Neonatal survival of Steller sea lions (Eumetopias jubatus)

Neonatal survival of Steller sea lions ( Eumetopias jubatus ) are often considered inconsequential to their population dynamics. However, observations of dead animals on rookeries and in surrounding waters suggest that early mortality is not uncommon. This study used the natural markings of adult females in a mark and resighting framework to estimate the apparent survival (φ) of pups with the Cormack–Jolly–Seber model at two sites on Lowrie Island, Alaska from birth to 3 wk old. Estimates varied greatly by site and year; 2002 Area 5:     (95% CI: 0.199, 0.684; n = 21), 2002 Area 1:     (0.437, 0.916; n = 21), 2003 Area 5:     (0.414, 0.738; n = 56), and 2003 Area 1:     (0.695, 0.997; n = 32). The mean estimate across the four area × year combinations was     (0.569, 0.772). Survival was lowest on the first day of life and then leveled off at a higher rate. None of the four environmental covariates we considered (swell height, interaction of tide and swell heights, density, or birth date) were significantly related to neonatal survival. Our results suggest that estimates of first-year survival that do not account for mortality prior to dispersal from the natal rookery may significantly overestimate survival rate.     

Enzyme‐linked immunosorbent assay to quantitate serum ferritin in the northern fur seal (Callorhinus ursinus)

Serum ferritin concentration correlates with tissue iron stores in humans, horses, calves, dogs, cats, and pigs. Serum ferritin is considered the best serum analyte to predict total body iron stores in these species, and is more reliable than serum iron or total iron‐binding capacity, both of which may be affected by disorders unrelated to iron adequacy or excess (including hypoproteinemia, chronic infection, hemolytic anemia, hypothyroidism, renal disease, and drug administration). Iron overload has been documented to result in hemochromatosis in captive northern fur seals (Callorhinus ursinus); therefore, we developed an enzyme‐linked immunosorbent assay (ELISA) to measure serum ferritin in this species. The assay uses two murine anti‐canine ferritin monoclonal antibodies in a sandwich arrangement that was originally used in an ELISA to measure serum ferritin in dogs. Ferritin isolated from fur seal liver was used as a standard. Ferritin standards were linear from 0 to 50 ng/ml. Recovery of purified ferritin from fur seal serum varied from 89% to 99%. The within‐assay variability was 6%, and the assay‐to‐assay variability for two different samples was 10% and 16%. Zoo Biol 23:79‐84, 2004.© 2004 Wiley‐Liss, Inc.     

Otolith size and location in digestive tracts of northern fur seals (Callorhinus ursinus): Implications for dietary interpretations

Walleye pollock (Theragra chalcogramma) otoliths (n= 2,706) recovered from stomachs, small intestines, and colons of 43 northern fur seals (Callorhinus ursinus) were evaluated for size and wear by location in the digestive tract. Pollock fork length was regressed on otolith length after correction for erosion, and age was estimated from the calculated body size. Age‐1+ pollock otoliths (≥6.3‐mm length) were concentrated in stomachs while age‐0 otoliths (≤6.2‐mm length) were concentrated in colons. Less than 10% of otoliths were found in the small intestines. Pollock age decreased with progression along seal gastrointestinal tracts. Otolith quality increased along gastrointestinal tracts in numbers ≥20, which was typical of age‐0 otoliths recovered from colons. Otolith distribution by age and quality along gastrointestinal tracts suggests that small (≤12 cm) schooling prey are consumed in large volume and passed as a bolus rapidly through the digestive tract before significant erosion of bony remains occurs; while larger prey are eaten in smaller volume and subjected to otolith erosion due to longer retention in the stomach. Our results illustrate the importance of multiple sampling strategies to comprehensively represent prey size in pinniped diet.     

Characterization of eight microsatellite loci in Steller sea lions (Eumetopias jubatus)

Steller sea lions (Eumetopias jubatus) are listed as an endangered species in western Alaska and have exhibited a significant population decline throughout their range. Eight microsatellite loci were isolated from genomic DNA libraries. In addition, all these markers were found to be variable in nine individuals of the California sea lion (Zalophus californicus). This panel of markers was developed to analyse population structure in Steller sea lions throughout their range.     

Broad thermal capacity facilitates the primarily pelagic existence of northern fur seals (Callorhinus ursinus)

Thermoregulatory capacity may constrain the distribution of marine mammals despite having anatomical and physiological adaptations to compensate for the thermal challenges of an aquatic lifestyle. We tested whether subadult female northern fur seals (Callorhinus ursinus) experience increased thermoregulatory costs in water temperatures potentially encountered during their annual migration in the Bering Sea and North Pacific Ocean. Metabolic rates were measured seasonally in 6 captive female northern fur seals (2.75–3.5 yr old) in ambient air and controlled water temperatures of 2°C, 10°C, and 18°C. Rates of oxygen consumption in ambient air (1°C–18°C) were not related to environmental temperature except below 2.5°C (winter only). However, metabolism was significantly higher during the fall seasonal trials (September–October) compared to other times of year, perhaps due to the costs of molting. The fur seals appeared thermally neutral in all seasons for all water temperatures tested (2°C–18°C) except during the summer when metabolic rates were higher in the 2°C water. Comparing this broad thermal neutral zone to the average sea surface temperatures potentially encountered during annual migrations indicates wild fur seals can likely exploit a large geographic area without added thermal metabolic costs.     

The decline of Steller sea lions Eumetopias jubatus in Alaska: a review of the nutritional stress hypothesis

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 population could compromise the health of Steller sea lions and hinder their recovery.     

Field anesthesia of juvenile Steller sea lions (Eumetopias jubatus) using inhalation anesthesia

Between 1998 and 2008, 621 Steller sea lions (Eumetopias jubatus, SSL) were captured underwater by SCUBA divers and anesthetized with isoflurane (n = 602) or sevoflurane (n = 19). We found significantly faster induction time ( ± SD) for sevoflurane (11 ± 6 min) compared to isoflurane (14 ± 6 min), as well as an interaction between anesthetists using the isoflurane protocol. Severe hypothermia with temperatures <35°C were measured in 22% of all animals, and had significant associations with month, length of anesthesia, and sex. Mortality rate was low (0.33%). We conclude that both isoflurane and sevoflurane anesthesia were effective for field anesthesia to safely handle and sample SSL.     

Foraging habitats based on the diet of female northern fur seals (Callorhinus ursinus) on the Pribilof Islands, Alaska

Scats (fecal samples) collected between 1987 and 2000 on northern fur seal Callorhinus ursinus rookeries of St Paul ( n =2968) and St George Islands ( n =1203), Alaska, were used to examine the relationship between breeding sites and food habits of adult female seals. On the basis of the frequency of occurrence (FO) and per cent minimum number of individual prey (%MNI) in scats, juvenile walleye pollock Theragra chalcogramma and gonatid squid Gonatopsis borealis/Berryteuthis magister and Gonatus madokai/Gonatus middendorffi were the dominant prey species consumed overall. Other primary prey (FO>5%) included Pacific sand lance Ammodytes hexapteus , Pacific herring Clupea pallasi , northern smoothtongue Leuroglossus schmidti , Atka mackerel Pleurogrammus monopterygius , Pacific salmon ( Oncorhynchus spp.) and other squid of the Gonatus genus. We identified five rookery complexes from a cluster analysis of the FO of primary prey in scats. Rookery complexes were separated geographically and each was further defined by characteristic patterns in the representation of prey types typically associated with specific hydrographic domains. Diet differences were observed among rookeries on the north and south side of St George Island and on the east, south and south-west side of St Paul Island. The rookery clusters observed in this study provide evidence of resource partitioning among adult female northern fur seals and have important implications for fur seal conservation and management.     

Ontogeny of total body oxygen stores and aerobic dive potential in Steller sea lions (Eumetopias jubatus)

Two key factors influence the diving and hence foraging ability of marine mammals: increased oxygen stores prolong aerobic metabolism and decreased metabolism slows rate of fuel consumption. In young animals, foraging ability may be physiologically limited due to low total body oxygen stores and high mass specific metabolic rates. To examine the development of dive physiology in Steller sea lions, total body oxygen stores were measured in animals from 1 to 29 months of age and used to estimate aerobic dive limit (ADL). Blood oxygen stores were determined by measuring hematocrit, hemoglobin, and plasma volume, while muscle oxygen stores were determined by measuring myoglobin concentration and total muscle mass. Around 2 years of age, juveniles attained mass specific total body oxygen stores that were similar to those of adult females; however, their estimated ADL remained less than that of adults, most likely due to their smaller size and higher mass specific metabolic rates. These findings indicate that juvenile Steller sea lion oxygen stores remain immature for more than a year, and therefore may constrain dive behavior during the transition to nutritional independence.     

Prey selection of subadult male northern fur seals (Callorhinus ursinus) and evidence of dietary niche overlap with adult females during the breeding season

During the breeding season northern fur seals (Callorhinus ursinus) congregate on the Pribilof Islands in large numbers creating the potential for intraspecific competition. Due to the declining trend in the Pribilof Islands population of fur seals, it is important to understand how prey resources are partitioned among the population. Fur seals exhibit a high degree of sexual dimorphism resulting in energetic differences among age and sex classes. Therefore, we hypothesized that subadult male and adult female fur seals would differ in the type and size of prey consumed. We examined the diets of subadult male (age 2–8; mean mass 28–176 kg) and adult female (age ≥ 3 yr; mean mass 13–50 kg) seals on St. Paul Island from 1992 to 2000. Prey remains found in fecal samples were compared using niche overlap indices. There was nearly complete dietary niche overlap between subadult male and adult female fur seals. Walleye pollock (Theragra chalcogramma), Pacific salmon (Oncorhynchus spp.), Pacific herring (Clupeia pallasi), and cephalopods were common prey items found in the diets of both groups. We found differences in the size of pollock consumed and that geographic location of sample collection may be important in determining diet differences. Our results indicate high levels of dietary overlap among subadult male and adult female fur seals.     

Short‐term survival of Steller sea lion (Eumetopias jubatus) pups: Investigating the effect of health status on survival

We estimated survival probabilities for Steller sea lion (Eumetopias jubatus) pups from 3 wk to 6 wk old and from 6 wk to 1 yr at three rookeries in southeastern Alaska. We also investigated the effect of mass, body condition, health variables, and the genetic origin on 3–6 wk survival. Survival differed substantially among rookeries and between sexes, with survival lowest at Hazy Islands, intermediate at White Sisters, and highest at Graves Rocks and survival lower for males than females. Body mass, body condition, and hematocrit were positively related to survival and blood %H₂O and haptoglobin level (for females; no relationship for males) were negatively related to survival. Taking predictor variables collectively, sea lion pups at Hazy Islands, which had the lowest survival probability, had the lowest mass, hematocrit, and hemoglobin, and had high levels of blood %H₂O, and hookworm infection. Values from Graves Rocks, which had the highest survival, were the opposite of those from Hazy Island (e.g., high mass, body condition, hematocrit, and hemoglobin), while those from White Sisters (intermediate survival) had varying means (e.g., high hematocrit and hemoglobin and low hookworms, but also low body condition); these patterns suggest that physiological factors potentially underlie rookery differences in survival.     

Body mass and composition responses to short-term low energy intake are seasonally dependent in Steller sea lions (Eumetopias jubatus)

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 day⁻¹), and at a lower rate during summer (1.2 ± 0.32 kg day⁻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.     

Effects of research disturbance on the behavior and abundance of Steller sea lions (Eumetopias jubatus) at two rookeries in Alaska

We examined the effects of research disturbance on the behavior and abundance of Steller sea lions (Eumetopias jubatus) at rookeries on Marmot and Ugamak Islands in Alaska. During 3 of 6 yr, researchers intentionally drove all adult and juvenile sea lions off at least part of the beach in order to permanently mark and measure sea lion pups. The research disturbance occurred after the majority of females had bred and when most pups were 1 mo old. We used generalized linear models to determine the relationship between research disturbance and sea lion behavior or abundance. Research disturbance was related to changes in the proportion of sea lions exhibiting two to three of nine behavior metrics: agonistic and resting females and active males at Marmot, and active and resting males and females at Ugamak. Model results indicated that changes lasted between 3 and 20 d depending on the sex, behavior, and rookery. Inclusion of research disturbance into Marmot abundance models did not improve the fit to the data, if variability between years was permitted. Optimally timed, low‐frequency research disturbance did not appear to have long‐term effects on sea lion behavior or abundance and was largely associated with changes that were similar to natural variation.     

Serum indices of body stores of iron in northern fur seals (Callorhinus ursinus) and their relationship to hemochromatosis

Iron storage disease (hemochromatosis) has been reported in many species of both captive and free‐ranging animals. In this study we examined the relationship between this disease and concentrations of iron analytes in aquarium‐held northern fur seals (Callorhinus ursinus). Sera were analyzed for iron, total iron‐binding capacity (TIBC), ferritin, ceruloplasmin, and haptoglobin concentrations in a retrospective study that included samples taken over a 14‐year period. The animals ranged in age from <1 year to an estimated 23 years. Serum ferritin was measured using an enzyme‐linked immunosorbent assay (ELISA) for canine sera. The results from this assay are the first reported for any pinniped. Serum iron concentrations in presumed healthy animals ranged from 37 to 196 µg/dl, and TIBC ranged from 136 to 484 µg/dl. The transferrin saturation percentage differed significantly between male (41%) and female (63%) adult fur seals, as did the ferritin levels (54 ng/ml for males vs. 500 ng/ml for females). There was a trend toward increased serum ferritin and percent transferrin saturation with age, especially in females. The data also showed a relationship between serum iron and transferrin saturation among eight mother–pup pairs, which suggests that pups may develop increased iron levels due to placental transfer of iron and/or transfer of iron through the milk from iron‐overloaded females. Diet was considered as a factor in the development of hemochromatosis in at least three geriatric female northern fur seals, and their diets were analyzed for iron concentrations. On the basis of these results, the diets were altered by replacing a portion of the high‐iron‐content fish (herring) with a lower‐iron‐content item (squid), and discontinuing iron and vitamin C supplementation (via a multivitamin tablet). Sera were analyzed before, and 1 and 4 years after the dietary changes were implemented. Paired t‐tests showed no significant changes in the iron analytes from pre‐ to post‐diet‐change samples, which indicates that it may be too late to affect iron levels by diet alone in older animals with a chronic history of elevated iron levels. Zoo Biol 23:205–218, 2004. © 2004 Wiley‐Liss, Inc.     

Comparative biology of Uncinaria spp. in the California sea lion (Zalophus californianus) and the northern fur seal (Callorhinus ursinus) in California

Studies on several aspects of the life cycle of hookworms (Uncinaria spp.) in the California sea lion (Zalophus californianus) and northern fur seal (Callorhinus ursinus) were conducted on material collected on San Miguel Island (SMI), California and at The Marine Mammal Center, Sausalito, California in 1997, 1998, and 1999. Examination of Z. californianus intestines for adult hookworms and feces for eggs revealed that longevity of these parasites in pups is about 6-8 mo, and infections are probably not present in older sea lions. Parasitic third-stage larvae (L3) were recovered from the ventral abdominal tissue of Z. californianus, suggesting transmammary transmission. Callorhinus ursinus pups had no hookworm eggs in their feces or adult worms (except for 1 probable contaminant) in their intestines in the fall and early winter, revealing that adult Uncinaria spp. are spontaneously lost at <3 mo of age of the pups. Sand samples from rookeries, used by both Z. californianus and C. ursinus, on SMI were negative for free-living, L3 in summer months but positive in fall and winter months, indicating seasonality occurred.     

Organochlorine exposure and health effects in stranded Steller sea lions (Eumetopias jubatus) and Pacific harbor seals (Phoca vitulina richardii) from Oregon and southern Washington coasts

Organochlorine (OC) pesticides and polychlorinated biphenyls (PCBs) have been detected in a variety of marine mammal species at levels associated with adverse health effects. Little is known about OC levels and impacts on health in pinnipeds with different life histories. We determined the health and levels of 18 OC pesticides and 16 PCB congeners in blubber samples from 20 Steller sea lions and 39 Pacific harbor seals stranded from Oregon and Southern Washington. The most commonly detected OC at the highest concentration was p,p′- dichlorodiphenyldichloroethylene (DDE). PCBs were detected in all samples as well. Hypothesis testing indicated that diseased Steller sea lions (males and females combined) had higher contaminant concentrations than healthy Steller sea lions, and diseased Pacific harbor seals had higher concentrations of total OCs than healthy animals. Differences were also noted between diseased and healthy animals when looking at individual sexes of each species. Diseased Steller sea lions had higher mean contaminant levels than diseased harbor seals and healthy Steller sea lions had higher mean contaminant concentrations than healthy Pacific harbor seals. These results show that species differences exist in both contaminant loads and sensitivity to contaminants, which may be due to differences in life histories and physiology.     

Spatial patterns and scaling behaviors of Steller sea lion (Eumetopias jubatus) distributions and their environment

Fractal geometry and other multi-scale analyses have become popular tools for investigating spatial patterns of animal distributions in heterogeneous environments. In theory, changes in patterns of animal distributions with changes in scale reflect transitions between the controlling influences of one environmental factor or process over another. In an effort to find linkages between Steller sea lions (Eumetopias jubatus) and their environment, the objective of this study was to determine if the spatial distribution of Steller sea lions at sea displayed similar scaling properties to the variation of two environmental features, including bathymetry and sea surface temperature (SST). Additionally, distributions of Steller sea lion point patterns were examined with respect to measurements of bathymetric complexity. From February 2000 to May 2004, satellite transmitters were deployed on 10 groups of juvenile Steller sea lions (n=52) at eight different locations within the Aleutian Islands and Gulf of Alaska. Indices of fractal dimension were calculated for each group of sea lions using a unit square box-counting method, whereas indices of bathymetry and SST patchiness were derived by conducting a variance ratio analysis over the same scales. Distributions of Steller sea lions at sea displayed self-similar fractal patterns, suggesting that individuals were distributed in a continuous hierarchical set of clumps within clumps across scales, and foraging behavior was likely influenced by a scale invariant mechanism. Patterns of bathymetric variability also were self-similar, whereas patterns of SST variability were scale dependent and failed to retain self-similar spatial structure at larger scales. These results indicate that the distributions of Steller sea lions at sea were more influenced by bathymetry than SST at the scales examined, but scale-dependent patterns in the distribution of Steller sea lions at sea or linkages with SST may have been apparent if analyses were conducted at finer spatial scales.