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A novel presence-only validation technique leads to improved habitat descriptions for a wide-ranging marine predator, the Steller sea lion (Eumetopias jubatus). Gregr, E.J. and A.W. Trites. (in press). Marine Ecology Progress Series abstract We used published information about foraging behaviour, terrestrial resting sites, bathymetry, and seasonal ocean climate to develop hypotheses relating life history traits and physical variables to the at-sea habitat of a wide-ranging marine predator, the Steller sea lion (Eumetopias jubatus). We used the hypotheses to develop a series of habitat models that predicted the probability of sea lions occurring within 3 x 3 km2 grids overlaid on the Gulf of Alaska and Bering Sea; and compared these deductive model predictions with opportunistic at-sea observations of sea lions (presence-only data) using 1) a likelihood approach in a small area where effort was assumed to be uniformly distributed, and 2) an adjusted skewness (Skadj) test that evaluated the distribution of the predicted values associated with true presence observations. We found the Skadj statistic was comparable to the likelihood test when using pseudo-absence data, but it was more powerful for assessing the relative performance of the different predictive spatial models. We also found that the habitat maps we produced for adult female sea lions using the deductive modelling approach captured a higher proportion of presence observations than the current habitat model (Critical Habitat) used by fisheries managers since 1993 to manage Steller sea lions. Such improved predictions of habitat are necessary to effectively design, implement, and evaluate fishery mitigation measures. The deductive approach we propose is suitable for modelling the habitat use of other age- and sex- classes, and for integrating these age/sex class specific models into a revised definition of Critical Habitat for Steller sea lions. It can also be readily used to identify the at-sea habitat of other central place foragers.
Evaluating Quantitative Fatty Acid Signature Analysis (QFASA) using harbour seals (Phoca vitulina richardsi) in captive feeding studies. Nordstrom, C.A., L.J. Wilson, S.J. Iverson and D.J. Tollit. (in press). Marine Ecology Progress Series abstract Quantitative fatty acid (FA) signature analysis (QFASA) has recently been developed to estimate the species composition of predator diets by statistically comparing FA signatures of predator adipose tissue with that of their potential prey. Captive feeding trials were used to test the technique with newly-weaned harbour seals (Phoca vitulina richardsi, N = 21). Two groups of seals were fed monotypic diets of either Pacific herring (Clupea pallasii) or surf smelt (Hypomesus pretiosus) for 42 days while a third group was fed smelt (21 days) followed by herring (21 days). Blubber biopsies were taken dorsally at day 0, 21 and 42. Specific calibration coefficients (CC) required by QFASA were developed from 4 juvenile harbour seals and in some cases differed by two-fold with previously reported phocid CC. QFASA diet estimates were evaluated using 2 CC sets, 15 FA subsets and a library of 3 – 11 potential prey species. Diet switches were best tracked using the harbour seal CC and a new FA subset. Overall prey misclassifications were apparent (mean = 12%, range = 4 – 25%) when modeled with 8 additional prey not fed, often consistent with overlapping prey FA signatures. Blubber FA turnover rates were not strictly linear and in the order of 1.5 – 3 months in newly-weaned animals. Following model parameter optimization, QFASA estimates reflected major diet trends in the feeding study, but were sensitive to the CC and FA subsets used as well as to prey species with similar FA signatures. Our results have important implications in the application of QFASA to study pinniped diets in more complex conditions.
Hormone changes indicate that winter is a critical period for food. Rosen, D.A.S., Kumagai, S. (in press). Journal of Comparative Physiology B abstract Given that many marine mammals display seasonal energetic priorities, it is important to investigate whether the impact of unexpected food restriction differs during the year. Steller sea lions (Eumetopias jubatus) fed restricted diets for up to 9 days during spring, summer, fall, and winter lost an average of 10% of their initial body mass. We tracked changes in the levels of three hormones (cortisol, total thyroxine—TT4, total triiodothyronine—TT3) and one blood metabolite (blood urea nitrogen—BUN) following a food restriction in relation to season, body mass, body composition, and metabolism. Degree of changes in cortisol, TT3, and BUN after food restriction was significantly affected by season. The greatest changes in cortisol (+231%), BUN (+11.4%), TT4 (-23.3%), and TT3 (-35.6%) occurred in the winter (November/December) when rates of body mass loss were also greatest. Changes in cortisol levels were positively related to total body mass loss, while changes in TT3 levels were negatively related. While greater increases in BUN were related to greater rates of mass loss, the use of BUN levels as an indicator of metabolic state is complicated by the type and level of food intake. The observed changes in hormone levels support morphological data suggesting Steller sea lions may be more strongly impacted by short-term, reduced energy intake during winter than at other times of the year.
Diets of mature male and female Steller sea lions differ and cannot be used as proxies for each other. Trites, A.W., and D.G. Calkins. (in press). Aquatic Mammals abstract Disturbance of otariid breeding sites (rookeries) to determine diet from fecal remains (scats) could be eliminated if the diets of males using adjoining bachelor haulouts could be used as a proxy for diets of breeding females. We collected scats from sexually mature Steller sea lions (Eumetopias jubatus) at one male resting site (haulout) and three female dominated breeding sites (rookeries) at Forrester Island, Southeast Alaska (June-July, 1994–1999) to test whether the diets of bachelor bulls differed from that of breeding females. Female diets were fairly evenly distributed between gadids, salmon and small oily fishes (forage fish), and contained lesser amounts of rockfish, flatfish, cephalopods and other fishes. Female diet did not differ significantly between the 3 rookeries, but did differ significantly from that of males. Males consumed significantly fewer salmon, and more pollock, flatfish and rockfish compared to females. The males also consumed larger pollock compared to females. These dietary differences may reflect a sex-specific difference in foraging areas or differences in hunting abilities related to the disparity in physical sizes of males and females. The similarity of the female diets between rookeries suggests that female diets can be determined from samples collected at a single site within a rookery complex. Unfortunately, summer diets of breeding females cannot be ascertained from hard parts contained in the scats of mature male Steller sea lions.
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.
Evaluating network analysis indicators of ecosystem status in the Gulf of Alaska. Heymans, S.J.J., S. Guénette and V. Christensen. 2008. 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 hali! but (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.
Marine Mammals in the Lab: Tools for Conservation and Science. Rosen, D.A.S. and A.W. Trites. 2008. In North Pacific Universities Marine Mammal Research Consortium. Vancouver, BC. pp. 15 pages abstract Twenty-two participants from a variety of backgrounds and interests discussed how to improve the nature of research with marine mammals in the laboratory and ensure its continuation as a vital scientific resource in the future. There was agreement that captive marine mammals represent a valuable scientific asset. Many of the pressing conservation and scientific research questions pertaining to marine mammals cannot be carried out with their wild counterparts. However, studying marine mammals in the laboratory incurs specific financial, scientific, and logistical challenges. The workshop generated potential solutions to many of these issues. Participants expressed the need for greater cooperation and coordination between scientists to optimize the scientific value of research with captive marine mammals, and to minimize the costs of such research. This could be enhanced through scheduled in-person gatherings and web-based portals for listing active and proposed research. Better use must also be made of scientific resources and expertise, and novel sources of revenue have to be generated. There should also be greater sharing of documents relating to experimental design and research permitting. The effectiveness of research will benefit from greater communication between researchers and husbandry staff at institutions holding animals for research. Such efforts should raise the profile (and acceptance) of captive marine mammals science within the scientific community and for program administrators, leading to greater financial and research opportunities. Nine specific recommendations were forwarded that could be immediately implemented to enhance communication and increase the value of captive marine mammal science: 1. Produce a list of research resources (animals, specialized skills and equipment); 2. Create a list of on-going captive marine mammal studies; 3. Produce a list of publications derived from research with captive marine mammals; 4. Develop a set of guidelines for communication, responsibilities, and intellectual ownership for collaborative projects; 5. Implement means for coordination of future studies (both web-based and scheduled workshop/meetings); 6. Design a means for sharing standard Operating Procedures; 7. Hold a workshop to increase statistical rigor and standards in experimental design; 8. Introduce the use of annual survival rates into institutions holding marine mammals; and 9. Heighten the awareness of the value and prevalence of captive studies to the Us Marine Mammal Commission.
Quantification of terrestrial haul-out and rookery characteristics of Steller sea lions. Ban, S. and A.W. Trites. 2007. Marine Mammal Science 23:496-507. abstract Steller sea lions (Eumetopias jubatus)are known to have occupied the same terrestrial haul-out and rookery sites across the North Pacific rim for centuries, but it is not known why they choose and stay at these locations, or what defines their preferred habitat. Classifying and comparing the shoreline type of haulouts and rookeries against sites not used by Steller sea lions showed that they preferentially locate their haulouts and rookeries on exposed rocky shorelines and wave-cut platforms. However, no preference was found for selecting rookeries on sheltered shore-types. Shoreline types used less frequently by sea lions included fine-to-medium-grained sand beaches, mixed sand and gravel beaches, gravel beaches, and sheltered rocky shores. Quantifying the shoreline types used by sea lions confirms anecdotal reports of habitat preferences and may prove useful in identifying and protecting sea lion terrestrial habitat, or in forecasting how climate change might affect the distribution of sea lions.
Testing the generality of the trophic cascade paradigm for sea otters: a case study with kelp forests in northern Washington, USA. Carter, S.K., G.R. VanBlaricom and B.L. Allen. 2007. Hydrobiolgia 579:233-249. abstract Trophic cascade hypotheses for biological communities, linking predation by upper trophic levels to major features of ecological structure and dynamics at lower trophic levels, are widely subscribed and may influence conservation policy. Few such hypotheses have been evaluated for temporal or spatial generality. Previous studies of sea otter (Enhydra lutris predation along the outer coast of North America suggest a pattern, often elevated to the status of paradigm, in which sea otter presence leads to reduced sea urchin (Strongylocentrotus spp.) biomass and rapid increases in abundance and diversity of annual algal species, followed by a decline in diversity as one or a few perennial algal species become dominant. Both sea otter predation and commercial sea urchin harvest are ecologically and economically important sources of urchin mortality in nearshore benthic systems in northern Washington marine waters. We recorded changes in density of macroalgae in San Juan Channel, a marine reserve in the physically protected inland waters of northern Washington, resulting from three levels of experimental urchin harvest: (1) simulated sea otter predation (monthly complete harvest of sea urchins), (2) simulated commercial urchin harvest (annual size-selective harvest of sea urchins), and (3) no harvest (control). The two experimental urchin removal treatments did not significantly increase the density of perennial (Agarum and Laminaria) or annual (Desmarestia, Costaria, Alaria and Nereocystisi) species of macroalgae after 2 years, despite significant and persistent decreases in urchin densities. Our results suggest that other factors such as grazing by other invertebrates, the presence of dense Agarum stands, and recruitment frequency of macroalgae and macroinvertebrates may play a large role in influencing community structure in San Juan Channel and other physically protected marine waters within the range of sea otters.
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.
Quantitative analysis of prey DNA in pinniped faeces: potential to estimate diet composition? Deagle, B.E. and D.J. Tollit. 2007. Conservation Genetics 8:743-747. abstract Recent studies have shown prey DNA can be consistently recovered from faeces and effectively used to provide dietary information. We investigate the possibility of using the relative amounts of DNA recovered from different prey in faeces to obtain quantitative diet composition data. Faecal samples were obtained from captive Steller seas lions (Eumetopias jubatus) being fed a fish diet consisting of 50% Pacific herring (Clupea pallasii), 36% surf smelt (Hypomesus pretiosus) and 14% sockeye salmon (Oncorhynchus nerka) by mass. Quantitative real-time PCR was used to measure the amount of mtDNA from the three fish species in: (i) a blended tissue mix representative of the sea lion diet and (ii) the sea lion faecal samples. The percent composition of fish mtDNA extracted from the undigested tissue samples corresponded reasonably well to the mass of fish in the mixture. In the faecal samples (n = 23) the absolute amount of fish mtDNA recovered varied 100-fold, but the percent composition of the three fish was relatively consistent (57.5 ± 9.3% for herring, 19.3 ± 6.6% for smelt and 23.2 ± 12.2% for salmon). Differences between the mtDNA proportions in the tissue samples compared to the faecal samples indicate there are prey-specific biases in DNA survival during digestion. These biases may be less than those commonly observed in the conventional analysis of prey hard remains. Further investigation of this approach is warranted.
Population trends, diet, genetics, and observations of Steller sea lions in Glacier Bay National Park. Gelatt, T., A.W.Trites, K. Hastings, L. Jemison, K. Pitcher, and G. O’Corry-Crowe. 2007. In J.F. Piatt and S.M. Gende (eds), Proceedings of the Fourth Glacier Bay Science Symposium, U.S. Geological Survey, Juneau , Alaska. pp. 145-149. abstract We are using demographics, scat analysis, and genetic measurements of Steller sea lions (SSLs)to understand the factors affecting population status throughout Alaska. Steller sea lions are listed as threatened throughout Southeast Alaska including Glacier Bay National Park where they frequent at least five terrestrial sites, including a recently established rookery on Graves Rock. Breeding season counts in GBNP increased at ~6 percent/yr between 1989 and 2002. Brand resighting during 2003 revealed 16 western stock SSLs seen within the park. Survival to two months of age was 90 percent. Fifty pups were branded at Graves Rock in 2002. It is necessary to mark more animals to estimate annual survival rates of juveniles and adults. Sandlance and pollock were top prey items at Graves Rock and South Marble Island. Mitochondrial DNA analysis indicates that the Graves Rock rookery was established in part by females from the western sea lion stock (west of 144° W longitude).
Adaptive classification of marine ecosystems: identifying biologically meaningful regions in the marine environment. Gregr, E.J. and K. Bodtker. 2007. Deep-Sea Research Part 1 54:385-402. abstract The move to ecosystem-based management of marine fisheries and endangered species would be greatly facilitated by a quantitative method for identifying marine ecosystems that capture temporal dynamics at meso-scale (10?s or 100?s of kilometers) resolutions. Understanding the dynamics of ecosystem boundaries, which may differ according to the species of interest or the management objectives, is a fundamental challenge of ecosystem-based management. We present an adaptive ecosystem classification that can accommodate these different needs. To demonstrate the approach, we quantitatively bounded distinct, biologically meaningful marine regions in the North Pacific Ocean based on physical oceanography. We identified the regions by applying image classification algorithms to a comprehensive description of the ocean?s surface, derived from an oceanographic circulation model. Our resulting maps illustrate 15 distinct marine regions. We investigated seasonal and long-term c! hanges in the pattern of regions and their boundaries by dividing the oceanographic data into four seasons and two 10-year time periods, one on either side of the 1976 ? 1977 North Pacific Ocean climate regime shift. The size and location of our mapped regions related well to previously described water masses in the North Pacific. We compared our results for each season across the regime shift and for sequential seasons within regimes using the Kappa Index of Agreement and the index of Average Mutual Information. Seasonal patterns were more similar between regimes than from one season to the next within a regime. The magnitude of seasonal transitions also appeared to differ before and after the regime shift. We assessed the biological relevance of the identified regions using seasonal maps derived from remotely sensed chlorophyll-a concentrations ([chl-a]). We used Kruskal-Wallis and Wilcoxon rank sum tests to evaluate the correspondence between the [chl-a] maps and our pos! t-regime shift regions. There was a significant difference in ! [chl-a] among the regions in all seasons. We found that the number of regions with distinct chlorophyll signatures, and the associations between different regions, varied by season. The overall pattern of association between the regions was suggestive of observed, broad-scale patterns in the seasonal development and distribution of primary production in the North Pacific. This demonstrated that regions with different biological properties can be delineated using only physical variables. The flexibility of our approach will enable researchers to visualize the geographic extents of regions with similar physical conditions, providing insight into ocean dynamics and changes in marine ecosystems. It will also provide resource managers with a powerful tool for broad application in ecosystem-based management and conservation of marine resources.
Ecosystem models of the Aleutian Islands and Southeast Alaska show that Steller sea lions are impacted by killer whale predation when sea lion numbers are low. Guénette, S., S.J.J. Heymans, V. Christensen, A.W. Trites. 2007. In J.F. Piatt and S.M. Gende (eds), Proceedings of the Fourth Glacier Bay Science Symposium, U.S. Geological Survey, Juneau , Alaska. pp. 150-154. abstract We constructed ecosystem models using the Ecopath with Ecosim software to evaluate whether predation by killer whales might explain the decline of Steller sea lions since the late 1970s in the western Aleutian Islands. We also sought to understand why sea lions increased in the presence of killer whales in Southeast Alaska. Modeling results reproduced the time series of abundances for exploited species and sea lions in both ecosystems. Simulation results suggest that killer whale predation contributed to the decline of sea lions in the western Aleutians, but that predation was not the primary cause of the population decline. Predation could however have become a significant source of mortality during the 1990s when sea lions numbers were much lower. In Southeast Alaska, predation was also found to be a significant source of mortality in the 1960s when sea lions were low, but ceased to control population growth through the 1980s and 1990s. Overall, the ecosystem models suggest that large populations of Steller sea lions can withstand predation, but that small populations are vulnerable to killer whales.
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.
Comparison of fatty acid profiles of spawning and non-spawning Pacific herring, Clupea harengus pallasi. Huynh, M.D., D.D. Kitts, C. Hu and A.W. Trites. 2007. Journal of Comparative Biochemistry and Physiology, Part B 146:504-511. abstract Crude lipid and fatty acid composition from liver, intestine, roe, milt and flesh of spawning and non-spawning Pacific herring Clupea harengus pallasi were examined to determine the relative effects of spawning on the nutritional value of herring. Depletion of lipid due to spawning condition was significant (Pb0.01) in all organ tissues and flesh of spawning herring. The lipid content ranged from an average of 1.9 to 3.4% (wet weight basis) in different organ tissues of spawning herring, to 10.5 to 16% in non-spawning fish. The fatty acid profile exhibited many differences in the relative distribution of individual fatty acids among organ tissues and between the two fish groups. Oleic acid (C18:1n-9), a major monounsaturated fatty acid (MUFA) found in all tissue lipids, decreased significantly (Pb0.01) in spawning fish. The two monoenes, C20:1n-9 and C22:1n-11, occurred at high concentrations in the flesh but at only minor proportion in the digestive organs and gonads. Spawning herring also had significantly (Pb0.01) higher polyunsaturated fatty acids (PUFA) content in the organ tissues, particularly in the milt and ovary, with docosahexaenoic acid (C22:6n-3, DHA) having the greatest proportion. Among the n-6 fatty acids, only C18:2n-6 and C20:4n-6 occurred at notable amounts and were present in higher proportions in spawning fish. We concluded that although relatively higher n-3 fatty acid content was found in the organ lipids of spawning herring, they are not an energy-dense prey food source due to the fact that both flesh and gonads contain a very low amount of lipid.
Diet quality and season affect physiology and energetic priorities of captive Steller sea lions during and after periods of nutritional stress. Jeanniard du Dot, T. 2007. MSc Thesis, University of British Columbia, Vancouver. 142 pages abstract The ability of animals to contend with unpredictable seasonal shifts in quality and quantity of prey has implications for the conservation of wildlife. Steller sea lions (Eumetopias jubatus) were subjected to different quantities and qualities of food to determine what physiological and endocrine responses would occur and whether they differed between season (summer and winter) or diet (high-lipid Pacific herring Clupea pallasi vs. low-lipid walleye pollock Theragra chalcogramma). Eight females were divided among two groups. One (Group H) were fed herring for 28 days (baseline), then received a reduced caloric intake for a subsequent 28 days (restriction) to induce a 15% loss of body mass. The second (Group P) were also fed herring during the baseline followed by a reduced isocaloric diet of pollock during the restriction. Both groups subsequently returned to their baseline intake of herring for a 28-day controlled re-feeding. The two groups of sea lions lost identical mass during restrictions independent of species eaten, but did differ in the type of internal energy reserve (protein vs. lipids) they predominantly used. Group H lost significantly more lipids and less lean mass than Group P in both seasons. In summer, Group H also increased activity levels and decreased thermoregulation capacity to optimize energy allocation. No such changes were observed for Group P whose capacity to adjust to the reduced caloric intake seemed to have been blocked by the pollock diet. During winter, the sea lions spared energy allocated to activity (especially Group H) and preserved thermoregulation capacity. Changes in body mass was negatively related to free cortisol and positively related to IGF-1 in winter, but only IGF-1 was related to changes in mass in summer when lean mass regulation seemed more important. Levels of IGF-1 were associated with changes in protein metabolism in both seasons for both groups, but changes in body condition were never explained by the measured metabolites or hormones. The cap! acity to compensate for mass loss was seasonally dependent with sea lions displaying compensatory growth (by restoring lipid stores) in winter but not in summer. Summer appears to be a more difficult season for sea lions to recover from mild nutritional stress. These physiological findings can be used to refine bioenergetic models needed for the conservation of Steller sea lion populations.
Ecotypic variation and predatory behavior among killer whales (Orcinus orca) off the eastern Aleutian Islands, Alaska. Matkin, C., L.G. Barrett-Lennard, H.Yurk, D. Ellifrit, and A.W. Trites. 2007. Fishery Bulletin 105:74-87. abstract From 2001 to 2004 in the eastern Aleutian Islands, Alaska, killer whales (Orcinus orca) were encountered 250 times during 421 days of surveys that covered a total of 22,491 miles. Three killer whale lineages (resident, transient, and offshore) were identified acoustically and genetically. Resident killer whales were found 12 times more frequently than transient killer whales, while offshore killer whales were only encountered once. A minimum of 901 photographically-identified resident whales used the region during our study. A total of 165 mammal-eating transient killer whales were identified, with the majority (70%) encountered during spring (May and June). The diet of transient killer whales in spring was primarily gray whales (Eschrichtius robustus), while northern fur seals (Callorhinus ursinus) were primary prey in summer. Steller sea lions (Eumetopias jubatus) did not appear to be a preferred prey or major prey item during spring and summer. The majority of killer whales in the eastern Aleutian Islands are the resident ecotype, which do not consume marine mammals.
Killer whale feeding ecology and non-predatory interactions with other marine mammals in the Glacier Bay a region of Alaska. Matkin, D.R., J.M. Straley, and C.M. Gabriele. 2007. In J.F. Piatt and S.M. Gende (eds), Proceedings of the Fourth Glacier Bay Science Symposium, U.S. Geological Survey, Juneau , Alaska. pp. 155-158. abstract Populations of killer whales in southeastern Alaska overlap with populations inhabiting Prince William Sound, Alaska and British Columbia, Canada. We synthesize the results of a 20-year study in Glacier Bay and Icy Strait, Alaska. Individuals were photo-identified and predation events documented. Foraging strategies of killer whales were compared to those documented in similar studies in adjacent areas. One hundred twenty of the resident form of killer whales, 150 of the West Coast transients, 13 of the Gulf of Alaska transients and 14 of the offshore form were photo-identified in the study area. Residents preyed primarily on silver salmon and Pacific halibut. The prey of transients were harbor seals (40 percent), harbor porpoise(23 percent), Steller sea lions (16 percent), seabirds (14 percent), Dall’s porpoise (5 percent) and minke whale (2 percent). Humpback whales were observed closely approaching transient groups that were attacking other marine mammals. Nonpredatory interactions also occurred between killer whales and Steller sea lions.
Utilization of stored energy reserves during fasting varies by age and season in Steller sea lions. Rea, L.D., D.A.S. Rosen and A.W Trites. 2007. Canadian Journal of Zoology 85:190-200. abstract Nine captive Steller sea lions (Eumetopias jubatus (Schreber, 1776), 1.75–6 years of age) were fasted for 7–14 d to test the effect of short-term fasting on changes in body mass and body condition. Trials were repeated during both the summer breeding season and the nonbreeding season in seven animals to elucidate whether there was a seasonal component to the ability of Steller sea lions to adapt to limited food resources. Mean percent mass loss per day was higher during the breeding season in juveniles (1.8% ± 0.2%·d–1) than in subadults (1.2% ± 0.1%·d–1), but there were no significant age-related differences during the nonbreeding season (juveniles, 1.5% ± 0.3%·d–1; subadults, 1.7% ± 0.3%·d–1). A decrease in the rate of mass loss occurred after the first 3 d of fasting only in subadults during the breeding season. Percent total body lipid ranged from 11% to 28% of total body mass at the initiation of fasting trials. Animals with lower initial percent total body lipid exhibited higher subsequent rates of mass loss and a lower percentage of tissue catabolism derived from lipid reserves. There was no evidence of metabolic adaptation to fasting in juveniles, which suggests that juvenile sea lions would be more negatively impacted by food limitation during the breeding season than would subadults.
Thermal and digestive constraints to foraging behavior in marine mammals. Rosen, D.A.S., A.J. Winship, and L.A. Hoopes. 2007. Philosophical Transactions, Royal Society of London B 362:2151-2168. abstract While foraging models of terrestrial mammals are concerned primarily with optimizing time/energy budgets, models of foraging behavior in marine mammals have been primarily concerned with physiological constraints. This has historically centered on calculations of aerobic dive limits. However, other physiological limits are key to forming foraging behavior, including digestive limitations to food intake and thermoregulation. The ability of an animal to consume sufficient prey to meet its energy requirements is partly determined by its ability to acquire prey (limited by available foraging time, diving capabilities and thermoregulatory costs) and to process that prey (limited by maximum digestion capacity and the time devoted to digestion). Failure to consume sufficient prey will have feedback effects on foraging, thermoregulation, and digestive capacity through several interacting avenues. Energy deficits will be met through catabolism of tissues, principally the hypodermal lipid layer. Depletion of this blubber layer can affect both buoyancy and gait, increasing the costs and decreasing the efficiency of subsequent foraging attempts. Depletion of the