MEPS 231:229-236 (2002)  -  doi:10.3354/meps231229

Predator aggregations during eulachon Thaleichthys pacificus spawning runs

Brian H. Marston1,*, Mary F. Willson2, Scott M. Gende3

1Alaska Department of Fish and Game, Wildlife Conservation, 333 Raspberry Road, Anchorage, Alaska 99518, USA
25230 Terrace Place, Juneau, Alaska 99801, USA
3US Forest Service, Pacific Northwest Research Station, 2770 Sherwood Lane, Juneau, Alaska 99801, USA

ABSTRACT: Predators congregated in large numbers during the 1996 and 1997 spring spawning runs of eulachon Thaleichthys pacificus Richardson (Osmeridae) in the lower reaches of the rivers entering Berners Bay, southeastern Alaska. Predator abundance rose rapidly at the beginning of the runs and was significantly correlated with an index of eulachon abundance within years. Gulls (Laridae) were the most abundant predators, with a daily average peak of 40000 during the 1996 run, at a density of 3000 km-2. A daily average peak of over 250 Steller sea lions Eumetopias jubatus and harbor seals Phoca vitulina fed on eulachon early in the run in both years. Daily average counts of bald eagles Haliaeetus leucocephalus approached 600 on the lower reaches of the rivers, and many others foraged upstream. Eulachon are unusually high in lipid content, and many of the prodigious spawning runs in Alaska and British Columbia occur in spring, when predator energy demands are high. We suggest that spring spawning runs of eulachon and other forage fishes are an ecological cornerstone for regional coastal ecosystems, supporting large numbers of wildlife species.


KEY WORDS: Eulachon · Thaleichthyes pacificus · Osmeridae · Southeast Alaska · Steller sea lion · Harbor seal · Laridae


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