Temporary Tags Will Help
Scientists Make Accurate
Counts of Seal Populations
NMFS Northeast Fisheries Science Center
N E W SWoods Hole, Mass. – A team of biologists began tagging harbor seals last week in coastal waters off Chatham and Wellfleet. The tagging project will continue throughout the month and will help scientists make more accurate estimates of harbor seal populations.
The federal Marine Mammal Protection Act requires an annual report on all mammal populations living in U.S. waters. Seal stock assessments in the Northeast are conducted by scientists from NOAA's Northeast Fisheries Science Center in Woods Hole.
"Every four years or so since 1981 we have conducted an aerial survey during the May/June pupping season from Massachusetts to the Maine/Canadian border," explains Dr. Gordon Waring, a NOAA Fisheries Biologist. "We take photographs of haul-out sites such as ledges and beaches, and then count the seals."
The coast-wide aerial surveys have shown harbor seal populations have been increasing at an estimated 4.2 percent per year since 1981. The most recent survey was conducted in 1997 and resulted in an abundance estimate of 30,990 harbor seals, including 5,359 pups. Because many seals are in the water (or not "hauled-out") at any one time, the seal counts obtained in aerial surveys are thought to be a minimum estimate of the total seal population.
In the work begun last week, the biologists are planning to mark approximately 60 seals with radio tags. During the coast-wide survey planned for the pupping season May and June this year, the radio tags will allow researchers to locate hauled-out seals from aircraft equipped with tracking antennas. Waring and his colleagues will use information from the tagged seals to develop a "correction factor" to estimate the fraction of the total seal population normally missed by aerial surveys.
"We don't expect the tagging will cause the seals any distress," Waring said, noting that the techniques for capturing, handling, tagging and releasing harbor seals are well documented and have been tested on the West Coast, in Alaska, and in Maine's Penobscot Bay in 1999.
Seal researchers from the University of Maine, Maine Department of Marine Resources, Marine Environmental Research Institute, New England Aquarium, University of Massachusetts, Center for Coastal Studies, Riverhead Foundation for Marine Research and Preservation, Norwalk Aquarium, University of Alaska, and NOAA Fisheries are involved in the Cape Cod tagging project.
The biologists are using two or three small boats and research gillnets to capture small groups of seals. The scientists monitor the condition of each seal by checking its breathing rate, alertness, flipper temperature, and activity level. The team measures and weighs each seal and takes samples of blood, blubber, and hair. Forty-five seals will be double tagged with two radio tags (one on the shoulder and one on the hind flipper). An additional 15 seals will be tagged with shoulder tags but not hind flipper tags.
The tags are temporary tags, most of which will be shed during the seals' molting season in July and August.
The research is being conducted under a Marine Mammal Research Permit issued by the NOAA Fisheries Office of Protected Resources. The biologists also have Special Use Research Permits issued by the National Park Service, Cape Cod National Seashore and Monomoy National Wildlife Refuge.