Lorrie D. Rea

Changes in Standard Metabolism during Long-Term Fasting in Northern Elephant Seal Pups (Mirounga angustirostris)

Measurements of body mass, body composition, and O₂ consumption rate V̇o2 were used to quantify some of the factors that influence metabolism during the first 4 mo of development in the northern elephant seal pup. During the 4-wk nursing period, average body mass of the pups increased from 42.0 ± 3.5 kg to 127.3 ± 15.9 kg. By the end of the 10-wk postweaning fast mean body mass declined to 83.1 ± 1.5 kg. Body fat increased from 4% of body mass near birth to approximately 48% at weaning but remained relatively constant throughout the fast. Dramatic changes in body mass and body composition such as these would be expected to influence metabolism significantly. To test this theory, O₂ consumption was measured in pups from birth to 18 wk of age through open-circuit respirometry. Changes in metabolism were correlated most strongly with increases in lean body mass (r² = .51, P < 0.01). Together, changes in lean body mass and age accounted for 75% of the variability seen in V̇o2 (P < 0.01). In addition, a 19% increase in lean mass-specific V̇o2 was documented with the onset of feeding in two laboratory animals, after a 10-wk postweaning fast. This implies a depression of metabolism, possibly as an adaptation for energy conservation during long-term fasting.

HEALTH STATUS OF YOUNG ALASKA STELLER SEA LION PUPS (EUMETOPIAS JUBATUS) AS INDICATED BY BLOOD CHEMISTRY AND HEMATOLOGY

Blood chemistry and hematology were examined in 238 Steller sea lion pups (Eumetopias jubatus) to assess the health status of pups <1 month of age. Failure of juvenile recruitment (possibly due to nutritionally or physiologically compromised pups) into breeding populations has been proposed as a cause of recent declines of this endangered species in Alaska. To identify potential correlations with areas of high population decline, blood chemistry data were considered for three areas: eastern Aleutian Islands (low rates of population decline to stable populations), Gulf of Alaska (high rates of decline), and Southeast Alaska (stable to increasing population). Southeast Alaska pups showed elevated ketone body concentrations (beta-hydroxybutyrate,(beta-HBA)) and depressed glucose levels than pups in the Gulf of Alaska. Over 40% of the pups from Southeast Alaska had elevated beta-HBA concentrations suggesting they underwent longer periods of fasting than seen in pups from other areas. Hematocrit (Hct), hemoglobin concentration (Hb) and water content of the blood exhibited typical mammalian relationships. In summary, blood chemistry and hematology data showed no indication that Steller sea lion pups <1 month old from areas of population decline were nutritionally compromised.

Temporary Captivity as a Research Tool: Comprehensive Study of Wild Pinnipeds Under Controlled Conditions

A new approach to the study of free-ranging, endangered western stock Steller sea lions (Eumetopias jubatus) was implemented at the Alaska SeaLife Center in Seward, Alaska. Groups of up to four juvenile (n = 16) Steller sea lions were held in temporary quarantine for research periods of up to three months. Hematological and blood chemistry parameters were collected at the beginning and end of captivity and compared to free-ranging juvenile controls to determine if animals in temporary captivity can provide accurate physiological data representative of their wild counterparts. Free-ranging pups and juveniles were compared for hematological differences related to developmental stage. Overall, temporarily captive animals did not differ from free-ranging juveniles. Seven of 17 blood parameters measured changed significantly during captivity, likely as a function of a regular schedule and low-impact nutritional studies (e.g., increased mass, cholesterol, total protein, and globulins). A decrease in white blood cells during the study period (10.4 ± 0.59 to 7.9 ± 0.33 m/mm 3 ) to levels lower than that of free-ranging animals (10.7 ± 0.40 m/mm 3 ) indicated a drop in overall stress during captivity despite research and handling procedures. Calcium increased with captivity duration, suggesting that physiological changes can begin in even limited time frames. Eight parameters related to immune status and diet differed significantly between juveniles and pups from the same geographical region. A strategy that combines the benefits of an extended research design with temporary holding of free-ranging animals is proposed as an alternative to traditional field methods for some types of focused physiological studies.

PLASMA HAPTOGLOBIN LEVELS IN THREATENED ALASKAN PINNIPED POPULATIONS

We evaluated the plasma concentration of the acute phase protein haptoglobin (Hp) from Steller sea lions (Eumetopias jubatus) and harbor seals (Phoca vitulina) in regions of Alaska (USA) where the populations of these pinnipeds were declining and compared the values with concentrations of Hp from the same species in areas where the populations were stable. Samples were collected from 1992 through 1994 at sites in Southeast Alaska, Prince William Sound, the Gulf of Alaska, and the Aleutian Islands. Significantly higher levels of Hp were found in the samples from the areas of decline compared to those from stable populations. Based on these findings, we propose that one may be able to distinguish these compromised pinniped populations using Hp as a biomedical indicator.

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.

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.

Differential expression of immune response genes in Steller sea lions (Eumetopias jubatus): An indicator of ecosystem health?

Characterization of the polygenic and polymorphic features of the Steller sea lion major histocompatibility complex (MHC) provides an ideal window for evaluating immunologic vigor of the population and identifying emergence of new genotypes that reflect ecosystem pressures. MHC genotyping can be used to measure the potential immunologic vigor of a population. However, since ecosystem-induced changes to MHC genotype can be slow to emerge, measurement of differential expression of these genes can potentially provide real-time evidence of immunologic perturbations. MHC DRB genes were cloned and sequenced using peripheral blood mononuclear leukocytes derived from 10 Steller sea lions from Southeast Alaska, Prince William Sound, and the Aleutian Islands. Nine unique DRB gene sequences were represented in each of 10 animals. MHC DRB gene expression was measured in a subset of six sea lions. Although DRB in genomic DNA was identical in all individuals, relative levels of expressed DRB mRNA was highly variable. Selective suppression of MHC DRB genes could be indicative of geographically disparate environmental pressures, thereby serving as an immediate and sensitive indicator of population and ecosystem health.

Assessment of mercury and selenium tissular concentrations and total mercury body burden in 6 Steller sea lion pups from the Aleutian Islands.

Concentrations of total mercury ([THg]) and selenium ([TSe]) were measured in several tissue compartments in Steller sea lion (Eumetopias jubatus) pups; in addition we determined specific compartment and body burdens of THg. Compartmental and body burdens were calculated by multiplying specific compartment fresh weight by the [THg] (summing compartment burdens equals body burden). In all 6 pup tissue sets (1) highest [THg] was in hair, (2) lowest [THg] was in bone, and (3) pelt, muscle and liver burdens contributed the top three highest percentages of THg body burden. In 5 of 6 pups the Se:Hg molar ratios among compartments ranged from 0.9 to 43.0. The pup with the highest hair [THg] had Se:Hg molar ratios in 9 of 14 compartments that were ⩽ 0.7 potentially indicating an inadequate [TSe] relative to [THg].

Seasonal Differences in Biochemical Adaptation to Fasting in Juvenile and Subadult Steller Sea Lions (Eumetopias jubatus)

Nine Steller sea lions (Eumetopias jubatus) aged 1.75–6 yr were experimentally fasted for 7–14 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.