Telemetry of Ice Seals Captured During the USCG Healy and Oscar Dyson Research Cruises in the Eastern Bering Sea
Figure 4, click image to enlarge
Figure 5, click image to enlarge.
The National Marine Mammal Laboratory’s Polar Ecosystems Program (PEP) participated in three separate ice seal research cruises in the eastern Bering Sea this spring. Two cruises were aboard the U.S. Coast Guard icebreaker Healy (10 April – 12 May and 16 May – 18 June 2007) and one was aboard the NOAA ship Oscar Dyson (3–30 May 2007).
One of the main objectives for the cruises was to deploy a large number of 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 satellite-linked tags will provide critical information on haul-out behavior and seasonal changes in habitat use. Very little information is known about the movement of these seals, and the haul-out information will provide a key component for abundance estimates based on the extensive survey work done on the Healy.
We captured 48 seals in all, comprised of 32 ribbon and 16 spotted seals. We attached satellite transmitters to 28 ribbon and 12 spotted seals. Most of the transmitters were SPOT tags (Wildlife Computers, Redmond, WA) that were attached to the seals’ hind-flippers. These tags 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) that provide more detailed information about locations at sea and diving behavior; these tags must be glued to the hair on the seals’ back or head and, thus, could only be attached to seals that had sufficiently completed their annual molt.
The majority of the captures occurred during the Oscar Dyson cruise. The Oscar Dyson departed Kodiak, Alaska, on the afternoon of 3 May and arrived at the ice edge and began research operations on the morning of 6 May. Our typical day consisted of survey watches from 1000 to 2200 Alaska Daylight Time (about 0600 to 1800 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 four PEP biologists and two Alaska Natives from Kotzebue, Alaska. We conducted surveys or tagging operations daily until the evening of 28 May. The Oscar Dyson returned to Dutch Harbor, Alaska, on 30 May.
The sampling for each seal typically included length and girth measurements, mass, blood, a small piece of skin for genetic analysis, and any fecal material that was present on the ice for diet analysis. We obtained 13 blood, 45 skin, and 18 fecal samples from seals that we captured. In addition, we were able to collect 10 fecal samples and 14 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 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 preliminary information on movement and show some intriguing patterns (Figs. 4 and 5). Ribbon seals and spotted seals have a strong association with the sea ice while molting. As the sea ice retreated, ribbon seals followed the ice north through the Bering Strait or into the Gulf of Anadyr. The spotted seals tended to head towards more coastal habitats along Alaska or Russia.
These preliminary results are only the beginning of what we hope grows into a long-term dataset on ice seal behavior and ecology.
