Prey consumption by Steller sea lions in Alaska: how much do they require?

Arliss Winship, A W Trites

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43 Citations (Scopus)

Abstract

The effects of seasonal and regional differences in diet composition on the food requirements of Steller sea lions (Eumetopias jubatus) were estimated by using a bioenergetic model. The model considered differences in the energy density of the prey, and differences in digestive efficiency and the heat increment of feeding of different diets. The model predicted that Steller sea lions in southeast Alaska required 45-60% more food per day in early spring (March) than after the breeding season in late summer (August) because of seasonal changes in the energy density of the diets (along with seasonal changes in energy requirements). The southeast Alaska population, at 23,000 (+/-1660 SD) animals (all ages), consumed an estimated 140,000 (+/-27,800) t of prey in 1998. In contrast, we estimated that the 51,000 (+/-3680) animals making up the western Alaska population in the Gulf of Alaska and Aleutian Islands consumed just over twice this amount (303,000 [+/-57,500]t). In terms of biomass removed in 1998 from Alaskan waters, we estimated that Steller sea lions accounted for about 5% of the natural mortality of gadids (pollock and cod) and up to 75% of the natural mortality of hexagrammids (adult Atka mackerel). These two groups of species were consumed in higher amounts than any other. The predicted average daily food requirement per individual ranged from 16 (+/-2.8) to 20 (+/-3.6) kg (all ages combined). Per capita food requirements differed by as much as 24% between regions of Alaska depending on the relative amounts of low-energy-density prey (e.g. gadids) versus high-energy-density prey (e.g. forage fish and salmon) consumed. Estimated requirements were highest in regions where Steller sea lions consumed higher proportions of low-energy-density prey and experienced the highest rates of population decline.

Original languageEnglish
Pages (from-to)147-167
Number of pages21
JournalFishery Bulletin
Volume101
Publication statusPublished - Jan 2003

Keywords

  • HERRING CLUPEA-PALLASI
  • SOMATIC ENERGY CONTENT
  • PROXIMATE COMPOSITION
  • WALLEYE POLLOCK
  • SEASONAL-CHANGES
  • THERAGRA-CHALCOGRAMMA
  • PHOCA-GROENLANDICA
  • ASSIMILATION EFFICIENCY
  • DIGESTIVE EFFICIENCY
  • FORAGING BEHAVIOR

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