Migration of northern fur seals (Callorhinus ursinus) off western North America / by Michael A. Bigg.: Fs97-6/1764E-PDF

"The annual migration of northern fur seals (Callorhinus ursinus) off western North America is described from an analysis of monthly and regional variations in the relative abundance of seals seen and collected at sea in three data sets collected during 1955-77. Three main patterns of migration are apparent. The first is undertaken by males age 1-3 yr and females age 1-2 yr. These seals remain offshore in the eastern North Pacific for much of the year with some seasonal entry in coastal regions between the Bering Sea and California. The second involves males age 4+ yr. They leave the Pribilof Islands in September-October and winter offshore in Alaska and enter coastal regions of Alaska in April-May and the Pribilof Islands in June-July. The third pattern is undertaken by females age 3+ yr. They migrate from the Pribilof Islands to the coast of California by January-February with some wintering in more northern coastal regions. The majority from California return to the Pribilof Islands by July-September using an offshore route to the Gulf of Alaska and then along the Alaskan coast. Most of the remaining seals between California and British Columbia take a direct route across the eastern North Pacific to the Aleutian Islands with others taking a coastal route. The return migration of seals up to age 4 yr is later with decreasing age and involves progressively more individuals with increasing age. Males tend to migrate before females and pregnant females before nonpregnant females of the same age. The complex migration appears related to inherited factors associated particularly with the onset of sexual maturity at age 3-5 yr and learned behaviors associated with food location"--Abstract, page iii.

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