Cytochrome P4501A biomarker indication of the timeline of chronic exposure of Barrow’s goldeneyes to residual Exxon Valdez oil

► Barrow’s goldeneye are sea ducks that winter on the Pacific coast of North America. ► They occur in areas contaminated by the 1989 Exxon Valdez oil spill. ► CYP1A biomarker of oil exposure declined substantially from 1996–1997 to 2005 and 2009. ► Return to near background levels took nearly 2 decades. ► Exposure following large spills can persistent in some species for long periods. We examined hepatic EROD activity, as an indicator of CYP1A induction, in Barrow’s goldeneyes captured in areas oiled during the 1989 Exxon Valdez spill and those from nearby unoiled areas. We found that average EROD activity differed between areas during 2005, although the magnitude of the difference was reduced relative to a previous study from 1996/1997, and we found that areas did not differ by 2009. Similarly, we found that the proportion of individuals captured from oiled areas with elevated EROD activity (⩾2 times unoiled average) declined from 41% in winter 1996/1997 to 10% in 2005 and 15% in 2009. This work adds to a body of literature describing the timelines over which vertebrates were exposed to residual Exxon Valdez oil and indicates that, for Barrow’s goldeneyes in Prince William Sound, exposure persisted for many years with evidence of substantially reduced exposure by 2 decades after the spill.