61.2 Jan. 7 Interannual variability in the foraging behavior of California sea lions: behavioral responses to environmental variation KUHN, Carey E.*; COSTA, Daniel P.; University of California, Santa Cruz; University of California, Santa Cruz Kuhn@biology.ucsc.edu
The California sea lion (Zalophus californianus) is an abundant predator along the west coast of the United States and populations continue to grow at a rate of over 6% per year. Previous research has shown that El Niño events significantly impact California sea lions, causing changes in foraging trip durations, dive behavior, and pup survival rates. These studies have demonstrated the impact of extensive environmental change; however, little is known about how these animals respond to more typical environmental variation. This study examined the winter foraging behavior of 30 adult female California sea lions over 3 years (2003, 2004, and 2005), using satellite transmitters and dive recorders. As females are constrained to return to the rookery to nurse young pups, we hypothesized trip durations would be maintained and females would alter foraging locations and dive behavior in response to environmental variation. Among years, there were significant differences in movement parameters (transit rate: p<0.01; trip duration: p<0.01; total distance travelled: p=0.01; percent time at-sea: p<0.01), but no significant differences in dive behavior. Females had significantly longer trip durations in 2004 and 2005, but travelled farther from the rookery in 2004 (up to 445 km). Time spent in transit, diving and hauled out varied among years with the greatest amount of time in transit occurring in 2004 (43.1 ± 2.6%). The differences in movement patterns among years correlated with increased sea surface temperatures, decreased upwelling, and decreased commercial fish landings. Ultimately, the flexibility in foraging behavior measured may be linked to the continuing success of growing California sea lion populations.