Minute amounts of copper in rivers can deaden a spawning salmon's ability to detect danger in rivers.
Jenifer McIntyre, a postdoctoral research associate at Washington State University, published her findings in Ecological Applications.
When a fish is injured, the smell given off alerts the rest of the fish that a predator is near. The fish will then freeze, making them harder to detect. But when copper is added to the water, even in very minute quantities, the smell from the injury is not picked up by the rest of fish who keep swimming and open themselves up to attack.
Quantities as little as five parts copper per billion can impact salmon.
McIntyre is studying spawning salmon in rivers located in urban locations and looking at run-off from roads that can wash minute amounts of metals into the rivers.
She says the findings also have applicability to mining operations.
"My scenarios are potentially more like a hard-rock copper mining situation than storm water runoff, which typically carries dissolved organic matter along with the copper and other contaminants,” McIntyre told WSU News.