STELLER SEA LION RESEARCH

Biology and Ecology Related Publications

General and Diving Physiology |  Population Dynamics |  Ecology of Marine Mammals |  Biology

GENERAL AND DIVING PHYSIOLOGY


2017
 
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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2016
 
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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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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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
 
Quantifying the costs of dive behaviours and foraging strategies in Steller sea lions (Eumetopias jubatus).
Goundie, E.T. 2015.
MSc Thesis, University of British Columbia, Vancouver, B.C. 80 pages
abstract
Air-breathing divers, such as marine mammals, should adjust their diving behaviours in relation to the depth and density of their prey to minimize the energetic costs and maximize the benefits of foraging. However, there is little experimental data to test these predictions or to develop models to predict the responses of marine mammals to changes in prey availability. The objectives of my study were to 1) determine how changes in prey availability affect dive behaviour and foraging efficiency in Steller sea lions (Eumetopias jubatus) and 2) develop models with data from free-diving captive Steller sea lions to estimate foraging costs in wild animals and evaluate energetic trade-offs between different foraging strategies. I measured the diving metabolic rate, dive durations, and food intake of 4 trained sea lions diving in the open ocean on simulated prey patches of high- or low-densities at 10 m and 40 m. I also measured diving metabolic rates of sea lions performing 4 controlled dive types that allowed me to estimate the separate costs of different dive components (i.e., surface time, bottom time, and transiting to and from depth). I found that animals diving on prey patches with low prey density altered their dive behaviours and spent proportionally less time actively foraging, which ultimately decreased their foraging efficiency. I also found that making single, longer dives were less energetically costly than making multiple shorter dives in a bout, but that the sea lions replenished oxygen stores more efficiently when making a bout of dives. Finally, I determined the metabolic cost of transiting to and from depth (20.5Ä…13.0 ml O2 min-1 kg-1) was greater than the cost of foraging during the bottom portion of a dive (13.5Ä…4.1 ml O2 min-1 kg-1). With these values, I generated a predictive equation to estimate the diving costs of free-ranging animals. Overall, my results indicate that Steller sea lions do alter their dive behaviour in relation to prey availability and that different foraging strategies have different energetic costs. These results can be used to understand how changes in prey availability affect the overall energy balance and health of Steller sea lions.

keywords     Steller sea lion, foraging energetics, diving physiology
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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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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
 
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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Oxygen stores, carbon dioxide accumulation and nutritional status as determinants of diving ability of Steller sea lions (Eumetopias jubatus).
Gerlinsky, C.D. 2014.
M.Sc. Thesis, University of British Columbia, Vancouver, B.C. 105 pages
abstract
The diving ability of marine mammals is limited by body oxygen stores (TBO) and rates of oxygen depletion (diving metabolic rate; DMR), which can be expressed as the calculated aerobic dive limit (cADL). Diving ability must also be influenced by CO₂ production and control of ventilation. I investigated the factors that limit the diving ability of Steller sea lions (Eumetopias jubatus), including the effect of nutritional stress on the cADL. Specifically, I 1) determined the cADL of Steller sea lions by measuring TBO and DMR, 2) determined whether nutritional stress alters the cADL and 3) examined the post-dive elimination of CO₂, and the sensitivity of Steller sea lions to hypercapnia (high inspired CO₂). TBO was estimated from measured blood oxygen stores and body composition―and metabolic rate, breathing frequency and dive behaviour were recorded prior to and during a period of nutritional stress where animals lost ~10% of their mass. Animals breathed ambient, hypercapnic or hypoxic (low O₂) air to experimentally alter pCO₂ levels and decrease rates of CO₂ elimination and O₂ consumption. I found that the TBO (35.9 ml O₂ kg-¹) and cADL (3.0 minutes) in actively diving Steller sea lions were lower than previously reported for other species of sea lions and fur seals. I also found a significant increase in mass-specific DMR and blood volume (resulting in higher TBO) in nutritionally stressed animals that resulted in a longer cADL. Hypercapnia was found to significantly affect ventilation, but had no effect on dive behaviour―and elimination of CO₂ between dives took longer than replenishing O₂ stores. Overall, nutritional stress and hypercapnic conditions did not directly limit the diving ability of the Steller sea lions, but had an indirect effect on foraging efficiency by increasing the time they spent on the surface between dives. Accumulation of CO₂ over several dives in a foraging bout also appeared to reduce foraging efficiency, which likely ultimately limits the time a sea lion spends in apnea and therefore overall foraging duration and net energy intake.
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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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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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2013
 
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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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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2011
 
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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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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2010
 
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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2008
 
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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2007
 
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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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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2006
 
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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2005
 
Biomechanics of turning manoeuvres in Steller sea lions (Eumetopias jubatus).
Cheneval, O. 2005.
MSc Thesis, University of British Columbia, Vancouver. 64 pages
abstract
Otariids such as the Steller sea lion (Eumetopias jubatus) are among the most manoeuvrable of marine mammals (expressed as a minimum turning radius and speed during manoeuvres). They evolved in terrestrial and aquatic environments that are structurally complex, and feed on prey that are an order of magnitude smaller than themselves. Compared to other aquatic organisms, Steller sea lions have an unstable body design and are presumed to invoke swimming techniques that reflect their need to be highly manoeuvrable. Detailed information was experimentally obtained about the turning techniques employed by otariids through jointly analysing kinematic and kinetic parameters measured from video recordings of three captive Steller sea lions. Centripetal force and thrust production were determined by examining body movements throughout a series of turns. Results showed that most of the thrust was produced during the power phase of the stroke cycle of the pectoral flippers. As ! opposed to previous findings, very little or no thrust was generated during initial abduction of the pectoral flippers and during the final drag-based paddling style of the stroke cycle. Peak of the thrust force was reached halfway through the power phase, while the centripetal force reached its maximum value at the beginning of the power phase. Kinematic aspects of the manoeuvres changed with the tightness of the turns and the initial velocities. The degree of dorsal flexion of the body changed with the turning radius and the degree of flipper abduction varied with swimming speed. However, the general manoeuvring technique and turning sequence remained the same in all the recorded manoeuvres. Contrasting the turning performance of the Steller sea lion with a simple dynamic model of unpowered manoeuvres in aquatic animals showed significant departures from model predictions due to the hydrodynamic effects of body movements. Overall, the turning sequence of the Steller sea lion was found to be very consistent, and their manoeuvrability was found to come from their ability to vary the duration and intensity of movements within the turning sequence.
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Spatial variation of heat flux in Steller sea lions: evidence for consistent avenues of heat exchange along the body trunk.
Willis, K., M. Horning, D.A.S. Rosen and A.W. Trites. 2005.
Journal of Experimental Marine Biology and Ecology 315:163-175.
abstract
Maintaining insulative fat stores is vital for homeothermic marine mammals foraging in cold polar waters. To accomplish this, animals must balance acquisition and expenditure of energy. If this balance is shifted, body condition can decrease, challenging thermal homeostasis and further affecting energy balance. Prior studies of temperature regulation in sea lions have neither quantified basic all-inclusive heat flux values for animals swimming in cold water, nor determined whether they exhibit consistent spatial patterns of heat flux. Heat flux and skin temperature data were thus collected from four captive Steller sea lions using heat flux sensors (HFSs) with embedded thermistors. Optimal sensor placement was established using infrared thermography to locate the major areas of heat flux along the surface of the animals. Experiments were conducted on swimming animals in a large habitat tank with and without a drag harness, and on stationary animals in a temperature- and current controlled swim flume. All heat flux measurements were corrected by a previously determined correction factor of 3.42 to account for insulative effects of the HFSs and attachment mechanism. Heat flux from shoulders and hips was consistently greater than from mid-trunk and axillary areas in both swimming and stationary animals, suggesting that certain areas of the body are preferentially used to offload excess heat. Mean heat flux for animals swimming with a drag harness was significantly greater than for unencumbered animals, indicating a likely increase in heat production beyond minimum heat loss. Thus, thermal stress does not appear to constitute significant costs for Steller sea lions swimming under conditions of increased drag at speeds of approximately 1 m/s in water temperatures of approximately 8.0 °C.
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2002
 
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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2000
 
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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POPULATION DYNAMICS


2014
 
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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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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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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2011
 
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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2006
 
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
 
Modelling and characterization of Steller sea lion haulouts and rookeries using oceanographic and shoreline type data.
Ban, S. 2005.
Graduate Thesis, University of British Columbia, Vancouver. 103 pages
abstract
Steller sea lions range across the Pacific rim from Southern California in the east to northern Japan in the west, where they have continuously occupied terrestrial resting sites (haulouts) and breeding sites (rookeries) for hundreds of years, if not longer. Why they choose (and stay) at these locations, and what their preferred habitat is, remains unknown. Thus, two aspects of the Steller sea lion?s habitat usage were examined?the oceanographic and the terrestrial. For the oceanographic aspect, spatial models were constructed to determine which oceanographic factors are associated with haulouts and rookeries, and how conditions near sites might differ from conditions elsewhere. The two modelling techniques employed (logistic regression and supervised classification) were evaluated using the kappa statistic (Kno), and receiver-operating characteristic(ROC) plots. Supervised classification was found to produce better-fitting models than logistic regression. In general, Steller sea lions showed preferences for sites associated with waters that were relatively shallow, well-mixed, had higher average tidal speeds and less-steep bottom slopes. Conditions within 1 nautical mile of land were better predictors of haulout and rookery locations than were conditions within 10, 20, and 50 nautical miles. No consistent differences were found in the physical characteristics of waters surrounding sites in the eastern and western populations of Steller sea lions, or between haulouts and rookeries. Regarding the terrestrial aspect of their habitat, anecdotal accounts describe Steller sea lions as predominantly occupying exposed, rocky shorelines, but this habitat preference has never been quantified. Locations of haulouts and rookeries were compared against a coastline type database to identify the shoreline preferences of Steller sea lions and to look for other spatial trends in site characteristics. Haulouts and rookeries were preferentially located on exposed rocky shorelines and wave-cut platforms. No relationship was found between either latitude or longitude of a site and its average non-pup count. The results indicate that there are differences in both the oceanographic and terrestrial characteristics of sites used by Steller sea lions versus areas of coastline where they are not found. The models could be used to predict changes in habitat use given changing physical conditions, and could be applied to any central-place forager.
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2001
 
Implications of three viability models for the conservation status of the western population of Steller sea lions (Eumetopias jubatus).
Gerber, L.R. and G.R. VanBlaricom. 2001.
Biological Conservation 102:261-269.
abstract
Two distinct viability models are developed for Steller sea lions (Eumetopias jubatus )to evaluate the sensitivity of extinction risk to various levels of stochasticity,spatial scale and density dependence.These models include a metapopulation model,Analysis of the Likelihood of Extinction (ALEX;Possingham et al.,1992; Possingham,H., Davies,I.A.,Noble,I.1992.ALEX 2.2 Operation Manual.Department of Applied Mathematics,University of Adelaide,Adelaide,SA 5005;Australia.),and a model that incorpo- rates both sampling and process error in estimating population parameters from timeseries data (Gerber and DeMaster,1999; Gerber,L.R.,DeMaster,D.P.1999.An approach to endangered species act classification of long-lived vertebrates:a case study of north Pacific humpback whales.Conservation Biology 13 (5);1203 –1214.).Results are compared with a third model that encompasses three different geographic scales (York et al.,1996;York,A.E.,Merrick,R.L.,Loughlin,T.R.1996.An analysis of the Steller Sea lion metapopulation in Alaska.In:McCullough,D.R.(Ed.),Metapopulations and Wildlife Conservation.Island Press, Covelo,CA pp.259 –292).The combination of modeling approaches provides a basis for considering how model parameterization and the selection of classification criteria affect both model results and potential status determinations.Results from the models generally agree with regard to central tendency,25th and 75th percentile times to extinction.For Steller sea lions,the distributions of time to extinction for each model were narrower than the range of extinction distributions between models.If this finding applies generally to listed species,it would suggest that more than one viability model should be considered when listing decisions are made.On a more applied basis,the results of our analysis provide a quantitative assessment of extinction risk of Steller sea lions in the context of its status pursuant to the US Endangered Species Act.
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1998
 
Steller Sea Lions (Eumetopias jubatus): Causes for their Decline and Factors Limiting their Restoration.
Trites, A.W. 1998.
Marine Mammal Research Unit, University of British Columbia, Fisheries Centre.
abstract
Hatch, quoted by Francis et al. (1998), states that “the principal factor responsible for unfavorable trends in marine birds and pinnipeds in the Gulf of Alaska is availability of suitable food resources. Food limitation, in turn, may be caused by recent climatically driven ecosystem shifts forcing increased production of pelagic and demersal predatory fish (e.g., adult pollock, cod, salmon, and various flatfishes, especially arrow tooth founder and halibut) at the expense of forage species (capelin, sandlance, juvenile pollock, herring, and myctophids) on which marine bird and mammal species depend.” Reviewing the available information concerning Steller sea lions supports this view and provides no indication that Steller sea lions are limited because they cannot get enough pollock to eat. The data indicate the following:  The composition of major predator and prey populations in the Gulf of Alaska and Bering Sea underwent a rapid change beginning in the mid 1970s.  The diet of Steller sea lions reflects this change in prey available to them and shows a relationship between high rates of decline and consumption of large amounts of pollock.  There is no evidence that pollock are in short supply for either fisheries or sea lions, or that the two are competing. Catching adult pollock appears to reduce cannibalism and results in more juvenile pollock being available to Steller sea lions and other top predators.  There appear to be negative health consequences for Steller sea lions if they eat primarily pollock.  Recovery of Steller sea lions will probably occur if they can obtain a more diverse diet of fattier fishes. This appears to be a function of natural changes in the marine environment and not something that can be controlled by humans.  Changes that people can invoke by altering amounts of pollock caught in time and space can have unexpected and undesirable results.
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1997
 
Endangered Species Act (ESA) status of the western population of Steller sea lions based on the World Conservation Union (IUCN) classification scheme.
Gerber, L.R. and G.R. Van Blaricom. 1997.
Washington Cooperative Fish and Wildlife Research, University of Washington. pp. 54
abstract
The World Conservation Union (IUCN) classification scheme is applied to the western population of Steller sea lions to determine the population's status pursuant to the U.S. Endangered Species Act (ESA). Analysis methods suggested by the IUCN, such as population viability analysis (PVA) and minimum viable population (MVP), are examined as tools for determining quantitative and objective risk classification criteria. To provide an informative estimate of the extinction distribution for Steller sea lions, three PVA models are considered, and results of each model are compared. Results of all three models meet the classification criteria for vulnerable. Under no circumstances did the probability of extinction within 20 years exceed 20%, and all models indicated that within 100 years the species had at least a 10% probability of extinction. Results of the MVP analysis are highly sensitive to assumptions about sex ratio (1:3 for adult sex ratio, 1:15 for breeding sex ratio) and the specified effective population size (500 or 5000). ~egardless of the uncertainty in both PVA and MVP estimates, the Western population of Steller sea lions would be considered as endangered if the IUCN classification scheme was strictly followed because at least one of the five criteria has been met. The population woulh be considered as threatened under the ESA when none of the five criteria for endangered are met, but at least one of the criteria for vulnerable is met. Results are based upon the assertion that the IUCN categories of critically endangered and endangered are jointly comparable to the ESA category of endangered, and the IUCN category of vulnerable is comparable to the ESA category of threatened.
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ECOLOGY OF MARINE MAMMALS


2013
 
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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2007
 
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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2006
 
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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2003
 
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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2001
 
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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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
 
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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1996
 
Concepts and issues in marine ecosystem management.
Larkin, P.A. 1996.
Reviews in Fish Biology and Fisheries 6:139-164.
abstract
Ecosystem management means different things to different people, but the underlying concept is similar to that of the long-standing ethic of conservation. Current interest in marine ecosystem management stems from concerns about overexploitation of world fisheries and the perceived need for broader perspectives in fisheries management. A central scientific question is whether the effects of harvesting (top down) or changes in the physical environment (bottom up) are responsible for major changes in abundance.

Historically, ecology, fisheries biology, oceanography, fisheries management and the fishing industry have gone somewhat separate ways. Since the 198Os, increasing attention has been given to multispecies aspects of fisheries, the linkages between oceanography and fish abundance and more holistic approaches to fisheries management.

Sorting out the causes and effects of fluctuations in fish abundance is complicated by the lack of reliability of fisheries statistics. Discards, dishonesty and the inherent logistic difficulties of collecting statistics all combine to confuse interpretation. The overcapacity of fishing fleets and their unrestricted use are widely recognized as a contributing cause to overfishing and declines in fish stocks in many parts of the world.

Ecosystem management, as shorthand for more holistic approaches to resource management, is, from a fisheries management perspective, centred on multispecies interactions in the context of a variable physical and chemical environment. Broader perspectives include social, economic and political elements which are best considered pragmaticaily as a part of the context of fisheries management.

Objectives in marine ecosystem management are varied. From a biological perspective, an underlying principle of management is commonly assumed to be a sustained yield of products for human consumption. Whether that should be taken to mean that the yield . should always be of the same products is less certain. Fishing commonly changes the relative abundance of species of fishes. Thus, a biological objective should specify the species mix that is desired.

Concern for the maintenance of global diversity has generated a substantial literature on threatened and endangered species. In general, it has not been considered likely that marine fish species could be rendered extinct and greatest attention has been given to marine mammals, sea birds and sea turtles. The provision of marine parks and sanctuary areas are obvious first steps in providing a measure of protection, at least for the less widely ranging species.

Related to the current concepts of ecosystem management are expressions such as ecosystem health and ecosystem integrity which are given a wide range of different meanings, none of which are readily translated into operationa language for resource management. These and similar expressions are best assessed as rhetorical devices. The essential components of ecosystem management are sustainable yield, maintenance of biodiversity and protection from the effects of pollution and habitat degradation.

Theory for marine ecosystem management has a long history in fisheries and ecological literature. Ecological models such as Lotka-Volterra equations, ECOPATH, trophic cascades and chaos theory do not give practical guidance for managcmcnt. Fleet interaction and multispecies virtual population analysis models hold more promise for fisheries managers.

Alaska provides particular opportunities for developing new concepts in fisheries management. Statistics of catch are good, stock assessments are at the state-of-the-art level and management has been prudent. Debate is active on the causes of substantial changes in abundance of many species including marine mammals, because substantial changes in the fisheries have been accompanied by major changes in oceanographic conditions.

As elsewhere, the resultant changes may be a consequence of top-down and bottom-up effects. The bottom part is beyond human control, and ecosystem management is centred on managing the top-down or fisheries component in the context of special measures of protection for particuiar species.

Whether that is a realistic goal depends in part on how much special protection is to be afforded to which species. Marine mammals, for example, are given high priority for special protection, but like fisheries they too may have significant roles in shaping the structure of marine ecosystems. Eventually, ecosystem management must come to grips with the question of how much protection of particular species is desirable in achieving optimal use of living marine resources.

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BIOLOGY


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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2013
 
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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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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2007
 
Otariid seals.
Haulena, M. 2007.
In D. Heard and N. Caulkett G. West (eds), Zoo Animal and Wildlife Immobilization and Anesthesia. Blackwell Publishing, Ames. pp. 469-478.
abstract
The family Otariidae (sea lions and fur seals) within the order Pinnipedia is composed of 14 species. Otariids bear weight on all four flippers, climb, locomote quickly, and are more adept on land than phocid seals. However, their aquatic adaptations are less developed and they generally do not dive as deep or for as long as phocids. Anatomical and physiological adaptations for diving (e.g., large venous sinuses and dive response) therefore, are not as extreme. Some of these differences make otariids more difficult to physically or mechanically restrain than phocids of the same weight. Additionally, they are less sensitive to immobilization drugs and anesthetic regimens are similar to those of terrestrial carnivores. As with any species, successful otariid anesthesia is dependent upon adequate planning and availability of the proper equipment. The animal’s size, species, sex, and physiological status are important considerations in choosing the best immobilization method. The site (captive facility versus free-living animals in the field), experience of the personnel, and availability of equipment and drugs often dictate the method chosen. Finally, the degree of invasiveness and expected duration of the procedure affect decisions.
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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
 
Steller Watch: timing of weaning and seasonal patterns in numbers and activities of Steller sea lions at a year-round haulout site in Southeast Alaska.
Marcotte, M.L. 2006.
M.Sc. thesis, University of British Columbia, Vancouver, BC. 82 pages
abstract
Variability in length of lactation and maternal association allows otariids flexibility to buffer their young against changes in nutrition. It also increases the chance of their young surviving to sexual maturity, which is particularly important in a declining species such as Steller sea lions (Eumetopias jubatus). Timing of weaning is a critically important event in mammalian development that can affect subsequent aspects of an animal‘s adult life, and may hold the key to understanding the population dynamics of Steller sea lions. Unfortunately no studies have yet fully documented the behavioural ecology of Steller sea lions outside of the breeding season. The goal of my study was to document suckling behaviour over 13 consecutive months to determine the timing of weaning for male and female Steller sea lions under three years of age at Southwest Brothers Island, Southeast Alaska (July 2004 – July 2005). I also wanted to ascertain the haulout patterns and activity levels of the colony in relation to season, prey availability, time of day, and weather. Finally, I sought to evaluate the feasibility of using an automated, time-lapse camera system to monitor sea lions and its potential for future use. Male Steller sea lions were found to suckle longer than females, with a greater proportion of males than females suckling at one year. Time spent suckling declined with age suggesting that the animals became more independent as they grew older, most likely as they increased their ability to forage successfully on their own. Male sea lions that remained with their mother for longer than one year may have had reduced exposure to predation, and obtained more calories with less energy expenditure from milk, compared to females that became nutritionally independent sooner. As a result, this may provide males with a chance to grow as big as possible, as fast as possible, and increase their ability to hold a territory and have access to mates later in life. The number of sea lions onshore at Southwest Brothers Island was influenced by weather on a daily time-scale, but also displayed seasonal changes that may have been related to prey availability and the timing of breeding. The colony abandoned the island mid-March to mid-April, coinciding with the herring spawn and eulachon runs, which are high-fat species and spatio-temporally predictable prey. High daily variability in numbers of animals at Southwest Brothers likely reflected movement of animals to and from other nearby haulouts. Activity levels varied throughout the year, with proportionally more animals resting in the summer and more animals engaged in low activities in the winter. This suggests a higher behavioural expenditure of energy in the winter, contributing to their need for high quality nutrition. June and July is an optimum time to assess sea lion numbers due to the high number of animals onshore at that time and a greater predictability in sea lion behaviour. The counts obtained from the automated time-lapse camera system‘s digital images correlated with counts obtained from direct observation (r2 = 0.99). The direct counts were on average 22% greater than the digital images. While direct observation is the best method for obtaining a greater variety of data, the camera systems have a good potential to be used to monitor Steller sea lions and other species when researchers cannot be physically present.
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Steller sea lions (Eumetopias jubatus) of Oregon and northern California: seasonal haulout abundance patterns, movements of marked juveniles, and effects of hot-iron branding on apparent survival of pups at Rogue Reef.
Scordino, J. 2006.
M.Sc. thesis, Oregon State University, Corvalis. 112 pages
abstract
The Steller Sea Lion Research Initiative was passed in 2001 to provide funding to help scientists determine causes and solutions for the population crash of Steller sea lions (Eumetopias jubatus). In response to need to understand population dynamics of Steller sea lions, NOAA Fisheries has spearheaded a large-scale, range-wide research program. The study involved capturing and hot-iron branding sea lions at rookeries from northern California around the Pacific Rim to Russia to provide individually recognizable animals for studies of behavior and vital rates. I report the results of monitoring pups branded and tagged at Rogue Reef, Oregon and St. George Reef, California to determine movement patterns and the affects of branding on apparent survival of Steller sea lion pups immediately after branding. Counts of Steller sea lion adult female, adult male, juveniles, and pups were collected at haulouts and rookeries of Oregon and northern California from 2002 through 2005. Movement patterns of Steller sea lions were inferred from count data. Adult males were seasonal inhabitants of Oregon and California during the breeding season from May through September before dispersing to northern feeding grounds. Females, juveniles, and pups were dispersed throughout haulouts in Oregon and northern California during all seasons but have seasonally high concentrations at Sea Lion Caves, Oregon in the winter and at the breeding rookeries during the summer breeding season. The high wintertime abundance of females and pups at Sea Lion Caves suggests that it should be considered as critical habitat for Steller sea lions of the eastern stock. Resights of marked sea lions collected between northern California and Alaska between 2001 and 2005 were analyzed to determine juvenile and pup dispersal patterns. Most pups stay close to their natal rookery, although 9 - 22% of individuals each year were observed to disperse further than 500 km. As 1-year olds, the mean maximum dispersal range expanded, which may have been a sign of weaning. Sexually dimorphic patterns in sea lion movements were apparent at 3 years of age as males were observed to disperse farther north than females. The percentage of females observed at their natal rookery increased each year to a maximum of 87% as 4-year-olds. This suggested that sexual maturity occurs at, or close to, 4 years of age for females. Branding provided a useful tool for analyzing movements of Steller sea lions, yet it may have impacts on survival of individuals. Concerns raised by NOAA Fisheries over branding impacts on pup survival were addressed with a study at Rogue Reef in 2005. One-hundred-and-sixty pups captured on 18 July, 2005 were randomly assigned to a treatment of flipper tag only (unbranded pups) or flipper tag and hot-iron branding (branded pups). Aside from the treatment of branding, all pups were handled and treated identically. Over the 73-day course of this study, I found lower apparent survival for branded pups than unbranded pups, with a final apparent survivorships of 0.23 (95% CI 0.01 – 0.48) for branded pups and 0.46 (95% CI 0.15 – 0.77) for unbranded pups. Apparent survivorship includes both mortality and emigration, so differences may be due to differences in emigration rates of the two groups, mortality rates, or both. The scope of inference for this study is only to Rogue Reef in 2005. However, it should provide a good model for future brand evaluation studies at other rookeries and for other pinniped species. Branding is currently the best and only available tool for long-term studies of survival, reproduction rates, and age at sexual maturity which are all critical for demographic models. Nonetheless, researchers should assess the impacts of branding at each rookery, and will need to consider whether knowledge from branding Steller sea lions is worth the potential reduction in pup survival or change in pup emigration behavior observed in this study.
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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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2005
 
International survey of scientific collections of Steller sea lions.
Miller, E.H., A.W. Trites, and Ø. Wiig. 2005.
Fisheries Centre Research Reports Vol 13(6) pp. 69
abstract
We examined or obtained information on specimens of Steller sea lions in museums and other collections. We report on 1740 specimens (complete or partial skulls) in 44 collections in Canada, Germany, Japan, the Netherlands, Russia, the United Kingdom, and the United States. At least several hundred other specimens also exist, mainly in Japan and Russia. Collection dates range from 1842 to the present. Geographically, specimens are well represented in both ?Western? and ?Eastern? regions (separated at 144 W longitude): 509 and 956, respectively. Collection localities within Alaskan regions 2 (Eastern Gulf of Alaska) to 8 (Eastern Bering Sea) are represented by 290 specimens; another 566 specimens are from Japan and Russia and 462 from Alaska region 1 (Southeastern Alaska) southwards. Thus specimens are well spread across the species? breeding range, including areas of population decline. Representation is also good for the period of population decline and earlier per! iods: 442 specimens are from before 1960, 352 from 1960-69, 370 from 1970-79, and 487 from 1980 onwards. There are some problems with quality of data, and with seasonal and geographic representation, but we conclude that ample specimens exist to permit research pertinent to population declines in parts of the species? range.
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2004
 
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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2003
 
The timing of moulting in wild and captive Steller sea lions (Eumetopias jubatus).
Daniel, R.G. 2003.
University of British Columbia, Vancouver, B.C. 64 pages
abstract
I documented the timing and progression of the moult by sex and age class in a wild population of Steller sea lions (Eumetopias jubatus) on Lowrie Island, Alaska (Jul-Nov 2001) and from captive animals at the Vancouver Aquarium Marine Science Centre (1993-2000). In the wild, juveniles (ages 1-2 years) were the first to moult followed by adult females, bulls and pups. The mean date when juveniles started their moult was 21 Jun which was significantly different from the mean start date of 07 Aug for adult females, and differed from the mean start date for pups of 01 Sep (one month later). Mean completion dates were also about one month apart (19 Sept for juveniles, 26 Oct for adult females and 17 Nov for pups). Duration of the moult was about 45 days for each age group (pups and adult females). However, duration of the moult for captive sea lions was longer (averaging 83.5 days) and differed among years and within age classes. Patterns of hair loss in the wild (i.e., the progression of the moult over the body surface) differed among (i) pups, (ii) juveniles and early moulting adult females, and (iii) bulls and later moulting adult females. Differences in the timing and progression of the moult may be related to physiological changes and interactions of hormones associated with body condition and the reproductive cycle.
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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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2002
 
Foraging behavior and energetics of adult female Steller sea lions.
Andrews, R.D., D.G. Calkins, R.W. Davis, B.L. Norcross, K. Peijnenberg and A.W. Trites. 2002.
In D. DeMaster and S. Atkinson (eds), Steller sea lion decline: Is it food II. University of Alaska Sea Grant, AK-SG-02-02, Fairbanks. pp. 19-22.
abstract
In June 1997,we conducted a test of the hypothesis that the current Steller sea lion decline is due to nutritional stress. Steller sea lions were studied at two of the central Aleutian Islands, Seguam and Yunaska, and at the Forrester Island rookery complex in southeast Alaska. Trip durations and the percent time spent at sea were much shorter for Steller sea lions from Seguam Island compared to those from the Forrester Island rookery. Dives at Seguam Island were shorter and shallower, but more frequent than those at Forrester Island The short trips at Seguam Island generally consisted of a single bout of uninterrupted dive cycles while at Forrester Island the trips were broken into dive bouts of varying length separated by periods spent traveling or resting at the surface. However, on average, the percent of a trip spent submerged was not significantly different. Another measure of foraging effort, the vertical travel distance per unit time at sea, was about 1. 5 times greater for Steller sea lions at Forrester Island. The at-sea field metabolic rates, however, were similar for both groups. Data on the time and distance elapsed from departure on a foraging trip until commencement of “foraging dives ” shows that at both rookeries Steller sea lions appear to begin searching for prey very soon after entering the water. However , the mean time from departure to first prey ingestion, identified by the stomach temperature record, was about five times longer for Steller sea lions at Forrester Island than at Seguam Island. The rough estimation of prey intake rate at Seguam Island was about two times greater than at Forrester Island. Therefore, it would appear that in 1997,adult female Steller sea lions at Seguam Island found suitable prey more quickly, and once they found it were able to ingest it at a much higher rate than Steller sea lions at Forrester Island. From this study it appears that a directly measured difference in prey availability may account for the observed difference in prey capture rate. This greater capture rate by Steller sea lions at Seguam Island may partially explain the greater pup growth rates observed there compared to Forrester Island. The lack of a single highly abundant prey species and the larger Steller sea lions population at Forrester Island may result in longer search times for Forrester Island Steller sea lions. An important value of this and the related studies to date is that we were able to demonstrate a correlation between prey availability, foraging success, and pup growth, a parameter that is potentially indicative of future survival and therefore adult female reproductive success.
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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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2001
 
An annotated bibliography of scientific literature (1751-2000) pertaining to Steller sea lions (Eumetopias jubatus) in Alaska.
Hunter, A.M.J. and A.W. Trites. 2001.
Fisheries Centre Research Reports Vol 9 pp. 45
abstract
We compiled an annotated bibliography of Steller sea lion literature that identifies the areas of research that have been undertaken to date, and whether or not they address the leading hypotheses proposed to explain the population decline in Alaska. We identified 272 scientific papers with a primary research focus on Steller sea lions. Of these, 111 articles were peer-reviewed publications in scientific journals, and 161 were other forms of publication (e.g., technical reports, unpublished reports, dissertations, etc.). The total number of Steller sea lion articles published per decade has risen exponentially from 4 in the 1940s to 128 in the 1990s. The bulk of scientific studies have focused on population distribution, population dynamics, ecology, census data, nutrition and behavior. Subject areas that have received low research attention include predation on Steller sea lions, captive studies, metabolism and parasitology. Only 59 of the 272 scientific articles contained information relevant to testing one of the 12 hypothesized causes of the Steller sea lion decline. The most frequently addressed hypothesis concerned juvenile mortality (25 papers). This was followed by starvation, competition with fisheries, human predation and regime shifts. Only 1 of the 272 articles addressed the role that killer whale predation may be playing in the decline of Steller sea lions. To date, over 9,228 pages pertaining to Steller sea lions have been printed (1,148 pages of primary publications and 8,080 pages of other publications). The relative number of articles that address or provide significant information to assess hypothesized causes of the population decline are few (< 30% of the sea lion literature per decade).
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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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