W9 PM Residual Oil and its Effects
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 339-340

(NEF-1117-820442) Effects of the Exxon Valdez Oil Spill on the Pink Salmon Population: an Ecological Risk Assessment.

Neff, J.¹, Brannon, E.², Maki, A.³, ¹ Neff & Associates LLC, Duxbury, MA, 02332² Universith of Idaho, Moscow, ID, USA³ Exxon Mobil Corp., Anchorage, AK, USA

ABSTRACT- Most wild-run pink salmon (Oncorhynchus gorbuscha) returning to Prince William Sound, AK, (PWS) spawn in tidal reaches of streams; eggs and alevins of these salmon were potentially at risk of exposure to crude oil from the March 24, 1989, Exxon Valdez oil spill (EVOS), particularly in the spring and fall of 1989 when shoreline oiling was heaviest. Emergent fry spend a short time in shallow coastal waters before migrating to the ocean and were potentially at risk of exposure to oil in the PWS water column during the summer of 1989. We have reviewed the many studies of effects of the spill on pink salmon and used ecological risk assessment principals to evaluate relationships between exposure to EVOS oil hydrocarbons and effects on the pink salmon population in PWS. Only a small fraction of wild run salmon embryos and fry was at risk of exposure to harmful amounts of EVOS oil. About 30 (2.5% of the total) salmon streams in PWS were oiled and about 70% of the alevins were in the tidal reaches of streams in the spring of 1989; < 2% of wild-run alevins were at risk of oil exposure in the spring of 1989. In the fall of 1989 and subsequent years, a smaller fraction of the eggs deposited in the streams during spawning was at risk of exposure to residual oil because natural processes and cleanup had removed most of the oil from stream bed and shoreline sediments. There was no effect of the spill on pre-emergent alevin survival in the spring of 1989. Eggs deposited in oiled streams in the fall of 1989 and in subsequent years bioaccumulated small amounts of petroleum polycyclic aromatic hydrocarbons (PAH); survival was slightly depressed in the most heavily oiled streams in 1989-90 but not in subsequent years. Growth of juvenile salmon in coastal waters in 1989 and 1990 was similar in spill path and non-spill path areas of PWS. Direct observations demonstrate that wild-stock escapements and spawner densities have been similar in oiled and reference streams every year from 1989 through 2004. Although some individual fish were harmed by the spill, there were no long-term effects on the PWS pink salmon population.

Key words: polycyclic aromatic hydrocarbons, growth, survival, exposure