MEPS 386:287-302 (2009)  -  doi:10.3354/meps08048

Using predator distributions, diet, and condition to evaluate seasonal foraging sites: sea ducks and herring spawn

Eric M. Anderson1,5,*, James R. Lovvorn1,6, Daniel Esler2, W. Sean Boyd3, Kurt C. Stick4

1Department of Zoology and Physiology, University of Wyoming, 1000 E. University Avenue, Laramie, Wyoming 82071, USA
2Centre for Wildlife Ecology, Simon Fraser University, 5421 Robertson Road, Delta, British Columbia V4K 3N2, Canada
3Science and Technology Branch, Environment Canada, Pacific Wildlife Research Centre, 5421 Robertson Road, Delta, British Columbia V4K 3N2, Canada
4Washington Department of Fish and Wildlife, La Conner District Office, PO Box 1100, La Conner, Washington 98257, USA
5Present address: Centre for Wildlife Ecology, Simon Fraser University, 5421 Robertson Road, Delta, British Columbia V4K 3N2, Canada
6Present address: Department of Zoology, Southern Illinois University, Carbondale, Illinois 62901, USA

ABSTRACT: Identifying important foraging sites for highly mobile marine predators has relied mainly on relating their distributions to broadly defined habitat data. However, understanding functional dependencies on foraging sites also requires knowledge of the relative contributions of foods to predator condition. We coupled predator distributions with measures of their diet and condition to assess the importance of Pacific herring Clupea pallasii spawning events to 2 closely related and declining sea duck species. In Puget Sound, Washington, the numerical response of scoters to spawn increased with increasing biomass of spawning herring; this response was 4-fold greater for surf scoters Melanitta perspicillata than for white-winged scoters M. fusca after accounting for local differences in their abundances. In the Strait of Georgia, British Columbia, diets estimated from fatty acids and stable isotopes indicated that both scoter species gained mass by consuming spawn during late March to early April. At a site without spawn during this period, only male white-winged scoters gained mass. In contrast, body mass of male surf scoters declined appreciably before spawn became available in one study year, suggesting greater dependence on spawn for restoring depleted reserves. From winter to spring, surf scoters attained greatest body mass during late April to mid-May while migrating through southeast Alaska; during this period, plasma triglycerides suggested that fattening was not related solely to spawn consumption, yet surf scoters aggregated to consume spawn whenever it was available. Although it is not clear whether herring are essential to their population processes, surf scoters and a range of other predators for which spawning areas are clearly preferred foraging sites would likely benefit from efforts that preserve declining herring stocks.


KEY WORDS: Clupea pallasii · Herring spawn · Melanitta fusca · Melanitta perspicillata · Spring migration · Surf scoter · White-winged scoter


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Cite this article as: Anderson EM, Lovvorn JR, Esler D, Boyd WS, Stick KC (2009) Using predator distributions, diet, and condition to evaluate seasonal foraging sites: sea ducks and herring spawn. Mar Ecol Prog Ser 386:287-302

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