Recent Work on Steller Sea Lions and Northern Fur Seals
Figure 1. Temporal dynamics of the counts of adult male northern fur seals on St. Paul and St. George Islands, 1990-2006, showing territorial males with females (filled circles) and idle males (territorial without females and nonterritorial combined) (triangles).
The Alaska Ecosystems Program (AEP) is responsible for investigating hypotheses for the decline of Steller sea lions and northern fur seals in Alaska. In past years, the field work throughout summer and fall has seen a greater emphasis on sea lion work as compared to fur seal projects. However, summer and fall of 2006 were unique with nearly all field work attributed to northern fur seals. There are two explanations for this. First, a recent lawsuit filed by the Humane Society of the United States effectively halted all Steller sea lion field work as of 31 May 2006 until the agency completes an Environmental Impact Statement. Second, 2006 was the year of our biennial fur seal pup estimate survey on the Pribilof Islands and also included two large projects examining fur seal behavior.
In July-September 2006, AEP’s Steller sea lion research effort was limited (by the court-ordered cessation of all permitted Steller sea lion research) to the field camps at Beach 4 and 7 on Marmot Island (near Kodiak, Alaska). Five researchers (Kathryn Chumbley, Erin Kunisch, Rhonda Dasher, Mary Malley, and Robin Solfisburg) spent July overlooking rookeries on the island collecting information on attendance, pup production, population demography, behavior, and sightings of permanently-marked animals. Maximum pup counts on the island totaled 428 in July 2006, which is similar to the 433 counted in late June 2005.
A total of 58 unique, permanently-marked sea lions were observed: 48 were originally marked as pups in 1987 (n=1) or between 2000 and 2004 (n=47) on Marmot Island, 4 on Sugarloaf Island, 1 on Forrester Island in Southeast Alaska, and 1 on St. George Reef in northern California; the remaining 4 were captured and marked as juveniles as part of foraging studies. Of the 26 marked females age 4 or older observed on Marmot Island, 4 were observed nursing a pup born in 2006, while 1 was observed nursing a juvenile most likely born in 2005. The remaining 21 marked, mature females were not seen with a pup in 2006.
During 2006, the AEP conducted population monitoring of northern fur seals in Alaska. The number of territorial and idle fur seal bulls on the Pribilof Islands has been counted regularly since 1911. This occurs in mid-July each year and has provided one metric of the population trend during and since the years of substantial commercial harvest. Counts of adult males occurred during 2006 on St. Paul Island, St. George Island, and Bogoslof Island. Counts of territorial males with females (“harem” males) on St. George decreased by over 20% compared to 2005, while idle males increased in comparison to last year (about 2.4%).
On St. Paul, the idle males increased by 7.5% and the “harem” males increased by 4.2% (Fig. 1 above). Overall, the total number of adult males counted on the Pribilof Islands was 11,322, representing an increase of 4.0% from 2005. The total number of territorial males with females remained about the same for the Pribilof Islands, declining about 0.7%. On Bogoslof Island, 1,200 (compared to 1,123 in 2005) adult male northern fur seals were counted.
The second component of northern fur seal population monitoring involved pup production estimates. The number of pups born in the Pribilof Islands is estimated every 2 years using mark-recapture methods. The project requires up to 15 people working for a week or more to mark in excess of 10,000 pups. Pup production data were obtained during August on St. Paul Island and St. George Island and are currently being analyzed to determine the final estimates for each island.
Behavioral work included the final field season of the collaborative COFFS (Consequences of Fur Seal Foraging Strategies) project, funded by the North Pacific Research Board, which focuses on adult female behavior during the nursing period and over winter. This project, a collaboration between AEP staff, the University of Alaska Fairbanks, and Dalhousie University, compares the behavior of fur seals in the decreasing St. Paul Island population with a smaller but increasing population at Bogoslof Island in the eastern Aleutian Islands. Twenty adult females and their pups were captured at each island in July for physiological studies of condition and to attach satellite transmitters and dive recorders. During October, the pairs were recaptured to retrieve the instruments and to repeat the measurements of condition.
Finally, the program finished the first full season of a 2-year project examining the over-winter behavior of newly weaned fur seal pups. In October-November of 2005, 99 satellite tags were attached to pups at all four North American rookeries (St. Paul and St. George Islands, Bogoslof Island, and San Miguel Island, California) before they began their over-winter migration. An additional 70 tags are now being deployed to complete the field work of that particular project.
