Mortality Estimate:	300
Population Status:	Possibly stable, but not recovering
Continuing Chronic or Sublethal Effects:	Unknown
Comments / Discussion:	Many seals were directly oiled. There was a greater decline in population indices in oiled areas compared to unoiled areas in PWS in 1989 and 1990. Population was declining prior to the spill and no recovery evident in 1992. Oil residues found in seal bile were 5 to 6 times higher in oiled areas than unoiled areas in 1990.

Injury and Recovery Commentary

Harbor seal numbers were declining in the Gulf ofAlaska, including in Prince William Sound, before the oil spill. Exxon Valdez oil affected harbor seal habitats, including key haul-out areas and adjacent waters, in Prince William Sound and as far away as Tugidak Island, near Kodiak. Estimated mortality as a direct result of the oil spill was about 300 seals in oiled parts of Prince William Sound. Based on aerial surveys conducted at trend-count haulout sites in central Prince William Sound before (1988) and after (1989) the oil spill, seals in oiled areas declined by 43 percent, compared to II percent in unoiled areas.

In a declining population deaths exceed births, and harbor seals in both oiled and unoiled parts of Prince William Sound have continued to decline since the spill. For the period 1989-1997, the average estimated annual rate of decline was about 5 percent, and for that reason harbor seals continue to be considered "not recovering." Environmental changes in the late 1970s may have reduced the amount or quality of prey resources, including such forage fishes as Pacific herring and capelin, available to harbor seals in the northern Gulf of Alaska ecosystem. These changes may have been responsible for or contributed to the initial prespill harbor seal decline, and the ecosystem may now support fewer seals than it did prior to the late 1970s. Recent studies, however, indicate that the seals in the sound, especially pups and yearlings, are in very good condition and do not show evidence of nutritional stress. Ongoing sources of mortality include killer whale predation, subsistence hunting, and commercial fishery interactions (e.g., drowning in nets). Satellite tagging studies sponsored by the Trustee Council indicate that harbor seals in the sound are largely resident throughout the year, suggesting that recovery must come largely through recruitment and survival within injured populations.

Harbor seals have been a major focus of research sponsored by the Trustee Council since the oil spill. This research includes documentation of population trends in the field, improved statistical techniques for the analysis of aerial survey data, and exploration of possible sources of mortality and lack of recovery in the population, including health and diet. One study quantified normal blood chemistry values for several hundred seals; this database serves as a valu able tool for evaluating the health status of other seals. Starting in 1998, several projects exploring blood chemistry and other health parameters in relation to diet are being carried out at the Alaska SeaLife Center.

Harbor seals have long been a key subsistence resource in the oil-spill area. Subsistence hunting is affected by the declining seal population, and fewer opportunities to hunt seals have changed the diets of subsistence users who traditionally relied on these marine mammals. With partial support from the Trustee Council, the Alaska Native Harbor Seal Commission is working to involve Native hunters in re search on and management of harbor seals. Alaska Native subsistence hunters have been helpful by providing seal researchers with measurements and hard-to-obtain tissue samples from harvested seals.

Recovery Objective

Harbor seals will have recovered from the effects of the oil spill when their population is stable or increasing.