e.g.gadids)versus high–energy density prey (e.g. forage fish and salmon)consumed. Estimated require ments were highest in regions where Steller sea lions consumed higher proportions of low—energy-density prey and experienced the highest rates of population decline.
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2002
 
Ecological effects of regime shifts in the Bering Sea and eastern North Pacific Ocean.
Benson, A.J. and A.W. Trites. 2002.
Fish and Fisheries 3:95-113.
abstract
Large-scale shifts occurred in climatic and oceanic conditions in 1925, 1947, 1977, 1989 and possibly 1998. These shifts affected the mix and abundance of suites of coexisting species during each period of relative environmental stability- from primary producers to apex predators. However, the 1989 regime shift was not a simple reversal of the 1977 shift. The regime shifts occurred abruptly and were neither random variations nor simple reversals to the previous conditions. Timing of these anomalous environmental events in the North Pacific Ocean appears to be linked to physical and biological responses in other oceanic regions of the world. Changes in the atmospheric pressure can alter wind patterns that affect oceanic circulation and physical properties such as salinity and depth of the thermocline. This, in turn, affects primary and secondary production. Data from the North Pacific indicate that regime shifts can have opposite effects on species living in different domains, or can affect similar species living within a single domain in opposite ways. Climatic forcing appears to indirectly affect fish and marine mammal populations through changes in the distribution and abundance of their predators and prey. Effects of regime shifts on marine ecosystems are also manifested faster at lower trophic levels. Natural variability in the productivity of fish stocks in association with regime shifts indicates that new approaches to managing fisheries should incorporate climatic as well as fisheries effects.
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Acoustic identification of female Steller sea lions (Eumetopias jubatus).
Campbell, G.S., R.C. Gisiner, D.A. Helweg and L.L. Milette. 2002.
Journal of the Acoustical Society of America. 111:2920-2928.
abstract
Steller sea lion Eumetopias jubatus mothers and pups establish and maintain contact with individually distinctive vocalizations. Our objective was to develop a robust neural network to classify females based on their mother-pup contact calls. We catalogued 573 contact calls from 25 females in 1998 and 1323 calls from 46 females in 1999. From this database, a subset of 26 females with sufficient samples of calls was selected for further study. Each female was identified visually by marking patterns, which provided the verification for acoustic identification. Average logarithmic spectra were extracted for each call, and standardized training and generalization datasets created for the neural network classifier. A family of backpropagation networks was generated to assess relative contribution of spectral input bandwidth, frequency resolution, and network architectural variables to classification accuracy. The network with best overall generalization accuracy 71% used an input representation of 0–3 kHz of bandwidth at 10.77 Hz/bin frequency resolution, and a 2:1 hidden:output layer neural ratio. The network was analyzed to reveal which portions of the call spectra were most influential for identification of each female. Acoustical identification of distinctive female acoustic signatures has several potentially important conservation applications for this endangered species, such as rapid survey of females present on a rookery.
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Classifying prey hard part structures recovered from fecal remains of captive Steller sea lions (Eumetopias jubatus).
Cottrell, P.E. and A.W. Trites. 2002.
Marine Mammal Science 18:525-539.
abstract
Feces were collected from six Steller sea lions (Eumetopias jubatus) that consumed known amounts of Atka mackerel (Pleurogrammus monopterygius), Pacific herring (Clupea harengus), pink salmon (Oncorhynchus gorbuscha), walleye pollock (Theragra chalcogramma), and squid (Loligo opalacens). The goal was to determine the numbers and types of taxon-specific hard parts that pass through the digestive tract and to develop correction factors for certain abundantly occurring structures. Over 20,000 fish and squid were consumed during 267 d of fecal collection. During this period, over 119,000 taxon-specific hard parts, representing 56 different structures, were recovered. Skeletal structures and non-skeletal structures accounted for 72% and 28% of all hard parts respectively. The branchiocranium, axial skeleton, and dermocranium regions of the skeletal system accounted for the greatest number of hard parts recovered. Over 70% of all recovered hard parts were represented by one to six taxa specific structures for each prey type. The average number of hard parts (3.1-3.12) and structure types (2.0-17.7) recovered per individual prey varied across taxa and were used to derive correction factors (to reconstruct original prey numbers). A measure of the variability of hard part recovery among sea lions showed no difference for certain herring, pollock, and squid structures, however, there was a significant difference for salmon and Atka mackerel structures. Identifying all taxon-specific prey hard parts increases the likelihood of identifying and estimating the number of prey consumed.
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Diets of fin, sei and sperm whales in British Columbia: an analysis of commercial whaling records, 1963-1967.
Flinn, R.D., A.W. Trites, E.J. Gregr and I. Perry. 2002.
Marine Mammal Science 18:663-679.
abstract
Diets of fin (Balaenoptera physalus), sei (Balaenoptera borealis), and sperm whales (Physeter macrocephalus) were estimated from the stomach contents of individuals killed along the British Columbia coast from 1963 to 1967. The dominant prey types of fin whales were euphausiids, with minor contributions from copepods and fish. Sei whale stomachs contained primarily copepods in three years, whereas euphausiids or a variety of fish dominated the diet in the other two years. Sperm whales consumed primarily North Pacific giant squid (Moroteuthis robusta), but secondary prey differed between males and females. Female sperm whales frequently consumed ragfish (Icosteus spp.) and other fish, whereas the male diet also contained rockfish (Sebastes spp.). The high abundance of euphausiids along the British Columbia coast likely contributed to the presence of a summer resident population of fin whales. The high abundance of large copepods farther north probably influenced the migration of sei whales through the offshore waters of British Columbia. Sperm whale stomach contents differed by sex reflecting location and possibly breeding behaviors.
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Changes in metabolism in response to fasting and food restriction in the Steller sea lion (Eumetopias jubatus).
Rosen, D.A.S. and A.W. Trites. 2002.
Comparative Biochemistry and Physiology. 132:389-399.
abstract
Many animals lower their resting metabolism (metabolic depression) when fasting or consuming inadequate food. We sought to document this response by subjecting five Steller sea lions to periods of: (1) complete fasting; or (2) restricting them to 50% of their normal herring diet. The sea lions lost an average of 1.5% of their initial body mass per day (2.30 kg y d )during the 9 –14-day fast, and their resting metabolic rates decreased 31%, which is typical of a ‘fasting response ’. However, metabolic depression did not occur during the 28-day food restriction trials,despite the loss of 0.30% of body mass per day (0.42 kg y d). This difference in response suggests that undernutrition caused by reduced food intake may stimulate a ‘hunger response ’, which in turn might lead to increased foraging effort. The progressive changes in metabolism we observed during the fasts were related to, but were not directly caused by, changes in body mass from control levels. Combining these results with data collected from experiments when Steller sea lions were losing mass on low energy squid and pollock diets reveals a strong relationship between relative changes in body mass and relative changes in resting metabolism across experimental conditions.While metabolic depression caused by fasting or consuming large amounts of low energy food reduced the direct costs from resting metabolism, it was insufficient to completely overcome the incurred energy deficit.
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Cost of transport in Steller sea lions, Eumetopias jubatus.
Rosen, D.A.S. and A.W. Trites. 2002.
Marine Mammal Science 18:513-524.
abstract
The cost of swimming is a key component in the energy budgets of marine mammals. Unfortunately, data to derive predictive allometric equations are limited, and estimates exist for only one other species of otariid. Our study measured the oxygen consumption of three juvenile Steller sea lions (Eumetopias jubatus) swimming in a flume tank at velocities up to 2.2 m sec-1. Minimum measured cost of transport ranged from 3.5-5.3 J kg-1, m-1, and was reached at swimming speeds of 1.7-2.1 m s-1. These cost-of-transport values are higher than those reported for other marine mammals. However, once differences in stationary metabolic rate were accounted for, the locomotor costs (LC) for the Steller sea lions were commensurate with those of other marine mammals. Locomotor costs (LC in J m-1) appeared to be directly proportional to body mass (M in kg) such that LC = 1.651M1.01. These estimates for the cost of locomotion can be incorporated into bioenergetic models and used to determine the energetic consequences of observed swimming behavior in wild marine mammals.
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Predator-prey relationships.
Trites, A.W. 2002.
In W.F. Perrin, B. Wursig and H.G.M. Thewissen (eds), Encyclopedia of Marine Mammals. Academic Press, San Diego. pp. 994-997.
abstract
Marine mammal predator-prey interactions occur over different spatial and temporal scales, making it difficult to empirically decipher the influences they have on one another and on their ecosystems. However, their coexistence suggests that marine mammal predators and their prey have had profound influences on each other’s behaviors, physiologies, morphologies, and life history strategies. The diversity of niches filled by marine mammals makes if difficult to generalize about the evolutionary consequences of their interactions with prey, beyond stating the obvious: marine mammals have adapted to catch food, while their prey have adapted to avoid being caught. On the shorter ecological time scale, marine mammals can affect the abundance of other species by consuming or out-competing them. They can also indirectly affect the abundance of nontargeted species by consuming one of their predators, and can have strong impacts on the overall dynamics and structure of their ecosystems. One of the best tools for understanding marine mammal predator-prey interactions is the ecosystem model. However, more work is required through experimental manipulations and observational studies to evaluate the choices made by marine mammals and the costs of obtaining different species of prey.

keywords     predation
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Attendance patterns of Steller sea (Eumetopias jubatus) lions and their young during winter.
Trites, A.W. and B.T. Porter. 2002.
Journal of Zoology, London Vol 256
abstract
Winter attendance patterns of lactating Steller sea lions Eumetopias jubatus and their offspring were recorded during the late stages of nursing when the young were expected to move milk to independent foraging. Trip duration and nursing visits to shore by 24 mothers with pups (7-9 months old) and six mothers with yearlings (19-21 months old) were noted during 600h of observations (from 22 January to 1 April 1996) at a non-breeding haulout site in south-eastern Alaska. Pups and yearlings tended to stay on or near the haulout while their mothers were away and showed no signs of weaning during winter. Their average trips to sea were 43% shorter in duration than those of lactating females, suggesting that pups and yearlings make independent trips away from the haulout while their mothers forage. The winter attendance cycle of lactating females (consisting of one trip to sea and one visit on land) averaged about 3 days, with the mothers of pups spending an average of 15h of this time onshore with their offspring. The winter attendance cycle of pups and yearlings averaged just over 2 days, with the immature sea lions spending an average of 22h on shore. Foraging trips by mothers of yearlings were significantly longer than those by mothers of pups. However, there was no significant difference in the foraging times of mothers of male and female pups. Lactating females spent more time at sea during winter than during summer. The probability of sighting an individual on the winter haulout during daylight hours was 15% for lactating females and 40% for immature animals.
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Behavioural responses of killer whales (Ornicus orca) to whale-watching: opportunistic observations and experimental approaches.
Williams, R., A.W. Trites and D.E. Bain. 2002.
Journal of Zoology, London. 256:255-270.
abstract
Johnstone Strait provides important summer habitat for the northern resident killer whales Orcinus orca of British Columbia. The site is also an active whale-watching area. A voluntary code of conduct requests that boats do not approach whales closer than 100 m to address perceived, rather than demonstrated, effects of boat traffic on killer whales. The purpose of the study was to test the relevance of this distance guideline. Relationships between boat traffic and whale behaviour were studied in 1995 and 1996 by shore-based the odolite tracking of 25 identifiable focal animals from the population of 209 whales. Individual killer whales were repeatedly tracked in the absence of boats and during approaches by a 5.2 m motorboat that paralleled each whale at 100 m. In addition, whales were tracked opportunistically, when no effort was made to manipulate boat traffc. Dive times, swim speeds, and surface-active behaviours such as breaching and spy-hopping were recorded. On average, male killer whales swam significantly faster than females. Whales responded to experimental approaches by adopting a less predictable path than observed during the preceding, no-boat period, although males and females used subtly different avoidance tactics. Females responded by swimming faster and increasing the angle between successive dives, whereas males maintained their speed and chose a smooth, but less direct, path. Canonical correlations between whale behaviour and vessel proximity are consistent with these conclusions, which suggest that weakening whale-watching guidelines, or not enforcing them, would result in higher levels of disturbance. High variability in whale behaviour underscores the importance of large sample size and extensive experimentation when assessing the impacts of human activity on killer whales.
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Behavioral responses of male killer whales to a ‘leapfrogging’ vessel.
Williams, R.M., D.E. Bain, J.K.B. Ford and A.W. Trites. 2002.
Journal of Cetacean Research 4:305-310.
abstract
The research and whalewatching communities of Johnstone Strait, British Columbia, Canada have worked closely together to identify whalewatching practices that minimise disturbance to northern resident killer whales. Local guidelines request that boaters approach whales no closer than 100m. Additionally, boaters are requested not to speed up when close to whales in order to place their boat in a whale’s predicted path: a practice known as ‘leapfrogging’. A land-based study was designed to test for behavioural responses of killer whales to an experimental vessel that leapfrogged a whale’s predicted path at distances greater than 100m. Ten male killer whales were repeatedly approached and the animals responded on average by adopting paths that were significantly less smooth and less straight than during preceding, control conditions. This adoption of a less ‘predictable’ path is consistent with animals attempting to evade the approaching boat, which may have negative energetic consequences for killer whales. The results support local consensus that leapfrogging is a disruptive style of whalewatching, and should be discouraged. Similarly, as the experimental boat increased speed to overtake the whale’s path, the source level of engine noise increased by 14dB. Assuming a standard spherical transmission loss model, the fast-moving boat would need to be 500m from the whale for the received sound level to be the same as that received from a slow-moving boat at 100m. Whalewatching guidelines should therefore encourage boaters to slow down around whales, and not to resume full speed while whales are within 500m.
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A bioenergetic model for estimating the food requirements of Steller sea lions (Eumetopias jubatus) in Alaska.
Winship, A.J., A.W. Trites and D.A.S. Rosen. 2002.
Marine Ecology Progress Series 229:291-312.
abstract
A generalized bioenergetic model was used to estimate the food requirements of Steller sea lions <i>Eumetopias jubatus</i> in Alaska, USA. Inputs included age and sex-specific energy require-ments by date, population size and composition, and diet composition and energy content. Error in model predictions was calculated using uncertainty in parameter values and Monte Carlo simulation methods. Our model suggests that energy requirements of individuals were generally lowest in the summer breeding season (June to August) and highest in the winter (December to February) and spring (March to May) mainly due to changes in activity budgets. Predicted relative daily food requirements were highest for young animals (12 ± 3% SD and 13 ± 3% of body mass for 1 yr old males and females respectively) and decreased with age (5 ± 1% and 6 ± 1% of body mass for 14 yr old males and 22 yr old females respectively). The mean daily food requirement of pregnant females predicted by the model was only marginally greater than the predicted mean daily food requirement of non-pregnant females of the same age. However, the model suggested that the mean daily food requirement of females nursing pups was about 70% greater than females of the same age without pups. Of the 3 sets of model parameters (diet, population, and bioenergetic), uncertainty in diet and bioenergetic parameters resulted in the largest variation in model predictions. The model provides a quantitative estimate of the Steller sea lion population’s food requirements and also suggests directions for future research.
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Cultural transmission within maternal lineages: vocal clans in resident killer whales in southern Alaska.
Yurk, H., L. Barrett Lennard, J.K.B. Ford and C.O. Matkin. 2002.
Animal Behavior 63:1103-1119.
abstract
Abstract: Cultural lineages are based on learned social traditions that are stable for several generations. When cultural lineages also reflect common ancestry and/or are shared by individuals that live together they are called clans. The existence of clans among killer whales has been previously proposed but has not been confirmed. Here, we show that clans exist among resident type killer whales, Orcinus orca, in southern Alaska. Resident killer whales live in stable matrilines from which emigration of either sex has not been observed. Matrilines that associate regularly (50% observation time) are called pods. Pods are believed to consist of closely related matrilines and share a unique repertoire of discrete call types. Pods that share parts of their repertoire form what Ford (1991, Canadian Journal of Zoology, 69, 1454–1483) called an acoustic clan. Here, we identified discrete call types of seven pods from southern Alaska, using a method based on human discrimination of distinct aural and visual (spectrogram) differences. Mitochondrial DNA of members of each pod was also analysed. The repertoires of the seven pods were compared and two acoustically distinct groups of pods were identified. Each group was monomorphic for a different mitochondrial D-loop haplotype. Nevertheless, pods from different clans associated frequently. It thus appears that the acoustic similarities within groups, which we presume to be cultural, reflect common ancestry, and that these groups therefore meet the above definition of clans. We also argue that a combination of cultural drift and selection are the main mechanisms for the maintenance of clans.
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2001
 
Predictions of critical habitat for five whale species in the waters of coastal British Columbia.
Gregr, E.J. and A.W Trites. 2001.
Canadian Journal of Fisheries and Aquatic Sciences 58:1265-1285.
abstract
Whaling records from British Columbia coastal whaling stations reliably report the positions of 9592 whales killed between 1948 and 1967. We used this positional information and oceanographic data (bathymetry, temperature, and salinity) to predict critical habitat off the coast of British Columbia for sperm (Physeter macrocephalus), sei (Balaenoptera borealis), fin (Balaenoptera physalus), humpback (Megaptera novaeangliae), and blue (Balaenoptera musculus) whales. We used generalized linear models at annual and monthly time scales to relate whale occurrence to six predictor variables (month, depth, slope, depth class, and sea surface temperature and salinity). The models showed critical habitat for sei, fin, and male sperm whales along the continental slope and over a large area off the northwest coast of Vancouver Island. Habitat models for blue, humpback, and female sperm whales were relatively insensitive to the predictor variables, owing partially to the smaller sample sizes for these groups. The habitat predictions lend sup-port to recent hypotheses about sperm whale breeding off British Columbia and identify humpback whale habitat in sheltered bays and straits throughout the coast. The habitat models also provide insights about the nature of the link-ages between the environment and the distribution of whales in the North Pacific Ocean.
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Marine mammal trophic levels and interactions.
Trites, Andrew W. 2001.
In J. Steele, S. Thorpe and K. Turekian (eds), Encyclopedia of Ocean Sciences. Academic Press, London, UK. pp. 1628-1633.
abstract
Calculating trophic levels is necessary first step to quantifying and understanding trophic interactions between marine mammals and other species in marine ecosystems. This can be achieved using dietary information collected from stomachs and scats, or by measuring isotopic ratios contained in marine mammal tissues. These data indicate that marine mammals occupy a wide range of trophic levels beginning with dugong and manatees (trophic level 2.0), and followed by baleen whales (3.35), sea otters (3.45), seals (3.95), sea lions and fur seals (4.03), toothed whales (4.23), and polar bears (4.08). With the aid of ecosystem models and other quantitative analyses, the degree of competition can be quantified, and the consequences of changing predator-prey numbers can be predicted. These analyses show that many species of fish are major competitors of marine mammals. A number of field studies have also shown negative effects of reduced prey abundance on body size and survival of marine mammals. However, there are fewer examples of marine mammal populations affecting their prey due perhaps to the difficulty of monitoring such interactions, or to the complexity of most marine mammal food webs.

keywords     PhdTLmarine mammalsdietbackground
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Growth in body size of the Steller sea lion.
Winship, A.J., A.W. Trites and D.G. Calkins. 2001.
Journal of Mammalogy 82:500-519.
abstract
Growth models (mass and length) were constructed for male (>1 year old), female (>1 year old), and pregnant female Steller sea lions (Eumetopias jubatus) shot on rookeries or haulouts, or in coastal waters of southeastern Alaska, the Gulf of Alaska, or the Bering Sea ice edge between 1976 and 1989. The Richards model best described growth in body length and mass. Females with fetuses were 3 cm longer and 28 kg heavier on average than females of the same age without fetuses. Males grew in length over a longer period than did females and exhibited a growth spurt in mass that coincided with sexual maturity between 5 and 7 years of age. Average predicted standard lengths of males and females >12 years of age were 3.04 and 2.32 m, respectively, and average predicted masses were 681 and 273 kg, respectively. Maximum recorded mass was 910 kg for an adult male. Males achieved 90% of their asymptotic length and mass by 8 and 9 years of age, respectively, compared with 4 and 13 years, respectively, for females. Residuals of the size-at-age models indicated seasonal changes in growth rates. Young animals (<6 years old) and adult males grew little during the breeding season (May–July), and adult males did not resume growth until sometime after November.
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2000
 
Dialect change in resident killer whales (Orcinus orca): Implications for vocal learning and cultural transmission.
Deecke, Volker B., John K.B. Ford and Paul Spong. 2000.
Animal Behaviour 60:629-638.
abstract
Variation in vocal signals among populations and social groups of animals provides opportunities for the study of learning and its importance in generating and maintaining variation in behavioural traits. In this study, we analyse 2 call types made by 2 matrilineal social groups of resident killer whales (Orcinus orca) over a period of 14 years. We use a neural network-based index of acoustic similarity to identify mechanisms of call differentiation. A test for structural modification of the calls detected significant changes in one call type in both groups, but not in the other. For the modified call type, the rate of differentiation between the two groups was significantly lower than the rate of modification within either group showing that calls are modified in a similar fashion in the two groups. An analysis of structural parameters detected no strong directionality in the change. The detected pattern of call modification could be caused by maturational changes! to the calls, or, if killer whale dialects are learned behavioural traits, cultural drift in the structure of the calls together with horizontal transmission of modifications between the two groups. Such vocal matching between members of different matrilineal groups would suggest that vocal learning is not limited to vertical transmission from mother to offspring, as required for some models of gene-culture coevolution.
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Migration and population structure of northeast Pacific whales off the coast of British Columbia: analysis of commercial whaling records from 1908–1967.
Gregr, E., L. Nichol, J. Ford, G. Ellis and A.W. Trites. 2000.
Marine Mammal Science 16:699-727.
abstract
Data recorded from 24,862 whales killed by British Columbia coastal whaling stations between 1908 and 1967 revealed trends in the abundance, sex ratios, age structure, and distribution of sperm (Physeter macrocephalus), fin (Balaenoptera physalus), sei (Balaenoptera borealis), humpback (Megaptera novaeangliae), and blue (Balaenoptera musculus) whales. The catch data were analyzed using annual and monthly mean values. Monthly and annual variation in whaling effort was deduced from accounts of the history of British Columbia coastal whaling, and biases arising from changes in effort were considered in the interpretation of the results. During the later years of whaling (1948-1967), the mean lengths of captured whales declined significantly and pregnancy rates dropped to near zero in fin, sei, and blue whales. Monthly patterns in numbers killed revealed a summer migration of sei and blue whales past Vancouver Island, and confirms anecdotal suggestions that local populations of fin and humpback whales once spent extended periods in the coastal waters of British Columbia. Furthermore, the data strongly suggest that sperm whales mated (April-May) and calved (July-August) in British Columbia’s offshore waters. The historic whaling records reveal much about the migratory behavior and distribution of the large whales species as they once were, and may continue to be, in the northeastern Pacific. Verifying the persistence of these trends in the remnant populations is a necessary and logical next step.
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The reliability of skinfold-calipers for measuring blubber thickness of Steller sea lion pups (Eumetopias jubatus).
Jonker, R.A.H. and A.W. Trites. 2000.
Marine Mammal Science 16:757-766.
abstract
Twelve dead Steller sea lion pups (Eumetopias jubatus) aged 3-14 d were recovered from rookeries in Southeast Alaska. They had a wide range of body sizes and conditions (small to large and fat to no fat). The ability of calipers to estimate the thickness of their blubber layer was assessed with a set of skinfold calipers. Average error of measurement for skin and blubber thickness was an acceptable 5.4%, but the skin and blubber of the pups were highly compressible. Skinfold thickness increased with body mass but did not necessarily reflect the development of blubber, given that pups with no blubber also showed an increase in skinfold thickness with increases in body mass. Skinfold thickness of sea lion pups appears to predict body size better than it predicts blubber thickness, making it difficult if not impossible to develop a simple index of body condition or a calculation of percent body fat for Steller sea lion pups from skinfold caliper measurements.
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Digestive efficiency and dry-matter digestibility of Steller sea lions fed herring, pollock, salmon and squid.
Rosen, D.A.S. and A.W. Trites. 2000.
Canadian Journal of Zoology 78:234-239.
abstract
Dry-matter digestibility and energy digestive efficiency were measured in six juvenile Steller sea lions (Eumetopias jubatus) fed three diets each consisting of a single species: herring, pollock, and squid. Two of the animals were also fed pink salmon. Dry-matter digestibility (DMD) and digestive efficiency (DE) were measured using the energy and manganese concentration in fecal and food samples. DE values were high for all prey species (herring: 95.4 &amp;plusmn; 0.7% (mean &amp;plusmn; SD), pollock: 93.9 &amp;plusmn; 1.4%, salmon: 93.4 &amp;plusmn; 0.5%, squid: 90.4 &amp;plusmn; 1.3%). Steller sea lions appear to digest prey of high energy density more efficiently than prey of low energy density. DMD values were also high for all prey species (herring: 90.1 &amp;plusmn; 1.8%, pollock: 86.5 &amp;plusmn; 3.4%, salmon: 87.3% &amp;plusmn; 2.6, squid: 90.5 &amp;plusmn; 1.2%). The low DMD value for pollock compared with herring and squid was due to the high proportion of bony material in pollock. There was a strong linear relationship between DE and DMD for each prey type, but the terms cannot be used interchange-ably. DE measures are more meaningful than DMD in conveying the energetic benefits derived by sea lions from dif-ferent types of prey. Species-specific measures of the digestible energy obtained from an array of prey items are a necessary component in understanding the bioenergetic consequences of consuming different prey species.
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Pollock and the decline of Steller sea lions: testing the junk-food hypothesis.
Rosen, D.A.S. and A.W. Trites. 2000.
Canadian Journal of Zoology 78:1243-1258.
abstract
The decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and the Aleutian Islands may be the result of them eating too much pollock (a gadid fish) instead of a more balanced and diverse diet containing fattier fishes, such as herring or sandlance. We sought to test this junk-food hypothesis by feeding six captive Steller sea lions (ages 0.9–4.5 years) only pollock or herring. All sea lions gained mass while eating herring. However, eating only pollock for short periods (11–23 d) caused the study animals to lose an average of 6.5% of their initial body mass (0.6 kg/d) over an average feeding trial of 16 d (initial mass averaged 125 kg). The animals were allowed to eat as much pollock as they wanted but did not increase their food intake to compensate for the low energy they were receiv-ing. The sea lions showed progressive metabolic depression while losing body mass on a pollock-only diet. The loss of body mass while eating pollock was due to the lower gross energy content of pollock versus herring, the higher cost of digesting pollock, and the increased energy loss from digesting the larger quantity of fish needed to compensate for the lower energy content of pollock. Thus, our sea lions would have had to eat 35–80% more pollock than herring to maintain similar net energy intakes. Results from our captive-feeding studies are consistent with the junk-food hypothe-sis and have serious implications for Steller sea lions that have been eating primarily pollock in the Gulf of Alaska and the Aleutian Islands.
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Effect of ration size and meal frequency on assimilation and digestive efficiency in yearling Steller sea lions, Eumetopias jubatus.
Rosen, D.A.S., L. Williams and A.W. Trites. 2000.
Aquatic Mammals 26:76-82.
abstract
Assimilation and digestive efficiencies were measured in four juvenile Steller sea lions (Eumetopias jubatus) fed three ration sizes of herring (3%, 6%, or 9% of body mass) at three frequencies (2, 3, or 4 times daily). Assimilation efficiency (dry matter digestive efficiency) was 90.0 ± 2.0% (mean ± 1SD). Digestive efficiency (efficiency of energy digestion) was 95.5 ± 1.0%. There was a strong linear relationship between digestive and assimilation efficiency, but no significant differences in either assimilation or digestive efficiency with changes in feeding frequency or changes in daily food intake within the ranges offered.
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Hydrodynamic drag in Steller sea lions (Eumetopias jubatus).
Stelle, L.L., R.W. Blake and A.W. Trites. 2000.
Journal of Experimental Biology 203:1915-1923.
abstract
Drag forces acting on Steller sea lions (Eumetopias jubatus) were investigated from ‘deceleration during glide’ measurements. A total of 66 glides from six juvenile sea lions yielded a mean drag coefficient (referenced to total wetted surface area) of 0.0056 at a mean Reynolds number of 5.5´10 6 . The drag values indicate that the boundary layer is largely turbulent for Steller sea lions swimming at these Reynolds numbers, which are past the point of expected transition from laminar to turbulent flow. The position of maximum thickness (at 34 % of the body length measured from the tip of the nose) was more anterior than for a ‘laminar’ profile, supporting the idea that there is little laminar flow. The Steller sea lions in our study were characterized by a mean fineness ratio of 5.55. Their streamlined shape helps to delay flow separation, reducing total drag. In addition, turbulent boundary layers are more stable than laminar ones. Thus, separation should occur further back on the animal. Steller sea lions are the largest of the otariids and swam faster than the smaller California sea lions (Zalophus californianus). The mean glide velocity of the individual Steller sea lions ranged from 2.9 to 3.4ms -1 or 1.2–1.5 body lengths s -1 . These length-specific speeds are close to the optimum swim velocity of 1.4 body lengths s -1 based on the minimum cost of transport for California sea lions.
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Morphometric measurements and body condition of healthy and starving Steller sea lion pups (Eumetopias jubatus).
Trites, Andrew W. and Remco A.H. Jonker. 2000.
Aquatic Mammals 26:151-157.
abstract
The thickness and weight of skin, blubber, and body core were measured from 12 dead Steller sea lion pups (Eumetopias jubatus). These necropsied pups represented a wide range of body sizes and conditions (small to large, and fat to no-fat), and were chosen to compare the relative body conditions of healthy and starved pups. Seven of the pups lacked blubber and were significantly lighter for a given length compared to the five that had fat at their time of death. Volume exceeded mass by a factor of 1.3% with density averaging 0.987g cm-3. Skin and blubber were not uniformly thick over the body surface. Skin was thinnest on the head and around the flippers (3mm), and became thicker towards the rump (5mm). Skin thickness did not differ between dorsal and ventral sides, unlike blubber, which was thickest on the ventral side, increasing from the snout (1.5mm)to midtrunk (7mm) and decreasing posteriorly (5mm at the tail). Along the back, blubber increased from 1 mm at the snout to about 4.5mm at mid-trunk. The five pups that died of trauma had about 13% skin and 10% blubber (expressed as a proportion of total body mass). Starvelings lost an estimated 43% of their body mass before dying (10% blubber, and 33% body core). Morphometric measurements applied to three proposed indices of body condition suggest that girth is not a good predictor of body condition for Steller sea lion pups. Only the ratio of observed to predicted body mass derived from standardized mass-length relationships could distinguish starvelings from pups with body fat.

keywords     morphometric measurements, body condition, Steller sea lions, pups, skin, volume, density, starvation, #2
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Experimental attempts to reduce predation by harbour seals (Phoca vitulina) on outmigrating juvenile salmonids.
Yurk, H. and A.W. Trites. 2000.
Transactions of the American Fisheries Society 129:1360-1366.
abstract
During spring, harbor seals Phoca vitulina feed at night under two bridges spanning the Puntledge River in Courtenay, British Columbia, Canada. Posi-tioned parallel to one another, ventral side up, the seals form a feeding line across the river to intercept thou-sands of out-migrating salmonid smolts. During a 4-week observation period in the spring of 1996, we at-tempted to disrupt the seals’ feeding patterns by (a) de-ploying a mechanical feeding barrier (cork line), (b) al-tering the lighting conditions (lights on a bridge were turned off), and (c) installing an acoustic harassment device. We found acoustic harassment to be the most effective feeding deterrent. Of the other two deterrents, turning off the bridge lights was more effective than deploying a cork line, which had little effect. Acoustic harassment devices appear to be the most effective, non-lethal means for protecting juvenile salmonids from har-bor seal predation in portions of the Puntledge River. Natural predators that prey upon both out-mi-grating and returning anadromous fish can detri-mentally affect the survival of depressed fish pop-ulations (Bigg et al. 1990; Fraker 1994; Olesiuk et al. 1995). In the northeast Pacific, seals and sea lions are commonly observed feeding on returning adult Pacific salmon Oncorhynchus spp. in rivers and estuaries during summer and fall (Spalding 1964; Olesiuk et al. 1990). Seals also intercept out-migrating smolts in spring and early summer (Ole-siuk et al. 1995). Among the better-studied seal– salmon interactions are those in the Puntledge Riv-er on Vancouver Island, British Columbia (Bigg et al. 1990; Olesiuk et al. 1995; Trites et al. 1996; Figure 1). Harbor seals Phoca vitulina in the Puntledge River regularly position themselves side by side, ventral side up, in the upstream shadow of two bridges near the light–shadow boundary. The seals * Corresponding author: yurk@zoology.ubc.ca Received November 29, 1999; accepted June 5, 2000 swim against the river current and hold their po-sition in the water. Minimal movements of their hind flippers cause no apparent disturbance to the surface waters. This feeding strategy allows the seals to form an almost continuous barrier so they can intercept smolts that drift downstream near the surface. Apparently, the seals are assisted in their feeding efforts by the bridge lights that illuminate the water surface. One way to enhance the survival of salmonids is to disrupt the feeding patterns of their predators. Techniques vary, but include making the smolts foul-tasting, creating a mechanical barrier that pre-vents seals from entering estuaries or river sys-tems, and installing optic or acoustic harassment devices (AHD) to hinder the seals from feeding in particular areas (Gearin et al. 1986; Mate and Har-vey 1987; Pfeifer 1989) The AHDs are generally considered to be ef-fective in deterring seals and sea lions from prey-ing on fish in certain areas. The widespread use of these devices by aquaculture operators, who use them to deter seals and sea lions from entering net-pens, attests to this claim. The AHDs have also deterred a large number of California sea lions Zalophus californianus from preying on returning winter steelhead Oncorhynchus mykiss in the Chit-tenden Locks, Seattle, Washington (Fox et al. 1996). However, at aquaculture sites and at the Chittenden Locks, some pinnipeds appear to be-come acclimated to AHD sounds and may have to be physically removed (Fox et al. 1996). The goal of our study was to disrupt the feeding patterns of harbor seals feeding on smolts in the Puntledge River. During an observation period in April and May 1996, we evaluated three methods: installation of a mechanical feeding barrier, alter-ation of artificial light on the river, and deployment of an AHD.
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1999
 
Mitochondrial and microsatellite DNA analyses of harbour seal population structure in the northeast Pacific Ocean.
Burg, T.M., A.W. Trites and M.J. Smith. 1999.
Canadian Journal of Zoology 77:930-943.
abstract
The genetic diversity and population structure of harbour seals (Phoca vitulina richardsi) along the coasts of British Columbia and parts of Alaska were investigated using both mitochondrial DNA (mtDNA) and nuclear DNA. A 475-bp fragment of the mitochondrial control region was amplified and sequenced from 128 animals. Sixty variable sites defined 72 mtDNA haplotypes with pairwise nucleotide differences as high as 5%. Fifty-eight haplotypes were represented by a single individual, and shared haplotypes were generally restricted to a small geographic range. Phylogenetic reconstruction revealed two distinct populations comprising (i) southern British Columbia and (ii) northern British Columbia – southeast Alaska. Furthermore, the order of the clades suggests that the Pacific Ocean was colonized at least twice, 670 000 and 380 000 years ago. Haplotypes from the first invasion are restricted to a small number of seals around southern Vancouver Island. Analyses of five polymorphic microsatellite loci showed significant differences between the populations of southern British Columbia and northern British Columbia – Alaska. Migration rates for males based on microsatellite data (3–22 seals/generation) were higher than those obtained for females from mtDNA data (0.3 females/generation). Combining all the DNA data collected to date suggests that there are at least three populations of harbour seals in the Pacific composed of seals from (i) Japan, Russia, Alaska, and northern British Columbia, (ii) southern British Columbia and Puget Sound, Washington, and (iii) the outer coasts of Washington, Oregon, and California. The data do not support the existence of two subspecies of harbour seals in the Pacific Ocean.
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Quantifying complex patterns of bioacoustic variation: Use of a neural network to compare killer whale (Orcinus orca) dialects.
Deecke, Volker B., John K.B. Ford and Paul Spong. 1999.
Journal of the Acoustical Society of America 105:2499-2507.
abstract
A quantitative measure of acoustic similarity is crucial to any study comparing vocalizations of different species, social groups, or individuals. The goal of this study was to develop a method of extracting frequency contours from recordings of pulsed vocalizations and to test a non-linear index of acoustic similarity based on the error of an artificial neural network at classifying them. Since the performance of neural networks depends on the amount of consistent variation in the training data, this technique can be used to assess such variation from samples of acoustic signals. The frequency contour extraction and the neural network index were tested on samples of one call type shared by 9 social groups of killer whales. For comparison, call similarity was judged by 3 human subjects in pairwise classification tasks. The results showed a significant correlation between the neural network index and the similarity ratings by the subjects. Both measures of acoustic ! similarity were significantly correlated with the groups' association patterns, indicating that both methods of quantifying acoustic similarity are biologically meaningful. An index based on neural network analysis therefore represents an objective and repeatable means of measuring acoustic similarity, and allows comparison of results across studies, species, and time.
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Seasonal differences in adaptation to prolonged fasting in juvenile Steller sea lions (Eumetopias jubatus).
Rea, L.D., D.A.S. Rosen and A.W. Trites. 1999.
In The FASEB Journal (Federation of American Societies of Experimental Biology). Washington, D.C., April 17-21, 1999. Vol 13(5) pp. A740
abstract
Five juvenile Steller sea lions (Eumetopias jubatus) between the ages of 3 and 4 years were experimentally fasted for 9 to 14 d to assess changes in mass and in key plasma metabolites indicative of biochemical adaptation to fasting. The 5 sea lions lost 20.4 to 35.1 kg each, at a rate of 1 to 2% of their initial body mass per day. Two animals fasted during the natural breeding season (June) exhibited a mean daily loss of 1.6 +/- 0.1kg d-1. This was significantly lower than the mean 2.8 +/- 0.1kg d-1 lost by sea lions fasted outside the normal breeding season in April, October and November (p<0.001). The two sea lion studied in June maintained low BUN concentrations throughout the remainder of the study, while the remaining 3 animals showed significant increases after 7 d of fasting. Only the two juveniles fasted during the breeding season maintained a protein sparing metabolism, typical of the species adapted to long-term fasting. With the exception of the smallest female (after 12 d of fasting), ketone body levels ranged from 0.03 to 0.17 mM. Seasonal differences in how sea lions adapt to fasting suggests that these animals would be more severely impacted by limited food resources during the non-breeding season.
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Metabolic effects of low-energy diet on Steller sea lions, Eumetopias jubatus.
Rosen, D.A.S. and A.W. Trites. 1999.
Physiological Zoology 72:723-731.
abstract
Diets of six Steller sea lions (Eumetopias jubatus) were switched between a high (herring) and a low (squid) energy density food for 14 d to determine the effects on ingested prey mass, body mass, resting metabolic rate, and the heat increment of feeding. Body mass was measured daily, and resting metabolism was measured weekly by gas respiro-metry. Ingested food mass did not differ significantly be-tween the squid diet and the control or the recovery herring diet periods. As a result of differences in energy density, gross energy intake was significantly lower during the squid diet phase than during either the control or recovery pe-riods. As a result, sea lions lost an average of 1.1 kg/d, totaling 12.2% of their initial body mass by the end of the experimental period. The heat increment of feeding for a 4-kg squid meal was significantly lower than for a similarly sized meal of herring. Decreases in both absolute (24.0 to 18.0 MJ/d, 224%) and mass-corrected (903 to 697 kJ/d/ kg 0.67 , 220%) metabolism were observed by the end of the squid feedings. This study suggests that sea lions can depress their resting metabolism in response to decreases in energy intake or body mass, regardless of satiation level.
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Ecosystem Considerations and the limitations of ecosystem models in fisheries management: insights from the Bering Sea.
Trites, A.W., P.A. Livingston, M.C. Vasconcellos, S. Mackinson, A.M. Springer and D. Pauly. 1999.
In Ecosystem Approaches for Fisheries Management. Alaska Sea Grant College Program, Alaska. pp. 609-619.
abstract
Over the past 10 years there has been increasing criticism of management decisions that are based on singlespecies approaches and a call for the implementation of ecosystem approaches. The major criticism of singlespecies models is that they cannot predict changes in community structure. Unfortunately, our experience in modeling the Bering Sea shows that these same criticisms can also be leveled against ecosystem models. We employed trophic massbalance models (Ecopath and Ecosim) to examine some possible explanations for the changes that occurred in the Bering Sea between the 1950s and 1980s. We removed fish and mammalsfrom the modeled system and tracked how other components of the ecosystem responded. Our massbalance models indicate that neither whaling nor commercial fisheries were sufficient to explain the 400% increase in pollock biomass and other changes that may have occurred between the two time periods. The simulations further suggest that environmental factors, affecting recruitment or primary production, may be more important in determining the dynamics of the Bering Sea ecosystem than predator prey interactions alone. These findings illustrate that mass balance models that do not account for the impact of climate variability on yearclass strength cannot provide reliable estimates of trends in marine fish production. However, our models can show how predation and fishing can affect trophic interactions among species. As such, ecosystem models are a useful scientific tool to identify gaps in understanding and data needs, but are unlikely to ever replace singlespecies models. They may instead complement and provide parameters to singlespecies models. Ecosystem models such as ours are still in the early stages of development and will become increasingly more important as a management tool as they begin to incorporate spatial and oceanographic/climatic information.

keywords     PhD MMecosystem modelmodeling limitations Bering Sea fisheries management
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1998
 
Diet composition and trophic levels of marine mammals.
Pauly, D., A.W. Trites, E. Capuli and V. Christensen. 1998.
ICES Journal of Marine Science 55:467-481.
abstract
Standardized diet compositions were derived for 97 species of marine mammals from published accounts of stomach contents as well as from morphological, behavioural and other information. Diet was apportioned among eight categories of prey types (benthic invertebrates, large zooplankton, small squids, large squids, small pelagic fishes, mesopelagic fishes, miscellaneous fishes and higher invertebrates). Trophic levels were estimated for each species of marine mammals and compared with published estimates derived using stable isotope ratios. Trophic levels ranged from 3.2–3.4 in baleen whales and sea otters, to 3.8–4.4 in most pinnipeds and odontocete whales, to 4.5–4.6 in killer whales. Such information can be used for ecosystem modelling and related studies.

keywords     marine mammals; diets; trophic levels; food organisms; stomach content; Cetacea; Balaenoptera; Odontocetes; Orcinus orca; Pinnipedia; Enhydra lutris; cetaceans; whales; Finback whales; Rorquals; Sea otter; Killer whale; Bering Sea species;
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Estimating mean body masses of marine mammals from maximum body lengths.
Trites, A.W. and D. Pauly. 1998.
Canadian Journal of Zoology 76:886-896.
abstract
Generalized survival models were applied to growth curves published for 17 species of cetaceans (5 mysticetes, 12 odontocetes) and 13 species of pinnipeds (1 odobenid, 4 otariids, 8 phocids). The mean mass of all individuals in the population was calculated and plotted against the maximum body length reported for each species. The data showed strong linearity (on logarithmic scales), with three distinct clusters of points corresponding to the mysticetes (baleen whales), odontocetes (toothed whales), and pinnipeds (seals, sea lions, and walruses). Exceptions to this pattern were the sperm whales, which appeared to be more closely related to the mysticetes than to the odontocetes. Regression equations were applied to the maximum lengths reported for 76 species of marine mammals without published growth curves. Estimates of mean body mass were thus derived for 106 living species of marine mammals.
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1997
 
Heat Increment of Feeding in Steller sea lions, Eumetopias jubatus.
Rosen, D.A.S. and A.W. Trites. 1997.
Comparative Biochemistry and Physiology 118A:877-881.
abstract
The heat increment of feeding (HIF) was measured in six captive, juvenile Steller sea lions (Eumetopias jubatus), fed meals of either 2 or 4 kg of herring. HIF was calculated as the post-prandial increase in metabolism above baseline levels, and was measured using open-circuit (gas) respirometry. It averaged 12.4 +/- 0.9% (SE) of ingested energy intake for the 4-kg meal trials, and 9.9 +/- 0.9% for the 2-kg meal size. The effect lasted 8-10 hr for the larger meal size. Metabolism peaked 3.7 hr after feeding, and was 2.13 times higher than baseline levels. For the 2-kg meal size, the effect lasted 6-8 hr, with metabolism peaking 2.8 hr after ingestion at 1.76 times baseline levels. Our estimates of HIF for Steller sea lions are at the lower end of estimates for terrestrial mammals, and are consistent with estimates for other marine mammals.

keywords     digestion, heat increment of feeding, pinnipeds, specific dynamic action, Steller sea lion
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The role of pinnipeds in the ecosystem.
Trites, A.W. 1997.
In G. Stone, J. Goebel and S. Webster (eds), Symposium of the 127th Annual Meeting of the American Fisheries Society. New England Aquarium, Conservation Department, Boston. pp. 31-38.
abstract
The proximate role played by seals and sea lions is obvious: they are predators and consumers of fish and invertebrates. Less intuitive is their ultimate role (dynamic and structural) within the ecosystem. The limited information available suggests that some pinnipeds perform a dynamic role by transferring nutrients and energy, or by regulating the abundance of other species. Others may play a structural role by influencing the physical complexity of their environment; or they may synthesize the marine environment and serve as indicators of ecosystem change. Field observations suggest the ultimate role that pinnipeds fill is species specific and a function of the type of habitat and ecosystem they occupy. Their functional and structural roles appear to be most evident in simple short-chained food webs, and are least obvious and tractable in complex long-chained food webs due perhaps to high variability in the recruitment of fish or nonlinear interactions and responses of predators and prey. The impact of historic removals of whales, sea otters and seals are consistent with these observations. Many of these removals produced unexpected changes in other components of the ecosystem. Better insights into the role that pinnipeds play and the effect of removing them will come as better data on diets and predator-prey functional responses are included in ecosystem models.

keywords     pinnipeds, ecosystems, predators, interactions, models, #4
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Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean.
Trites, A.W., V. Christensen and D. Pauly. 1997.
Journal of Northwest Atlantic Fishery Science. 22:173-187.
abstract
The degree of competition between fisheries and marine mammals in the Pacific Ocean was estimated for 7 statistical areas defined by the Food and Agriculture Organization of the United Nations (FAO). Catch statistics compiled from FAO sources show that the amount of fish caught in the Pacific Ocean rose from 2 million tons in the late-1940s to over 50 million tons in the early-1990s. Recent stagnation and declines occurring in some areas of the Pacific suggest that Pacific fisheries cannot continue to expand as they had previously. Based on estimates of population size, total biomass and daily consumption rates, it was estimated that the 84 species of marine mammals inhabiting the Pacific Ocean con-sume about three times as much food as humans harvest. A large fraction (>60%) of the food caught by marine mammals consisted of deep sea squids and very small deep sea fishes not harvestable by humans, thus limiting the extent of direct competition between fisheries and marine mammals. Moreover, the most important consumers of commercially exploited fish are other predatory fish, not marine mammals. Although direct competition between fisheries and marine mammals for prey appears rather limited, there may be considerable indirect competition for primary production. The primary production required to sustain marine mammals in each of the 7 FAO areas varies within a narrow range, suggesting that the diversity and abundance of marine mam-mals may have slowly evolved to fully exploit their niche and maximize their use of avail-able primary production. This contrasts with the rapid expansion of fisheries and their relatively recent dependence on primary production, which may have led to what we call ‘ food web competition’.

keywords     competition, fisheries, food, feeding, marine mammals, Pacific Ocean, #3
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1996
 
Assessing the use of hard parts in faeces to identify harbor seal prey: results of captive feeding trials.
Cottrell, P.W., A.W. Trites and E.H. Miller. 1996.
Canadian Journal of Zoology 74:875-880.
abstract
Faeces were collected from four captive harbour seals (Phoca vitulina) that consumed known amounts of herring (Clupea harengus), walleye pollock (Therugru chalcogrumma), Pacific hake (Merluccius productus), surf smelt (Hypomesus pretiosus), and juvenile chinook salmon (Oncorhynchus tshmvytschu). The goal was to determine which structures (hard parts) passed through the digestive tract (e.g., eye lenses, scales, vertebrae, otoliths), and which of these could be used to determine the type and number of fish consumed. Nearly 5000 fish were consumed, from which over 50000 hard parts were recovered from seal faeces. Scales were the most numerous of the 23 structures recovered (> 20 000), followed by vertebrae, eye lenses, and otoliths. Morphological distinctiveness and digestive erosion of the structures varied among fish taxa. Two to five structures accounted for over 90% of the taxon-specific elements recovered, depending upon the species of fish consumed. Otoliths, which are used routinely to characterize pinniped diets, accounted for only 17% of the identified taxon-specific hard parts. The variation in types of structures and rates of recovery across taxa underscores the importance of using several types of hard parts to identify prey. Identifying several different prey structures increases the likelihood of identifying a prey type.
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