Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4568
Title: Energy Content of Pacific Salmon as Prey of Northern and Southern Resident Killer Whales
Author: Sandra Marie O'Neill, Gina Marie Ylitalo, James E. West
Publication Year: 2014
Journal: Endangered Species Research
Volume: 25
Pages: 265-281
Keywords: energetics,Pacific salmon,killer whales,

Recovery of depleted species is difficult but it can be especially complex when they interact strongly with other depleted species.  Such is the case for northern and southern resident killer whales, Orcinus orca, listed as Endangered under the U.S. Endangered Species Act (ESA) and Canada’s Species at Risk Act. These resident killer whale populations prey heavily on Pacific salmon, Oncorhynchus spp., including several Evolutionarily Significant Units also listed under the ESA.  In response to concerns that a depleted prey base may affect killer whale recovery, we analyzed proximate composition and calculated caloric content of Pacific salmon to evaluate the importance of salmon species, population, body-size, and lipid levels in determining their energy content as prey for killer whales. We sampled all five species of Pacific salmon but emphasized Chinook salmon, a preferred prey of killer whales. Energy density (Kcal· kg-1) was highly correlated with lipid content whereas total energy value (Kcal· fish-1) was determined primarily by fish mass and secondarily by lipid content. To facilitate application of these results to the co-management of salmon and killer whales, we produced a simple relationship that uses fish length to predict total energy of Chinook salmon as prey where population-specific energy densities and fish masses are lacking. Benefits to killer whales from possible salmon fishery closures, or other activities that affect prey availability, will depend on the salmon species and populations involved.