Investigating life-history traits of Steller sea lions with multistate hidden Markov mark-recapture models: Age at weaning and body size effects.

The duration of offspring care is critical to female fitness and population resilience by allowing flexibility in life-history strategies in a variable environment. Yet, for many mammals capable of extended periods of maternal care, estimates of the duration of offspring dependency are not available and the relative importance of flexibility of this trait on fitness and population viability has rarely been examined. We used data from 4,447 Steller sea lions Eumetopias jubatus from the Gulf of Alaska and multistate hidden Markov mark-recapture models to estimate age-specific weaning probabilities. Maternal care beyond age 1 was common: Weaning was later for animals from Southeast Alaska (SEAK) and Prince William Sound (PWS, weaning probabilities: 0.536-0.648/0.784-0.873 by age 1/2) compared with animals born to the west (0.714-0.855/0.798-0.938). SEAK/PWS animals were also smaller than those born farther west, suggesting a possible link. Females weaned slightly earlier (+0.080 at age 1 and 2) compared with males in SEAK only. Poor survival for weaned versus unweaned yearlings occurred in southern SEAK (female survival probabilities: 0.609 vs. 0.792) and the central Gulf (0.667 vs. 0.901), suggesting poor conditions for juveniles in these areas. First-year survival increased with neonatal body mass (NBM) linearly in the Gulf and nonlinearly in SEAK. The probability of weaning at age 1 increased linearly with NBM for SEAK animals only. Rookeries where juveniles weaned at earlier ages had lower adult female survival, but age at weaning was unrelated to population trends. Our results suggest the time to weaning may be optimized for different habitats based on long-term average conditions (e.g., prey dynamics), that may also shape body size, with limited short-term plasticity. An apparent trade-off of adult survival in favor of juvenile survival and large offspring size in the endangered Gulf of Alaska population requires further study.

Regional variations and relationships among cytokine profiles, white blood cell counts, and blood mercury concentrations in Steller sea lion (Eumetopias jubatus) pups.

The Steller sea lion (SSL) population west of 144°W longitude experienced a significant population decline. While there appears to be a stable or increasing population trend in rookeries in the Gulf of Alaska (GOA) and Southeast Alaska (SEA), some rookeries within the Aleutian Islands (AI) have failed to recover. Previous studies found regional differences in whole blood total mercury concentrations ([THg]) showing more than 20% of AI pups had [THg] above critical thresholds for increased risk of immunological effects and other adverse outcomes. Measurements of immune cell-signaling proteins can be used to evaluate the immune status of marine mammals in relation to [THg]. We compared serum cytokine and chemokine concentrations in pups among regions (AI, eastern GOA, SEA), and examined associations among cytokines, chemokines, white blood cell (WBC) counts, and [THg]. Considering liver is an important target organ for mercury and immune protein synthesis we additionally examined the relationship of [THg] with liver-related enzymes serum aspartate (AST) and alanine aminotransferase (ALT). We observed regional differences in cytokine and chemokine measurements and immune protein associations. There was a positive association between total WBC counts and [THg] in AI pups, whereas a negative association between lymphocytes and [THg] in SEA pups. These findings may indicate regional variation in proliferation and differentiation of hematopoietic cells, differences in immune system development, and/or a difference in antigenic stimuli. No associations between [THg] and cytokines, chemokines, AST or ALT were found. Observed regional differences in cytokine and chemokine milieu during gestational and early development in SSL pups could lead to an imbalance in cell differentiation that could impact immunological resiliency in juvenile and adult life stages. We report concentration ranges of a suite of cytokines and chemokines which may prove to be a useful metric for ecotoxicology and risk assessment studies in SSLs and other wildlife.

Whiskers as a novel tissue for tracking reproductive and stress-related hormones in North Pacific otariid pinnipeds.

Keratinized tissues, including whiskers, are ideal for acquiring a record of physiological parameters. Most tissues provide a snapshot of physiological status; however, whiskers may support longitudinal sampling for reproductive and stress-related hormones, if hormones are incorporated as whiskers grow and concentrations change with physiological state. Whiskers from female Steller sea lions (Eumetopias jubatus) and northern fur seals (Callorhinus ursinus) were serially sectioned and pulverized and steroid hormones were extracted. Standard methods were used to validate enzyme immunoassay kits for cortisol, progesterone, 17ß-estradiol and testosterone. All hormones were measurable in whisker segments from both species with progesterone concentrations showing cyclical patterns, which appear to signify previous pregnancies or luteal phases. Yearly progesterone concentrations were greater in years a pup was produced compared with years when no pup was observed. Free-ranging female Steller sea lions had reproductive rates between 0 and 1.0 (0.53 ± 0.33, n = 12) using a yearly progesterone concentration of 30 pg/mg or greater to classify a reproductive year as producing a pup and below 30 pg/mg as non-reproductive. Cortisol concentrations were greater near the root and rapidly declined, lacking any obvious patterns, throughout the rest of the whisker. Progesterone and testosterone concentrations were able to help determine sex of unknown individuals. Immunohistochemistry revealed that steroid hormones most likely do not leach out of whiskers based on the deposition patterns of progesterone and cortisol being present throughout the whisker length. Overall, measuring steroid hormones in whiskers can reveal individual reproductive histories over multiple years in sea lions and fur seals. Cyclical patterns of δ15N were useful for identifying periods of up to ~10 years of growth within whiskers, and measuring both stable isotopes and hormones may be useful for differentiating periods of active gestation from diapause and potentially track multi-year reproductive histories of female otariids.

Stress-related and reproductive hormones in hair from three north Pacific otariid species: Steller sea lions, California sea lions and northern fur seals.

Assessing the physiological impact of stressors in pinnipeds is logistically challenging, and many hormones are altered by capture and handling, limiting the utility of metabolically active tissues. Hair is increasingly being used to investigate stress-related and reproductive hormones in wildlife populations due to less-invasive collection methods, being metabolically inert once grown and containing multiple biomarkers of ecological interest. We validated enzyme immunoassays for measuring aldosterone, cortisol, corticosterone, and testosterone in lanugo (natal hair grown in utero) samples collected from Steller sea lions (Eumetopias jubatus), California sea lions (Zalophus californianus), and northern fur seals (Callorhinus ursinus). We applied laboratory validation methods including recovery of added mass, parallelism and dilution linearity. We found no effects due to differences in alcohol- versus detergent-based cleaning methods. Further, there were no significant differences in hormone concentrations in hair samples collected immediately after the molt and the subsequent samples collected over 1 year, indicating steroid hormones are stable once deposited into pinniped hair. We found no sex differences in any hormone concentrations, likely due to the lanugo being grown in utero and influenced by maternal hormone concentrations. For Steller sea lion and California sea lion pups, we found hormone concentrations significantly differed between rookeries, which warrants future research. Hair provides a novel tissue to explore the intrinsic or extrinsic drivers behind hormone measurements in otariids, which can be paired with multiple health-related metrics to further investigate possible drivers of physiological stress.

Organochlorine contaminant concentrations in blubber of young Steller sea lion (Eumetopias jubatus) are influenced by region, age, sex, and lipid stores.

Contaminant exposure is particularly important for species and populations of conservation concern, such as the Steller sea lion (Eumetopias jubatus). We used blubber samples (n = 120) to determine organochlorine concentrations, including polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane (DDTs), and blood samples (n = 107) to estimate total body lipids based on the hydrogen isotope dilution method. We assessed the influence of age, sex, condition, and geographic area on contaminant concentrations in blubber and contaminant body load. The concentration of ΣPCBs was highest in pups (<6 months) from the Aleutian Islands, and the concentrations in males were higher than females in all regions. The ΣPCBs and ΣDDTs concentrations and loads decreased with increasing mass in pups, however, there were no regional or sex differences in contaminant load. Within each of the five age classes, the concentrations of ΣPCBs and ΣDDTs decreased with increasing mass, but overall these OCs increased with age. Further, accounting for the lipid content, a potential proxy for energy balance, in the animal load reduced or removed the regional and sex effects present in age models for contaminants. We propose, that adjusting OCs concentration by the lipid content of the blubber sample alone may not fully account for the variability in OC concentrations associated with differences in condition or energy states between young Steller sea lions.

Regional differences in the spatial and temporal heterogeneity of oceanographic habitat used by Steller sea lions.

Over the past three decades, the decline and altered spatial distribution of the western stock of Steller sea lions (Eumetopias jubatus) in Alaska have been attributed to changes in the distribution or abundance of their prey due to the cumulative effects of fisheries and environmental perturbations. During this period, dietary prey occurrence and diet diversity were related to population decline within metapopulation regions of the western stock of Steller sea lions, suggesting that environmental conditions may be variable among regions. The objective of this study, therefore, was to examine regional differences in the spatial and temporal heterogeneity of oceanographic habitat used by Steller sea lions within the context of recent measures of diet diversity and population trajectories. Habitat use was assessed by deploying satellite-depth recorders and satellite relay data loggers on juvenile Steller sea lions (n = 45) over a five-year period (2000-2004) within four regions of the western stock, including the western, central, and eastern Aleutian Islands, and central Gulf of Alaska. Areas used by sea lions during summer months (June, July, and August) were demarcated using satellite telemetry data and characterized by environmental variables (sea surface temperature [SST] and chlorophyll a [chl a]), which possibly serve as proxies for environmental processes or prey. Spatial patterns of SST diversity and Steller sea lion population trends among regions were fairly consistent with trends reported for diet studies, possibly indicating a link between environmental diversity, prey diversity, and distribution or abundance of Steller sea lions. Overall, maximum spatial heterogeneity coupled with minimal temporal variability of SST appeared to be beneficial for Steller sea lions. In contrast, these patterns were not consistent for chl a, and there appeared to be an ecological threshold. Understanding how Steller sea lions respond to measures of environmental heterogeneity will ultimately be useful for implementing ecosystem management approaches and developing additional conservation strategies.

REGIONAL AND AGE-RELATED VARIATIONS IN HAPTOGLOBIN CONCENTRATIONS IN STELLER SEA LIONS ( EUMETOPIAS JUBATUS) FROM ALASKA, USA.

Varying concentrations of the highly conserved acute phase response protein, haptoglobin, can indicate changes to the health and disease status of mammals, including the Steller sea lion (SSL; Eumetopias jubatus). To better understand factors relating to acute phase response in SSLs, circulating haptoglobin concentrations (Hp) were quantified in plasma collected from 1,272 individuals sampled near rookeries and haulouts off the coast of Alaska, US. We compared Hp in SSLs between sexes and among different age classes (young pups, young-of-the-year, yearlings, subadults, and adults) sampled within distinct regions in Alaska (Aleutian Islands, Gulf of Alaska, Southeast Alaska). Regional and age-related differences were observed, particularly in younger SSLs. No sex-related differences were detected. We identified weakly significant relationships between Hp and hematology measurements including white blood cell counts and hematocrit in young pups from the Aleutian Islands and Southeast Alaska. No relationship between Hp and body condition was found. Lastly, a nonlinear relationship of plasma Hp and whole blood total mercury concentrations (THg) was observed in SSLs from the endangered western distinct population segment in Alaska. These results demonstrated that regional variation in Hp, especially in younger SSLs, may reflect regional differences in health and circulating THg.

Organochlorine contaminant concentrations in multiple tissues of free-ranging Steller sea lions (Eumetopias jubatus) in Alaska.

The relationships of selected organochlorine (OC) contaminants between blubber, blood, feces, and milk of young, free-ranging Steller sea lions (Eumetopias jubatus) were examined. Both between and within each tissue there was considerable individual variation. In spite of the variation, similar patterns were observed across the tissues for most of the selected PCB congeners. In all four tissues, the major PCB congeners were PCB101, PCB118, PCB138, and PCB153. The most prominent congener, both as a weight (ng/g lipid) and as a percentage of summed PCBs (∑PCBs), was PCB 153. Comparisons between paired tissues showed that ∑DDTs in blubber samples were related to concentrations in blood, feces, and milk. The ∑PCBs in blubber were related to concentrations in milk and fecal samples, though the relationship with feces was weak. Our findings show milk samples, in particular, are useful for assessing OCs in young sea lions. Blubber concentrations of PCB101, PCB118, and PCB138 were an order of magnitude higher than those in milk, supporting the biomagnification of these PCB congeners in SSL tissues. The findings indicate alternative tissues may be used as indicators of relative contaminant exposure in lieu of surgical blubber biopsy.

Maternal Steller sea lion diets elevate fetal mercury concentrations in an area of population decline.

Total mercury concentrations ([THg]) measured in western Aleutian Island Steller sea lion pup hair were the highest maximum [THg] documented in this endangered species to date. Some pups exceeded concentrations at which other fish-eating mammals can exhibit adverse neurological and reproductive effects (21% and 15% pups above 20 and 30 µg/g in hair, respectively). Of particular concern is fetal exposure to mercury during a particularly vulnerable stage of neurological development in late gestation. Hair and blood [THg] were highly correlated and 20% of pups sampled in the western Aleutian Islands of Alaska exceeded mammalian risk thresholds established for each of these tissues. Higher nitrogen isotope ratios suggested that pups accumulated the highest [THg] when their dams fed on higher trophic level prey during late gestation.

Serum chemistry reference ranges for Steller sea lion (Eumetopias jubatus) pups from Alaska: stock differentiation and comparisons within a North Pacific sentinel species.

Blood chemistry and hematologic reference ranges are useful for population health assessment and establishing a baseline for future comparisons in the event of ecosystem changes due to natural or anthropogenic factors. The objectives of this study were to determine if there was any population spatial structure for blood variables of Steller sea lion (Eumetopias jubatus), an established sentinel species, and to report reference ranges for appropriate populations using standardized analyses. In addition to comparing reference ranges between populations with contrasting abundance trends, data were examined for evidence of disease or nutritional stress. From 1998 to 2011, blood samples were collected from 1,231 pups captured on 37 rookeries across their Alaskan range. Reference ranges are reported separately for the western and eastern distinct population segments (DPS) of Steller sea lion after cluster analysis and discriminant function analysis (DFA) supported underlying stock structure. Variables with greater loading scores for the DFA (creatinine, total protein, calcium, albumin, cholesterol, and alkaline phosphatase) also were greater for sea lions from the endangered western DPS, supporting previous studies that indicated pup condition in the west was not compromised during the first month postpartum. Differences between population segments were likely a result of ecological, physiological, or age related differences.

Mercury concentrations in hair from neonatal and juvenile Steller Sea Lions (Eumetopias jubatus): implications based on age and region in this northern Pacific marine sentinel piscivore.

Mercury is a global contaminant of concern for the fetus and the neonate of piscivores. Methylmercury, produced within marine ecosystems, is of particular concern as a readily absorbed neurotoxicant transported across the blood brain barrier and transplacentally. In the North Pacific Ocean, Steller sea lions are broadly distributed apex predators and, as such, integrate complex food webs and the associated exposure and possible adverse effects of toxic and infectious agents. Hair, including lanugo, was examined using regional and age groupings to assess mercury concentrations in young Alaskan Steller sea lions. The highest concentrations of mercury occurred in the youngest animals, likely via in utero exposure. Based on the adverse developmental outcomes of methylmercury toxicity this specific cohort is of concern. Regionally, higher concentrations of mercury were observed in the endangered western population of Steller sea lions and mirrored patterns observed in human biomonitoring studies of Alaskan coastal communities. These data have broader implications with respect to human and ecosystem health as Steller sea lions rely on similar prey species and foraging areas as those targeted by commercial fisheries and subsistence users and are therefore valuable sentinels of marine ecosystem health.