Recovery of Pink Salmon Spawning Areas after theExxon ValdezOil Spill

Abstract

Up to 70% of wild pink salmon Oncorhynchus gorbuscha in Prince William Sound, Alaska, spawn in intertidal stream areas, many of which were contaminated 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 hydrocarbon concentration at 172 stream deltas (1-8 samples each) was bimodally distributed: 85 deltas had no detectable petroleum hydrocarbons (detection limit, 2 g/g), whereas 87 deltas had a concentration of 2-90,000 g/g. In 1995, petroleum hydrocarbons were still detected at eight of nine oiled streams that we resampled, with mean concentration up to 242 g/g. The polynuclear aromatic hydrocarbon (PAH) fraction was also analyzed in 1995 to determine its origin, state of weathering, and toxic potential of the residual oil. The PAH fraction consisted mostly of the more toxic compounds with high molecular weight (e.g., phenanthrenes and chrysenes), and PAH composition was consistent with weathered Exxon Valdez oil. Total PAH concentration in 1995 averaged 0-1,300 ng/g, which was below the minimum sediment concentration (3,800 ng/g) shown to reduce salmon embryo survival in the laboratory. Interpolation between 1989 and 1995 indicated that residual PAH concentration exceeded 3,800 ng/g at some stream deltas through 1993, but all streams were below this level by 1994. We conclude that tidal leaching of PAH from weathered oil into incubation substrate could explain persistent elevated embryo mortality observed in pink salmon through 1993, and that spawning habitat had recovered to below lethal threshold by 1994.

Mechanism for transport of oil-contaminated groundwater into pink salmon redds

“…The study was completed in June 2000 at 2 pink salmon streams in western PWS, Sleepy Creek on (Gundlach et al 1990) and studied by Brannon et al (1995), Bue et al (1996Bue et al ( , 1998, Craig et al (1999), and Murphy et al (1999). Evidence of oil persisted in beaches around both streams through at least 1995 (Murphy et al 1999), and pink salmon egg survival was monitored through 1997 (Bue et al 1998, Craig et al 1999.…”

“…Evidence of oil persisted in beaches around both streams through at least 1995 (Murphy et al 1999), and pink salmon egg survival was monitored through 1997 (Bue et al 1998, Craig et al 1999. Dye injection wells were intentionally located in previously oiled beach areas and adjacent to reaches of stream previously monitored for egg survival.…”

“…Although flowing freshwater did not allow oil to directly contaminate stream channels, shorelines surrounding both study streams and many others in western PWS were coated with oil (Brannon & Maki 1996, Geiger et al 1996, Craig et al 1999, Murphy et al 1999. Aliphatic and aromatic hydrocarbons dissolve into water surrounding oil-coated rock at rates related to the energy required for escape , and the resultant contamination is sufficient to cause toxicity (Marty et al 1997, 2000.…”

“…Dissolved PAH are most likely responsible for this toxicity, which increases with molecular weight (Rice et al 1977, Neff 1979, Black et al 1983, 2000. Murphy et al (1999) detected high molecular weight PAH in sediment surrounding streams in PWS and concluded that concentrations at some streams were likely toxic through 1993. For example, mean total PAH concentrations in intertidal sediments adjacent to 7 oiled spawning streams in 1989 ranged from 13 to 823 µg g -1 (Murphy et al 1999), greater than concentrations known to damage pink salmon embryos (3.8 µg g -1 , Heintz et al 1999).…”

“…Extensive areas of shoreline were coated with oil, including beaches surrounding the intertidal reaches of streams used by these fish (Brannon & Maki 1996, Murphy et al 1999. These intertidal reaches are a critical spawning habitat for pink salmon; up to 75% of spawned eggs are deposited here (Helle et al 1964, Heard 1991.…”