ARCUS | Arctic Research Consortium of the United States

7th Annual ARCUS Award for Arctic Research Excellence


Submitted by   Monica Bando
Authors  
Category   Life Science
Title   Comparing the Nutritional Quality of Steller Sea Lion (Eumetopias jubatus) Diets
Affiliation   Marine Biology, University of Alaska, Fairbanks, Fairbanks, AK, USA

Abstract

Steller sea lion populations have been declining precipitously over the past three decades and although the primary cause(s) remains unknown, one hypothesis is nutritional stress. Nutritional stress may be attributable to reduced preferred prey availability and/or prey quality and could be the result of commercial fisheries removals or, alternately, environmental changes such as climactic regime shifts. At the Alaska SeaLife Center (ASLC), researchers have formulated three different feeding regimes representative of Steller sea lion diets: prior to their population decline (Gulf of Alaska, 1970s), during their decline (Gulf of Alaska, 1980s), and from a stable or growing population (southeast Alaska, 1990s). The purpose of this project was to compare the nutritional quality of these three Steller sea lion diets that differ in prey species composition. Proximate composition and bomb calorimetry were used to determine energy density of prey species. Variations in the proximate composition of prey species, such as high energy herring and low energy octopus, affected the overall energy densities of the different diets. While the pre-decline and stable diets were composed of more high fat fish such as herring, capelin and pink salmon, the decline diet contained more lower fat prey items, such as octopus, Dover sole and rock sole. The resulting overall energy densities provided by the pre-decline and stable diets are similar to one another and significantly higher in energy density than the decline diet. Assuming that the ten prey species analyzed for this study adequately represent the bulk of prey consumed by Steller sea lions and that these formulated diets are representative of Steller sea lion diets prior to and during their population decline and in stable populations, results from this study are consistent with the possibility that nutritional stress was a cause of the Steller sea lion decline.