The Exxon Valdez Oil Spill: Long-Term Effects and Pathways of Exposure to Nearshore Vertebrates

Oil from the 1989 Exxon Valdez spill persists in intertidal areas of western Prince William Sound, Alaska, presenting a risk of chronic exposure for species that utilize nearshore areas.  Over the past two decades, extensive efforts have been made to identify and understand the long-term consequences of the spill and the process of recovery of injured species.  Exposure of nearshore vertebrates has been measured with indicators of cytochrome P450 1A induction, comparing individuals from areas that were heavily oiled in 1989 to those from nearby unoiled areas.  Studies on a suite of species (2 mammals, 2 fishes, 4 birds) have suggested that all were exposed to oil, with strong evidence for declining exposure over time.  Harlequin ducks and sea otters are two species which forage on invertebrates in nearshore areas, and for both species, recent data indicate that exposure continues.  For harlequins, evidence of oil exposure initially correlated with reduced survival.  Although exposure appears to be persisting, demographic injury is no longer evident, and models suggest the population is recovering.  For sea otters, abundance in areas that were most heavily oiled remains below the estimated pre-spill number, with reduced survival implicated as cause, although recent survey data suggest recovery is underway.  It appears that through excavation of intertidal foraging pits, sea otters are simultaneously gaining exposure to lingering oil and contributing to the diminishment of subsurface oil remaining on shorelines.  Sea otters, harlequin ducks and other species at risk are vulnerable to exposure and potential effects as long as oil remains in sediments, perhaps for several more decades.  The long timeline over which impacts from lingering Exxon Valdez oil are being documented is an unanticipated finding, made possible by the extended support of studies implemented after the spill.