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National Marine Mammal Laboratory (NMML)

Alaska Ecosystems Research Program

Winter Migrations of Adult Female and Newly Weaned Northern Fur Seals

Map showing winter movement patterns of northern fur seals
Figure 1.  Winter movement patterns of northern fur seal pups from St. Paul Island (dark gray), St. George Island (black), Bogoslof Island (white) and San Miguel Island (light gray) from Ocober-November 2005 until 31 December 2005.

In October/November 2005 the Alaska Ecosystems Program of the National Marine Mammal Laboratory (NMML) began a yearlong study tracking the winter movements of newly weaned northern fur seal pups (Callorhinus ursinus). Currently the Eastern Pacific stock of the northern fur seal Alaskan population is declining at a rate of 6% per annum and is listed as depleted under the Marine Mammal Protection Act. Approximately 60% of the global northern fur seal population, estimated at 1.2 million, resides on the Pribilof Islands in western Alaska (57N, 170W). Reasons for the decline are not fully understood and may include anthropogenic factors such as disturbance, entanglement, pollution, and indirect or direct fisheries interactions, and environmental factors, such as regime shifts in the North Pacific Ocean and Bering Sea, possibly affecting prey availability.

The movement and distribution of newly weaned pups is poorly understood as yearlings are rarely seen, and survival of pups in their first year away from the rookeries is thought to be less than 50%. Pups are weaned and begin their migration from the rookeries in November. During migration, pups must navigate for the first time in the open ocean to reach suitable winter habitat and must consume enough prey to sustain themselves.

Documenting the winter migrations of newly weaned fur seals will provide crucial information on winter foraging habitat preferences and the potential importance of oceanographic features to the foraging behavior and survival of this age group. This project aims specifically to determine 1) the migratory movements and winter destinations of northern fur seals in their first year at sea; 2) the foraging activity of this age group as inferred from diving data, when available, or with less certainty, from the amount of time spent in an area; and 3) the environmental factors influencing the spatial and temporal distributions of migration and foraging within and between years.

Research is being conducted at long-term study sites at seven breeding colonies on St Paul (SNP) and St George Islands (SNG), Pribilof Islands, and at the newer growing breeding colonies on Bogoslof Island (BOG, 54N, 168W) and, in cooperation with NNMLs California Current Ecosystem Program, at San Miguel Island (SMI, 34N, 120W), California.

In October/November 2005, 99 satellite transmitters were deployed on 48 female (F) and 51 male (M) pups at the various breeding sites (SNP (21F/23M); SNG (10F/10M); SMI (7F/8M); BOG (10F/10M)). All 99 pups are being tracked while at sea, and dive data are also being collected for 40 of the pups.

A cooperative study program was initiated on St. Paul Island with the local school where students are also involved in the study. A talk about the project was given to the students in November, and a web page is being developed to enable the students to track the pups (with their newly appointed Aleut names) in real time from their classroom.

By Mary-Anne Lea and Tom Gelatt


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