New Data on Proximate Composition and Energy Density of Steller Sea Lion (Eumetopias jubatus) Prey Fills Seasonal and Geographic Gaps in Existing

Abstract: Energy density data of prey items are necessary to estimate food requirements of predators. The goal of this study was to provide proximate composition and energy density information for Steller sea lion (Eumetopias jubatus) prey species where there are seasonal and/or geographic gaps in the existing data. Opportunistic collections were made on board National Oceanic and Atmospheric Administration fisheries research surveys in the Aleutian Islands region, eastern Bering Sea, and Gulf of Alaska, targeting particular species of interest. Proximate analyses were conducted in the laboratory and energy density was calculated from lipid and protein content. Pacific herring, sand lance, and rockfish were found to contain the highest amount of lipid and provide the most energy. Atka mackerel, surf smelt, capelin, salmon, sandfish, pollock, yellow Irish lords, Pacific cod, squid, skates, and rock sole had intermediate energy densities. Smooth lumpsucker and snailfish were found to contain the least amount of energy. This study is the first to provide proximate composition data for adult pollock during the nonspawning seasons in the Gulf of Alaska and Aleutian Islands region. This study also provides the first proximate composition data for juvenile pollock in the Aleutian Islands region and eastern Bering Sea, and for Pacific cod in the eastern Bering Sea. This study fills another critical gap by presenting the only information on proximate composition of adult Atka mackerel, one of the most important prey of Steller sea lions in the Aleutian Islands region. These improvements in the seasonal and geographic coverage of fish proximate and energy density data will allow for seasonally and geographically specific estimates of Steller sea lion prey requirements, a necessary improvement over annual estimates made previously. These data can also contribute to bioenergetic modeling of prey requirements of other predators in Alaska such as groundfish, fur seals, and marine birds.


Document Type: Research article

DOI: 10.1578/AM.31.1.2005.62

Page Numbers: 62 – 82

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