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This paper presents results of a field program designed to monitor the status of wildstock pink salmon populations in Prince William Sound following the Exxon Valdez oil spill. Field counts of spawning salmon were conducted each year from 1989 through 1992 to test for spill effects on the distribution and abundance of pink salmon adults spawning in selected streams in the southwestern portion of Prince William Sound, including streams from the most heavily oiled areas. Counts of whole-stream and intertidal escapement density were statistically compared for 40 study streams in 1989 and for a subset of those streams in successive years. Measurements of residual hydrocarbons were made from stream-bed sediments to test for correlations with spawning behavior.
Adult pink salmon in the postspill years of 1990 and 1991, progeny of the year classes considered most vulnerable to the oil spill, returned in high numbers, with the wildstock spawners exceeding their parent year returns. In 1989, adult returns reflected the relatively weak run for that year with a mean spawner density of 0.68 fish/m2 in reference streams and 0.69 fish/m2 in oiled streams. In 1990, mean escapement density for reference streams was 1.40 fish/m2 and 1.55 fish/m2 for oiled streams, indicating the strongest run of the four study years. Trends in polycyclic aromatic hydrocarbon (PAH) concentrations for the majority of oiled streams show a general decline from 1989 to background levels by 1990. The measured PAH concentrations indicate low-level exposure to residual hydrocarbons that have not produced detectable differences in spawning behavior or escapement between streams from oiled areas compared with unoiled streams.
In Part 1 of this paper, elements of the early lifestage survival of potentially affected year classes of pink salmon were examined by Brannon et al. (this volume). Conclusions indicate measures of early lifestages were largely indistinguishable between oiled and unoiled streams. The early lifestage data, in combination with observations of the strength of postspill returns and analyses of escapement reported herein, are the basis for the conclusion that changes in the wildstock pink salmon population in Prince William Sound could not be attributed to the oil spill.
pink salmon, escapement, wildstock, oil pollution, Prince William Sound, Exxon Valdez
Exxon Company, Houston, TX
University of Idaho, Moscow, ID
Genesis Technical Services, Pacific Beach, WA
MJM Research, Bainbridge Island, WA
University of Washington, Seattle, WA