SEALS
It is early June, a cold June. Six seal counters have been ready for several days for the weather to calm down and the ice to shift a bit in Johns Hopkins Inlet. Shifting ice will allow the small park service boat, the Arete, to ease between the ice and reach the rocky outwash about l/2 mile from the face of Johns Hopkins Glacier. It is the only campsite for miles in this narrow fjord. The deck of the Arete is piled high with bear cannisters of food, dry bags full of warm clothes, flares, tents, binoculars, tripods, and temporary fencing.
The Arete maneuvers past Jaw Point, slowly easing through masses of shifting ice to the dropoff point, and the seal counters disembark. They will be here for several weeks, sending out radio messages to cruise ships should they come within 4 miles of this rock at Jaw Point. No boats besides kayaks will come farther than that until late summer, in order to protect the seal pups born here on the ice.
Day after day, the seal counters set up tripods and take shifts to count and record behavior of harbor seals. Hundreds come here each summer to give birth on the floating ice. Watching them is cold precise work, necessitating patience, steadiness, and a love of this place. This work, as well as records from the Beardslee Islands, will help scientists determine trends in seal behavior, the effects of human and other disturbances, and the questions to ask about the decline in numbers of Harbor Seals in Glacier Bay.
Declines in Numbers of Harbor Seals in
Glacier Bay National Park, 1992-2001
Elizabeth A. Mathews1 and Grey W. Pendleton2
1University of Alaska S.E. Biology Program
11120 Glacier Highway, Juneau, AK 99801
Beth.Mathews@uas.alaska.edu
2Alaska Department of Fish and Game
Division of Wildlife Conservation
P.O. Box 240020, Douglas, AK 99824
Grey_Pendleton@fishgame.state.ak.us
November 2001
Numbers of harbor seals (Phoca vitulina richardsi) on haulouts (resting areas) in Glacier Bay National Park declined by 35-50% from 1992 to 1999 and numbers remained low in 2001. We counted approximately 6,300 seals on haulouts throughout Glacier Bay during systematic surveys in August, 1992 and 3,200 in August, 2001. We typically observe 65-75% of these seals on icebergs in Johns Hopkins Inlet (JHI), a tidewater glacial fjord system.
From 1992-2001, we systematically counted seals in JHI in August from an elevated shore site, and we used aerial photography to count seals at terrestrial haulouts throughout the remainder of Glacier Bay during low tides in August. We calculated trends in numbers of seals using models that control for environmental and observer-related covariables, such as tide height, survey date, and observer experience. We detected negative trends from 1992 to 1999 for non-pups in Johns Hopkins Inlet (-5.9%/yr in June and -7.5%/yr in August) and for terrestrial sites (-9.3%/yr) in August. (Trend analysis for 1992-2001 has not yet been completed.) Overall declines for non-pups in Glacier Bay during the 1992-1999 study period range from -35% (JHI, June) to 42% (JHI, August) and -50% (terrestrial sites, August). High counts of seals in Glacier Bay also declined from 1992-2001 from 6,300 to 3,200 seals with an apparent steeper decline after 1995 or 1996 (Figure 1). Survey effort (number of days of surveys) has increased over the study period.
Seals counted during surveys could be lower if seals were spending less time on haulouts, or if seals have left Glacier Bay, or if mortality has increased. There is some evidence that seals are not spending more time in the water. While the causes for the declines remain unknown, human disturbance may be a partial factor for at least one large resting site, and increased predation and competition may also be involved. Other possible causes for the declines, such as changes in prey availability, are being explored.
Please report any information on dead or dying seals in the Glacier Bay/Icy Strait area to
Beth Mathews (Beth.Mathews@uas.alaska.edu; 465-1827).
