TRITES, AW; HUNT, KE*; WYNNE, K; WASSER, SK; Univ. British Columbia; Univ. Washington; Univ. Alaska; Univ. of Washington: Noninvasive assessment of possible nutritional stress in Steller sea lions (Eumetopias jubatus) using fecal glucocorticoid and dietary analyses

The western population of the Steller sea lion (Eumetopias jubatus) experienced a pronounced population decline in the 1970’s-90’s. The initial decline is thought to have involved reduced quantity or quality of prey, but it is unclear what factors are now preventing population recovery. To enable noninvasive assessment of physiologic stress of free-living sea lions, we validated a fecal glucocorticoid assay using ACTH (adrenocorticotropic hormone) injections in four captive Steller sea lions. All four showed pronounced elevations in fecal glucocorticoids after ACTH injection, indicating that assay results reflect adrenal activity. We assayed 206 scats from Steller sea lion haul-outs in the declining (Gulf of Alaska) population, and 265 scats from the stable (Southeast Alaska) population. Diet was determined from hard parts recovered from scats, and dietary energy content was estimated from known caloric densities of prey. Both populations had significantly higher fecal glucocorticoid concentrations and significantly lower dietary energy density in winter compared to summer. During winter, sea lions in the declining population consumed a richer diet, and had significantly lower fecal glucocorticoids, than sea lions in the stable population. No significant differences were seen between glucocorticoid levels of the two populations in summer. Glucocorticoid differences were noted in summer between mature males, mature females and immature animals. Though many questions remain to be answered, these results suggest that the Gulf of Alaska population is not currently suffering from nutritional stress, and that other factors such as orca predation may now be more important in preventing population recovery.