Copper Makes Salmon Vulnerable to Predators

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
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.