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Pink salmon, Oncorhynchus gorbuscha, is the main salmon species of commercial importance in Prince William Sound. Unlike other Pacific salmon, they have a two-year life cycle and have adapted to spawn in the intertidal reaches of numerous small streams throughout the oil-spill area. Thus, they represent the species at highest potential risk for spill-related injury. This paper discusses results of field programs initiated within a few days of the spill and designed to assess spill effects on critical early life stages of pink salmon in postspill years.
Samples of water and stream sediments from throughout the spill area were used to define the exposure of pink salmon to residual hydrocarbons from the spill. Mean sediment concentrations of polycyclic aromatic hydrocarbons (PAH) up to 300 ppb were measured in oiled streams in 1989 and generally followed a downward trend toward background in 1990 and 1991. These PAH concentrations were then used in regression analyses of potential effects on key early life stages of pink salmon. Water samples taken from both nearshore feeding and rearing areas and offshore migratory areas show that hydrocarbon concentrations were from one to four orders of magnitude lower than concentrations reported in the literature to cause acute or chronic effects on fish species.
The postspill field and laboratory studies of pink salmon early life stages included examination of potential effects on 1989, 1990, and 1991 eggs, fry, and juveniles. Generally high survival, ranging from 77% to 100%, was observed in both oiled and reference streams in 1989, and a weak correlation was indicated with stream sediment PAH at only one of the three tide levels sampled (12 feet). In 1990, egg viability was 90.6% from reference streams and 91.1% from oiled streams, as determined through incubation studies. Mean condition index, kD, was 1.76 for fry from reference streams and 1.79 from oiled streams, indicating normal developmental timing.
Study results show that no substantial effects on critical early life stages of pink salmon in Prince William Sound are attributable to the spill. Results of incubation experiments with eggs from the spill-affected area provide no indication of sterility or abnormal development. Our results are consistent with the pink salmon returns in 1990 and 1991 that yielded returns over three times the size of the parental year class.
pink salmon, toxicity, wildstock, oil pollution, Prince William Sound, Exxon Valdez
University of Idaho, Moscow, ID
MJM Research, Bainbridge Island, WA
Genesis Technical Services, Pacific Beach, WA
Exxon Company, Houston, TX
University of Washington, Seattle, WA