FORAGING BEHAVIOR OF ADULT FEMALE AND YOUNG-OF-THE-YEAR STELLER SEA LIONS IN ALASKAN WATERS

One explanation for recent declines in the Alaskan Steller sea lion (E umetopias jubatus) population is that the availability of preferred pr ey has changed. Part of our evaluation of this hypothesis involved the use of conventional radio and satellite-linked time-depth recorder tr ansmitters to compare summer and winter foraging of adult female and y oung-of-the-year Steller sea lions in Alaska waters. Foraging effort w as not significantly different seasonally for postpartum adult females , though females with dependent young in winter may increase their for aging effort. In winter, all adult females made longer trips over larg er home ranges and dove deeper. Young sea lions exerted less foraging effort, had the shallowest and briefest dives, and had home ranges int ermediate in size to the two groups of adult females. Their foraging a bility appears to develop throughout the first year. We conclude that adult female sea lions can exploit prey throughout the Gulf of Alaska and Bering Sea, and are constrained only by their reproductive status and seasonal changes in prey availability. Young sea lions' diving is more limited because their physiological and behavioral development co nstrains them from diving like an adult. Perhaps most important, dives remain shallow through the first year. Consequently, young sea lions could be more easily food-limited by changes in prey distribution.