DOI: 10.5063/f1057cvk
title: Aerial Surveys of Harbor Seals in Prince William Sound, Alaska: 1989 - 2001

description: Study History: Restoration Project 01064 began in 1993 as a continuation of the initial post-spill study effort conducted as Marine Mammal Study Number 5 (Assessment of Injury to Harbor Seals in Prince William Sound, Alaska, and Adjacent Areas) in 1989 through 1991 and reclassified as Restoration Study Number 73 (Harbor Seal Restoration Study) in 1992. A final report was issued in 1994 for the combined Marine Mammal Study Number 5 and Restoration Study Number 73, entitled Assessment of Injury to Harbor Seals in Prince William Sound, Alaska, and Adjacent Areas Following the Exxon Valdez Oil Spill. Subsequently, annual reports were submitted entitled Habitat Use, Behavior, and Monitoring of Harbor Seals in Prince William Sound: 1994 Annual Report, 1995 Annual Report, 1996 Annual Report , 1997 Annual Report, 1998 Annual Report, and 1999 Annual Report . Fatty acid studies funded under Restoration Project 94320-F (Trophic Interactions of Harbor Seals in Prince William Sound) were included in the 1994 annual report for 94064. Fatty acid studies were continued and reported as part of this study for the duration of the project.

Abstract: We used aerial counts to monitor the trend in numbers of harbor seals in Prince William Sound, Alaska, following the 1989 Exxon Valdez oil spill. Repetitive counts were made at 25 haul-out sites during the annual molt period each year from 1990 through 1997. A generalized linear model indicated that time of day, date, and time relative to low tide significantly affected seal counts. When Poisson regression was used to adjust counts to a standardized set of survey conditions, results showed a highly significant decline of 4.6% per year. Unadjusted counts indicated a slight, but not statistically significant, decline in the number of seals. The number of harbor seals on the trend-count route in eastern and central PWS has been declining since at least 1984, with an overall population reduction of 63% through 1997. Programs to monitor long-term changes in animal population sizes should account for factors that can cause short-term variations in indices of abundance. The inclusion of such factors as covariates in models can improve the accuracy of monitoring programs.

Publications:

Adkison, M. D., T. J. Quinn II, and R. J. Small. 2003. Evaluation of the Alaska harbor seal population (Phoca vitulina) population survey: a simulation study. Marine Mammal Science 19: 764-90.

Boveng, P. L., J. L. Bengtson, D. E. Withrow, J. C. Cesarone, M. A. Simpkins, K. J. Frost, and J. J. Burns. 2003. The abundance of harbor seals in the Gulf of Alaska. Marine Mammal Science 19: 111-27.

Frost, K.J., Lowry, L.F., Ver Hoef, J.M., Iverson, S.J., Simpkins, M.A. 2005. Monitoring Habitat Use, and Trophic Interactions of Harbor Seals in Prince William Sound, Alaska. Exxon Valdez Oil Spill Trustee Council Report (Project #01064, 99064, 98064, 97064, 96064, 95064, 94064, 93064, R073, MM05). Alaska Department of Fish and Game, Fairbanks, Alaska.

Frost, K. J., L. F. Lowry, and J. Ver Hoef. 1999. Monitoring the trend of harbor seals in Prince William Sound, Alaska, after the Exxon Valdez oil spill. Marine Mammal Science 15, no. 2: 494-506.

Ver Hoef, J. M., and K. J. Frost. 2003. A Bayesian hierarchical model for monitoring harbor seal changes in Prince William Sound, Alaska. Environmental and Ecological Statistics 10: 201-9.