Tagging Sea Otters for Tracking
Step one of the NPRB–funded project Sea Otter Recolonization and Interactions with Commercially Important Macroinvertebrates in Southeast Alaska
A previously tagged otter recaptured in the tangle net.
A VHF transmitter is sterilized before being implanted into a captured otter.
After tagging, an otter is released from its capture box.
A newly released otter swims away, showing both right and left flipper tags.
The expertise of commercial fisherman Dave Beebe was especially welcome during net-setting in the strong currents of central Southeast Alaska waters.
From May 14 to 27, 2011, researchers with the Southern Southeast Alaska Sea Otter Project captured 31 otters using tangle nets at the northwest side of Keku Strait, in Saginaw Bay, and at the mouth of Security Bay.
After capture, each otter was removed from the net, transferred to a specialized otter transport box, and taken to the surgical area aboard a specially modified fishing boat where all were sampled and measured. Researchers took blood, whiskers, samples for microbiology and virology, urine, and a premolar tooth, to gather information on disease, diet, biotoxins (such as PSP), and age. Finally, they implanted VHF radio tags in 30 of the otters, and attached uniquely colored and numbered flipper tags to both rear flippers. Flipper tags are expected to last several years, and VHF radio transmitters will continue to transmit for a minimum of 2 years.
Of the 31 otters captured, 15 were females with an estimated age range of less than 1 year to 9 years. Female weights were from 38 to 76 pounds (17.3 to 34.5 kg). The 16 captured males had an estimated age range of 1 to 10 years, and weights were from 45 to 102 pounds (20.5 to 46.4 kg). Three mother/pup pairs were captured.
Over the next two years, researchers will track the radio-tagged otters during regular flights out of Petersburg, and analyze distances and movement patterns at the colonizing front of the population. In addition, researchers will observe foraging of tagged otters, paying special attention to individuals moving into previously unoccupied areas. Biologists will determine sea otter diet in the capture area by examining isotope markers in collected otter whiskers. These data will be combined with foraging data to further refine the understanding of otter diet.
The diet and movement data will quantify the amount of each species eaten by sea otters as they move into new areas. The long-term goal of the study is to identify current and potential trends in the conflict for resources between sea otters and commercial and subsistence fisheries.
Microbiology and virology information will also be examined to address health questions pertinent to subsistence users who rely on shellfish. Sea otters are a keystone species in the nearshore marine ecosystem, have a high metabolic rate, are long-lived, and are the smallest marine mammal in the world. These distinctions make them one of the best bio-indicators for the ocean. Sea otters consume about 25% of their body weight per day, eating mainly suspension-feeding shellfish and detritus-feeding invertebrates like crabs and clams. These prey organisms, also sought by humans, process terrestrial pollutants and pathogens flushed into the nearshore environment.
The urine samples collected to measure PSP and domoic acid levels will be of particular interest, since record levels of harmful algal blooms were recorded in the nearby Ketchikan area during the time of sea otter capture.
A Cooperative Effort
The capture process was truly a cooperative effort, bringing together wildlife biologists and managers, researchers, commercial fishermen, veterinarians, a local teacher (see sidebar) and an ecotourism business to help lay the groundwork for a greater understanding of sea otter movements, diet, and health in the waters of southern Southeast Alaska. Dennis Rogers, skipper of the M/V Northern Song, very generously donated his vessel as a base for the field crew, and ever-capable mate Leanna Stern provided services. Dave Beebe, one of many area dive and crab fishermen impacted by the growing otter population, provided his vessel, the F/V Jerry O, to house the sampling and surgery facility.
Many people volunteered their time to help the capture team, including Marc Kramer, veterinarian from Miami, Florida; Eliana Ardila, veterinarian technician from Miami; Bonnie Easley-Appleyard, intern with the U.S. Fish and Wildlife Service (USFWS); Pam Tuomi, Alaska SeaLife Center senior veterinarian; Kristin Worman, biological technician with USFWS; and Tracy Goldstein, researcher with the Marine Ecosystem Health Diagnostic and Surveillance Laboratory at the University of California Davis Wildlife Health Center.
Special thanks also go to Northern Song clients whose donations helped house and feed the research crew: Kymberlee Black, Ted Ollier, Jeff Ollier, and Jessica Adams.
The boat, capture, and surgery crews during the first week of capture efforts.
Teacher at Sea, Jo Ann Day
With additional funding provided by Alaska Sea Grant, Petersburg Middle School science teacher Jo Ann Day joined us for one week in the waters of Keku Strait to observe the research and tagging project up close, and gather materials for use in her classrooms.
Jo Ann also created a customized lesson plan [Microsoft Word document] based on what she learned. It is available for use by any teachers interested in the subject. For more information, contact Jo Ann at firstname.lastname@example.org.
A related lesson plan, The Case of the Missing Sea Otter, was developed as part of the Alaska Seas and River curriculum.