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API 4411

1985 Edition, 1985

Complete Document

Effect of Prudhoe Bay Crude Oil on the Homing of Coho Salmon in Marine Waters

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Product Details:

  • Revision: 1985 Edition, 1985
  • Published Date: September 1985
  • Status: Not Active, See comments below
  • Document Language: English
  • Published By: American Petroleum Institute (API)
  • Page Count: 63
  • ANSI Approved: No
  • DoD Adopted: No

Description / Abstract:

Executive Summary

With the accelerated development of the outer continental shelf for oil and gas exploration and production, questions have been asked by resource managers and the fishing industry about possible impacts of oil spills on the homing ability of adult salmon migrating toward their home stream to spawn.

Adult coho salmon were exposed for one hour to the following concentrations (if uniformly mixed): Prudhoe Bay crude (PBC) oil, 913 ppm; dispersed oil, 105 ppm; and dispersant alone, 10.5 ppm. The untreated oil lay on the water surface and the fish were exposed principally to soluble hydrocarbons (C1 to C10) that ranged from 35 ppb at 10 min after oil addition to 99 ppb at the end of one hour. The dispersed oil mixed fairly well, and the total oil measured by infrared spectrophotometry was 59 ppm in water samples collected at half depth. The C1 to C10 hydrocarbons in the dispersed oil tank were 1040 ppb after 10 min, but decreased to 758 ppb at the end of one hour. The dispersant alone was uniformly mixed.

The exposed and control fish were released about seven kilometers from their home stream to determine the effects of treatment on success, and speed, of return of fish in marine waters.

Of 314 coho salmon treated at Big Beef Creek and released at King Spit, Hood Canal, 62 or 19.7% returned successfully. Statistical analysis showed that the proportion of successful returns was independent of treatments. In other words, the return data provided no reason to believe short-term exposure to PBC oil, dispersant, or dispersed oil had any deleterious effect on homing success. Not only did the coho salmon return successfully but the treatments compared with controls did not affect the speed of return as measured by the number of "days out" (number of days from time of tagging and release to the time of recapture at the home stream). Some caution is needed in the final conclusions simply because of the relatively small number of successful returns (62 fish) of the 314 treated coho released. The very intense commercial net fishery along the migratory path of the returning fish most likely took a heavy toll; the 19.7% successful return is in sharp contrast with the 72% return observed in a similar experiment using chinook salmon in protected waters without a net fishery (Nakatani, et al., 1983).

Some test salmon from each treatment group were not released but held in live pens to observe possible latent differential mortalities due t o treatments. No differences due to treatments were observed. However, there was a significant difference in the mean days alive due to age (two-year-old vs. three-year-old fish) of the coho salmon. The larger three-year-old adult coho salmon lived 10.3 ± 6.5 days, compared with 26.7 ± 19.9 days for the two-year-old "jack" coho salmon.