Aerial and land-based surveys of Steller sea lions (Eumetopias jubatus)  in Alaska, June and July 1999 and 2000

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 July 1999 and June 2000. The 1999 aerial survey was restricted to the eastern Gulf of Alaska, where we counted 2,072 non-pup Steller sea lions on 23 rookery and haul-out sites. In June 2000, we counted a total of 37,801 non-pups on 289 rookery and haul-out sites from Southeast Alaska through the western Aleutian Islands. Of these non-pups Alaska-wide, 28,187 were on the 94 trend rookery and haul-out sites, which was a decline of 3.2% from 1998 and 26.1% from 1990. The 33 trend rookeries Alaska-wide included 20,298 non-pups, indicating declines of 3.8% from the 1998 count and 26.4% from 1990. Estimated average annual rates of decline from 1990 to 2000 were 3.2% (P < 0.001: 95% C.I.= 2.5% to 3.9%) for all trend sites and 3.3% (P < 0.001: 95% C.I.= 2.7% to 3.9%) for the 33 trend rookeries.

Most of the sites surveyed in 2000 (264 of 289: 91%) are part of the western stock, which includes animals from the eastern Gulf of Alaska (144° W long.) through the western Aleutian Islands. The June 2000 count of 25,384 non-pups at all 264 sites in the western-stock indicated declines of 13.9% from 1998 and 31.7% from 1991, with an estimated annual decline of 4.0% (P < 0.001: 95% C.I.= 3.1% to 4.9%). At 82 rookery and haul-out trend sites in the western stock, the June 2000 count of 18,325 represented declines of 10.3% from 1998 and 40.0% from 1990. The 13,402 non-pups at the 30 western-stock trend rookeries indicated declines of 18.5% from 1998 and 39.9% from 1990. The estimated average annual decline from 1990 to 2000 was 5.1% for all western-stock trend sites (P < 0.001: 95% C.I.= 4.7% to 5.6%), as well as for western-stock trend rookeries (P < 0.001: 95% C.I.= 4.3% to 5.8%).

In the Kenai Peninsula to Kiska Island index area, a subarea within the Alaska portion of the western stock, we counted 21,381 non-pup sea lions at 227 surveyed sites, a decline of 12.3% from 1998 and 22.1% since 1991. Of these, 15,279 were at 69 trend sites (26 rookeries and 43 haulouts), and 11,738 were at 26 trend rookeries. These counts represented declines from 1998 to 2000 of 6.9% and 3.1%, respectively, for all trend sites and for trend rookeries, and declines of 32.9% and 37.2% since 1990. Overall declines in the Kenai to Kiska area have been more than 80% since 1976 and about 70% since 1985. Estimated annual rates of decline in the Kenai to Kiska index area were 2.5% (P < 0.003: 95% C.I.=1.4% to 3.6%) for all 227 surveyed sites from 1991 to 2000, 3.9% (P < 0.001: 95% C.I.= 3.5% to 4.3%) for the 69 trend sites and 4.7% (P < 0.001: 95% C.I.= 3.9% to 5.5%) for the 26 trend rookeries from 1990 to 1998.

The eastern stock is represented in Alaska only by Southeast Alaska, where we counted 12,417 non-pups at all 25 sites in June 2000. The count of 9,862 non-pups at 12 trend sites represented increases of 13.4% from 1998 and 29.3% from 1990. At the three trend rookeries in Southeast Alaska, we counted 6,896 non-pups, which represented increases of 4.4% from 1998 and 25.6% from 1990. Estimated annual increases from 1990 to 2000 in Southeast Alaska were 1.9% (P = 0.058: 95% C.I.= 3.8% to -0.1%) for all trend sites and 1.6% for  trend rookeries  (P = 0.041: 95% C.I.= 3.0% to 0.1%).

National Marine Fisheries Service personnel counted 1,924 live pups at 9 rookeries and 75 live pups at three haul-out sites in Alaska during June and July 2000. Taken together, the number of pups at the 9 rookeries declined by 4.1% from 1998 to 2000, but this decline represented a difference of only 83 pups.


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