KUHN, C.E.*; COSTA, D; Univ. of California, Santa Cruz: Examination of the foraging strategies of a top marine predator: the California sea lion

Studies of the foraging behavior of marine predators have primarily been limited to investigations of diet from stomach content or scat analysis. While this provides useful information on foraging at the population level, it does not allow examination of individual foraging strategies. Research on sea otters, where individuals can be readily observed feeding, has shown that the population is composed of animals that forage in fundamentally different ways. It is likely that this specialization occurs in other marine predators as well. The California sea lion (CSL) is an abundant predator along the west coast of the US and Mexico and is a considered a generalist predator, feeding on a variety of prey species. We tested the hypothesis that like sea otters, individual sea lions exhibit unique foraging patterns, consistent with prey specialization. This was tested by studying the at-sea movements and diving behavior of 8 CSL females from San Nicolas Is., CA. We examined foraging at multiple levels including the average population behavior, differences between individuals, and differences between foraging trips of an individual. We compared distance traveled, trip durations, time spent diving, and mean dive depths and durations. On average CSL females remained close to the island during foraging trips (49km) and were shallow divers (45m). Significant differences were found between individuals for many parameters including distance traveled (range 11 to 90 km), trip duration (3 hours to 4.5 days), and average dive depth (21 to 105 m). Our data indicate while females’ foraging trips varied, the differences between females were much greater. Although CSLs are considered generalist predators, this study suggests that females may be exhibiting distinct foraging strategies resulting in potential niche separation.