EFFECT OF THE EXXON-VALDEZ OIL-SPILL ON INTERTIDAL FISH - A FIELD-STUDY

The purpose of this study was to evaluate the impact of the March 1989 Exxon Valdez oil spill and subsequent cleanup activities on density, biomass, and species diversity of intertidal fishes in Prince William Sound, Alaska. Intertidal fish were sampled in a quasi-experimental, m atched-pairs (oiled-cleaned versus reference sites) design stratified by three habitat types with random selection of oiled-cleaned (O-C) si tes. Site pairs were sampled twice in 1990 and in 1991. Of 21 fish tax a, 5 made up 98% and 1 made up 74% of total abundance. There were no s ignificant differences in species diversity between reference and O-C sites. Density, however, was significantly greater at reference sites for all habitats combined for both visits in 1990. In contrast, densit y in 1991 was about equal at reference and O-C sites. Total biomass fo r all habitats combined was greater at reference than O-C sites during both visits in 1990, but differences were not statistically significa nt. In 1991, however, the total biomass at reference and O-C sites was about equal. Forward stepwise multiple logistic regression models ind icated that presence of oil was a significant predictor of reduced den sity at mid-intertidal levels in 1990 but not in 1991. From the genera l pattern of lower density and biomass on O-C sites in 1990 followed b y no significant differences in 1991 and corroborating evidence of mul tiple-regression modeling, we conclude that the presence of oil and su bsequent cleanup activities had a negative impact on intertidal fishes in 1990 and that there was evidence that recovery was underway in 199 1.