Seattle Aquarium mammal biologist Julie Carpenter recently assisted scientists from NOAA’s National Marine Fisheries Service (NMFS) with their pup count, which happens every two years in the Pribilof Islands, Alaska. The Pribilofs are home to the largest breeding colonies (or rookeries) of northern fur seals in the world, representing over half of the world’s northern fur seal population. Collaborating on the research and participating in it side-by-side with the field researchers provided Julie with firsthand experience and knowledge about the research techniques and technical challenges involved in working with the wild northern fur seal population—making her uniquely suited to bring a deeper understanding of this work back to the staff and visitors of the Seattle Aquarium. Through this cooperative relationship, our hope is to continue to educate people about the critical population studies being conducted in these far-off islands and the many issues surrounding the Pribilof fur seals. Learn about Julie’s experience in the Pribilof Islands in this four-part blog series.
Part 3: beach combing
In the past three days, we’ve combed four rookeries (Morjovi, Reef, Little Zapadni, and Lukanin) for dead pups. This gives the NMFS researchers information on total mortality of pups in each rookery as well as total northern fur seals born this year (determined by adding the numbers of live and dead pups). Even though I looked at carcasses all day, the island was still beautiful, filled with life and the sounds of fur seal pups and crashing waves. I can’t complain!
In addition to counting animals, we also gathered teeth from adult carcasses for future age determination. Scientists can determine the age of a seal by looking at the inside of an extracted tooth and counting lines in the teeth, similar to counting rings in a tree. We also collected biological samples, such as regurgitated food and feces, to determine the fish and squid species eaten by fur seals.
Earlier in the mornings a few NMFS researchers began the “recapture” part of the “mark and recapture” study—without actually having to touch the animals again. Small groups of fur seals were methodically scanned from a distance using binoculars to determine the number of pups with sheared versus unsheared heads. Each rookery was observed two separate times and an average was taken. Scientists can estimate the total number of live pups in the rookery based on the ratio of sheared to unsheared pups.
This information, combined with total number of pup mortalities, helps researchers understand just how many pups were born this year and whether the population is decreasing or increasing. The 2012 official count won’t be published for months, but in recent years the pup population on St. Paul has been declining by about 6% each year.
Stay tuned for the next blog post. To learn more about northern fur seals, come visit the Aquarium!
The work described here was authorized under Marine Mammal Permit No. 14327 issued to the National Marine Mammal Laboratory, AFSC, NMFS.