Project Description

The population of northern fur seals on the Pribilof Islands has continued to decrease in recent years. The cause of this decline remains a mystery. Equally perplexing is a complete understanding of the behavior of northern fur seals during their winter migration from the Pribilofs into the Bering and North Pacific Oceans. This project proposes to use satellite telemetry to monitor the behavior of two separate age classes of northern fur seals during their winter migrations. Adult females and juveniles of both sexes will be instrumented with satellite tags that provide both location and for some, dive information throughout the time the animals are at sea. By comparing animal behavior to available information on oceanographic and other environmental conditions, we hope to understand more about what northern fur seals do, where they do it, and what effects it may have on their ultimate success.

Issues & Justification

The abundance of northern fur seals (Callorhinus ursinus) on the Pribilof Islands of St. Paul and St. George has declined in recent decades, yet the reasons for the decline are unclear. The total number of pups born on the Pribilof Islands in 2006 was estimated as being less than one third the number born during the 1950's when the population was assumed to be at its peak. In contrast, annual pup production at Bogoslof Island increased at 15% between 1997 and 2005.

Survival and health of northern fur seals is likely related to the quality of the habitat they occupy and use for foraging. The location and duration of lactating adult female foraging trips during the summer months in the Bering Sea have been previously explored using satellite telemetry. However, fur seals spend approximately three quarters of the year away from the breeding islands. Little is known about the habitat used during the winter migration by young age classes of northern fur seals, particularly recently weaned pups, and yearlings.

We attached satellite transmitters to a total of approximately 50 juveniles (yearlings and/or 2-year olds) and adult females from St. Paul Island prior to the 2007 fall migration. These animals are being monitored through the winter of 2007-2008. This research will define the travel routes and winter destinations of fur seals from different islands, and aid in understanding if population health is associated with habitat quality. This project will build on data acquired from satellite telemetry of young pups, juveniles and adult females during 2005-2007, and will provide additional information on annual variability and winter habitat use by other young age classes of northern fur seals. Additionally, it will address movements of young age classes of fur seals from the islands. The project will also help to continue to identify oceanographic resources, features or regions essential to the survival of fur seals.

Goals

• Define the travel routes and destinations of northern fur seals migrating away from the Pribilof Islands.
• Compare travel routes and destinations among animals from different islands.
• Compare travel routes and timing between different age classes of fur seals.
• Assess the oceanographic conditions/features affecting habitat quality and movements of fur seals.

Methods

The study will be conducted on the Pribilof Islands (St. Paul and St. George) during the fall of 2007. Prior to their departure from the island, juvenile and adult female fur seals will be captured with a padded noose pole or net, and may be held down on a restraint board. Approximately 40 juveniles and 10 adult females were captured. Satellite transmitters were attached to the pelage on the dorsal surface of the fur seal's back with epoxy. Remote sensed data (sea surface temperature, sea surface chlorophyll a, and sea surface height anomalies) will be integrated with the fur seal location data to address oceanographic conditions/features for the duration of the satellite tracking.