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We investigated effects of the 1989 Exxon Valdez oil spill on the abundance, distribution, and pup production of sea otters (Enhydra lutris) in Prince William Sound (PWS) by comparing counts made during 1990 and 1991 with counts made by researchers 5–12 years before the spill. We observed no evidence of avoidance or attraction to spill-affected shorelines 1–2 years after the spill. Despite a substantial loss of sea otters immediately following the spill, we counted fewer otters than prespill investigators at only one of three heavily oiled islands, and from 1990 to 1991 our counts at this one site increased to a level equivalent to the latest (1985) prespill count.
We followed the methods of prespill investigators and found close agreement between our counts of otters and those of two other concurrent investigations using the same survey technique. This agreement among counts, and our involvement in counts made prespill, suggested that inter-observer variability could not explain our unexpectedly high counts at oiled sites. Some otters killed in the spill were likely replaced by otters from other parts of PWS. However, we suggest that a modest population increase prior to the spill, but after the last prespill counts, is the most plausible explanation for the concurrence of our postspill counts and counts from the early 1980s. At three heavily oiled sites, pup production 1–2 years after the spill was as high or higher than witnessed before the spill. Although the increase in pupping observed at one island was greater in lightly oiled than in heavily oiled areas, no such trend occurred at another oil-affected island. Mortality, as indicated by the number of carcasses found on beaches a year after the spill, was similar to what had been observed historically. The diet also was unchanged. If the otter population indeed was growing before the spill, these results indicate the potential for renewed population growth.
Alaska, counts, diet, Exxon Valdez, foraging, mortality, oil spill, population growth, Prince William Sound, pup production, sea otter, surveys
ABR. Inc., Fairbanks, AK
Minnesota Department of Natural Resources (MDNR), Grand Rapids, MN