Injury
Barrow's goldeneyes are sea ducks that winter in protected nearshore marine waters in Prince William Sound and feed in the intertidal zone, consuming primarily mussels.
Some acute mortality of Barrow's goldeneyes was observed in the weeks and months immediately following the Exxon Valdez oil Spill in March 1989. Total acute mortality of Barrow's goldeneyes is difficult to determine, given uncertainty in carcass identification and recovery rates, but sea ducks generally were vulnerable to acute mortality and constituted approximately 25 percent of the carcasses recovered in Prince William Sound. Given the number of Barrow's goldeneyes present at the time of the Spill, acute mortality was likely in the low thousands.
Of more concern are longer-term effects due to either chronic exposure to lingering oil or indirect effects of trophic web disruption. Because Barrow's goldeneyes occur exclusively in intertidal and shallow subtidal habitats, they are particularly vulnerable to lingering oil exposure and the potential for physiological effects. Similarly, reliance on intertidal invertebrate prey suggests that Barrow's goldeneyes are particularly vulnerable to disruptions of intertidal communities. Barrow's goldeneyes were shown to have higher levels of induction of cytochrome P4501A (CYP1A) in oiled areas compared to unoiled areas of PWS in 1996, 1997 and 2005. However, in March 2009, average CYP1A was similar between areas, suggesting that exposure to residual oil had abated by that time.
Recovery Objective
Barrow's goldeneyes will have recovered when demographics and biochemical indicators of hydrocarbon exposure in goldeneyes in oiled areas of Prince William Sound are similar to those of goldeneyes in unoiled areas.
Recovery Status
Within their wintering range, Prince William Sound is an important area, supporting between 20,000 and 50,000 wintering individuals. Survey data from the U.S. Fish and Wildlife Service indicated that winter numbers of goldeneyes on oiled areas were stable from 1990-1998, in contrast to significantly increasing numbers on unoiled areas during that same time period. That was interpreted as evidence of lack of recovery, as the prediction would be that lack of continued injury would result in parallel population trajectories and that recovery would be indicated by more positive trajectories on oiled areas. However, US Fish and Wildlife Service surveys through April 2012 show that population growth rates were the same between oiled and unoiled sites and remained relatively unchanged between 1998 and 2012.
A 2012 study of Barrow's goldeneye habitat use in oiled and unoiled portions of Prince William Sound found that densities of birds in oiled areas were at expected levels, given the habitat in the oiled areas, suggesting that food limitations in the intertidal zone within oiled areas were not restraining recovery. There is no evidence that Barrow's goldeneyes are currently being exposed to lingering oil in the intertidal habitat.
Interpretation of surveys and habitat selection is constrained by lack of full understanding of Barrow's goldeneye demography, particularly rates of site fidelity and dispersal. These values have important implications for understanding the process of population recovery.
Lack of elevated CYP1A in oiled relative to unoiled areas suggests that exposure to lingering oil has ceased in the Barrow's goldeneyes. Surveys from 2009- 2012 indicate that populations in oiled and unoiled areas have converged and the total population in Prince William Sound has remained stable since the Spill. Barrow's goldeneyes are considered to be recovered from the effects of the Spill.
Click HERE for more information on Trustee Council funded studies of Barrow's goldeneyes.
