61.6 Jan. 7 Individual-based foraging strategies in male California Sea Lions (Zalophus californianus) WEISE, M.J.*; COSTA, D.P.; UC Santa Cruz; UC Santa Cruz email@example.com
Historically conspecifics were often treated as ecological equivalents in studies of foraging theory, but more recently the variation among individuals is no longer considered as irrelevant noise, but a focus of interest. California sea lions are one of the most abundant apex predators along the West Coast of North America and likely affect the dynamics and community structure of coastal ecosystems, yet we know little about their foraging behavior. In this study satellite-linked dive recorders were used to investigate the foraging strategies of sub-adult and adult male California sea lions following the breeding season during 2003-04 and 2004-05. Multivariate analyses were used to reduce the number of behavioral variables used to characterize foraging strategies, identify individually based foraging strategies in multidimensional space, and classify each individual into a cluster or foraging strategy. Approximately 81.1% of the variation among individuals in diving behavior could be explained by three factors; diving patterns, foraging effort, and surface behavior. Individuals could be classified into three distinct groups based on their diving behavior (shallow, mixed depth, and deeper divers), and jack-knife re-sampling of the data resulted in correct group assignment 86% of the time. Differences among individual strategies were partially explained by size dimorphism, in that, larger animals dove deeper and longer and likely reflected differences in the distribution of targeted prey. Individual-based foraging strategies in sea lions have broad ramifications for models of intraspecific competition, predator-prey dynamics, and food web structure in the coastal ecosystem.