Abstract
Seasonal and annual dynamics of California sea lion feeding on Pacific hake were examined in relation to prey availability using otoliths found in spewings and scats. Sea lions fed most heavily on 2- to 4-year-old hake in spring and summer (ca. 90% of the diet is hake). When hake moved offshore in the spawning season, sea lions fed more on other species (30–50% of the diet is hake). The strong 1973 year class of hake had a great impact on the size and species composition of the prey consumed because sea lions fed heavily on the juveniles of this year class. When 2- to 3-year-old hake were not abundant due to year class failures, sea lions fed more on larger hake and on other species, mostly rockfish. It is estimated that California sea lions annually consume from about 100 000 to 250 000 tons of Pacific hake. An empirical model is used as an aid to discuss the effects of prey density, availability of alternative prey and predator switching behavior on the intensity of sea lion feeding on hake.
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