Changes in prey density, quality and diversity, ultimately resulting in inadequate energy intake and nutritionally stressed animals is one of the leading hypotheses to explain the decline of the Western stock. Over fishing and/or the 1976 – 77 climate regime shift in the Bering Sea and eastern North Pacific Ocean, both having considerable impact on prey distribution patterns could explain such shift in prey type or availability. In the 1970s, the diet of both populations consisted of mainly fatty fishes (such as salmonids and herring) with a high energy content and small proportions of low energy fish such as gadids (for a example pollock). In the 1990s, this ratio was reversed for sea lions foraging in western Alaska while the eastern stock still feeds mainly of fatty fish. This switch has led to the “junk-food hypothesis” which suggests that the diet change to prey with lower energy content could have severe effects on the health of the Steller sea lion population. In addition, the most severe decline of Steller sea lions has been observed in areas with the lowest fish density. The situation has consequently led to a substantial interest in how Steller sea lions are affected by changes in body condition due to alterations in food intake.
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Last updated: 05/26/08