A Washington State University researcher says in a new report in the journal Ecological Applications that minute amounts of copper from mining operations can affect salmon in a way the results in them being eaten easily by predators.
Jenifer McIntyre, a postdoctoral research associate in WSU’s Puyallup Research and Extension Center, said she found the metal affects salmon’s sense of smell so much that they won’t detect a compound that ordinarily alerts them to be still and wary.
Her research was conducted for a University of Washington doctorate with colleagues at UW and the National Oceanic and Atmospheric Administration.
“My paper builds off of a large body of literature on this topic, mostly led by NOAA scientists,” she said in an interview July 16.
Earlier research showed that copper is neurotoxic to a fish’s sense of smell. Other research showed that when a salmon’s sense of smell is affected, its behavior changes.
McIntyre put the two together, exposing juvenile coho salmon to varying amounts of copper and placing them in tanks with cutthroat trout, a common predator.
The results, she reported, were striking.
Salmon are attuned to smell a substance called Schreckstoff, German for “scary stuff,” which is released when a fish is physically damaged, alerting nearby fish to the predator’s presence.
In her experiments, conducted in a four-foot-diameter tank, fish that were not exposed to copper would freeze in the presence of Schreckstoff, making it harder for motion-sensitive predators to detect them. On average, half a minute would go by before they were attacked, McIntyre said.
By contrast, salmon in water with just five parts of copper per billion failed to detect the Schreckstoff, kept swimming, and were attacked in about five seconds, she said.
The unwary exposed fish were also more likely to be killed in the attack, being captured 30 percent of the time on the first strike. Unexposed fish managed to escape the first strike nearly nine times out of ten, most likely because they were already wary and poised to take evasive action.
McIntyre also noticed that the behavior of predators was the same whether or not they had been exposed to copper.