NOAA Technical Memorandum
NMFS-AFSC-99
Aerial and land-based surveys of Steller sea lions (Eumetopias jubatus) in Alaska, June and July 1996
Abstract
The National Marine Fisheries Service and the Alaska Department of Fish and Game conducted aerial and land-based surveys of Steller sea lions (Eumetopias jubatus) during June and July 1996 from Southeast Alaska to the western Aleutian Islands. We counted a total of 41,529 adult and juvenile (non-pup) sea lions at 280 rookery and haul-out sites. Of these sea lions, 30,454 (73.3%) were at 95 trend sites (rookeries and haulouts) and 22,562 (54.3%) were at 33 trend rookeries. The 1996 count at the 95 trend sites was a decline of 18.0% since 1991, 12.6% since 1992, and 7.6% since 1994. Overall declines were slightly less for all surveyed sites. The average annual rate of decline from 1991 to 1996 was about 3.7% for trend sites and trend rookeries and 2.1% for all surveyed sites.
The western stock of Steller sea lions in Alaska includes animals from the eastern Gulf of Alaska through the western Aleutian Islands. In 1996 we counted 30,622 non-pups at 222 surveyed sites. Of these, 22,223 (72.6%) were on 82 trend sites and 16,358 (53.4%) were on 30 trend rookeries. For the 82 trend sites, the 1996 count represented declines of 27.2% from 1990, 24.5% from 1991, 18.6% from 1992, and 7.9% from 1994. The annual rates of decline were about 5.5% for trend sites and trend rookeries (1990 to 1996) and 3.8% for all surveyed sites (1991 to 1996). In the Kenai Peninsula to Kiska Island index area, a sub-area within the Alaska portion of the western stock, we counted 24,625 non-pup sea lions at 189 surveyed sites. Of these, 17,900 (72.7%) were at 69 trend sites, and 13,905 (56.5%) were at 26 trend rookeries. The 1996 count for the 69 trend sites was a decline of 21.3% from 1990, 17.7% from 1991, 13.4% from 1992, and 4.3% from 1994. 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. In 1996 we counted 10,907 non-pups at 58 surveyed sites: 8,231 (75.5%) at 13 trend sites and 6,204 (56.9%) at 3 trend rookeries. Non-pup numbers at the 13 trend sites increased by 6.7% to 8.9% compared to the 1990, 1991, and 1992 surveys but declined 6.7% since 1994. Overall, non-pup numbers in Southeast Alaska increased by an average of about 2% per year from 1990 to 1996.
Pup count trends were not consistent at all rookeries. The number of pups at the three rookeries in Southeast Alaska in 1996 (3,714) was an increase of 3.2% from 1990 but a decline of 1.5% from 1994. Pup counts at the two rookeries in the eastern Gulf of Alaska experienced greater declines from 1994 to 1996 of 24% at Seal Rocks (352 pups) and 41% at Fish Island (232). The 632 pups at Marmot Island was a decline of 61% from 1991 and 21% from 1994. The pup count at Outer Island (114) changed little from 1994, after a decline of 67% from 1990 to 1994. Pup counts at Atkins Island (366) in the western Gulf of Alaska and at Ugamak Island (706) in the eastern Aleutian Islands declined 15% to 17% from 1990 but increased 13% to 23% compared to 1994.
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