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Marine Ecology Progress Series

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MEPS 241:271-286 (2002)  -  doi:10.3354/meps241271

Harlequin duck population recovery following the 'Exxon Valdez' oil spill: progress, process and constraints

Daniel Esler1,*, Timothy D. Bowman2, Kimberly A. Trust3, Brenda E. Ballachey1, Thomas A. Dean4, Stephen C. Jewett5, Charles E. O'Clair6

1US Geological Survey, Alaska Biological Science Center and
2US Fish and Wildlife Service, 1011 East Tudor Road, Anchorage, Alaska 99503, USA
3US Fish and Wildlife Service, 605 West 4th Avenue, Room G62, Anchorage, Alaska 99501, USA
4Coastal Resources Associates, Inc., 1185 Park Center Drive, Suite A, Vista, California 92083, USA
5Institute of Marine Science, University of Alaska Fairbanks, Room 118, OŒNeill Building, Fairbanks, Alaska 99775, USA
6National Oceanographic and Atmospheric Administration, Auke Bay Laboratory, 11305 Glacier Highway, Juneau, Alaska 99801, USA

ABSTRACT: Following the 1989 'Exxon Valdez' oil spill in Prince William Sound, Alaska, we studied the status of recovery of harlequin duck Histrionicus histrionicus populations during 1995 to 1998. We evaluated potential constraints on full recovery, including (1) exposure to residual oil; (2) food limitation; and (3) intrinsic demographic limitations on population growth rates. In this paper, we synthesize the findings from our work and incorporate information from other harlequin duck research and monitoring programs to provide a comprehensive evaluation of the response of this species to the 'Exxon Valdez' spill. We conclude that harlequin duck populations had not fully recovered by 1998. Furthermore, adverse effects continued as many as 9 yr after the oil spill, in contrast to the conventional paradigm that oil spill effects on bird populations are short-lived. These conclusions are based on the findings that (1) elevated cytochrome P450 (CYP1A) induction on oiled areas indicated continued exposure to oil in 1998; (2) adult female winter survival was lower on oiled than unoiled areas during 1995 to 1998; (3) fall population surveys by the Alaska Department of Fish and Game indicated numerical declines in oiled areas during 1995 to 1997; and (4) densities on oiled areas in 1996 and 1997 were lower than expected using models that accounted for effects of habitat attributes. Based on hypothesized links between oil contamination and demography, we suggest that harlequin duck population recovery was constrained primarily by continued oil exposure. Full population recovery will also be delayed by the time necessary for intrinsic population growth to allow return to pre-spill numbers following cessation of residual oil spill effects. Although not all wildlife species were affected by the 'Exxon Valdez' oil spill, and some others may have recovered quickly from any effects, harlequin duck life history characteristics and benthic, nearshore feeding habits make them susceptible to both initial and long-term oil spill effects.

KEY WORDS: Demography · 'Exxon Valdez' · Harlequin duck · Histrionicus histrionicus · Marine birds · Oil contamination · Population recovery

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