CHANGES IN DIETS OF RIVER OTTERS IN PRINCE WILLIAM SOUND, ALASKA - EFFECTS OF THE EXXON-VALDEZ OIL-SPILL

We studied the effects of the Exxon Valdez oil spill on the diets of r iver otters (Lutra canadensis) from oiled and nonoiled areas of Prince William Sound, Alaska, U.S.A., in 1989 and 1990. On the basis of iden tification of prey remains in their feces, otters fed principally on m arine, bottom-dwelling fishes. Marine gastropods, bivalves, and crusta ceans composed most of the invertebrates in the diet of otters; freshw ater and terrestrial food items seldom occurred in their feces. The di ets of otters included 149 different taxa, most of which rarely occurr ed in their feces. Sixty-five taxa occurred greater than or equal to 5 times in our combined data set. Species richness and diversity of pre y remains in otter feces were similar on oiled and nonoiled study area s in late winter(April) 1989 (before the oil spill) and during summer (June-October) 1989 following the spill. By summer (July-September) 19 90, however, there were significant declines in the richness and diver sity of species (mostly bony fish, molluscs, and bivalves) in otter di ets on the oiled area. Likewise, the relative abundance of prey remain s in otter feces showed strong differences between areas and years, an d an area by year interaction. Members of the Perciformes and Archaeog astropoda declined from 1989 to 1990 on the oiled area while they incr eased on the nonoiled site; Malacostraca exhibited the opposite patter n. These outcomes, when considered with other data on body mass and bl ood chemistry, strongly suggest that some effects of the oil spill on otters were delayed.