Predictability of prey available to Steller sea lions in southeastern Alaska

Predictability of prey available to Steller sea lions in southeastern Alaska

S.M. Gende, and M.F. Sigler

Predictability of prey available to Steller sea lions in southeastern AlaskaThis is part of Sea Lions of the World
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Description

The ability to predict the distribution of prey in space and time can influence foraging efficiency for marine vertebrates: search efforts can be concentrated in a specific area at a specific time of year, reducing energy expended randomly searching for prey. We examined the predictability of pelagic fish distributions during 24 months of surveys in Lynn Canal, Southeast Alaska. The spatial distribution of available prey (measured as energy density) during a given month was examined to determine if it was an accurate indicator of prey distribution during the following month (monthly time scale) or during the same month the following year(annual time scale). We also examined how predictability varied among seasons and across several spatial scales. Pacific herring (Clupea pallasii) dominated the prey energy available to Steller sea lions (Eumetopias jubatus), often occurring at densities several orders of magnitude greater than walleye pollock (Theragra chalcogramma), particularly during the winter months. Prey distribution in one month was a good indicator of prey distribution the same month the following year, but mostly during the winter months. This was due to the formation of large schools of herring in consistent locations during both winters. The distribution of prey in one winter month was also a good indicator of the distribution of prey the following month. However, significant month-to-month correlations were less frequent than at annual time scales due to a southerly movement of herring aggregations as the winter progressed. High densities and predictable distributions of high-energy prey, such as herring, at relatively small spatial scales may facilitate efficient foraging by Steller sea lions and play a central role in the nutritional health of the stable or increasing populations in this area.

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