MORTALITY OF SEA OTTERS IN PRINCE-WILLIAM SOUND FOLLOWING THE EXXON-VALDEZ OIL-SPILL

This paper presents an estimate of the total number of sea otters that died as a direct consequence of the oil spill that occurred when the T/V Exxon Valdez grounded in Prince William Sound, Alaska on 24 March 1989. We compared sea otter counts conducted from small boats througho ut the Sound during the summers of 1984 and 1985 to counts made after the spill during the summer of 1089. We used ratio estimators, correct ed for sighting probability, to calculate otter densities and populati on estimates for portions of the Sound affected by die oil spill. We e stimated the otter population in the portion of Prince William Sound a ffected by the oil was 6,546 at the time of the spill and that the pos t-spill population in the summer of 1989 was 3,898, yielding a loss es timate of approximately 2,650. Bootstrapping techniques were used to a pproximate confidence limits on die loss estimate of about 500-5,000 o tters. The wide confidence limits are a result of die complex scheme r equired to estimate losses and limitations of the data. Despite the un certainty of the loss estimate it is dear that a significant fraction of the otters in the spill zone survived. We observed otters persistin g in relatively dean embayments throughout the oil spill zone suggesti ng that the highly convoluted coastline of Prince William Sound produc ed refuges that allowed some. sea otters in the oil spill area to surv ive.