Status of Selected Bottomfish and Crustacean Species in Prince William Sound Following the Exxon Valdez Oil Spill

Exposure and possible adverse effects of the Exxon Valdez oil spill (EVOS) at depth were studied between 1989 and 1991 on several species of crustaceans, molluscs, and finfish that are characterized by ontogenetic shifts in distribution from meroplanktonic larvae to benthic and demersal juveniles and adults. Our approach was to search for 1) evidence of exposure to Exxon Valdez crude oil (EVC) at depth (generally between 20 to 150 m) and 2) measurable perturbations at both the individual and population levels. Primary species targeted were Tanner crab (Chionoecetes bairdi), several pandalid shrimps (Pandalus platyceros, P. hypsinotus, P. borealis), flathead sole (Hippoglossoides elassodon), and several bivalves including scallops (Chlamys rubida) and infaunal clams (Nuculana, Yoldia, and Macoma spp.). Our survey design provided a comparison between variables measured in“oiled” bays around Knight Island and “non-oiled” bays at other locations within Prince William Sound. “Oiled” was defined in terms of degree of shoreline oiling, sediment and tissue hydrocarbon concentrations with the EVC signature, elevated concentrations of fluorescent aromatic compounds (FACs) in bile of flathead sole, and frequency of oil in benthic trawls. Statistical analyses of catch-per-unit-of-effort (CPUE; relative abundance determined by pots and trawls) were focused on detection of differences in trends through time (that is, “time-by-oil” interaction) rather than on magnitude of differences, thereby avoiding the problem of inherent differences in baseline CPUE levels between bays and the influence of non-random application of oil to bays. Polycyclic aromatic hydrocarbons (PAHs) of petrogenic origin were measured in all bays sampled in this study and levels of PAHs derived from EVC were elevated in the “oiled” bays following the spill, yet attenuated to less than 200 ng/g sediment by 1991. Total PAHs in scallop tissues were higher in “oiled” bays in 1989 but decreased 15-fold to a mean of 16 ng/g by 1990. Clam tissues from “oiled” bays in 1991 had higher PAH concentrations, but only samples from Bay of Isles had alkylated PAHs (about 90 ng/g) indicative of EVC exposure. Mean concentrations of FACs in flathead sole bile were significantly higher in “oiled” than “non-oiled” bays (about 27 and 14 ng/g, respectively) in both 1990 and 1991, and corresponded to elevated tissue levels of PAHs in clams, which are the major prey of sole in these bays. Virtually no evidence of significant adverse effects was detected at either the individual or population levels across all the life history stages sampled. Larval Tanner crabs were widely distributed in the plankton in early summer of 1989 and 1990; adult female fecundity and trends in CPUE of juveniles did not differ significantly between the two categories of bays. In spring of 1990, 16 dead juvenile Tanner crabs were caught in three “oiled” bays and mortality was significantly correlated with elevated FACs in bile of flathead sole. Such mortality was likely linked to inordinately low bottom-water salinity that spring, and dead crabs were not found on any other cruise prior to or after this event. Pandalid shrimp were ubiquitous throughout the study area, and no significant differences were measured between “oiled” and “non-oiled” bays in trends of CPUE of P.borealis (the best quantified) and fecundity of P. platyceros. Fecundity in the case of P. hypsinotus was reduced in 1990 compared with 1989 irrespective of bay, but fecundity was also about 30% lower among females from the “oiled” compared with “non-oiled” bays. In the case of flathead sole, mean abundance of young-of-the-year fish declined significantly in “non-oiled” bays and mean abundance of older fish increased significantly in “oiled” bays. In contrast to lack of evidence of adverse effects on target species caused by the EVOS, substantial declines in fishery landings of several crabs and shrimps had occurred in PWS, some to the point of closure, prior to the spill. Long-term trends in abundance of populations of these species due to natural environmental causes or fishing pressures are likely to be far more important than fluctuations attributable to EVOS.