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National Marine Mammal Laboratory (NMML)

Alaska Ecosystems Research Program

Resight Surveys for Branded Steller Sea Lions in Gulf of Alaska and Eastern Aleutian Islands

In order to estimate movement patterns, survival, and other vital rates of Steller sea lions (Eumetopias jubatus), the National Marine Mammal Laboratory (NMML) and Alaska Department of Fish and Game have been marking pups with brands or flipper tags at rookeries in the eastern Aleutian Islands, in the central and eastern Gulf of Alaska, and in Southeast Alaska. During the last 2 weeks of May 2005, ship-based surveys were conducted in the Gulf of Alaska and the eastern Aleutian Islands to resight branded and tagged Steller sea lions.

Resights were conducted at 64 sea lion haulouts and rookery sites in the eastern Aleutian Islands and western/central Gulf of Alaska between 169 15 W (Samalga Island) and 155 39.5 W (Chirikof Island) aboard the chartered fishing vessel Aleutian Mariner. Fifty-eight branded sea lions were observed among a total of approximately 6,146 nonpup sea lions seen at all sites. Most of the branded sea lions observed were branded as pups at Ugamak Island rookeries 2001 (n = 20) or 2003 (n = 28). Other sea lions branded as pups that were observed included two from Marmot Island, one from Sugarloaf Island, and two from Forrester/Lowrie Island. Additionally, five sea lions that were initially dive-captured as yearlings or juveniles were resighted.

A second resight cruise was conducted at 40 sea lion haulouts and rookery sites in the Kodiak Archipelago and along the Alaska and Kenai Peninsulas aboard the chartered vessel Waters. Eighty-three branded sea lions were observed among a total of approximately 2,590 nonpup sea lions seen at all sites. The majority of branded sea lions observed in this area were branded as pups on Marmot and Sugarloaf Islands in 2000 (n = 16), 2002 (n = 14), and 2004 (n = 40). Five branded animals from Southeast Alaska were also sighted, including two each from Forrester and Hazy Islands and one from Graves Rock. Two sea lions that were initially dive-captured as yearlings or juveniles were resighted, and an 18-year-old female, "763," which was branded on Marmot Island in 1988, was observed on Sugarloaf Island.

During these surveys, fecal samples were collected for diet and genetic analysis. Additionally, the Aleutian Mariner delivered field camp supplies and cabin building materials to Ugamak Island for scientists doing land-based brand resights and behavioral observations of Steller sea lions.


Steller Sea Lion Pup Survey

The Alaska Ecosystems Program conducted its annual Steller sea lion pup survey cruise aboard the U.S. Fish and Wildlife Service (USFWS) research vessel Tiglax in the eastern Aleutian Islands through the central Gulf of Alaska from 20 June through 6 July 2005. Live pups (n = 3,395) and dead pups (n = 80) were counted at 12 rookeries and haulouts to monitor population trends. Pups were branded at Ugamak (n = 200) and Seal Rocks (n = 80) rookeries for studies estimating survival and other vital rates. In order to assess condition and health status, morphometrics (weight, girth, length) and tissue samples (blood, tissue, fecal) were collected from 50 randomly selected pups at Akutan (Cape Morgan), Jude, and Chowiet Islands, and from 40 pups at Clubbing Rocks South. Four freshly-dead pups were collected from Seal Rocks, a rookery with high pup mortality, for necropsies. Additionally, 74 scats were collected for dietary analysis, and 73 previously branded and tagged sea lions were resighted.


Steller Sea Lion Field Camps

Scientists from the Alaska Ecosystem Program were stationed on Marmot and Ugamak Islands beginning in late May and running through July 2005. Steller sea lions breed and give birth at rookeries on both islands, and the program has branded pups born there since 2000 (and in 1987-88 at Marmot). Scientists living on the island collect data on Steller sea lion vital rates and dispersal (brand resights), behavior, abundance, and attendance. Three scientists and a carpenter were transferred by helicopter to Ugamak Island from Dutch Harbor beginning in late May. Materials to build a cabin at Ugamak were transferred by helicopter to the island from the Aleutian Mariner on 30 May. The carpenter was transferred off Ugamak to the Tiglax in late June during the pup survey cruise so that he could travel to Marmot Island and begin building a cabin at the south end of the island in early July. Cabin materials were delivered from Kodiak to the south end of Marmot Island by amphibious vessel in May and were moved to the top of the island by helicopter in early June when the four NMML scientists arrived. For the first time, field camps at both the north and south ends of Marmot Island were occupied, permitting simultaneous and complete coverage of both rookery beaches (beaches 4 and 7).

By Tonya Zeppelin and Lowell Fritz


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