Long-term impacts of the Exxon Valdez oil spill on sea otters, assessed through age-dependent mortality patterns

We use age distributions of sea otters (Enhydra lutris) found dead on beach es of western Prince William Sound, Alaska, between 1976 and 1998 in conjun ction with time-varying demographic models to test for lingering effects fr om the 1989 Exxon Valdez oil spill. Our results show that sea otters in thi s area had decreased survival rates in the years following the spill and th at the effects of the spill on annual survival increased rather than dissip ated for older animals. Otters born after the 1989 spill were affected less than those alive in March 1989, but do show continuing negative effects th rough 1998. Population-wide effects of the spill appear to have slowly diss ipated through time, due largely to the loss of cohorts alive during the sp ill. Our results demonstrate that the difficult-to-detect long-term impacts of environmental disasters may still be highly significant and can be rigo rously analyzed by using a combination of population data, modeling techniq ues, and statistical analyses.