Long-term oil spill impact on Alaskan fish revealed. fis.com. September 09, 2015. A team of researchers have concluded that embryonic salmon and herring exposed to very low levels of crude oil can develop hidden heart defects that compromise their later survival, settling the long-lasting controversy. This conclusion was reached by NOAA scientists after investigating the effects of the Exxon Valdez oil spill in 1989 on Alaskan communities and ecosystems for 25 years. The new findings, published in the online journal Scientific Reports, suggest that the delayed effects of the spill may have been important contributors to the herring and salmon stock declines.

Salmon afected by oil spill. (Photo Credit: Exxon Valdez Oil Spill Trustee Council)"These juvenile fish on the outside look completely normal, but their hearts are not functioning properly and that translates directly into reduced swimming ability and reduced survival," pointed out John Incardona, a research toxicologist at NOAA Fisheries’ Northwest Fisheries Science Center in Seattle.
"In terms of impacts to shore-spawning fish, the oil spill likely had a much bigger footprint than anyone realized," the scientist added.
The research builds on earlier work by the Auke Bay Laboratories, part of NOAA Fisheries’ Alaska Fisheries Science Center, which found much reduced survival of pink salmon exposed as embryos to polycyclic aromatic hydrocarbons (PAH) from crude oil.
"Our findings are changing the picture in terms of assessing the risk and the potential impacts of oil spills," claimed Nat Scholz, leader of the NWFSC’s ecotoxicology program and a coauthor of the new study.
"We now know the developing fish heart is exquisitely sensitive to crude oil toxicity, and that subtle changes in heart formation can have delayed but important consequences for first-year survival, which in turn determines the long-term abundance of wild fish populations," Scholz explained.
The scientists participating in the study used swimming speed as a measure of cardiorespiratory performance and found that fish exposed to the highest concentrations of oil swam the slowest. Slower swimming is an indication of reduced aerobic capacity and cardiac output, and likely makes fish easier targets for predators.
"With this very early impact on the heart, you end up with an animal that just can’t pump blood through its body as well, which means it can’t swim as well to capture food, form schools, or migrate," stated Mark Carls, toxicologist at the Alaska Fisheries Science Center.
As part of the study, the scientists reviewed data on measured oil concentrations in surface water samples collected in Prince William Sound after the oil spill and during the 1989 herring spawning season. Most of the 233 samples contained less oil than was believed to be toxic to herring at the time, based on gross developmental abnormalities. However, nearly all of the samples contained oil at or above concentrations shown in the new study to alter heart development.
The study also concludes that the impacts of the Exxon Valdez spill on nearshore spawning populations of fish are likely to have been considerably underestimated in terms of both the geographic extent of affected habitat and the lingering toxicity of low levels of oil.
“The findings will likely contribute to more accurate assessments of the impacts of future oil spills,” Incardona said. "Now we have a much better idea of what we should be looking for".
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