Whale Watching

Photography

Birding

Alaskan
Experience

Fishing

Hunting

Archealology

Sponsored Research

Research

Alaska Side Trips

Petersburg
Side Trips

Flightseeing

Customer
Comments

Cruise Guide

Travelogs

Site Map

Investigating Vital Rates and Indices of Health in the Declining Population of Harbor Seals in Glacier Bay

Harbor seals hauled out on a small bergie bit.

Sponsorship prospectus:
Harbor seals in Glacier Bay have declined by as much as 75% (a loss of approximately 6500 animals) since 1992, when annual surveys were initiated to monitor population trends for seals in the park (Mathews and Pendleton 2006). Other populations of harbor seals in southeastern Alaska are stable or increasing (Small et al. 2003), suggesting that factors contributing to the decline in Glacier Bay may be area-specific. The observed average rate of decline (15.5%/year; 1992-2004) in harbor seal numbers at terrestrial sites in Glacier Bay exceeds the maximum observed annual reproductive rate (12.5%) for harbor seals in Pacific regions (Olesiuk et al. 1990). If this decline continues at the current rate and immigration of seals into Glacier Bay does not occur, the endemic population (which may be genetically distinct from other harbor seals in Alaska; O’Corry-Crowe et al. 2003), could be extirpated. Harbor seals are top-level predators, effectively functioning as an important indicator species for marine ecosystems. Biological samples obtained from seals assessing diet and condition provide a means of determining whether contaminants in concentrations too low to detect at lower trophic levels, or reduced body condition in prey species thereby reducing their nutritional value for predators, are bio-magnified in top-level predators, potentially leading to lower reproductive rates, delayed age of first reproduction, or reduced survival of offspring.

It is likely that multiple factors are contributing to the harbor seal declines observed in the park, thus several studies are underway and data from numerous sources will be synthesized to gain a better understanding of the dynamics affecting this complex system. The most direct manner in which to understand fluctuations in population abundance is by estimating survival and reproduction (i.e., vital rates), and quantifying the effect that proximate factors (e.g., diet, nutritional stress, predation risk, health factors, disease, and contaminants) have on these vital rates. In 2004 the Alaska Department of Fish and Game initiated studies in Glacier Bay to capture and sample harbor seals in Glacier Bay to assess health, disease, and contaminant status, and to equip a subset of those seals with multiple-year, subcutaneously implanted VHF transmitters to assess long-term vital rates. These surgically implanted transmitters allow researchers to follow seals through 5 years (nearly ¼ of their life span) to determine whether seals with certain parameters (e.g., a particular diet, low body fat, elevated liver enzymes, high contaminant loads) have lower survival, delayed age of first reproduction, or whether particular females are less likely to give birth in subsequent years. Moreover, long-term radiotracking and further genetics studies may clarify characteristics of the seasonal migration of large numbers of seals into and out of the park, perhaps determining whether wintering grounds beyond Glacier Bay represent greater risk for seals. Radiotracking may also determine whether glacial habitat provides protection from predators, potentially attracting non-resident, pregnant females to give birth in the icy habitat.

We have also been conducting studies on foraging ecology in Glacier Bay in collaboration with other researchers; equipping seals with external transmitters that allow us to intensively track seals for shorter time periods and obtain detailed data on their dive behavior, foraging areas, and prey availability at those foraging sites. We have noted distinct differences in the foraging behavior of seals captured in ice and those captured in terrestrial habitat, but further studies are needed to determine whether these behaviors are representative of long-term behavior or were an effect of ephemeral conditions (e.g., prey distribution, vessel traffic, or environmental conditions) in a particular year. Results from these studies contribute to our understanding of the ecology, behavior, and life-history of harbor seals, which is central to understanding causative factors in the decline and thus proper management of this large, but rapidly declining breeding population in Glacier Bay.

This research in Glacier Bay is one of several projects conducted by the Alaska Department of Game’s Harbor Seal Research Program. This statewide program conducts annual assessments of population trends for harbor seals throughout the state along with several other research projects on population dynamics in other areas of the state. Our research is funded by annual congressional appropriations; however, in 2006-07 our funding has been reduced by approximately 25%. We are struggling to keep these important research projects going and thus we are seeking other means by which to supplement our funding or logistical support for conducting research.

LITERATURE CITED
Mathews, E.A. and G.W. Pendleton. 2006. Declines in harbor seal (Phoca vitulina) numbers in Glacier Bay National Park, Alaska, 1992-2002. Marine Mammal Science 22(1): 167-189.

O'Corry-Crowe, G. M., K. K. Martien, and B. L. Taylor. 2003. The analysis of population genetic structure in Alaskan harbor seals, Phoca vitulina, as a framework for the identification of management stocks. Pages 53. Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, La Jolla, California.

Olesiuk, P. F., M. A. Bigg, and G. M. Ellis. 1990. Recent trends in the abundance of harbor seals, Phoca vitulina, in British Columbia. Can. J. Fish. Aquat. Sci. 47: 992-1003.

Small, R. J., G. W. Pendleton, and K. W. Pitcher. 2003. Trends in abundance of Alaska harbor seals, 1983-2002. Marine Mammal Science 19: 344-362.

Contact us if you are interested in sponsoring any of our research partner's projects at;

1+907.772.4700

or