Harbor Seal Population Decline in the Aleutian Archipelago

Populations of Steller sea lions, northern fur seals, and northern sea otters declined substantially during recent decades in the Bering Sea and Aleutian Islands region, yet the population status of harbor seals has not been assessed adequately. We determined that counts obtained during skiff-based surveys conducted in 1977–1982 represent the earliest estimate of harbor seal abundance throughout the Aleutian Islands. By comparing counts from 106 islands surveyed in 1977–1982 (8,601 seals) with counts from the same islands during a 1999 aerial survey (2,859 seals), we observed a 67 percent decline over the approximately 20-year period. Regionally, the largest decline of 86 percent was in the western Aleutians, followed by 66 percent in the central Aleutians, and 45 percent in the eastern Aleutians. Harbor seal counts decreased at the majority of islands in each region. The number of islands with more than 100 seals decreased approximately 70 percent, and the number of islands with no seals counted increased approximately 80 percent, indicating that harbor seal abundance throughout the Aleutian Islands was substantially lower in the late 1990s than in the 1970s and 1980s.

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Robert J. Small, Peter L. Boveng, G. Vernon Byrd, and David E. Withrow. Published in Marine Mammal Science, 24(4): 845–863 (October 2008). DOI: 10.1111/j.1748-7692.2008.00225.x