Telemetry of Ice Seals Captured During a Research Cruise Aboard the McArthur II in the Eastern Bering Sea
Figure 3. Preliminary map of ribbon seal movements from ARGOS satellite tags, May–July 2009. Click to enlarge.
The National Marine Mammal Laboratory’s Polar Ecosystems Program (PEP) participated in an ice-seal research cruise in the eastern Bering Sea this spring, 13 May–11 June 2009, aboard the NOAA ship McArthur II. A primary objective for the cruise was to deploy satellite-linked tags on ribbon and spotted seals. Ribbon seals and spotted seals are closely associated with sea ice during this time of year. The data collected by the satellite-linked tags will, together with information collected during similar cruises since 2005, provide critical information on haul-out and dive behavior and seasonal movements. Both ribbon and spotted seals have been the subject of petitions for listing under the U.S. Endangered Species Act, primarily out of concerns about global warming and the loss of sea-ice
habitat. Information on the timing of haul out is critical for calculating abundance estimates from previous aerial surveys, and data on movements and dive behavior will help to identify important habitat.
We captured 69 seals in all, comprising 37 ribbon, 31 spotted, and 1 ringed seal. We attached satellite transmitters to 22 ribbon and 30 spotted seals. Most of the transmitters were SPOT tags (Wildlife Computers, Redmond, WA), attached to the seals’ hind-flippers, which will provide long-term movement data and haul-out timelines—but only when the seals are hauled out with their flippers exposed. The remaining transmitters were SPLASH tags (Wildlife Computers) which provide more detailed information about locations at sea and diving behavior; these tags must be glued to the hair on the seal’s back or head and thus could only be attached to seals that had sufficiently completed their annual molt.
The McArthur II departed Kodiak, Alaska, on the afternoon of 13 May and arrived at the ice edge and began research operations on the morning of 16 May. A typical day consisted of survey watches from 9 a.m. to 9 p.m. Alaska Daylight Time (about 6 a.m. to 6 p.m. local apparent time), interrupted by small-boat excursions to capture and tag seals when we encountered sufficient concentrations of seals and suitable ice. Seals were captured on ice floes with hand-held landing nets. Our field crew consisted of eight PEP biologists and one veterinarian. We conducted surveys or tagging operations daily until the evening of 8 June. The McArthur II returned to Dutch Harbor, Alaska, on the morning of 11 June.
Figure 4. Preliminary map of spotted seal movements from ARGOS satellite tags, May–July 2009. Click to enlarge.
The sampling for each seal typically included length and girth measurements, mass, blood, a small piece of skin for genetics analysis, and any fecal material that was present on the ice for diet analysis. We obtained 61 blood, 67 skin, 67 viral swab, and 33 fecal samples from seals that we captured. In addition, we were able to collect 10 fecal samples and 17 samples of skin shed during the molt from seals that escaped our capture attempts. The dark flakes of skin are easy to find in the vicinity of the molting seals’ resting sites, and they contain sufficient DNA to support genetic analyses for investigation of stock structure.
Data from the deployed tags are already providing information (Figs. 3, 4). As observed from tags deployed in previous years, both ribbon and spotted seals have a strong association with the sea ice. As sea ice retreated in early summer, the spotted seals tended to head towards more coastal habitats along Alaska or Russia, while ribbon seals remained in the ice-free waters near the shelf break and over the Aleutian Basin.
