Aerial and ship-based surveys of Steller sea lions (Eumetopias jubatus) in Southeast Alaska, the Gulf of Alaska, and Aleutian Islands during June and July

Abstract

Aerial and ship-based surveys of Steller sea lions (Eumetopias jubatus) were conducted during June and July 1994 from Forrester Island in Southeast Alaska to Attu Island in the western Aleutian Islands. A total of 32,945 adults and juvenile Steller sea lions were counted at 95 trend rookery and haulout sites. This represents decreases of 5.5% from 1992 counts (34,844) and 13.7% from 1990 (38,154). Annual rates of change, as estimated by linear regression, were -2.8% from 1992 to 1994 (P < 0.05) and -3.7% from 1990 to 1994 (P = 0.008). In 1994, 23,452 adult and juvenile sea lions were counted on trend rookery sites throughout Alaska. This represents a decrease of 14.9% from 1990 counts (27,563) and a 9.3% decrease from 1992 counts (25,849). Estimated annual rates of change for 32 trend rookeries throughout Alaska were -3.9% (P = 0.017) for 1990-94 and -4.9% (P < 0.005) for 1992-94.

The area between the Kenai Peninsula and Kiska Island includes 69 trend rookery and haulout sites. Since 1990, adult Steller sea lions decreased 17.8% on these trend sites. Between 1992 and 1994, the number of adult Steller sea lions on trend sites decreased 9.5%. Annual rates of change of adult Steller sea lions on trend sites have been -4.9% (P < 0.001) for 1990-94, and -5.0% (P < 0.001) for 1992-94.

The 26 trend rookeries contained 14,505 sea lions in 1994. This represents a decrease of 22.4% from the 1990 count (18,694) and a 12.6% decrease from the 1992 count. Annual rates of change were -7.1% (P = 0.028) for 1990-94, and -6.7% (P < 0.001) for 1992-94. Throughout Alaska the greatest decreases at trend rookery sites were seen in the central Gulf of Alaska (-28.0%; 4,306 in 1992 to 3,099 in 1994) and the western Aleutian Islands (-28.3%; 2,531 in 1992 to 1,815 in 1994). The smallest decreases were in the western Gulf of Alaska (-4.8%; 3,313 in 1992 to 3,155 in 1994) and the eastern Aleutian Islands (-5.3%; 3,712 in 1992 to 3,515 in 1994). The only increase occurred in Southeast Alaska, up 9.3% from the 1992 count (5,945 in 1992 to 6,496 in 1994).

A total of 13,850 live pups were counted at 33 rookeries from Southeast Alaska through the central Aleutian Islands in 1994; there were no pup counts conducted in the western Aleutian Islands during 1994. Since 1991-92, pup production has decreased at rookeries in all of the Alaska subareas: Southeast Alaska (-11.3%), eastern Gulf of Alaska (-11.4%), central Gulf of Alaska (-27.4%), western Gulf of Alaska (-8.0%), and eastern Aleutian Islands (-14.5%). The number of pups counted has decreased by 24% in the central Aleutian Islands since 1989-90. At Walrus Island (Bering Sea) a total of 61 pups were counted in 1994, compared to 63 pups counted there in 1992--a decrease of 3.1%.


View Online  (.pdf, 1.12 MB).