Project Description
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. . 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. The critical nursing period occurs during the summer months in the Bering Sea. We will purchase and attach satellite transmitters to address foraging behavior of different sexes and age classes of fur seals during the summer months. This research will define the travel routes and summer foraging habitat of fur seals from different rookeries and islands, and aid in understanding if population health is associated with habitat quality. This project will build on data acquired from adult females during past years and will provide additional information on annual variability and habitat use. This project will also help to continue to identify oceanographic resources, features or regions essential to the survival of fur seals. In addition, we will explore the utility of stomach-pill telemeters in combination with GPS tags to identify the occurrence and precise location of feeding events. Preliminary work with GPS tags in the summer of 2007 suggested that these instruments will provide information on fur seal behavior at a much finer resolution than previously collected.
Issues & Justification
Recent declines of northern fur seals on the Pribilof Islands may be affected or compounded by variability in foraging habitat quality. Fur seal population monitoring studies were conducted during 2006 on the Pribilof Islands, and indicate continued declines in the number of northern fur seals. The 2006 pup production estimate for St. Paul Island is 10.5% less than the estimate in 2004 and 24.6% less than the estimate in 2002. The 2006 pup production estimate for St. George Island is 1.2% greater than the estimate in 2004 and 3.0% less than the estimate in 2002 (Towell et al 2006). The overall decrease in pup production for St. Paul and St. George Islands combined from 2004 to 2006 is approximately 9.1%. By contrast, a relatively small population at Bogoslof Island (eastern Aleutian Islands) has been increasing in recent years. During the summer months, adult female fur seals make regular foraging trips from their breeding islands, returning to nurse and transfer energy to their pups. The habitat and ocean conditions encountered by all age classes during summer are critical to their survival and the successful rearing of dependent offspring. To identify the location of actual at-sea foraging events, we will use stomach temperature telemetry on animals being handled for foraging ecology studies. This technology will record the time and depth when a fur seal consumes prey and, when used in combination with GPS tags, indicate the exact location of prey consumption events in the Bering Sea. Analysis of recovered data will also help to understand the age specific foraging behavior of northern fur seals, and characterize important foraging habitat and areas of potential conflict with human activities.
Goals
- Define the summer foraging locations and behavior of northern fur seals in the Bering Sea.
- Compare travel routes and destinations among animals from different islands.
- Address the use of stomach temperature telemeters to assess prey consumption events.
- Compare the location data determined via Argos to the data acquired the by GPS tags.
- 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 summer of 2008. Fur seals will be captured and restrained with a padded noose pole or net, and may be held down on a restraint board. Budget allowing, we will instrument between 15 and 20 adult females. Other sex age classes will be instrumented with satellite telemetry tags and five of those females with stomach pill recorders. Animals will be released and monitored via Argos. Remote sensed data (sea surface temperature, sea surface chlorophyll a, and sea surface height anomalies) will be obtained and integrated with the fur seal location data to address oceanographic conditions/features for the duration of the satellite tracking.