Species and stock identification of prey consumed by endangered southern resident killer whales in their summer range

M. Bradley Hanson; Robin W. Baird; John K. B. Ford; Jennifer Hempelmann-Halos; Donald M. Van Doornik; John R. Candy; Candice K. Emmons; Gregory S. Schorr; Brian Gisborne; Katherine L. Ayres; Samuel K. Wasser; Kenneth C. Balcomb; Kelley Balcomb-Bartok; John G. Sneva; Michael J. Ford

doi:10.3354/esr00263

ESR

Endangered Species Research

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ESR 11:69-82 (2010) - DOI: https://doi.org/10.3354/esr00263

Species and stock identification of prey consumed by endangered southern resident killer whales in their summer range

M. Bradley Hanson^1,*, Robin W. Baird², John K. B. Ford³, Jennifer Hempelmann-Halos¹, Donald M. Van Doornik⁴, John R. Candy³, Candice K. Emmons¹, Gregory S. Schorr ², Brian Gisborne³, Katherine L. Ayres⁵, Samuel K. Wasser⁵, Kenneth C. Balcomb⁶, Kelley Balcomb-Bartok^6,8, John G. Sneva⁷, Michael J. Ford¹

¹National Marine Fisheries Service, Northwest Fisheries Science Center, Seattle, Washington 98112, USA
²Cascadia Research Collective, Olympia, Washington 98501, USA
³Fisheries and Oceans Canada, Pacific Biological Station, Nanaimo, British Columbia V9T 6N7, Canada
⁴Northwest Fisheries Science Center, Manchester Research Station, Manchester, Washington 98353, USA
⁵University of Washington, Center for Conservation Biology, Department of Biology, Seattle, Washington 98195, USA
⁶Center for Whale Research, Friday Harbor, Washington 98250, USA
⁷Washington Department of Fish and Wildlife, Olympia, Washington 98501, USA
⁸Present address: Renton City Hall, Renton, Washington 98057, USA

*Email: brad.hanson@noaa.gov

ABSTRACT: Recovery plans for endangered southern resident killer whales Orcinus orca have identified reduced prey availability as a risk to the population. In order to better assess this risk, we studied prey selection from 2004 to 2008 in 2 regions of the whales’ summer range: San Juan Islands, Washington and the western Strait of Juan de Fuca, British Columbia. Following the whales in a small boat, we collected fish scales and tissue remains from predation events, and feces, using a fine mesh net. Visual fish scale analysis and molecular genetic methods were used to identify the species consumed. Chinook salmon, a relatively rare species, was by far the most frequent prey item, confirming previous studies. For Chinook salmon prey, we used genetic identification methods to estimate the spawning region of origin. Of the Chinook salmon sampled, 80 to 90% were inferred to have originated from the Fraser River, and only 6 to 14% were inferred to have originated from Puget Sound area rivers. Within the Fraser River, the Upper Fraser, Middle Fraser, South Thompson River and Lower Fraser stocks were inferred to currently be sequentially important sources of Chinook salmon prey through the summer. This information will be of significant value in guiding management actions to recover the southern resident killer whale population.

KEY WORDS: Resident killer whales · Prey selection · Chinook salmon · Genetic stock identification

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Cite this article as: Hanson MB, Baird RW, Ford JKB, Hempelmann-Halos J and others (2010) Species and stock identification of prey consumed by endangered southern resident killer whales in their summer range. Endang Species Res 11:69-82. https://doi.org/10.3354/esr00263

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