abstract
Variation in concentrations of thyroid hormones shed in feces may help to identify physiological states of animals, but the efficacy of the technique needs to be validated for each species. We determined whether a known physiological alteration to thyroid hormone production was reflected in hormone concentrations in the feces of Steller sea lions (Eumetopias jubatus). We quantified variation of triiodothyronine (T3) and thyroxine (T4) concentrations in feces following two intramuscular injections of thyrotropin (thyroid-stimulating hormone, TSH) at 24 h intervals in four captive female sea lions. We found fecal T3 concentrations increased 18-57% over concentrations measured in the baseline sample collected closest to the time of the first TSH injection (p=0.03) and 1-75% over the mean baseline concentration (p=0.12) for each animal of all samples collected prior to injections. The peak T3 response occurred 48 h post injection in three animals and 71 h in the fourth. Post-injection T4 concentrations did not differ between the baseline sample collected closest to the time of the first TSH injection (p=0.29) or the mean baseline concentration (p=0.23) for each animal. These results indicate that induced physiological alterations to circulating thyroid hormone concentrations can be adequately detected through analyses of fecal T3 concentrations and that the technique may provide a means of non-invasively detecting metabolic changes in Steller sea lions.

abstract
Fluctuations in availability of prey resources can impede acquisition of sufficient energy for maintenance and growth. By investigating the hormonal mechanisms of the somatotropic axis that link nutrition, fat metabolism, and lean tissue accretion, we can assess the physiological impact of decreased nutrient intake on growth. Further, species that undergo seasonal periods of reduced intake as a part of their normal life history may have a differential seasonal response to nutrient restriction. This experiment evaluated the influence of season and age on the response of the somatotropic axis, including growth hormone (GH), insulin-like growth factor (IGF)-I, and IGF-binding proteins (BP), to reduced nutrient intake and re-alimentation in Steller sea lions. Eight captive females (five juveniles, three sub-adults) were subject to 28-day periods of food restriction, controlled re-feeding, and ad libitum recovery in summer (long-day photoperiod) and winter (short-day photoperiod). Hormone concentrations were insensitive to type of fish fed (low fat pollock vs. high fat herring), but sensitive to energy intake. Body mass, fat, and IGF-I declined, whereas GH and IGFBP-2 increased during feed restriction. Reduced IGF-I and IGFBP with increased GH during controlled re-feeding suggest that animals did not reach positive energy balance until fed ad libitum. Increased IGF-I, IGFBP-2, IGFBP-3, and reduced GH observed in summer reflected seasonal differences in energy partitioning. There was a strong season and age effect in the response to restriction and re-alimentation, indicating that older, larger animals are better able to cope with stress associated with energy deficit, regardless of season.

abstract
We attached accelerometers to the head and jaw of a Steller sea lion (Eumetopias jubatus) to determine whether feeding attempts in a controlled setting could be quantified by acceleration features characteristic of head and jaw movements. Most of the 19 experimental feeding events that occurred during the 51 dives recorded resulted in specific acceleration patterns that were clearly distinguishable from swimming accelerations. The differential acceleration between the head-mounted and jaw-mounted accelerometers detected 84% of prey captures on the vertical axis and 89% on the horizontal axis. However, the jaw-mounted accelerometer alone proved to be equally effective at detecting prey capture attempts. Acceleration along the horizontal (surge)-axis appeared to be particularly efficient in detecting prey captures, and suggests that a single accelerometer placed under the jaw of a pinniped is a promising and easily implemented means of recording prey capture attempts.

abstract
Stable isotope analysis is often used to examine diet choice and tropic relationships in marine mammals. However, the technique makes a number of largely untested assumptions. For example, researchers often assume localized biopsies to be representative of the whole animal—that is, that the isotopic signal is homogenous within a tissue. Further, isotopic composition may differ across the body within the same tissue type due to differential assimilation or catabolization rates. We investigated the homogeneity of 13C and 15N values in skin and muscle across the body per individual in three pinniped species: Steller sea lions (Eumetopias jubatus, n = 5), California sea lions (Zalophus californianus, n = 6), and harbor seals (Phoca vitulina, n = 7). We also assessed if there are consistent carbon and nitrogen isotope differences between these two commonly sampled tissues. Our results show that skin tissue was significantly 13C enriched when compared to muscle tissue, and more difficult to properly process. Despite expected differences across the body in physiological processes and biochemical composition, our data indicate stable isotope signal homogeneity across the body within both muscle and skin, for both carbon and nitrogen isotopes, in all three species. These results indicate that sufficient homogeneity exists within skin and muscle tissues to suggest that point sampling can be considered representative of entire tissues, and is thus a valid technique in stable isotope studies of marine mammals.

abstract
Morphometric measurements and daily feeding records of 62 captive Steller sea lions (Eumetopias jubatus) were analyzed to provide information about seasonal growth and food consumption that has been impossible to collect from wild animals. Data from nursing pups, intact and castrated males, pregnant, lactating and non-reproductive females were also used to determine differences in rates of maturity between males and females, and the effects that climate, sexual maturity, castration and pregnancy and lactation have on growth and food intake. Data were fit with seasonal (sine function) and annual (von Bertalanffy, logistic, Gompertz, Richard’s and maturity) growth models, and showed that males achieved larger body sizes than females by undergoing a growth spurt during puberty and by extending their growth throughout adulthood. Annual increases in the length and mass of females slowed significantly following sexual maturity. Males and females both experienced seasonal oscillations in body mass, but the seasonal fluctuation in male mass peaked later (April) and was far more dramatic than that of females. The mass of lactating and non-reproductive females peaked in early spring (March), while increases in the mass of pregnant females paralleled fetal growth, reaching a maximum before parturition. Changes in mass did not parallel changes in consumption. Fish intake by males and females peaked during winter and bottomed during late spring, while seasonal changes in body mass reached their high and low 3 to 4 months later than food intake. Pregnant and non-reproductive females differed little in the amount of prey they consumed, unlike lactating females that significantly increased their consumption during summer and winter. The differences between females highlight the relatively low additional energetic requirements of pregnancy and the high costs of lactation. Differences between neutered and intact males further suggest that testosterone affected overall male growth, but had smaller effects of seasonal oscillations in mass and did not affect food intake. The reproductive cycle and thermoregulatory requirements appeared to drive seasonal changes in body mass and food intake of male and female Steller sea lions but at different time scales. Our findings also indicate that mass is not a simple reflection of food intake, which has important implications for future nutritional research and bioenergetic modeling of wild pinnipeds.

abstract
Determining diets of pinnipeds by visually identifying prey remains recovered in faecal samples is challenging because of differences in digestion and passage rates of hard parts. Analyzing the soft matrix of fecal material using DNA-based techniques is an alternative means to identify prey species consumed, but published techniques are largely non-quantitative, which limits their applicability. I developed and validated a real-time PCR technique using species-specific mitochondrial DNA primers to quantify the diets of Steller sea lions (Eumetopias jubatus). I first demonstrated that the proportions of prey tissue DNA in mixtures of DNA isolated from four prey species could be estimated within a margin of ~12% of the percent in the mix. These prey species included herring Clupea palasii, eulachon Thaleichthyes pacificus, squid Loligo opalescens and rosethorn rockfish Sebastes helvomaculatus. I then applied real-time PCR to DNA extracted from faecal samples obtained from Steller sea lions that had been fed 11 different combinations of herring, eulachon, squid and Pacific ocean perch rockfish (Sebastes alutus), ranging from 7-75% contributions to a meal mix (by wet weight). The difference between the average percentage estimated by real-time PCR and the percentage of prey consumed was generally less than 12% for all diets fed when percentages of prey consumed were corrected for differences in mtDNA density among the prey items. My findings indicate that real-time PCR can detect the quantity of prey consumed for a variety of complex diets and prey species, including cephalopods and fish.

abstract
hirty-six aluminum oxide laminated discs were implanted into 12 young rabbits (18 with a 0.5 mm porous layer and 18 with 1 mm) to determine whether implants that are porous only on one side could fixate to subcutaneous tissue. After 3 months, discs were encased within thin pouches (0.02-0.14 mm) of fibrous connective tissue, as would have been expected of a completely porous implant. Solid sides showed no while the porous sides showed little attachment to pouches. 47% (17) of the discs had moved 1.4±0.8 cm beyond the 4.7 + 1 cm they had moved due to normal skin growth, while two others had moved between 6.2 and 6.5 cm beyond this measure. The proportion of 1 mm porous layer discs migrating within subcutaneous tissue was no greater than the proportion of 0.5 mm layer discs migrating (p=0.15). Porous layer height and disc migration did not affect the attachment strength of pouch to surrounding tissues (68 ±23 N, p=0.34). Pouch thickness, which has been associated to the level of applied forces in other studies, increased with migration distance (p=0.054). Results indicate that one sided porous disks are likely easier to retrieve than completely porous ones, but cannot be prevented from migrating in loose tissue of young animals. Data is being used to design subdermal radio frequency devices for endangered marine animals.

abstract
Physiological responses to changes in energy balance are tightly regulated by the endocrine system through glucocorticoids, IGF-I and thyroid hormones. Changes in these hormones were studied in eight captive female Steller sea lions that experienced changes in food intake, body mass, body composition, and blood metabolites during summer and winter. During a period of energy restriction, one group of sea lions was fed reduced amounts of Pacific herring and another was fed an isocaloric diet of walleye pollock, after which both groups returned to their pre-experimental diets of herring. Cortisol was negatively and IGF-I was positively associated with changes in body mass during periods of energy restriction (mass loss associated with increase in cortisol and decrease in IGF-I) and refeeding (body mass maintenance associated with stable hormone concentrations in summer and compensatory growth linked to decrease in cortisol and increase in IGF-I in winter). Cortisol and IGF-I were also correlated with changes in lipid and lean mass, respectively. Consequently, these two hormones likely make adequate biomarkers for nutritional stress in sea lions, and when combined provide indication of the energetic strategy (lipid vs lean mass catabolism) animals adopt to cope with changes in nutrient intake. Unlike type of diet fed to the sea lions, age of the animals also impacted hormonal responses, with younger animals showing more intense hormonal changes to nutritional stress. Thyroid hormones, however, were not linked to any physiological changes observed in this study.

abstract
Two groups of female Steller sea lions (Groups H and P) were subjected to periods of energy restriction and subsequent re-feeding during winter and summer to determine changes in energy partition among principal physiological functions and the potential consequences to their fitness. Both sea lion groups consumed high-quality fish (herring) before and after the energy restrictions. During restrictions, Group H was fed a lower quantity of herring and Group P a caloric equivalent of low-quality fish (pollock). Quantitative estimates of maintenance and production energies and qualitative estimates of thermoregulation, activity and basal metabolic rate were measured. During summer, all animals compensated for the imposed energy deficit by releasing stored energy (production energy). Group H also optimized the energy allocation to seasonal conditions by increasing activity during summer when fish are naturally abundant (foraging effort) and by decreasing thermoregulation capacity when waters are warmer. During winter, both groups decreased the energy allocated to overall maintenance functions (basal metabolic rate, thermoregulation and activity together) in addition to releasing stored energy, but preserved thermoregulatory capacity. Group H also decreased activity levels in winter when foraging in the wild is less efficient, unlike Group P. Overall, sea lions fed pollock did not change energy allocation to suit environmental conditions as readily as those fed herring. This implies that low energy density diet may further reduce fitness of animals in the wild during periods of nutritional stress.

abstract
Reduced availability of high energy-content prey (nutritional stress) is a predominant hypothesis to explain the decline of Steller sea lion (Eumetopias jubatus) populations in western Alaska from the late 1970's to the late 1990's. Animals may respond to eating insufficient prey by increasing stress levels and decreasing metabolic rates. It may thus be possible to identify nutritional stress by measuring concentrations of GC metabolites (stress) and thyroid hormones (metabolism) shed in the feces of Steller sea lions. However, techniques to measure thyroid hormone concentrations from sea lion feces have not been developed. We quantified variation of triiodothyronine (T3) and thyroxine (T4) concentrations in Steller sea lion feces following two injections of thyrotropin (TSH) at 24 h intervals into four captive animals. Glucocorticoid (GC) metabolites were also assayed to examine any relationship to stimulated thyroid hormone secretion. We found that fecal T3 peaked 48 h post-injection and increased 25-57% in three sea lions (all animals, p=0.03). Pre-injection GC increases indicated stress from isolation for baseline fecal collections, but post-injection increases could not be confirmed as a response to TSH injections or as a product of the study design. The results demonstrated that pre- and post-injection changes in fecal GC and T3 concentrations were consistent with predictions of an increased stress response and metabolic rate within the animals. We then measured T3 and GC concentrations in 834 Steller sea lion fecal samples collected in 2005 and 2006 from 15 resting (haulout) and breeding (rookery) sites between British Columbia and the Central Aleutian Islands. Overall, GC concentrations did not differ between haulout populations (western 2006 pre-pupping and eastern 2005 post-pupping). Fecal hard-part analyses revealed a lower energy-content diet in the western population, suggesting that diet quality is a relevant hypothesis to explain slightly higher GC concentrations found in the western population, specifically the Aleutian Islands region. However, the nutritional stress hypothesis could not be substantiated through T3 concentrations. The rookeries possessed the highest energy-content diets, but also exhibited a nutritional stress response with a significantly higher GC and lower T3 concentration than either haulout population (possibly related to lactation or decreased leptin levels), but T3 comparisons performed at scales of site and region were inconclusive.

abstract
Nine Steller sea lions (Eumetopias jubatus) aged 1.756 yr were experimentally fasted for 714 d during the breeding and nonbreeding seasons to identify changes in plasma metabolites that are indicative of fasting and to determine whether the ability of sea lions to fast varies seasonally or with age. Although some animals approached the limit of their protein-sparing ability by the end of our fasting experiments, there was no sign of irreversible starvation biochemistry. Plasma blood urea nitrogen (BUN) concentrations decreased in all animals within the first week of fasting, reflecting a shift to a fasting-adapted state; however, significant increases in plasma BUN concentration at the end of the nonbreeding season fasts suggest that subadult Steller sea lions were not able to maintain a protein-sparing metabolism for a full 14 d during the nonbreeding season. In contrast, juveniles were able to enter protein sparing sooner during the nonbreeding season when they had slightly higher initial percent total body lipid stores than during the breeding season. Subadult and juvenile sea lions had low circulating ketone body concentrations compared with young sea lion pups, suggesting an age-related difference in how body reserves are utilized during fasting or how the resulting metabolites are circulated and catabolized. Our data suggest that metabolite concentrations from a single blood sample cannot be used to accurately predict the duration of fast; however, threshold metabolite concentrations may still be useful for assessing whether periods of fasting in the wild are unusually long compared with those normally experienced.

abstract
1. Numbers of Steller sea lions Eumetopias jubatus in the North Pacific have declined. According to the Nutritional Stress Hypothesis, this decline is due to reduced food availability. Data from studies conducted on pinnipeds in the laboratory are used here to test whether the Nutritional Stress Hypothesis can explain the decline of Steller sea lions. 2. Overall, there is strong evidence for biologically meaningful differences in the nutritional quality of major prey species. Steller sea lions can partly compensate for low-quality prey by increasing their food consumption. 3. There appear to be no detrimental effects of low-lipid prey on sea lion growth or body composition when sea lions can consume sufficient quantities of prey. However, the ability to increase consumption is physiologically limited, particularly in young animals. Overall, it is more difficult to maintain energy intake on a diet of low-quality prey than on a normal diet. 4. Under conditions of inadequate food intake (either due to decreased prey availability or quality, or increased energy requirements) the overall impacts of nutritional stress are complex, and are dependent upon season, prey quality, age, and the duration and intensity of the nutritional stress event. 5. Studies on pinnipeds in the laboratory have been instrumental in identifying the conditions under which changes in sea lion prey can result in nutritional stress, and the nature of the physiological impacts of nutritional stress events.

abstract
We hypothesized that: (1) Steller sea lion Eumetopias jubatus diet choice is a function of prey availability, (2) sea lions move to take advantage of times and locations of seasonal prey concentrations and (3) the number present depends on the amount of prey available (numerical response). Over 3 yr, typically on a quarterly basis, in Frederick Sound, SE Alaska, multiple measurements were taken of Steller sea lion abundance (aerial surveys), diet (scats), dive behavior (satellite telemetry)and prey availability and caloric density (nearshore, pelagic and demersal fish surveys). We found that Steller sea lions shifted diet composition in response to changes in prey availability of pollock Theragra chalcogramma, hake Merluccius productus, herring Clupea pallasi and salmon Oncorhynchus spp. They selected intermediate-sized fish and avoided small (<10 cm) and large (>60 cm) fish, and moved between areas as prey became available seasonally. The number of sea lions present depended on the amount of prey available; a standing biomass of 500 to 1700 t of prey in a nonbreeding area such as Frederick Sound, depending on species composition, can attract and sustain about 500 sea lions. Pollock was more frequent in sea lion diet in inside waters of SE Alaska including Frederick Sound, Stephens Passage and Lynn Canal than anywhere else in Alaska and contributed about one-third of the dietary energy in Frederick Sound. This finding implies that a diet with substantial year-round contributions from less nutritious, but abundant prey such as pollock can form part of a healthy diet as long as more nutritious prey such as herring, salmon or eulachon Thaleichthys pacificus also are consumed. Our study supports the conclusion that the Steller sea lion is an opportunistic marine predator with a flexible foraging strategy that selects abundant, accessible prey and shifts among seasonally available species.

abstract
Changes in metabolic rates were measured in 3 captive female Steller sea lions (Eumetopias jubatus) that experienced fasts during summer and winter. Metabolic rates were measured (via O₂ consumption) before (MRs, surface) and after (DMR, dive + surface interval) the sea lions dove to 10–50 m depths. Measurements were obtained prior to 9-10 day fasts, and following a 14 day recovery period. The sea lions lost significantly more body mass (M_b) during the winter fast (10.6%), compared with the summer (9.5%). Mass-corrected dive metabolic rate (_cDMR = DMR • M_b^-0.714) was not affected by dive depth or duration, but increased significantly following the winter fasts (13.5 ± 8.1%), unlike the decrease during summer (-1.1 ± 3.2%). However, mass-corrected surface metabolic rate (_cMR_s) decreased significantly after both the summer (-16.4 ± 4.7%) and winter (-8.0 ± 9.0%) fasts. Consequently, the ratio between _cDMR and _cMR_c was significantly higher in winter, suggestive of an increased thermal challenge and convective heat loss while diving. Increased _cDM_s following the fast indicated that digestion began during foraging and was not deferred, implying that access to ingested energy was of higher priority than optimizing diving ability. _cDMR was elevated throughout the recovery period, independent of season, resulting in a 12% increase in foraging cost in winter and a 3% increase in summer. Our data suggest that Steller sea lions are more sensitive to changes in body condition due to food shortages in the winter compared with the summer.

abstract
Polymerase chain reaction techniques were developed and applied to identify DNA from >40 species of prey contained in fecal (scat) soft part matrix collected at terrestrial sites used by Steller sea lions (Eumetopias jubatus) in British Columbia and the Eastern Aleutian Islands, Alaska. Sixty percent more fish and cephalopod prey were identified by morphological analyses of hard parts compared with DNA analysis of soft parts (hard parts identified higher relative proportions of Ammodytes sp., Cottidae and certain Gadidae). DNA identified 213 prey occurrences of which 75 (35%) were undetected by hard parts (mainly Salmonidae, Pleuronectidae, Elasmobranchii and Cephalopoda), and thereby increased species occurrences by 22% overall and species richness in 44% of cases (when comparing 110 scats that amplified prey DNA). Prey composition was identical within only 20% of scats. Overall, diet composition derived from both identification techniques combined did not differ significantly from hard part identification alone, suggesting that past scat-based diet studies have not missed major dietary components. However, significant differences in relative diet contributions across scats (as identified using the two techniques separately) reflect passage rate differences between hard and soft digesta material and highlight certain hypothesized limitations in conventional morphological-based methods (e.g., differences in resistance to digestion, hard part regurgitation, partial and secondary prey consumption), as well as potential technical issues (e.g., resolution of primer efficiency and sensitivity, and scat subsampling protocols). DNA analysis of salmon occurrence (from scat soft part matrix and 238 archived salmon hard parts) provided species-level taxonomic resolution that could not be obtained by morphological identification, and showed that Steller sea lions were primarily consuming pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. Notably, DNA from Atlantic salmon (Salmo salar) that likely originated from a distant fish farm was also detected in two scats from one site in the Eastern Aleutian Islands. Overall, molecular techniques are valuable for identifying prey in the fecal remains of marine predators. Combining DNA and hard part identification will effectively alleviate certain predicted biases, and will ultimately enhance measures of diet richness, fisheries interactions (especially salmon related ones) and the ecological role of pinnipeds and other marine predators, to the benefit of marine wildlife conservationist and fisheries managers.

abstract
We developed methods to estimate the spatial variation in economic values of ocean fisheries, and applied the methods to estimate the cost of closing groundfish fisheries in Steller sea lion Critical Habitat in the Bering Sea and Gulf of Alaska. The research addressed two related goals: (1) explicitly linking spatial variability of fisheries biomass and profitability over time to environmental variables; and (2) developing estimates of opportunity costs of time and area closures to the fishing industry at scales relevant to management. The approach involved two stages of statistical analyses. First, environmental conditions measured at 3 km and 9 km spatial scales and two-week and one-month intervals were used to predict fish biomass and fisheries catch per unit of effort (CPUE). Environmental variables included bathymetry, remotely sensed physical and biological observations, and output from a physical oceanographic circulation model. Second, we used predicted CPUE and spatial regulatory and cost factors to explain the spatial distribution of fishing effort over time. Our results suggested that 2001 Critical Habitat closures cost the North Pacific groundfish trawl fisheries 5-40 percent of their total potential net earnings. The improved methods for estimating opportunity costs of fisheries closures we present have direct applications to evaluating boundary changes to marine protected areas and other spatial management decisions. Limitations include the extensive data requirements and the need to bootstrap confidence intervals. If further research demonstrates the robustness and stability of the estimated relationships over time, the methods could project spatial fishery effects of climate variability and change, leading to dynamic spatial models linking fisheries with ecosystems.

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 (MR_S) when dive duration increased from 1 to 7 min. Overall, these data suggest that DMR is almost the same as MR_S, 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.

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.

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.

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.

abstract
Controlled feeding experiments were undertaken with captive Steller sea lions (Eumetopias jubatus) to assess seasonal (winter vs. summer) physiological responses of individual animals to reduced quantities and qualities of food that are hypothesised to occur in the wild. Eight animals were randomly divided into two experimental groups fed isocaloric diets: Group H ate Pacific herring (Clupea pallasi) throughout the experiment while Group P was switched to walleye pollock (Theragra chalcogramma) during a 28-day food restriction (after a 28-day baseline) and back to herring during a 28-day controlled re-feeding. Diet type did not impact the rates of body mass lost when food was restricted, but did influence the type of internal energy reserve (protein vs lipids) the sea lions predominantly used. In both summer and winter, Group H lost significantly more lipids and less lean mass than Group P that was fed pollock during the restriction phase. The response of Group H was consistent with the predicted pattern of nutritional stress physiology (i.e. protein sparing and utilization of lipid reserves). Group P lost a surprisingly high proportion of body protein while consuming restricted levels of pollock, which could lead to muscle impairment and vital organ failure on a long-term basis. When given increased amounts of herring during the controlled re-feeding phase, the capacity of both groups to compensate for the previous mass loss was found to depend on season and was independent of previous diet. All of the sea lions increased their rates of mass gain and returned to their pre-experimental weight during winter, but not during summer. Some intrinsic energetic plasticity related to seasonal adaptation to the environment may render winter an easier period than summer to recover from nutritional stress.

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.

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.

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.

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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Recent studies have shown prey DNA can be consistently recovered from faeces and effectively used to provide dietary information. We investigate the possibility of using the relative amounts of DNA recovered from different prey in faeces to obtain quantitative diet composition data. Faecal samples were obtained from captive Steller seas lions (Eumetopias jubatus) being fed a fish diet consisting of 50% Pacific herring (Clupea pallasii), 36% surf smelt (Hypomesus pretiosus) and 14% sockeye salmon (Oncorhynchus nerka) by mass. Quantitative real-time PCR was used to measure the amount of mtDNA from the three fish species in: (i) a blended tissue mix representative of the sea lion diet and (ii) the sea lion faecal samples. The percent composition of fish mtDNA extracted from the undigested tissue samples corresponded reasonably well to the mass of fish in the mixture. In the faecal samples (n = 23) the absolute amount of fish mtDNA recovered varied 100-fold, but the percent composition of the three fish was relatively consistent (57.5 ± 9.3% for herring, 19.3 ± 6.6% for smelt and 23.2 ± 12.2% for salmon). Differences between the mtDNA proportions in the tissue samples compared to the faecal samples indicate there are prey-specific biases in DNA survival during digestion. These biases may be less than those commonly observed in the conventional analysis of prey hard remains. Further investigation of this approach is warranted.

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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).

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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.

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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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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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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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Crude lipid and fatty acid composition from liver, intestine, roe, milt and flesh of spawning and non-spawning Pacific herring Clupea harengus pallasi were examined to determine the relative effects of spawning on the nutritional value of herring. Depletion of lipid due to spawning condition was significant (Pb0.01) in all organ tissues and flesh of spawning herring. The lipid content ranged from an average of 1.9 to 3.4% (wet weight basis) in different organ tissues of spawning herring, to 10.5 to 16% in non-spawning fish. The fatty acid profile exhibited many differences in the relative distribution of individual fatty acids among organ tissues and between the two fish groups. Oleic acid (C18:1n-9), a major monounsaturated fatty acid (MUFA) found in all tissue lipids, decreased significantly (Pb0.01) in spawning fish. The two monoenes, C20:1n-9 and C22:1n-11, occurred at high concentrations in the flesh but at only minor proportion in the digestive organs and gonads. Spawning herring also had significantly (Pb0.01) higher polyunsaturated fatty acids (PUFA) content in the organ tissues, particularly in the milt and ovary, with docosahexaenoic acid (C22:6n-3, DHA) having the greatest proportion. Among the n-6 fatty acids, only C18:2n-6 and C20:4n-6 occurred at notable amounts and were present in higher proportions in spawning fish. We concluded that although relatively higher n-3 fatty acid content was found in the organ lipids of spawning herring, they are not an energy-dense prey food source due to the fact that both flesh and gonads contain a very low amount of lipid.

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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.

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Nine captive Steller sea lions (Eumetopias jubatus (Schreber, 1776), 1.75–6 years of age) were fasted for 7–14 d to test the effect of short-term fasting on changes in body mass and body condition. Trials were repeated during both the summer breeding season and the nonbreeding season in seven animals to elucidate whether there was a seasonal component to the ability of Steller sea lions to adapt to limited food resources. Mean percent mass loss per day was higher during the breeding season in juveniles (1.8% ± 0.2%·d–1) than in subadults (1.2% ± 0.1%·d–1), but there were no significant age-related differences during the nonbreeding season (juveniles, 1.5% ± 0.3%·d–1; subadults, 1.7% ± 0.3%·d–1). A decrease in the rate of mass loss occurred after the first 3 d of fasting only in subadults during the breeding season. Percent total body lipid ranged from 11% to 28% of total body mass at the initiation of fasting trials. Animals with lower initial percent total body lipid exhibited higher subsequent rates of mass loss and a lower percentage of tissue catabolism derived from lipid reserves. There was no evidence of metabolic adaptation to fasting in juveniles, which suggests that juvenile sea lions would be more negatively impacted by food limitation during the breeding season than would subadults.

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Abstract: Nine prey species (n = 7,431) were fed to four captive female Steller sea lions (Eumetopias jubatus (Schreber, 1776)) in eleven feeding trials over 75 days to investigate the effectiveness of different methods used to determine diet from prey hard remains. Trials aimed to replicate short (1-2 day) and long feeding bouts and consisted of single species and mixed daily diets. Overall, an average of 25.2% ± 22.2% (mean ± SD, range 0-83%) of otoliths were recovered, but recovery rates varied by species (ANOVA, P = 0.01) and were linearly related to otolith robustness (R2 = 0.88). Squid beaks were recovered at higher frequencies (mean = 96%) than the otoliths of all species. Enumerating both non-otolith skeletal structures and otoliths (together termed ?bones?) increased species recovery rates by twofold on average (P < 0.001), with increases up to 2.5 times for herring and 3-4 times for salmonids. Using bones reduced inter-specific differences (P = 0.08), but recovery ! varied among sea lions. Bones were distributed over more scats per meal (mean = 2.9 scats, range = 0-5) than otoliths (mean = 1.9 scats, range = 0-4). In three different 15-day mixed diet trials, biomass reconstruction (BR) indices performed better than frequency of occurrence indices in predicting diet fed. Applying our experimentally derived numerical correction factors (to account for species differences in complete prey digestion) further improved BR estimates, resulting in all twelve unweighted comparisons within 5% (for otoliths) and 12% (for bones) of the actual diet fed.

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Declines of Steller sea lion (Eumetopias jubatus) populations in the Aleutian Islands and Gulf of Alaska could be a consequence of physical oceanographic changes associated with the 1976-77 climate regime shift. Changes in ocean climate are hypothesized to have affected the quantity, quality and accessibility of prey, which in turn may have affected the rates of birth and death of sea lions. Recent studies of the spatial and temporal variations in the ocean climate system of the North Pacific support this hypothesis. Ocean climate changes appear to have created adaptive opportunities for various species that are preyed upon by Steller sea lions at mid-trophic levels. The east-west asymmetry of the oceanic response to climate forcing after 1976-77 is consistent with both the temporal aspect (populations decreased after the late 1970's) and the spatial aspect of the decline (western, but not eastern, sea lion populations decreased). These broad-scale climate variations appear to be modulated by regionally sensitive biogeographic structures along the Aleutian Islands and Gulf of Alaska, which include a transition point from coastal to open-ocean conditions at Samalga Pass westward along the Aleutian Islands. These transition points delineate distinct clusterings of different combinations of prey species, which are in turn correlated with differential population sizes and trajectories of Steller sea lions. Archaeological records spanning 4000 years further indicate that sea lion populations have experienced major shifts in abundance in the past. Shifts in ocean climate are the most parsimonious underlying explanation for the broad suite of ecosystem changes that have been observed in the North Pacific Ocean in recent decades.

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The hypothesis that commercial whaling caused a sequential megafaunal collapse in the North Pacific Ocean by forcing killer whales to eat progressively smaller species of marine mammals is not supported by what is known about the biology of large whales, the ecology of killer whales and the patterns of ecosystem change that took place in Alaska, British Columbia, and elsewhere in the world following whaling. A comparative analysis shows that populations of seals, sea lions and sea otters increased in British Columbia following commercial whaling, unlike the declines noted in the Gulf of Alaska and Aleutian Islands. The declines of seals and sea lions that began in western Alaska around 1977 were mirrored by increases in numbers of these species in British Columbia. A more likely explanation is the seal and sea lion declines and other ecosystem changes in Alaska stems from a major oceanic regime shift that occurred in 1977. Killer whales are unquestionably a significant predator of seals, sea lions and sea otters but not because of commercial whaling.

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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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Distributions of fish species were compared with diet information for Steller sea lions (Eumetopias jubatus) to assess the level of correspondence between potential prey availability and sea lion feeding habits. Fish distributions were compiled as part of the Sea Around Us Project at the UBC Fisheries Centre, and were based on published distributions and habitat preferences (e.g., latitude, depth). Sea lion scat samples were collected during the 1990s from seven geographic regions from Oregon to the western and central Aleutian Islands. The frequencies of occurrence of four prevalent species (walleye pollock, Theragra chalcogramma ; Pacific herring, Clupea pallasii ; Pacific cod, Gadus macrocephalus ; and North Pacific hake, Merluccius productus ) in the Steller sea lion diet were compared to their distributions in the North Pacific Ocean. The data suggest that Steller sea lion diets broadly reflect the distributions of these major prey species. However, some of the fish species that were regionally predicted to be present in high abundance were not proportionally reflected in the Steller sea lion diet, suggesting that other factors in addition to fish abundance influence their diets.

abstract
Springer et al. [Springer, A.M., Estes, J.A., van Vliet, G.B., Williams, T.M., Doak, D.F., Danner, E.M., Forney, K.A., Pfister, B., 2003. Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling? Proceedings of the National Academy of Sciences 100 (21), 12,223–12,228] hypothesized that great whales were an important prey resource for killer whales, and that the removal of fin and sperm whales by commercial whaling in the region of the Bering Sea/Aleutian Islands (BSAI) in the late 1960s and 1970s led to cascading trophic interactions that caused the sequential decline of populations of harbor seal, northern fur seal, Steller sea lion and northern sea otter. This hypothesis, referred to as the Sequential Megafaunal Collapse (SMC), has stirred considerable interest because of its implication for ecosystem-based management. The SMC has the following assumptions: (1) fin whales and sperm whales were important as prey species in the Bering Sea; (2) the biomass of all large whale species (i.e., North Pacific right, fin, humpback, gray, sperm, minke and bowhead whales) was in decline in the Bering Sea in the 1960s and early 1970s; and (3) pinniped declines in the 1970s and 1980s were sequential. We concluded that the available data are not consistent with the first two assumptions of the SMC. Statistical tests of the timing of the declines do not support the assumption that pinniped declines were sequential. We propose two alternative hypotheses for the declines that are more consistent with the available data. While it is plausible, from energetic arguments, for predation by killer whales to have been an important factor in the declines of one or more of the three populations of pinnipeds and the sea otter population in the BSAI region over the last 30 years, we hypothesize that the declines in pinniped populations in the BSAI can best be understood by invoking a multiple factor hypothesis that includes both bottom–up forcing (as indicated by evidence of nutritional stress in the western Steller sea lion population) and top–down forcing (e.g., predation by killer whales, mortality incidental to commercial fishing, directed harvests). Our second hypothesis is a modification of the top–down forcing mechanism (i.e., killer whale predation on one or more of the pinniped populations and the sea otter population is mediated via the recovery of the eastern North Pacific population of the gray whale). We remain skeptical about the proposed link between commercial whaling on fin and sperm whales, which ended in the mid-1960s, and the observed decline of populations of northern fur seal, harbor seal, and Steller sea lion some 15 years later.

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The timing and extent of the negative population trend in the abundance of the western stock of Steller sea lions has not been geographically uniform. A stochastic metapopulation dynamics model is developed for Steller sea lions. This model allows for geographical differences in factors affecting population processes, and can be parameterized to represent a wide range of hypotheses for the decline in Steller sea lion abundance. Bayesian and maximum likelihood methods are used to fit this model to pup and non-pup count data, age structure samples, and survival estimates. Inferences from model selection criteria highlight the spatial variability in the types of impact deemed to provide most parsimonious representation of the data. Bayesian posteriors for the estimated model parameters show that many combinations of parameter values are able to provide similar fits to the data, even given a specific hypothesis for the decline. This highlights the uncertainty in the precise nature of the impact of these hypotheses. Indeed, while pup production is generally estimated consistently among models, estimates of the size of other components of the Steller sea lion population (such as total population size) depend greatly on the assumptions regarding the cause of the decline. The results demonstrate that future simulation modeling approaches will require more formal, spatial, and mechanistic descriptions of the manner in which specific hypotheses for the decline affect the population.

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Steller sea lions (Eumetopias jubatus) increased in the eastern portion of their range while declining in the Gulf of Alaska and Aleutian Islands from the late 1970s to late 1990s. We constructed ecosystem models of the central and western Aleutians and of Southeast Alaska to simultaneously evaluate four hypotheses explaining sea lion dynamics: killer whale (Orcinus orca) predation, ocean productivity, fisheries, and competition with other species. Comparisons of model predictions to historical time series data indicate that all four factors likely contributed to the trends observed in sea lion numbers in both ecosystems. Changes in ocean productivity conveyed by the Pacific Decadal Oscillation influenced the abundance trajectory of several species. Fishing could have affected the ecosystem structure by influencing the abundance of Atka mackerel (Pleurogrammus monopterygius) in the Aleutians, and herring (Clupea pallasii) in Southeast Alaska. Halibut (Hypoglossus stenolepis) in the Aleutians and arrowtooth flounder (Reinhardtius stomias) in Southeast Alaska appear to impede sea lion population growth through competitive interactions. Predation by killer whales was important when sea lions were less abundant in the 1990s in the Aleutians and in the 1960s in Southeast Alaska, but appear to have little effect when sea lion numbers were high.

abstract
The costs associated with diving are a central component of a sea lions? energy budget. Accurate estimates of diving costs are needed to assess energetic and physiological constraints on foraging behavior, including the potential effects of changes in prey distribution or density. However, information on sea lion diving physiology is limited to relatively few species of pinnipeds, and there is currently no information for Steller sea lions. Information on diving energetics of pinnipeds has traditionally been gathered using either wild or captive animals. However, studies with wild animals are logistically challenging and are limited by the opportunistic nature of data collection, whilst studies in captivity have been constrained by the physical restrictions of the holding facility. To circumvent some of these limitations, we combined the best aspects of both techniques by conducting diving metabolism studies with trained Steller sea lions in an open ocean environment. Two captive-reared Steller sea lions were housed in a holding pen and transported by boat to a diving trial area. The animals were trained to dive to predetermined depths for controlled periods of time using an underwater light targeting system and a video system to monitor behavior. At the end of each dive the sea lions returned to a respirometry dome on the surface where oxygen consumption was measured to estimate diving metabolism. This paper describes the experimental setup used to evaluate diving metabolism, discusses the logistical challenges of the study and the advantages of using such an approach to carry out physiological experiments with sea lions, and provides preliminary data on the diving energetics of Steller sea lions.

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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.

abstract
This project was focused on the design and suitability of the housing component of a new telemetry device to be implanted into young Steller sea lions. The housings suitability is assessed on its long term performance for stable implantation for lifetimes of up to 30 years. An aluminum oxide ceramic material is selected as the housing material as it meets radio frequency, biocompatibility and strength requirements. The housing design consists of a solid base and porous top surface with an inner cavity for electronics potted in epoxy. Aptness of the design for implantation involved investigating the response of the housing to biological and mechanical factors. Biological response was examined by assessing tissue fixation of porous aluminum oxide. Disc implants (36), with a top porous surface of pore size 32 μm and thicknesses of 0.5 mm and 1.0 mm, were sub-dermally implanted into the backs of young rabbits. Due to surgical complications, 33 tags were inserted under the cutaneous trunci muscle, while the remaining were inserted above it. A favourable tissue reaction was assessed in all cases. All implants migrated with the skin growth a distance of 4.69 ± 1.48cm. Half of the implants moved an additional 1.74 ± 1.93cm caused by a combination of externally applied forces and loose tissue attachment. Loose tissue attachment was a result of implantation into subcutaneous fat tissue and the inability of implant encapsulated tissue in integrating with the fat layers. The response of the housing to me! chanical factors was examined by applying loading conditions (cyclic fatigue, compression, puncture and impact) that simulate what is expected in-service. Implants were able to resist fracture due to compression and puncture while impact suitability is achieved when considering energy absorption by the surrounding tissue. The derived housing design has good potential for future implantation into Steller sea-lions. Further research is required to examine implant fixation and migration in dermal tissue compared to subcutaneous tissue. As the implants will move from the insertion location in growing skin, cranial skin growth patterns should be considered prior to implantation into Steller sea lions.

abstract
Models used to describe pinniped diet can provide very different composition estimates. Occurrence indices as well as biomass reconstruction models (which use estimates of the number and sizes of prey consumed) are commonly used and increasingly utilize a variety of fish hard remains (bones) found in scats. However, the importance of any single fish can be overestimated if its bones are deposited in a succession of scats assumed to be from different fish. Similarly, the importance of a species will be underestimated relative to other species if the bones of one species are more fragile and are completely digested or if bones from different fish of the same species are contained in a single scat and assumed to be from a single fish. Species differences in the proportion of fish bones that survive digestion can be assessed from captive feeding studies where the number and species of prey consumed is known. Numerical correction factors can be calculated to take into account the levels of complete digestion. We performed computer simulations using data from captive feeding studies to investigate levels and sources of error in reconstructing simulated mixed species diets. Our simulations used different combinations of hard remains, were conducted both with and without the application of numerical correction factors, and compared four different diet indices (1. Modified frequency of occurrence, 2. Split sample frequency of occurrence, 3. Variable biomass reconstruction, 4. Fixed biomass reconstruction). Simulations indicated that levels of error were related to the MNI method of inferring fish numbers from prey remains, prey size, the number of identifiable prey structures used, and the robustness of the remains to digestive processes (recovery rate). The fewer fish fed, the higher the relative probability of counting the fish, particularly when a multiple element structure or all structure techniques are used. If recovery rates were assumed to be consistent across species, then large fish (particularly when fed in small amounts) were overestimated relative to smaller sized prey in all models, but particularly biomass reconstruction models and when using more than one paired structure. When recovery rates of a paired structure (otoliths) were varied across species (as observed in captive feeding studies) then biomass models tended to overestimate the species with high recovery rates. In contrast, frequency of occurrence models overestimated the contribution of smaller prey (particularly when fed in small amounts). Simulations also indicated correction factors can reduce levels of error in biomass reconstruction models, but cannot solve problems related to counting fish using MNI. Our work shows simulations can form a valuable component in assessing diet indices and the level (and direction) of associated errors in each.

abstract
Human intrusion within areas of sea lion habitat is increasing worldwide, leading to concerns about disruption of distribution and daily activities of sea lions. Sea lion responses to disturbance can be quantified by recording changes in behavioural patterns, documenting numbers of animals on shore before, during and after the disturbance, or by measuring physiological stress of individual animals. However, assessing recovery is not so straightforward, as highlighted by an example from a study of the short-term effects of disturbance on Steller sea lions. Recovery is generally recognized as a return to an original state or normal condition, but is often operationally defined as a percent-return to pre-disturbance numbers or behaviours. Simple interpretation of disturbance effects can be easily confounded by concurrent natural seasonal changes in behaviours or haulout patterns, or by daily variability in numbers that can be attributed to weather, tidal cycle stage and other factors. Overall, a range of recovery criteria needs to be simultaneously applied when assessing the effects of human disturbance on sea lion populations. Insights gained from research on the effects of disturbance on Steller sea lions may help guide the development of studies undertaken on other species of sea lions.

abstract
Steller sea lions (Eumetopias jubatus) were fed restricted iso-caloric amounts of Pacific herring (Clupea pallasi) or walleye pollock (Theragra chalcogramma) for 8-9 days, four times over the course of a year to investigate effects of season and prey composition on sea lion physiology. At these levels, the sea lions lost body mass at a significantly higher rate during winter (1.6 ± 0.14 kg d-1), and at a lower rate during summer (1.2 ± 0.32 kg d-1). Decreases in body fat mass and standard metabolic rates during the trials were similar throughout the seasons and for both diet types. The majority of the body mass that was lost when eating pollock derived from decreases in lipid mass, while a greater proportion of the mass lost when eating herring derived from decreases in lean tissue, except in the summer when the pattern was reversed. Metabolic depression was not observed during all trials despite the constant loss of body mass. Our study supports the hypothesis that restricted energy intake may be more critical to Steller sea lions in the winter months, and that the type of prey consumed (e.g., herring or pollock) may have seasonally-specific effects on body mass and composition.

abstract
The movements of otariids at sea are generally studied by satellite telemetry. At fine scales (1-20km), however, the level of precision provided by this technique (+- mean 1.5-19 km) may be insufficient to accurately reconstruct the track of an individual and/or integrate such movement data with habitat and environmental features. An alternative technique is the boat-based active tracking of individuals by very high frequency (VHF) or acoustic telemetry. By following an individual equipped with transmitters, detailed observations of habitat use, predator occurrence, social context, behavioral state, and prey availability may be integrated to provide a real-time context in which to place the animals? movements. For species such as the Steller sea lion (Eumetopias jubatus), which are difficult to recapture, such techniques enable the collection of much needed contextual information. Here we describe the methods we applied to actively track Steller sea lions. Twenty-o! ne juveniles were captured in southeast Alaska during October 2003 and February 2004. They were fitted with a variety of VHF, satellite, and/or acoustic tags and were tracked through the winter and spring of 2003-2004. The use of ship-based VHF telemetry in conjunction with real time navigation plotting software was highly successful and provided 37 fine-scale tracks of coastal and pelagic sea lion movements covering a total distance of 482 km. Acoustic telemetry techniques were less successful because of the suspected overlap in tag transmission frequency and sea lion hearing. The study represents the first active tracking of a sea lion species, highlighting the high-resolution tracks and contextual behavioral and habitat information that can be obtained using VHF telemetry at sea.

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.

abstract
A variety of reasons have been postulated for the decline of Steller sea lions (Otariidae: Eumetopias jubatus) in the Northeast Pacific. To date, however, it has proved impossible to distinguish among these reasons given the available data. In principle, experimental management based on spatial replication of treatments could be used to discriminate among some of these hypotheses. A simulation protocol was developed and applied to evaluate the power of a set of potential experiments to distinguish between whether the cause of the decline was fishing-induced or due to other factors. The simulations are based on an operating model that is individual-based and spatially explicit, and can be parameterized to represent the implications of a range of possible causes for the decline. This model can be used to generate the types of data typically available for the western stock of Steller sea lions. Experiments based on splitting four of the regions identified for past ana! lyses of population dynamics information into sectors that are either open to some fishing or completely closed are considered. The performance of these experiments is, however, poor, owing to the impact of movement, different historical trends in different areas, demographic stochasticity, and the likely size of the effect that the experiments are attempting to detect. These results suggest that the currently available information imply that large-scale experimental manipulation by means of additional spatial closures, where the results are analyzed by examining trends in pup counts, is unlikely to provide an effective means of discriminating among alternative hypotheses for the declining Steller sea lions in Alaska.

abstract
hanges in the proximate composition of prey can result in a nutritional imbalance in individual animals, regardless of total energy intake. This mechanism has been hypothesized to have contributed to the decline of Steller sea lions (Eumetopias jubatus). Yet little is known about how otariids react physiologically to short-term changes in prey quality and availability. A series of studies with young captive Steller sea lions tested several potential links between prey quality and sea lion health. Body composition (fat to total mass ratio) of animals fed constant, maintenance-level, isocaloric diets of high- or low-lipid prey changed with season, but overall was not aff ected by prey composition. The sea lions appeared to prioritize maintaining core growth rates even when energy was limited, electing to deplete lipid reserves to fulfi ll energy defi cits, resulting in changes in relative body condition. In contrast, sea lions subject to short- term, sub-maintenance diets of high- or low-lipid prey utilized a greater portion of their lipid reserves when losing body mass on low lipid prey. Experiments with diff erent ad libitum feeding regimes indicated that sea lions are readily able to alter food intake levels to compensate for diff erences in prey energy content and, to a lesser degree, prey availability. However, the results also suggest that decreases in prey quality and/or foraging opportunities can readily combine to require food intake levels that are greater than the digestive capacity of the individual. This is particularly true for young animals that may already be living ?on the edge? energetically.

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.

abstract
Accurate estimates of diets are vital to monitor impacts of sea lion populations on their ecosystems, their interactions with fisheries and to understand the role of food to animal nutrition and health. Approaches include using: (1) prey remnants in stomach contents, spews and scats, (2) prey DNA in scats (3) fatty acid signatures in blubber and (4) stable isotope ratios in predator's tissue. Each methodology has particular advantages and limitations, many of which can be assessed and improved through controlled captive feeding trials. Analysis of prey remnants from captive sea lion scats have shown significant variability in digestion between and within prey species, which coupled with preferential regurgitation and enumeration biases, can confound accurate diet quantification, but does not prevent spatial or temporal comparisons. Correction for partial digestion and use of additional structures besides otoliths can provide accurate prey size estimates. Prey DNA can be reliably isolated from soft remains in scats from captive sea lions and with further development this approach may allow quantification of diet. Genetic methods can be expensive and representative of only one to two days foraging (like prey remnant analysis), but may be less affected by differential digestion and can identify prey in scats that could not be identified through structural remnants. Validation of fatty acid signature analysis to quantify diet at longer temporal scales in sea lions is ongoing, but this new technique promises to be particularly useful to assess biases in traditional methods, identify the onset of weaning and to highlight what prey most contribute to lipid reserves. Stable isotope analysis of predator tissues gives only trophic level data, but can provide data on diet changes on many temporal scales. Remote video monitoring of foraging events and lavage/enema techniques can provide valuable diet information, but, like many newer techniques, animal capture is required. Ideally a suite of techniques should be used to study diet. While methods and correction factors developed for Steller sea lions can likely be applied to the other five sea lion species, they should be verified experimentally.

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.

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.

abstract
Apex predators such as pinnipeds, cetaceans, seabirds and sharks, are constrained by the sizes of prey they can consume and thus typically feed within a narrow range of trophic levels. Having co-evolved with their prey, they have influenced the behaviors, physiologies, morphologies and life history strategies of the species they target. In contrast, humans can consume prey of any size from all trophic levels using methods that can rapidly deplete populations. On an ecological time scale, fisheries, like apex predators, can directly affect the abundance of other species by consuming, or out-competing them; or they can indirectly affect the abundance of non-targeted species by removing other predators. However, there is growing evidence that the effects of fisheries go well beyond those imposed by apex predators. Theory and recent observations confirm that the continued development and expansion of fisheries over the past half century has led to a decrease in the! size and life spans of targeted species, with reproduction of fish occurring at earlier ages and at smaller sizes. Also, high levels of fishing have altered the makeup of many ecosystems, depressing the average trophic level of heavily fished ecosystems and speeding up the rate of nutrient turnover within them. An inevitable consequence of fishing down the food web is increased ecosystem instability, unsustainable fisheries and an inability for the ecosystem to support healthy abundant populations of apex predators.

abstract
Knowing the quantity of prey that sea lions consume is a prerequisite for assessing the role of sea lions in aquatic ecosystems and the potential for competition to occur with fisheries. We reviewed the different approaches that have been used to estimate the food requirements for the six species of sea lions. We reviewed data on the quantity of food consumed by sea lions in captivity, and examined how consumption varied by species, body size, and season. We also reviewed and quantified available information on the energetics of sea lions and assessed the potential application of these data to parameterize an existing bioenergetic model that was developed to estimate the food requirements of Steller sea lions. Our study provided ranges of estimates of food consumption for sea lions that can be used in various modeling strategies to assess the impact of sea lions on prey populations, including commercially exploited fish species. The approaches reviewed in our study shared common difficulties arising from the quantity and quality of data, and the integration of data across scales and species. Our modeling exercise, in particular, identified the major uncertainties involved in estimating the food requirements of each sea lion species using an energetics approach. Our results provide direction for future research aimed at improving the accuracy and comparability of estimates of food consumption for sea lions.

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.

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.

abstract
Serology data were examined to determine whether infectious disease may have played a role in the decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and Aleutian Islands. Available published data, historical unpublished data, and recent collections (1997-2000) were compared and reviewed. Data was stratified by geography in order to compare the declining western Alaska population in the Aleutian Islands regions through eastern Prince William Sound to the increasing population in Southeast Alaska.  Prevalences of antibodies from the 1970s to early 1990s were noted for Leptospira interrogans, Chlamydophila psittaci, Brucella spp., phocid herpesvirus 1, and canine parvovirus.  Serum samples collected and analyzed from 1997?2000 were tested for antibodies to these agents as well as to caliciviruses, marine mammal morbilliviruses, and canine adenoviruses 1 and 2.  Conclusions could not be drawn about changes in the prevalence of exposure to disease agents during the decline of Steller sea lions because data were not comparable either because of inconsistencies in test techniques, or because the samples were either not collected in all decades from all regions or were not tested for antibodies to the same disease agents in different decades.  Despite these shortcomings, the available data contained no convincing evidence of significant exposure of Steller sea lions to morbilliviruses, B. spp., canine parvovirus or L. interrogans.  Steller sea lions have been exposed to a phocid herpesvirus, caliciviruses, canine adenovirus, and C. psittaci or to cross reactive organisms in regions of both increasing and decreasing sea lion abundance.  These disease agents are not likely to have been the primary cause of the decline because they are found at comparable levels in both the increasing and the decreasing populations.  However they may have contributed to the decline or impeded recovery of the Steller sea lion population due to undetected mortality and morbidity, or reduction of fecundity and body condition in animals under other stresses.  Systematic monitoring for disease agents and their effects is needed to determine whether infectious disease is currently playing a role in the decline and lack of recovery of Steller sea lions.

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.

abstract
The DNA of prey present in animal scats may provide a valuable source of information for dietary studies. We conducted a captive feeding trial to test whether prey DNA could be reliably detected in scat samples from Steller sea lions (Eumetopias jubatus). Two sea lions were fed a diet of fish (five species) and squid (one species), and DNA was extracted from the soft component of collected scats. Most of the DNA obtained came from the predator, but prey DNA could be amplified using prey-specific primers. The four prey species fed in consistent daily proportions throughout the trial were detected in more than 90% of the scat DNA extractions. Squid and sockeye salmon, which were fed as a relatively small percentage of the daily diet, were detected as reliably as the more abundant diet items. Prey detection was erratic in scats collected when the daily diet was fed in two meals that differed in prey composition, suggesting that prey DNA is passed in meal specific puls! es. Prey items that were removed from the diet following one day of feeding were only detected in scats collected within 48 hours of ingestion. Proportions of fish DNA present in eight scat samples (evaluated through the screening of clone libraries) was roughly proportional to the mass of prey items consumed, raising the possibility that DNA quantification methods could provide semi-quantitative diet composition data. This study should be of broad interest to researchers studying diet since it highlights an approach that can accurately identify prey species and is not dependent on prey hard parts surviving digestion.

abstract
The North Pacific is a hot-bed for understanding how marine populations are impacted by humans as well as by environmental conditions. The 'Thompson-Burkenroad debate' has been ongoing since the late-1940s: what drives the marked fluctuations in Pacific halibut that has been observed over the past century' Dr William Thompson, who started up the work of the International Pacific Halibut Commission, IPHC, argued that the changes in halibut abundance could be fully explained by changes in fishing pressure, i.e. that they were the result of successful management on the part of IPHC, while his adversary, Dr Martin Burkenroad questioned if the populations trends could be accounted for by fishing pressure on its own, or if wasn't rather a question of environmental factors impacting halibut recruitment. While Thompson and Burkenroad actually never debated the relative role of fisheries and the environment ' indeed it may well be that they would actually agree that one factor in itself would not suffice to give us the full explanation their debate has lived on, and both sides still have proponents arguing for one over the other. Examining the Pacific halibut trends now, nearly 60 years after the debate started, still yields inconclusive answers only. We cannot name the culprit. The debate has widened since Thompson and Burkenroad's days, and we regularly hear about regime shifts in connection with the North Pacific. A notable debate in this context has emerged, seeking explanations for why the Steller sea lions have declined to become threatened in major parts of their North Pacific distribution area, while increasing in others. A multitude of explanations have been brought forward, and considerable research has been aimed at understanding the importance of nutritional conditions, of predators and of prey, of competition with commercial fisheries, of parasites and diseases, of the Pacific Decadal Oscillation Index, and of the potential impact of incidental culls, to mention some. As for the halibut, no conclusive explanation has emerged. Asking then, if the non-emergence of a single clear explanation may be due to the Steller sea lion being impacted by a combination of factors the North Pacific Universities Marine Mammal Research Consortium and the North Pacific Marine Science Foundation initiated a project 'Ecosystem analysis of Steller sea lion dynamics and their prey' through NOAA funding. The project, which was the brain child of Andrew Trites (Director of the Marine Mammal Research Unit, Fisheries Centre), employs ecosystem modelling of North Pacific ecosystems (Southeast Alaska, the Central Gulf of Alaska and the Western Aleutian Islands) in an attempt to evaluate (quantify) the relative role the various factors may have played in determining population trends. The methodologies applied for the modelling along with some of the preliminary findings from the study are described in this report. Notably, the models indicate that no single factor by itself can explain the population trends of Steller sea lion, several have to be invoked. In parallel to the work centered on Steller sea lion, the UBC 'Sea Around Us' project (www.seaaroundus.org) through funding from the Pew Charitable Trusts initiated a series of workshops aimed at evaluating the relative role of fisheries and environmental factors for North Pacific ecosystems. Bringing together researchers from the Department of Fisheries and Oceans, Pacific Biological Station, Nanaimo; the NOAA Alaska Fisheries Science Center, Seattle; the University of Washington, School of Fisheries, Seattle; and the University of British Columbia, Fisheries Centre, Vancouver, to analyze a series of ecosystems ranging from the Bering Sea to the Northern California Current, and coordinate the methodologies. We present descriptions of some studies in this report, while most of the findings are published separately. The present report also includes a reconstruction of North Pacific whale catches for the 20th century, which served to estimate the whale population at different periods in Southeast Alaska and the Western Aleutians. Finally, in the interest of preparing future work related to evaluating nutritional aspects of North Pacific ecosystems we have included a compilation of the energy content of invertebrates, fish and mammals in the Gulf of Alaska.

abstract
There is considerable interest in assessing and mitigating disruptive effects of humans on the behaviour of marine mammals, especially for species with uncertain or decreasing population trends. Steller sea lions (Eumetopias jubatus) have been under intensive study throughout their range over the past few decades in an attempt to identify the causes of a large population decline in the Gulf of Alaska and Aleutian Islands. Consequently, disturbance due to scientific research has also increased at rookeries and haulouts. The purpose of my study was to determine if there were measurable short-term effects of human disturbance on the numbers of Steller sea lions using terrestrial sites. Numbers and composition of sea lions were documented for 2 – 3 week periods in southeast Alaska and British Columbia during summer (n = 8 sites) and winter / spring (n = 6 sites). They revealed considerable daily variation in numbers of sea lions hauled out within and among study sites that was related in part to prevailing environmental conditions. However, counts could not be corrected to account for environmental influences on the total numbers of sea lions using haulouts. Hauling out trends were examined for pre- and post-disturbance periods across multiple sites over two seasons. Predetermined research disturbances occurred to collect scats at the haulouts, and to brand pups at the rookery. Three methods were explored to assess local population recovery that addressed both quantitative and temporal aspects of sea lions returning to the study locations. Disturbances resulted in significantly fewer sea lions using haulouts during the post-disturbance period. Variation in the numbers of animals using the haulouts increased following the disturbance, but rates of change in daily numbers did not differ significantly between periods. Six of ten disturbed sites reached full recovery (100% of the pre-disturbance mean) on average 4.3 days after the research disturbance. To determine if individual behaviour was affected by disturbance, sea lions arriving on shore were followed to determine normal patterns of interactions and behaviour. Significant differences were noted in hauling out behaviour between animals that remained on land and those that returned to the water. Sea lions that returned to the water exhibited higher rates of behaviour and interactions with other animals during the week that followed the disturbance. Seasonal differences were also noted in the rates of behaviour and interactions that may be indicative of certain times of the year when sea lions are more sensitive to human presence and disturbance. Increasing levels of human–sea lion contact are expected as more and more people visit the remote coastal habitat of Steller sea lions. Future studies are needed to assess the influence of disturbance on sea lion redistribution within a critical recovery period, as well as to determine the physiological effects that sea lions experience with repeated human disturbance. Disturbance studies are an important aspect of conservation initiatives because they can help guide policies and establish restrictions to protect wild populations from human intrusion.

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.

abstract
To aid in the development of a long-range subcutaneous radio frequency identification tag to monitor the fate sea lion pups, the dielectric properties of the cranial skin of young female otariids, and possible test subjects of similar size and age, or pigs (Sus scrofa) and sheep (Ovis aries)were obtained over a frequency range of 0.1 to 10 GHz at the base of their heads where the tag will be implanted. The resulting curves were similar in shape to adult human skin data, but the values were generally lower. Between ubjects, variations were noted in all the species. Circuitry for the RF-ID tag is being designed to account for antenna detuning as a result of the lossy media or skin and he variation in dielectric properties.

keywords     Keywords: dielectric constant, dielectric loss, skin thickness,

abstract
The effects of high- and low-lipid prey on the body mass, body condition, and metabolic rates of young captive Steller sea lions (Eumetopias jubatus) were examined to better understand how changes in prey composition might impact the physiology and health of wild sea lions and contribute to their population decline. Results of three feeding experiments suggest that prey lipid content did not significantly affect body mass or relative body condition (lipid mass as a percent of total mass) when sea lions could consume sufficient prey to meet their energy needs. However, when energy intake was insufficient to meet daily requirements, sea lions lost more lipid mass (9.16±1.80 kg±SE) consuming low-lipid prey compared with eating high-lipid prey (6.52±1.65 kg). Similarly, the sea lions lost 2.7±0.9 kg of lipid mass while consuming oil-supplemented pollock at maintenance energy levels but gained 5.2±2.7 kg lipid mass while consuming identical energetic levels of herring. Contrary to expectations, there was a 9.7±1.8% increase in metabolism during mass loss on submaintenance diets. Relative body condition decreased only 3.7±3.8% during periods of imposed nutritional stress, despite a 10.4±4.8% decrease in body mass. These findings raise questions regarding the efficacy of measures of relative body condition to detect such changes in nutritional status among wild animals. The results of these three experiments suggest that prey composition can have additional effects on sea lion energy stores beyond the direct effects of insufficient energy intake.

abstract
Diets of mammals are increasingly being inferred from identification of hard parts from prey eaten and recovered in fecal remains (scats). Frequencies with which particular prey species occur among collections of scats are easily compiled to describe the average diet, and can be used to compare diets between and within geographic regions, and across years and seasons. Important to these analyses is the question of statistical power. In other words, how many scats should be collected to compare the diet among and between species? We addressed this problem using Monte Carlo simulations to analytically determine the consequence of sample size on the dietary analysis of scats using frequency of occurrence methods. We considered two questions: 1) how is the statistical power affected by sample size; and 2) what is the likelihood of not identifying a prey species? We randomly sampled predetermined numbers of scats (n=10–200) from computer-generated populations of scats containing prey of known species and frequencies of occurrences. We also randomly sampled a large database of field-collected scats from Steller sea lions (Eumetopias jubatus). We then used standard contingency table tests such as chi-square and Fisher’s exact test to determine whether differences between our samples and populations were statistically significant. We found a minimum size of 59 scats is necessary to identify principal prey remains occurring in >5% of scats. However, 94 samples are required when comparing diets to distinguish moderate effect sizes over time or between areas. These findings have significant implications for the interpretation of published dietary data, as well as for the design of future scat-based dietary studies for pinnipeds and other species.

abstract
We present a design for long-term or removable attachment of heat flux sensors (HFSs) to stationary or swimming animals in water that enables collection of heat flux data on both captive and free-ranging pinnipeds. HFSs were modified to allow for independent, continuous, and long-term or removable attachment to study animals. The design was tested for effects of HFSs and the attachment mechanism on resultant heat flux. Effects were insulative and consistent across water temperatures and flow speeds, resulting in a correction factor of 3.42. This correction factor was applied to all measurements of heat flux from animal experiments to account for the thermal resistance of HFSs and insulative effects of the attachment mechanism. Heat flux and skin temperature data were collected from two captive Steller sea lions (Eumetopias jubatus) as they swam in a large habitat tank over time periods ranging from approximately 4 to 9 min. Of the 72 HFSs deployed using the attachm! ent mechanism, data were successfully retrieved from 70. The HFS attachment mechanism was also used on two wild free-ranging Weddell seals (Leptonychotes weddellii) off Ross Island, Antarctica, for up to 7 days. Heat flux data were retrieved from all eight sensors deployed. These results, along with those from Steller sea lions, suggest that HFSs can be deployed with success on captive and wild animals using the designed attachment mechanism.

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.

abstract
The objectives of this study were to compare Resting Metabolic Rate (RMR) from animals in the eastern and western Alaskan populations to discern whether there is any evidence of nutritional stress. Oxygen consumption data were collected from captive Steller sea lions held at the Vancouver Aquarium, Vancouver, BC and from free-ranging Steller sea lions captured from western and eastern Alaskan stocks. In water, RMR ranged from 33.3 to 56.7 MJ/day for sub-adult animals (109-158 kg, 2.9-4.6 times predicted for an adult animal) and from 20.0 to 26.6 MJ/day for pups (57-59 kg, 3.3-4.3 times predicted) at 2°C. RMR, generally decreased with increasing water temperature, but the relationship was not statistically significant. Reduced body condition had a noticeable impact on RMR in juvenile sea lions at colder water temperatures. The results of the present study suggest that young sea lions would be subject to even greater thermoregulatory demands if their body condition were reduced.

abstract
The Steller sea lion (Eumetopias jubatus) is listed as endangered in parts of its range and is suspected of suffering from ecological stressors that may be reflected by fecal glucocorticoid hormones. We validated a fecal glucocorticoid assay for this species with an adrenocorticotropic hormone (ACTH) challenge. Feces were collected from captive Steller sea lions (two males and two females) for 2 days before injection with ACTH, and for 4 or more days postinjection. Feces were freeze-dried, extracted with a methanol vortex method, and assayed for glucocorticoids. The assay demonstrated good parallelism and accuracy. All animals showed the expected peak of fecal glucocorticoid excretion after ACTH injection. However, the two males had higher baselines, higher peaks, and more delayed peaks than the females. Peak glucocorticoid excretion occurred at 5 and 28 h postinjection for the two females, and at 71 and 98 h for the two males. Correction for recoveries by the addition of tritiated hormones produced ACTH profiles that were virtually identical in pattern to uncorrected data, but with higher within-sample coefficients of variation. Based on these results, we conclude that this fecal glucocorticoid assay accurately reflects endogenous adrenal activity of Steller sea lions, and that recovery corrections are not necessary for this species when using the methanol vortex extraction method. More research is needed to address possible sex differences and other possible influences on fecal glucocorticoid concentrations.

abstract
A popular hypothesis for the noted steady decline in the population of Steller sea lions in the regions from Prince William Sound through the Aleutian Islands relates to their nutritional status. Sea lion diets appear to have shifted from primarily small schooling fatty fishes to low fat fish such as walleye pollock (Theragra chalcogramma). We examined the seasonal changes in proximate nutrients of pollock collected in the Bering Sea. Mean energy density (dry-weight) of pollock peaked in October then declined and remained low throughout winter. Energy recovery occurred in the summer months with strong recovery observed in female fish caught in July. Contrary to whole fish carcass energy contents, both total protein and moisture contents were at their highest levels in winter (January) when total crude lipid content was at its lowest (p<0.05). This trend gradually declined to its lowest levels in the fall, when lipid content was high. The decline in total lipi! ds during winter seasons appeared to parallel gonad development during the pre-spawning period. Sex differences in energy densities were not found. Nor did proximate analysis data for moisture, protein, ash and lipid content show any significant variation between males and females. Protein digestibility of pollock was higher (p<0.05) in the summer than in the spring, but not different for winter or fall seasons. We conclude that the nutrient content of pollock may have some impact on the Steller sea lions that feed on them, particularly the energetic value that appears to be low during important feeding periods for this marine mammal.

abstract

Steller sea lions (Eumetopias jubatus) were fed restricted iso-caloric amounts of Pacific herring (Clupea pallasi) or walleye pollock (Theragra chalcogramma) for 8-9 days, four times a year. At these levels, the sea lions lost an average of 10.1% of their initial body mass while on both experimental diets for up to nine days, but at a significantly higher rate in winter and at a lower rate in summer. Decreases in body fat mass and standard metabolic rates during the trials were similar throughout the seasons and for both diets. Metabolic depression was not always observed during the trials despite the constant loss of body mass. Changes in cortisol, triiodothyronine and blood urea nitrogen (BUN) were seasonally dependent. Over the course of the trials, serum levels of cortisol and BUN increased and total triiodothyronine decreased the most in winter. Serum cortisol levels correlated negatively with both body mass and body condition suggesting that cortisol may play an important role in body fat regulation in Steller sea lions. The mean ghrelin level in Steller sea lions correlated negatively with body mass, but ghrelin did not correlate with serum leptin. My findings support the hypothesis that restricted energy intake at different times of the year differentially affects Steller sea lions, and that diet type (herring or pollock) may have seasonally-specific effects on body mass and composition. Steller sea lions may be more severely impacted by reduced energy intake in winter than at other times of the year.

Changes in iron binding capacity were significantly greater in the herring-fed group than in the pollock-fed group, and a significantly greater decrease occurred in winter and spring compared to summer and fall. Iron saturation increased in the herring-fed group and decreased in the group fed pollock. These results suggested a potential anemia from a reduced diet of pollock in Steller sea lions. Serum iron, phosphorus, hematocrit and gamma glutamyltransferase showed consistent changes during food restriction, suggesting that these may serve as indicators of nutritional stress in Steller sea lions.

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.

abstract
This experiment examined the response of a suite of hematologic parameters to experimentally induced nutritional stress in a group of captive Steller sea lions. The goal was to identify a suite of parameters that could be used to diagnose comparable conditions among wild Steller sea lions. Previous studies, many with ruminant mammals, have shown that there are significant changes in blood characteristics with nutritional status. However, it is equally clear that there is no overwhelming choice of blood parameter to indicate nutritional stress across different species. Therefore, species-specific empirical tests such as the one carried out in the current study are essential to place results from wild studies in a biologically meaningful context.

abstract
Foraging theory predicts that animals should proportionately increase their food intake to compensate for reduced energy content and/or prey availability. However, the theoretical intake levels will – at some point – exceed the digestive capacity of the predator. We tested the ability of Steller sea lions (Eumetopias jubatus, Schreber, 1776) to compensate for short-term changes in prey energy density and availability, and quantified the maximum amount of food a young sea lion could consume. Five 1-2 year old captive Steller sea lions were alternately offered herring (high-energy) or capelin (low-energy) each day or every second day. When prey were available on a daily basis the sea lions compensated for differences in the energy content of herring and capelin by consuming sufficient quantities of each (8.3 vs. 14.0 kg d-1, respectively) to maintain an equivalent gross energy intake. When herring was available only on alternate days, the sea lions increased their consumption by 52% to 11.5 kg d-1, which was not sufficient to maintain an average gross intake equal to when herring was available every day. When capelin was available only on alternate days, some animals increased their intake for a few days, but average intake (15.2 kg d-1) was far below levels observed during daily feeding. Generally, the sea lions appeared to reach their digestive limit at a level equivalent to 14-16% of their body mass. Our findings suggest that Steller sea lions can alter their food intake in response to short-term changes in prey quality or availability, but that these variables can quickly combine to necessitate food intake levels that exceed the physiological digestive capacities of young animals.

abstract
Pup mortality and the timing of birth of South American sea lions Otaria flavescens were investigated to determine the possible relationship between fluctuations in prey availability in the Peruvian upwelling ecosystem and current and future reproductive success of sea lions during six consecutive breeding seasons. Our study from 1997 to 2002 encompassed the strongest El Nino on record and one La Nina event. Pup mortality ranged from 13% before El Nino to 100% during El Nino, and was negatively correlated with prey availability. Abortions were also more frequent when prey availability was low. However, pup mortality remained high following El Ni~no due to the punctuated short-term effects it had on population dynamics and subsequent maternal behaviour. Births occurred later in the season after years of low food availability and earlier following years of high food availability. The peak of pupping coincided with the peak of mortality in all years, and may have ! been the product of intensive competition between bulls at the peak of the breeding season. The stronger and more frequent El Ninos that appear to be occurring along the Peruvian coast may produce significant stochastic changes in future births and pup mortality, which may place the vulnerable South American sea lion population in Peru at greater risk.

abstract
Lengths of walleye pollock (Theragra chalcogramma) consumed by Steller sea lions (Eumetopias jubatus) were estimated using allometric regressions applied to seven diagnostic cranial structures recovered from 531 scats collected in Southeast Alaska between 1994-1999. Selected structural measurements were corrected for loss of size due to erosion using experimentally derived condition-specific digestion correction factors. Correcting for digestion increased the estimated length of fish consumed by 23%, and the average mass of fish consumed by 88%. Mean corrected fork length (FL) of pollock consumed was 42.4 11.6 cm (range=10.0-78.1 cm, n=909). Adult pollock (>45.0 cm FL) occurred more frequently in scats collected from rookeries along the open ocean coastline of Southeast Alaska during June and July (74% adults, mean FL=48.4 cm) than they did in scats from haulouts located in inside waters between October and May (51% adults, mean FL=38.4 cm). Overall, the contribution of juvenile pollock (20 cm) to the sea lion diet was insignificant, while adults contributed 44% to the diet by number and 74% by mass. On average, larger pollock were eaten in summer at rookeries throughout Southeast Alaska than at rookeries in the Gulf of Alaska or the Bering Sea. Overall it appears that Steller sea lions are capable of consuming a wide size range of pollock, with the bulk of fish falling between 20-60 cm. The use of cranial hard parts other than otoliths and the application of digestion correction factors are fundamental to correctly estimating the sizes of prey consumed by sea lions and for determining their overlap with commercial fisheries.

abstract
The lengths of otoliths and other skeletal structures recovered from the scats of pinnipeds, such as Steller sea lions (Eumetopias jubatus), correlate with body size and can be used to estimate the length of prey consumed. Unfortunately, otoliths are often found in too few numbers or are too digested to usefully estimate prey size. Techniques are therefore required to account for the degree of digestion of alternative diagnostic bones prior to estimating prey size. We developed a method (using defined criteria and photo-reference material) to assign the degree of digestion for key cranial structures of two prey species (walleye pollock, Theragra chalcogramma and Atka mackerel, Pleurogrammus monopterygius). The method grades each structure into one of three condition categories; good, fair or poor. We also conducted captive feeding trials to determine the extent of erosion and derive condition-specific digestion correction factors to reconstruct the original sizes of the structures consumed. In general, larger structures were relatively more digested than smaller ones. Mean size reduction varied between different types of structures (3.3-26.3%), but was not influenced by the size of the prey consumed. Results from the observations and experiments were combined to reconstruct the size of prey consumed by sea lions and other pinnipeds. The proposed method has four steps: 1) measure the recovered structures and grade the extent of digestion using defined criteria and photo-reference collection; 2) exclude structures graded in poor condition; 3) multiply measurements of structures in good and fair condition by their appropriate digestion correction factors to derive their original size; and 4) calculate the size of prey from allometric regressions relating corrected structure measurements to body lengths. This technique can be readily applied to piscivore dietary studies that use fish hard remains.

abstract
Ecosystem models were constructed for the Antarctic and the Bering Sea that incorporate current understanding of biological interactions of species within the ecosystem (i.e., who eats whom and how much). Within the limitations that are inherent to simulations, both models suggest that removal of large whales had little measurable effect on lower trophic levels or on the dynamics of other species in their polar ecosystems. Trophic interactions failed to explain the magnitude of changes in the biomass of the major species groups in the Antarctic and Bering Sea. Nor did fin-fisheries appear to have had a significant effect on the abundance of non-targeted species. This may mean that environmental effects (which were not modeled) play an important role in influencing the dynamics of marine ecosystems. Oceanographic factors such as changes in water temperature or ocean currents likely result in variations in ecosystem production and species recruitment patterns which are not captured by our Ecopath models. The Ecopath modeling approach is a powerful means of synthesizing knowledge about ecosystems and the factors that influence ecosystem dynamics. They provide a straightforward means for estimating trophic levels and niche overlaps with other species to assess the potential for resource competition. While the models failed to support the hypotheses that large whales play a significant structural role in the Antarctic and Bering Sea ecosystems, they do support what most already know ?- i.e., that populations of large whales are easily reduced to low numbers, but take a long, long time to recover. They also help in recognizing the need to consider factors other than food web interactions when assessing the status of cetaceans, as well as highlighting the potential tradeoffs that can result when other species are removed from ecosystems.

abstract
Prey size selectivity by Steller sea lions (Eumetopias jubatus) is relevant for understanding the foraging ecology of this declining predator, but studies have been problematic due to the erosion or absence of prey skeletal structures and otoliths usually used to estimate fish length. We developed regression formulae to estimate fish length from seven diagnostic cranial structures of walleye pollock (Theragra chalcogramma) and Atka mackerel (Pleurogrammus monopterygius). For both species, all structure measurements were related with fork length of prey (r squared range: 0.78 - 0.99). Fork length of walleye pollock and Atka mackerel consumed by Steller sea lions was estimated by applying these regression models to cranial structures recovered from scats (feces) collected between 1998 and 2000 across the range of the Alaskan western stock of Steller sea lions. Experimentally derived digestion correction factors were applied to take into account loss of size due to digestion. Fork lengths (FL) of walleye pollock consumed by Steller sea lions ranged from 3.7 to 70.8 cm FL (mean = 1 39.3 cm, SD = 14.3 cm, n = 1 666) and Atka mackerel ranged from 15.3 to 49.6 cm FL (mean = 1 32.3 cm, SD = 5.9 cm, n = 1,685). Although sample sizes were limited, a greater proportion of juvenile (less than to 20 cm) walleye pollock were found in samples collected on summer (June - September) haul-out sites (64% juveniles, n = 1 11 scats) than on summer rookeries (9% juveniles, n = 1 132 scats) or winter (February - March) haul-out sites (3% juveniles, n = 1 69 scats). Annual changes in the size of Atka mackerel consumed by Steller sea lions corresponded to changes in the length distribution of Atka mackerel resulting from exceptionally strong year classes. Considerable overlap (> 51%) in the size composition of walleye pollock and Atka mackerel taken by Steller sea lions and the commercial trawl fishery was demonstrated.

abstract
Results of serology studies conducted from 1975-1996 on Alaskan populations of Steller sea lions(Eumetopias jubatus) were synthesized and supplemented with analyses of archived sera to assess the chronological and spatial patterns of exposure to disease agents and the role that infectious disease may have played in the decline of Steller sea lions in the Gulf of Alaska and Aleutian Islands. Serum samples were obtained during three periods (1970s, 1980s and 1990s) and were tested for exposure to Leptospira interrogans, caliciviruses, Chlamydophila sittaci, Brucella sp, morbilliviruses, influenza A, oxoplasma gondii, phocid herpesviruses and canine parvovirus. Testing for these agents and canine adenoviruses 1 and 2 continued through 2000. In most cases, conclusions cannot be drawn about chronological changes in the prevalence of disease agents during the decline of Steller sea lions because the samples were not collected from all regions in each time period, nor from sufficient numbers of animals in each age class. In addition, samples were not all analyzed by the same laboratories, were not stored under controlled conditions, were not tested for the same disease agents, and assays were not validated for Steller sea lions.

There is no convincing evidence of significant exposure to influenza A, morbilliviruses, Brucella abortus, canine parvovirus and Leptospira sp. However, there is evidence of exposure to a herpesvirus, C. psittaci, caliciviruses, T. gondii and canine adenovirus in regions of both increasing and decreasing sea lion abundance. As these agents are either present throughout the areas examined, or were not evident in all of the animals examined, it is unlikely that these disease agents caused the population decline of sea lions by epidemic mortality. However, as the number of samples tested for morbillivirus is low, and the assays used have not been validated for Steller sea lions, exposure to a morbillivirus during the peak of the decline cannot be completely ruled out from the data available.

Some pathogens become endemic and interact with malnutrition or predation to decrease survival or reproduction—therefore preventing recovery of depleted populations. In other species, C. psittaci, herpesviruses, adenoviruses, and T. gondii are more readily expressed as clinical diseases when individuals are stressed. It is possible that these agents could be contributing to the lack of recovery by causing undetected mortality and morbidity, or by reducing fecundity and juvenile survival rates. A systematic disease agent monitoring protocol should therefore be initiated to adequately test for disease agents in different time periods and regions.

Serological studies are limited in that they only assess immunological response following exposure to infectious agents. They do not give information on the prevalence of disease agents, or on presence of clinical disease. Further sstudies should be aimed at detecting infectious agents directly, and determining their association with morbidity and mortality, as well as changes in host population dynamics.

abstract
I documented the timing and progression of the moult by sex and age class in a wild population of Steller sea lions (<i>Eumetopias jubatus</i>) 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.

abstract
The decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska appears to have been associated with a switch of diet from one dominated by fatty forage fishes (such as her-ring; Clupea pallasi ) to one dominated by low-fat fish (such as pollock; Theragra chalco-gramma). Observations made during the decline include reduced body size of sea lions, low pregnancy rates, and high mortality. We used the general mammalian model, the laboratory rat (Rattus norvegicus ), to test whether changing the quality of prey consumed could cause changes in size and reproductive performance. Five groups of twelve fiale, weanling rats were fed diets composed of herring (H), pollock (P), pollock suppliented with herring oil (PH), pollock suppliented with pollock oil (PP), or a sii-purified diet (ICN). Mean body weights were greatest for H, followed by PH, P, PP and finally ICN, although ICN was the only group significantly different from the others (P 0·05). Food intakes before mating were 10 % higher for groups on the lower-fat diets (P and ICN), resulting in similar energy intakes in all groups. The protein efficiency ratio was highest for the H diet, slightly lower for all pollock diets, and significantly lower for ICN (P 0·05). The fetal weights for mothers fed P were significantly reduced (P 0·05). The present study shows that the energy content was a major limiting factor in the nutritional quality of pollock. When food intake was adjusted to meet energetic requirients, there were no detrimental consequences from eating pollock. However, supplientation of pollock meal with additional pollock oil may reduce growth and reproductive performance, although the reasons for this were not apparent.

abstract
The discovery of flipper tags from 14 Steller sea lions (Eumetopias jubatus) in the stomach of a dead killer whale (Orcinus orca) in 1992 focused attention on the possible role of killer whale predation in the decline of Steller sea lions in western Alaska. In this study, mariners in British Columbia and Alaska were surveyed to determine the frequency and out-come of observed attacks on sea lions, the age classes of sea lions taken, and the areas where predatory attacks occurred. The 126 survey respondents described 492 killer whale/sea lion interactions, of which at least 32 were fatal attacks on the sea lion. The greatest rate of observed predation occurred in the Aleutian Islands. The stomach contents of dead and stranded whales also were examined. Stomachs that were not empty contained only fish or marine mammal remains, but not both. This supports earlier evidence of dietary segregation between fish-eating resident and marine mammal-eating transient killer whales in Alaska. Steller sea lion remains were found in two of 12 killer whale stomachs examined from Alaska between 1990 and 2001. Stomach contents fromtwo oVshore killer whales provided the first direct evidence that this third formof killer whale feeds on fish.

abstract
The validity of using heart rate to estimate energy expenditure in free-ranging Steller sea lions Eumetopias jubatus was investigated by establishing whether there is a relationship between heart rate (fH) and oxygen consumption rate (V . O·) in captive sea lions while swimming and resting. Four trained Steller sea lions (2 males and 2 females; mass 87.4–194.4·kg; age 16 months– 3 years) were each equipped with a datalogger and two dorsal subcutaneous electrodes to record electrocardiograms from which fH was calculated. V . O· (measured using open-circuit respirometry) was simultaneously recorded while the previously fasted animals were at rest within an enclosed dry metabolic chamber or while they swam in an enclosed swim mill against water currents of various speeds (0–1.5·m·s –1 ). The mean regression equation describing the relationship between fH (beats·min –1 ) and V . O· (ml·h –1 ·kg –0.60 ) for all four animals was V . O·=(71.3fH±4.3)–(1138.5±369.6) (means ± S.E.M.) (r 2 =0.69, P<0.01). The relationship demonstrated between fH and V . O· while fasting suggests that heart rate can potentially be used to monitor energy consumption in free-ranging Steller sea lions. However, a short-term feeding experiment revealed no significant increase in heart rate following a 6·kg or 12·kg meal to match the observed increase in rate of oxygen consumption. This suggests that heart rate may not accurately reflect energy consumption during digestion events. Additional research should be conducted to further elucidate how the relationship between heart rate and oxygen consumption is affected by such factors as digestive state, stress and age.

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.

abstract
The increase in metabolism during digestion—the heat increment of feeding—is often regarded as an energetic waste product. However, it has been suggested that this energy could offset thermoregulatory costs in cold environments. We investigated this possibility by measuring the rate of oxygen consumption of four juvenile Steller sea lions (Eumetopias jubatus) before and after they ingested a meal in water temperatures of 2-8 degrees C. Rates of oxygen consumption of fasted and fed animals increased in parallel with decreasing water temperature, such that the apparent heat increment of feeding did not change with water temperature. These results suggest that Steller sea lions did not use the heat released during digestion to offset thermoregulatory costs.

abstract
Populations of seals, sea lions, and sea otters have sequentially collapsed over large areas of the northern North Pacific Ocean and southern Bering Sea during the last several decades. A bottom-up nutritional limitation mechanism induced by physical oceano-graphic change or competition with fisheries was long thought to be largely responsible for these declines. The current weight of evidence is more consistent with top-down forcing. Increased predation by killer whales probably drove the sea otter collapse and may have been responsible for the earlier pinniped declines as well. We propose that decimation of the great whales by post-World War II industrial whaling caused the great whales’ foremost natural predators, killer whales, to begin feeding more intensively on the smaller marine mammals, thus ‘‘fishing-down’’ this element of the marine food web. The timing of these events, information on the abundance, diet, and foraging behavior of both predators and prey, and feasibility analyses based on demographic and energetic modeling are all consistent with this hypothesis. food web dynamics brought about by human overharvesting initiated the change.

abstract
We examined the digestion and passage times of bones and other hard parts from pollock, herring, salmon, and sandlance recovered from two juvenile captive Steller's sea lions (Eumetopias jubatus) subjected to varying activity levels. Key bones that could be identified to species were distributed over an average of 3.2 scats (range 1–6) following a single meal, with pollock remains occurring in significantly more scats than other species. Relying on otoliths alone to determine the presence of prey resulted in significantly fewer prey being identified than if other structures were also used (such as vertebrae, jaw bones, and teeth), particularly for salmon. Using either technique, there were significant differences in the likelihood that bones would be recovered from the series of scats produced following a meal, with pollock recovery exceeding herring (by three-fold) and sandlance (by eight-fold). Differences between species were reduced when recovery was calculated on a per scat basis rather than over multiple scats. Active animals passed greater numbers of bones, but the overall effect on prey recovery estimates was not significant. Defecation times of prey structures from a meal were variable and ranged from an initial 2–56 h to a final 28–148 h. The time interval to pass 95% of recovered structures varied by a factor of two among prey species, and was highest for pollock due to retention beyond 65 h.

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.

abstract

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

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

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

abstract
The effects of seasonal and regional differences in diet composition on the food requirements of Steller sea lions (Eumetopias jubatus)were estimated by using a bioenergetic model. The model considered differences in the energy density of the prey, and differences in digestive effciency and the heat increment of feeding of different diets. The model predicted that Steller sea lions in southeast Alaska required 45–60% more food per day in early spring (March) than after the breeding season in late summer (August) because of seasonal changes in the energy density of the diets (along with seasonal changes in energy require ments).The southeast Alaska population,at 23,000 (±1660 SD)animals (all ages), consumed an estimated 140,000 (±27,800) of prey in 1998. In contrast, we estimated that the 51,000 (±3680) animals making up the western Alaska population in the Gulf of Alaska and Aleutian Islands consumed just over twice this amount (303,000 [±57,500 ] t). In terms of biomass removed in 1998 from Alaskan waters,we estimated that Steller sea lions accounted for about 5% of the natural mortality of gadids (pollock and cod) and up to 75% of the natural mortality of hexagram mids (adult Atka mackerel).These two groups of species were consumed in higher amounts than any other.The predicted average daily food require ment per individual ranged from 16 (±2.8)to 20 (±3.6)kg (all ages com bined). Per capita food requirements differed by as much as 24% between regions of Alaska depending on the rel ative amounts of low–energy-density prey (e.g.gadids)versus high–energy density prey (e.g. forage fish and salmon)consumed. Estimated require ments were highest in regions where Steller sea lions consumed higher proportions of low—energy-density prey and experienced the highest rates of population decline.

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.

abstract
Large-scale shifts occurred in climatic and oceanic conditions in 1925, 1947, 1977, 1989 and possibly 1998. These shifts affected the mix and abundance of suites of coexisting species during each period of relative environmental stability- from primary producers to apex predators. However, the 1989 regime shift was not a simple reversal of the 1977 shift. The regime shifts occurred abruptly and were neither random variations nor simple reversals to the previous conditions. Timing of these anomalous environmental events in the North Pacific Ocean appears to be linked to physical and biological responses in other oceanic regions of the world. Changes in the atmospheric pressure can alter wind patterns that affect oceanic circulation and physical properties such as salinity and depth of the thermocline. This, in turn, affects primary and secondary production. Data from the North Pacific indicate that regime shifts can have opposite effects on species living in different domains, or can affect similar species living within a single domain in opposite ways. Climatic forcing appears to indirectly affect fish and marine mammal populations through changes in the distribution and abundance of their predators and prey. Effects of regime shifts on marine ecosystems are also manifested faster at lower trophic levels. Natural variability in the productivity of fish stocks in association with regime shifts indicates that new approaches to managing fisheries should incorporate climatic as well as fisheries effects.

abstract
Steller sea lion Eumetopias jubatus mothers and pups establish and maintain contact with individually distinctive vocalizations. Our objective was to develop a robust neural network to classify females based on their mother-pup contact calls. We catalogued 573 contact calls from 25 females in 1998 and 1323 calls from 46 females in 1999. From this database, a subset of 26 females with sufficient samples of calls was selected for further study. Each female was identified visually by marking patterns, which provided the verification for acoustic identification. Average logarithmic spectra were extracted for each call, and standardized training and generalization datasets created for the neural network classifier. A family of backpropagation networks was generated to assess relative contribution of spectral input bandwidth, frequency resolution, and network architectural variables to classification accuracy. The network with best overall generalization accuracy 71% used an input representation of 0–3 kHz of bandwidth at 10.77 Hz/bin frequency resolution, and a 2:1 hidden:output layer neural ratio. The network was analyzed to reveal which portions of the call spectra were most influential for identification of each female. Acoustical identification of distinctive female acoustic signatures has several potentially important conservation applications for this endangered species, such as rapid survey of females present on a rookery.

abstract
Feces were collected from six Steller sea lions (Eumetopias jubatus) that consumed known amounts of Atka mackerel (Pleurogrammus monopterygius), Pacific herring (Clupea harengus), pink salmon (Oncorhynchus gorbuscha), walleye pollock (Theragra chalcogramma), and squid (Loligo opalacens). The goal was to determine the numbers and types of taxon-specific hard parts that pass through the digestive tract and to develop correction factors for certain abundantly occurring structures. Over 20,000 fish and squid were consumed during 267 d of fecal collection. During this period, over 119,000 taxon-specific hard parts, representing 56 different structures, were recovered. Skeletal structures and non-skeletal structures accounted for 72% and 28% of all hard parts respectively. The branchiocranium, axial skeleton, and dermocranium regions of the skeletal system accounted for the greatest number of hard parts recovered. Over 70% of all recovered hard parts were represented by one to six taxa specific structures for each prey type. The average number of hard parts (3.1-3.12) and structure types (2.0-17.7) recovered per individual prey varied across taxa and were used to derive correction factors (to reconstruct original prey numbers). A measure of the variability of hard part recovery among sea lions showed no difference for certain herring, pollock, and squid structures, however, there was a significant difference for salmon and Atka mackerel structures. Identifying all taxon-specific prey hard parts increases the likelihood of identifying and estimating the number of prey consumed.

abstract
A dynamic bioenergetic model for Steller sea lions (Eumetopias jubatus) was built using the STELLA simulation modeling system. The model is intended as an aid for the exploration of ecological questions regarding growth and survival of immature Steller sea lions (ages 1-3) living along the Oregon coast under different nutritional scenarios. The ultimate goals were: 1) to identify features of the Oregon ecosystem that could contribute to the growth of the Steller sea lion population in contrast to the declining population in Alaska and 2) to provide a basis for examining the various hypotheses that have been put forward regarding the causes of the Steller sea lion decline in Alaska. The dynamic energetic model was composed of coupled submodels, created or adapted from the literature, that describe the energetic inputs and outputs of the animal. It is a mechanistic model based on biological principles that attempts to describe the connections and feedbacks between the different components and the allocation of energy to them under suboptimal nutrition. The model predicted that both changes in prey abundance and quality would have a more pronounced effect in one-year-old animals than in two- and three-year-old sea lions. A reduction in prey density could delay the attainment of sexual maturity, and this could have a significant negative effect on the population rate of increase. The seasonal migration of Pacific whiting was shown to be very important as a biomass influx into the system. In general, the model predictions were consistent with observations on the declining population of Steller sea lions in Alaska.

abstract
The western stock of Steller sea lions has declined from over 140,000 individuals in the 1960s to possibly fewer than 40,000 individuals in 2000. The primary hypotheses put forth by the National Marine Fisheries Service (NMFS) explaining this decline centers around food limitation.One alternative hypothesis that has recently received attention is that the decline or lack of recovery is due to the effects of predation by killer whales or sharks.Reports of large numbers of killer whales surrounding longline and trawl fishing vessels in western Alaska suggest that there are many killer whales in the region. In order to assess the impact of killer whale predation on this popula- tion decline,we need the following information:

1.Number of Steller sea lions.

2.Intrinsic growth rate of Steller sea lion population.

3.Number of killer whales that prey on Steller sea lions.

4.Percentage of the killer whale diet that consists of Steller sea lions and age class of sea lion that is consumed.

keywords     Predation

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.

abstract
Many animals lower their resting metabolism (metabolic depression) when fasting or consuming inadequate food. We sought to document this response by subjecting five Steller sea lions to periods of: (1) complete fasting; or (2) restricting them to 50% of their normal herring diet. The sea lions lost an average of 1.5% of their initial body mass per day (2.30 kg y d )during the 9 –14-day fast, and their resting metabolic rates decreased 31%, which is typical of a ‘fasting response ’. However, metabolic depression did not occur during the 28-day food restriction trials,despite the loss of 0.30% of body mass per day (0.42 kg y d). This difference in response suggests that undernutrition caused by reduced food intake may stimulate a ‘hunger response ’, which in turn might lead to increased foraging effort. The progressive changes in metabolism we observed during the fasts were related to, but were not directly caused by, changes in body mass from control levels. Combining these results with data collected from experiments when Steller sea lions were losing mass on low energy squid and pollock diets reveals a strong relationship between relative changes in body mass and relative changes in resting metabolism across experimental conditions.While metabolic depression caused by fasting or consuming large amounts of low energy food reduced the direct costs from resting metabolism, it was insufficient to completely overcome the incurred energy deficit.

abstract
Changes in the quality or quantity of food can have a dramatic effect on the population status of wild animals. Unfortunately, it is difficult to assess (or define) whether nutritional stress is a contributing factor to the decline of any particular species.The “nutritional quality ” of a diet to an animal is a complex matter to assess given the range of components that can influence its value.The effects of different diets on animal health are equally complex, and are particularly difficult to assess in large, wild animals. Research by the North Pacific Universities Marine Mammal Research Consortium with captive Steller sea lions is evaluating the possible mechanisms by which dietary changes might adversely affect the nutritional or health status of individual animals, and ultimately the population as a whole. The research investigates the three potential proximate mechanisms by which changes in diet might impact Steller sea lions:a decrease in energy intake, a decrease in the intake of some essential element, and the over-consumption of an element detrimental to sea lion health.

abstract
Marine mammal predator-prey interactions occur over different spatial and temporal scales, making it difficult to empirically decipher the influences they have on one another and on their ecosystems. However, their coexistence suggests that marine mammal predators and their prey have had profound influences on each other’s behaviors, physiologies, morphologies, and life history strategies. The diversity of niches filled by marine mammals makes if difficult to generalize about the evolutionary consequences of their interactions with prey, beyond stating the obvious: marine mammals have adapted to catch food, while their prey have adapted to avoid being caught. On the shorter ecological time scale, marine mammals can affect the abundance of other species by consuming or out-competing them. They can also indirectly affect the abundance of nontargeted species by consuming one of their predators, and can have strong impacts on the overall dynamics and structure of their ecosystems. One of the best tools for understanding marine mammal predator-prey interactions is the ecosystem model. However, more work is required through experimental manipulations and observational studies to evaluate the choices made by marine mammals and the costs of obtaining different species of prey.

keywords     predation

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.

abstract
A generalized bioenergetic model was used to estimate the food requirements of Steller sea lions <i>Eumetopias jubatus</i> in Alaska, USA. Inputs included age and sex-specific energy require-ments by date, population size and composition, and diet composition and energy content. Error in model predictions was calculated using uncertainty in parameter values and Monte Carlo simulation methods. Our model suggests that energy requirements of individuals were generally lowest in the summer breeding season (June to August) and highest in the winter (December to February) and spring (March to May) mainly due to changes in activity budgets. Predicted relative daily food requirements were highest for young animals (12 ± 3% SD and 13 ± 3% of body mass for 1 yr old males and females respectively) and decreased with age (5 ± 1% and 6 ± 1% of body mass for 14 yr old males and 22 yr old females respectively). The mean daily food requirement of pregnant females predicted by the model was only marginally greater than the predicted mean daily food requirement of non-pregnant females of the same age. However, the model suggested that the mean daily food requirement of females nursing pups was about 70% greater than females of the same age without pups. Of the 3 sets of model parameters (diet, population, and bioenergetic), uncertainty in diet and bioenergetic parameters resulted in the largest variation in model predictions. The model provides a quantitative estimate of the Steller sea lion population’s food requirements and also suggests directions for future research.

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.

abstract
Sea lion and seal populations in Alaskan waters underwent various degrees of decline during the latter half of the twentieth century and the cause(s) for the declines remain uncertain. The stable carbon ( 13 C/12 C) and nitrogen ( 15 N/14 N) isotope ratios in bone collagen from wild Steller sea lions (Eumetopias jubatus), northern fur seals (Callorhinus ursinus) and harbor seals (Phoca vitulina) from the Bering Sea and Gulf of Alaska were measured for the period 1951–1997 to test the hypothesis that a change in trophic level may have occurred during this interval and contributed to the population declines. A significant change in d 15 N in pinniped tissues over time would imply a marked change in trophic level. No significant change in bone collagen d 15 N was found for any of the three species during the past 47 years in either the Bering Sea or the Gulf of Alaska. However, the 15 N in the Steller sea lion collagen was significantly higher than both northern fur seals and harbor seals. A significant decline in d 13 C (almost 2 ‰ over the 47 years) was evident in Steller sea lions, while a declining trend, though not significant, was evident in harbor seals and northern fur seals. Changes in foraging location, in combination with a trophic shift, may offer one possible explanation. Nevertheless, a decrease in d 13 C over time with no accompanying change in d 15 N suggests an environmental change affecting the base of the foodweb rather than a trophic level change due to prey switching. A decline in the seasonal primary production in the region, possibly resulting from decreased phytoplankton growth rates, would exhibit itself as a decline in d 13 C. Declining production could be an indication of a reduced carrying capacity in the North Pacific Ocean. Sufficient quantities of optimal prey species may have fallen below threshold sustaining densities for these pinnipeds, particularly for yearlings and subadults who have not yet developed adequate foraging skills.

abstract
Growth rates of vibrissae (whiskers), which act as a temporal record of feeding in harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus), were estimated using 13 C- and 15 N-labeled glycine followed by stable-isotope analysis. The labeled glycine was incorporated into keratin and served as a temporal marker for growth-rate calculation. One captive harbor seal received two doses 147 days apart, while a second seal received one dose; vibrissae were analyzed after 86 and 154 days. The peak positions indicated that growth began in the fall, continued into spring, but ceased in June, with active growth rates of 0.33 mm/day. Two adult captive Steller sea lions each re-ceived two labeled doses during a 308-day period. After 427 days vibrissae in both sea lions showed two peaks corre-sponding to the markers; growth rates were calculated as 0.05–0.07 mm/day. Growth rates in captive juvenile and wild adult Steller sea lions, 0.10–0.17 mm/day, supported the assumption that major isotopic oscillations in vibrissae of wild sea lions were annual. The multiyear records imply that Steller sea lions retain their vibrissae; harbor seal vibrissae, in contrast, have periods of rapid growth and appear to be shed, at least in part, annually.

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).

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

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.

abstract
The western Alaska population of Steller sea lions has significantly declined over the past thirty-five years. A population estimate of 180,000 individuals in 1965 declined to a current estimate of 50,000. A widely accepted hypothesis for the cause of decline is from indirect competition with the commercial fishing industry. Analysis of Steller sea lion censuses have determined that decline is most evident in the juvenile portion of the population. This could be explained by a decrease in prey availability for juveniles which are physiologically and behaviorally limited in their ability to forage further and deeper for food. Although Steller sea lions naturally fast during their summer breeding season, they are not as biochemically adapted to handle food deprivation at other times of the year (Rea et al. 1999). This study addresses the physiological implications of food deprivation by analyzing the effects of fasting on serum lipid composition and content. Additionally, the breeding and non-breeding seasons were compared to determine if seasonality affects serum lipid composition and content.

abstract
Alternative animal models are desirable to assess the role of nutrition on the population dynamics of marine mammals. If an appropriate model could be found, it might be possible to identify population consequences and risks that face sea otters forced to eat fish after depleting local invertebrates, or for sea lions which switch from a fatty fish to a lean fish. From the arguments raised above, the rat appears to be a feasible model for studying marine mammal nutrition. A preliminary study exploring the effects of nutrition on population dynamics via parameters of growth and reproductive success is feasible. Although mink and harbor seal models are superior in their similarity to other marine mammals, the difficulty and time involved in breeding them is either extremely labor intensive or prohibitive. Again, the regular, five day cycle of the rat and shorter generation time allow for parameters of fertility and offspring viability in response to different diets to be examined in a cost effective and economic way. Additionally, because of the extensive use of rats in other nutritional studies, many signs and symptoms of specific nutritional shortcomings are known and easily detected. If a reliable model can be implemented in the study of marine mammal population dynamics, research can explore aspects of physiology nor available when using captive marine mammals or mammals in the wild. Development of a model also has the potential to reduce the number of mammals taken from the wild for scientific study, thereby helping to preserve many threatened species.

abstract
Compared to terrestrial mammals, marine mammals are generally perceived as having elevated metabolic rates and insatiable appetites, attributable to maintaining their high body core temperatures in a cold aquatic environment. The perception that marine mammals have higher metabolic rates than terrestrial mammals of similar body size is reinforced by a substantial body of literature that dates over half a century (Sergeant, 1973; Lavigne, 1982) and is further supported by reports of captive marine mammals ingesting large quantities of food (Sergeant, 1969, 1973; Bonner, 1982). However, within the past two decades, this convention has been challenged. Lavigne et al. (1986) failed to reject the hypothesis that physically mature phocids (true seals) have similar basal metabolic rates (BMRs) as terrestrial mammals of similar body weight, when measured under standard conditions. Innes et al. (1987) found similar results when comparing feeding rates (FRs) of seals and whales. However, much research has been conducted on the FRs and BMRs of marine mammals since these studies were completed. In our study, we re-investigated whether basal metabolic and feeding rates of marine mammals are similar to those predicted for terrestrial mammals. We also explored relationships between taxa and were able to predict the basal metabolic rates of species of marine mammals not previously studied. These estimates can also be used to assess the amount of prey consumed by species of marine mammals whose metabolisms have never been determined in the field or in the lab.

abstract
Twelve dead Steller sea lion pups (Eumetopias jubatus) aged 3-14 d were recovered from rookeries in Southeast Alaska. They had a wide range of body sizes and conditions (small to large and fat to no fat). The ability of calipers to estimate the thickness of their blubber layer was assessed with a set of skinfold calipers. Average error of measurement for skin and blubber thickness was an acceptable 5.4%, but the skin and blubber of the pups were highly compressible. Skinfold thickness increased with body mass but did not necessarily reflect the development of blubber, given that pups with no blubber also showed an increase in skinfold thickness with increases in body mass. Skinfold thickness of sea lion pups appears to predict body size better than it predicts blubber thickness, making it difficult if not impossible to develop a simple index of body condition or a calculation of percent body fat for Steller sea lion pups from skinfold caliper measurements.