Recovery of pink salmon spawning areas after the Exxon Valdez oil spill

Up to 70% of wild pink salmon Oncorhynchus gorbuscha in Prince William Soun d, Alaska, spawn in intertidal stream areas, many of which were contaminate d by the 1989 Exxon Valdez oil spill. To assess recovery of salmon habitat after the spill, we analyzed sediment samples from stream deltas throughout Prince William Sound from 1989 to 1991 and 1995. In 1989, petroleum hydroc arbon concentration at 172 stream deltas (1-8 samples each) was bimodally d istributed: 85 deltas had no detectable petroleum hydrocarbons (detection l imit, 2 mu g/g), whereas 87 deltas had a concentration of 2-90,000 mu g/g. In 1995, petroleum hydrocarbons were still detected at eight of nine oiled streams that we resampled, with mean concentration up to 242 mu g/g. The po lynuclear aromatic hydrocarbon (PAH) fraction was also analyzed in 1995 to determine its origin, state of weathering, and toxic potential of the resid ual oil. The PAH fraction consisted mostly of the more toxic compounds with high molecular weight (e.g., phenanthrenes and chrysenes), and PAH composi tion was consistent with weathered Exxon Valdez oil. Total PAH concentratio n in 1995 averaged 0-1,300 ng/g, which was below the minimum sediment conce ntration (3,800 ng/g) shown to reduce salmon embryo survival in the laborat ory. Interpolation between 1989 and 1995 indicated that residual PAH concen tration exceeded 3,800 ng/g at some stream deltas through 1993, but all str eams were below this level by 1994. We conclude that tidal leaching of PAH from weathered oil into incubation substrate could explain persistent eleva ted embryo mortality observed in pink salmon through 1993, and that spawnin g habitat had recovered to below lethal threshold by 1994.