NOAA Technical Memorandum
NMFS-AFSC-100
Aerial and land-based surveys of Steller sea lions (Eumetopias jubatus) in Alaska, June and July 1997 and 1998
Abstract
The National Marine Fisheries Service (NMFS) and the Alaska Department of Fish and Game (ADF&G) conducted aerial and land-based surveys of Steller sea lions (Eumetopias jubatus) in Alaska during June and July 1997 and 1998. During a limited-range survey in 1997, we counted a total of 16,249 non-pup Steller sea lions on 127 rookery and haul-out sites in the central and western Gulf of Alaska and eastern Aleutian Islands. In 1998, we counted a total of 39,597 non-pups on 236 rookery and haul-out sites Alaska-wide. Of these sea lions, 20,976 were on 33 trend rookeries, indicating declines of 7.0% from 1996 and 24.0% from 1990. The estimated average annual decline for the trend rookeries was 3.5% from 1990 to 1998.
The western stock of Steller sea lions in Alaska includes animals from the eastern Gulf of Alaska through the western Aleutian Islands. At 30 western-stock trend rookeries, we counted 14,368 non-pups in 1998, which indicated declines of 12.2% from 1996 and 35.0% from 1990. The estimated average annual rate of decline from 1990 to 1998 was 5.4%. Complete western-stock counts were not available for all rookery and haul-out trend sites because a number of sites were not surveyed in the eastern Gulf of Alaska in 1998. Counts for rookery and haul-out trend sites in the central Gulf of Alaska through the western Aleutian Islands suggested western-stock declines of 9.3% from 1996 and 26.6% from 1991, or an estimated average annual decline of 4.3% over the 7-year period.
In the Kenai Peninsula to Kiska Island index area, a sub-area within the Alaska portion of the western stock, we counted 24,318 non-pup sea lions at 203 surveyed sites. Of these, 16,315 were at 69 trend sites (26 rookeries and 43 haulouts), and 11,994 were at 26 trend rookeries. The 1998 count for the 69 trend sites was a decline of 8.9% from 1996 and 28.3% from 1990. The estimated annual rates of decline were 4-5% for trend sites and trend rookeries (1990 to 1996) and 2% for all surveyed sites (1991 to 1996).
The eastern stock is represented in Alaska only by Southeast Alaska, where we counted 8,693 non-pups at 11 trend sites (rookeries and haulouts). This indicated an increase of 5.6% from 1996, a decline of 1.5% from 1994, and an increase of 14.0% from 1990. The estimated average annual rate of increase from 1990 to 1998 for trend sites in Southeast Alaska was 1.8%. Overall changes were similar for the three trend rookeries in Southeast Alaska, as was the estimated annual increase of 2.0% from 1990 to 1998.
The ADF&G and NMFS counted 6,932 live pups at 12 rookeries in Alaska in 1997 and 13,607 pups at 40 rookeries Alaska-wide in 1998. The 1998 count included all rookeries in Alaska except Walrus Island in the Pribilof Islands. Pup numbers in the eastern stock (Southeast Alaska) increased by 12.3% from 1994 to 1998, and generally increased by about 2% per year since 1990. The western stock in Alaska (excluding the western Aleutian Islands) declined by 19.0% from 1994 to 1998. In the western Aleutian Islands, pup numbers declined 18% from 1997 to 1998, the only years for which comprehensive comparison is possible.
Considering non-pup and pup counts together, the western-stock region showing the most positive trend during recent years was the central Aleutian Islands. The worst observed declines were in the western Aleutian Islands: 13-16% overall for non-pups from 1996 to 1998 and 18% for pups from 1997 to 1998.
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