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National Marine Mammal Laboratory (NMML)

Polar Ecosystems Program

When the Ice Is Gone, Where Will the Seals Go?  

photo of South Sawyer Glacier
Figure 4.  Image of South Sawyer Glacier (in Tracy Arm) June 2005. Glacial areas like this are important to harbor seals which pup and nurse their young on these ice flows. The arrows indicate the extent of the glacier in June of 2004, which has receded nearly 2 kilometers in just the last year and the width reduced by about two-thirds.

There are more than 100,000 glaciers in Alaska covering 5% of the total land mass; most, however, are in rapid retreat. In 1983, there were 52 recorded tidewater glaciers (terminating in the ocean) in Alaska; in 2004 we documented 31 remaining and all but about 5 were receding. Harbor seals use the floating ice calved from at least 17 of these glaciers, which seem to provide relatively safe locations for the seals to pup, nurse their young, and molt, free from most predators and disturbance. Haul-out space on the floating ice is nearly always available and is independent of tide height.

Recent concerns for seals have arisen due to increased vessel traffic and disturbance by sightseeing and cruise ships in several tidewater glacial regions. The PEP is conducting research in collaboration with Alaska Native groups and the cruise ship industry to understand and mitigate the impact of this traffic on harbor seals in glacial areas. Each spring since 1998 to the present, Dave Withrow has censused three of the main glacial pupping areas in Southeast Alaska: Tracy Arm (Sawyer Glacier), Endicott Arm (Dawes Glacier), and LeConte Glacier. The seals at these sites have been composed almost entirely of mother-pup pairs. In June 2005, the Sawyer Glacier, which had been steadily decreasing by only tens of meters each year, was found to have receded by approximately 2 kilometers since 2004 (Fig. 4, above). The width of the glacier (at sea level) was reduced approximately 66%. If this retreat continues at its current rate, the Tracy Arm will no longer have a tidewater glacier within a year or two. The reduction of prime pupping habitat could have a significant impact on harbor seal populations in Alaska.

Detailed information on this research will be presented in December at the 16th Biennial Conference on the Biology of Marine Mammals in San Diego, California.

Capture Studies in Cook Inlet

From 28 April to May 14, members of the PEP participated in a harbor seal (Phoca vitulina) capture trip in lower Cook Inlet. The purpose of the trip was to practice capturing seals over a wide area in preparation for a much larger operation planned for September 2005. Seals were weighed and measured, and satellite transmitters were attached in order to track their movements over time. The research was funded by the Department of the Interiorís Minerals Management Service, which is interested in collecting baseline information on harbor seals prior to proposed oil development in the area.

Habitat Use of Harbor Seals in Bernerís Bay

Dave Withrow, along with Aleria Jensen and Erika Philips of the Alaska Regional Office, transited to Bernerís Bay, Alaska, north of Juneau aboard the NOAA vessel John N. Cobb. The purpose of the trip was to examine the habitat use of harbor seals during the pupping season. The Bernerís Bay region has gained much attention lately as roads and bridges may be built soon, as well as increased barge and vessel traffic, related to the reopening of a large gold mine in the area and possible connection of Juneau with the rest of the Alaska highway system. Dave Withrow also continued documenting harbor seal pupping sites and making counts in Southeast Alaska.

By Dave Withrow

Continued Studies of Potential Disturbance of Harbor Seals by Cruise Ships in Disenchantment Bay, Alaska

The PEP continued studies from 7 May to 8 June of research conducted in 2002 and 2004 on the potential disturbance of harbor seals by cruise ships in Disenchantment Bay, Alaska, during the sealsí annual pupping season. Eleven aerial photogrammetric surveys were conducted over the glacial ice field in Disenchantment Bay, where cruise ship traffic is high during the tourist season. Eight surveys were conducted in nearby Icy Bay, where cruise ships do not visit. Results from the Icy Bay surveys will be used as controls from which to compare results of the Disenchantment Bay surveys. This year, 12 additional survey transects were added over the more populated half of each bay, in-between the original 14 transects, in order to increase the sampling coverage of the highly clumped seal distributions.

High-resolution digital survey images will be georeferenced in a geographic information system (GIS) to enable mapping of the distribution and abundance of harbor seals in each bay. Observers from the PEP and the Yakutat Tlingit Tribe also boarded cruise ships entering Disenchantment Bay to record ship movements via portable GPS (global positioning system) units, as well as to count observed seal groups and measure their distance from the ships. Spatial models of harbor seal abundance and distribution, cruise ship movements, and glacial ice densities will be used to analyze possible impacts of cruise ship traffic on the harbor seal population in Disenchantment Bay. Similar efforts are planned for August 2005, during the harbor sealsí annual molting period.

By Shawn Dahle, John Jansen, Jay Ver Hoef, and Elizabeth Beckman


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