DOI: 10.5063/f1x63jtd
title: Evaluating Harlequin Duck Population Recovery: CYP1A Monitoring and Population Data (2006, 2007, 2009)

description: Harlequin ducks have been studied extensively in Prince William Sound during the restoration phase following the Exxon Valdez oil spill, leading to one of the most thorough considerations of wildlife population injury and recovery following a major oil spill ever undertaken. These efforts have included population monitoring by the U.S. Fish and Wildlife Service and the Alaska Department of Fish and Game, as well as a series of directed research projects designed to elucidate the process of, and constraints to, population recovery. These studies demonstrated that harlequin ducks were exposed to lingering oil over a much longer time frame (i.e., through at least 2005, 16 years following the spill) than expected at the time of the spill, based on elevated levels of cytochrome P4501A induction in birds from oiled areas. In addition, several lines of evidence suggested that population injury occurred through at least 1998. Specifically, female winter survival probabilities were found to differ between oiled and unoiled areas, and densities were shown to be lower in oiled than unoiled areas after accounting for habitat-related effects. More recent data have indicated that female winter survival did not differ between oiled and unoiled sites during 2000-03, suggesting that direct effects of oil exposure on demographic properties may have abated.
In response to the data described above, the work here was proposed to add to the existing cytochrome P4501A monitoring data to track the timeline of exposure to lingering oil, and to assemble the demographic data collected during previous restoration studies into a quantitative population model to allow consideration of the timing and magnitude of oil spill injury, the mechanisms by which injury occurred and population recovery was constrained, and the current status of recovery, including predictions for timing of full recovery.

 FINDINGS: We found that cytochrome P4501A induction during winters 2005, 2006-07, and 2009 was higher in harlequin ducks captured in areas of Prince William Sound oiled by the 1989 Exxon Valdez spill, relative to unoiled areas. Cytochrome P4501A induction did not vary in relation to age, sex, or mass of individuals, nor did it vary strongly by season in samples collected early and late in the winter. We interpret these results to indicate that harlequin ducks continued to be exposed to residual Exxon Valdez oil up to 20 years after the original spill. Population modeling efforts indicated that female mortality related to chronic exposure to lingering oil was nearly double that estimated during the acute phase (the weeks and months immediately post-spill). Full recovery to pre-spill numbers was estimated to require between 13 and 32 years, with the most likely recovery scenario requiring roughly 24 years. Taken together, the data presented in this report add to a growing body of literature suggesting that effects of oil spills on wildlife have the potential to be expressed over much longer time frames than previously assumed.

More details on methods and analysis can be found in the final report: Esler, D. and S. A. Iverson. 2010. Evaluating harlequin duck population recovery: CYP1A monitoring and a demographic population model. Exxon Valdez Oil Spill Restoration Project Final Report (Project 070816), Centre for Wildlife Ecology, Simon Fraser University, Delta, British Columbia, Canada.