Quantifying long-term risks to sea otters from the 1989 'Exxon Valdez' oil spill: Comment on Bodkin et al. (2012)

Abstract

Bodkin et al. (2012; Mar Ecol Prog Ser 447:273-287) assessed the frequency at which sea otters Enhydra lutris might encounter subsurface oil residues from the 'Exxon Valdez' oil spill. They concluded that a pathway exists for exposures of sea otters to residual oil in the intertidal zone, and imply that this pathway has delayed recovery of sea otters. We agree that the potential exposure pathway exists, and the Bodkin et al. (2012) estimates of the frequency of encountering subsurface oil residues (4 to 10 times per year) comport with our previously published studies (2 to 7 times per year). However, we disagree that this pathway constitutes a significant risk to sea otters. We discuss results from our quantitative ecological risk assessment using an individualbased model that specifically simulated this pathway of exposures to a population of 500 000 sea otters. This conservative model predicted that assimilated doses of polycyclic aromatic hydrocarbons in subsurface oil residues to the 1-in-1000th most-exposed sea otters would be 1 to 2 orders of magnitude below the chronic effects thresholds that we established using USEPA data and methodology. When we artificially increased the rate of encountering subsurface oil residues, it required 4 to 10 encounters per day to reach effects levels. We conclude that the subsurface oil residues from the oil spill could not plausibly be responsible for any individual-or populationlevel effect on the sea otters at northern Knight Island. © Inter-Research 2013.