Timelines and mechanisms of wildlife population recovery following the Exxon Valdez Oil Spill

In March 1989, the T/V Exxon Valdez ran aground in Prince William Sound (PWS), Alaska and spilled an estimated 42 million liters of crude oil (Wolfe et al. 1994). This oil subsequently spread over more than 26,000 km2 of water surface in PWS and the Gulf of Alaska and landed on more than 1000 km of shoreline (Spies et al. 1996, Short et al. 2004; see Fig. 1 in Esler et al., this report). Initial consequences for wildlife were immediate and obvious, Mortalities due to oil in the weeks following the spill were estimated to be in the hundreds of thousands of marine birds (Piatt et al. 1990), several thousand sea otters (Garrott et al. 1993, Ballachey et al. 1994), significant proportions of resident (33%) and transient (41%) pods of killer whales (Matkin et al. 2008), and varying numbers of a wide assortment of other wildlife species. These levels of mortality are consistent with expectations, given the amount of oil spilled, the size of the oil-affected area, the abundance of wildlife in the area, and the known toxic and thermoregulatory consequences of exposure to oil, particularly in cold-water environments. Other effects of oil spills on wildlife, including chronic or indirect effects, were not fully understood, recognized, or anticipated at the time of the Exxon Valdez oil spill (EVOS) (Peterson et al. 2003, Rice 2009). Thanks in large part to settlement funds managed by the Exxon Valdez Oil Spill Trustee Council (EVOSTC), including that for Gulf Watch Alaska in recent years, a considerable body of research has addressed wildlife recovery from the spill. This has allowed for an unprecedented and thorough understanding of the timelines and mechanisms of population recovery following catastrophic spills. In this document, we review the timelines and processes of recovery of wildlife from the EVOS. We alsoconsider factors that result in variation in recovery times across species, and present recent data for two species that showed protracted recovery related to exposure from lingering oil, the sea otter (Enhydra lutris) and harlequin duck (Histrionicus histrionicus).