Abundance and Distribution of the Steller Sea Lion

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Abstract
Observations of the Steller sea lion, Eumetopias jubata, including hauling-out habits, seasonal movements, and aerial surveys in eastern Bering Sea from Bering Strait to and including the Aleutian Islands, are presented. Sea lions haul out during winter and spring, prior to the breeding season, in greater numbers in afternoon hours than in morning hours; few haul out during storms. The dearth of animals seen in the water during aerial surveys indicates that the great majority are hauled out during fair weather in the spring. The Pribilof Islands are the northernmost breeding grounds but a number of animals, probably adult and sub-adult males, migrate north in late summer and early fall. As many as 1,000 regularly reach St. Lawrence Island and a few reach Bering Strait. These animals move south again with the advance of ice in the fall but ice does not cause them to desert the Pribilof Islands. Certain hauling grounds within the breeding range are used seasonally. Aerial surveys of all Aleutian Islands and areas near the end of the Alaska Peninsula in 1959 and 1960 revealed 98 rookeries and hauling grounds with an estimated total of about 100,000 animals. The total world population of this species, based on the present report and on previously published data, is estimated to be about a quarter of a million animals.