Oceanographic features related to northern fur seal migratory movements

Northern fur seals breeding on the Pribilof Islands are characterized by pelagic migrations that begin each fall and last approximately eight months. Previous studies have examined the early phases of the migration with respect to timing, location, and effects of ocean surface currents on movement. We used satellite telemetry and remotely sensed satellite data to examine relationships between oceanographic features and the movements of adult female fur seals in the Bering Sea and North Pacific Ocean during early, middle and late portions of their winter migration. Physical locations of 13 female fur seals were monitored during 2002–2003, and diving data were collected on a subset of the animals. Remotely sensed data were obtained to assess sea-surface temperatures, chlorophyll a concentrations, and sea-surface height anomalies encountered by the fur seals. Data from historical pelagic collection of fur seals also were summarized to describe winter diet and the distribution of different age and sex classes of the general migration of fur seals to the eastern North Pacific. Seals departed from the Pribilof Islands in November and moved in a southeasterly direction over the continental shelf as they left the Bering Sea. Their travel routes did not follow coastal or bathymetric features as they crossed the North Pacific Ocean, but instead corresponded to complementary water movement of the Alaska Gyre and the North Pacific Current. Winter foraging areas varied geographically and were associated with eddies, the subarctic–subtropical transition region, and areas that undergo coastal mixing due to the California Current. The results indicate that fur seals may cue on a variety of oceanographic features that aid in reducing energetic expenditures and optimize foraging opportunities.