Northern Sea Lion Population Decline in the Eastern Aleutian Islands

Abstract

From June 1975-June 1977, aerial surveys (6) were conducted along the eastern Aleutian Islands and north coast of the Alaska Peninsula to assess the distribution and abundance of northern sea lions (E. jubatus). Site-specific counts of sea lions on rookeries and haulout places were compared to counts made in 1957, 1960, 1965 and 1968. Analysis of total counts from sites replicated among survey years since 1957 indicated that a significant population decline occurred. The 1977 population estimate was below 25,000; in the late 1950''s and early 1960''s the population exceeded 50,000. The 1977 population level was 44.9-54.7% of the 1957 estimate, and it appeared that the population decline has been greatest since 1968. No cause for the decline was apparent, but several contributing factors are discussed.