Copper traces from brake linings may undermine salmon's ability to avoid predators. (Photo: youTube/washingtonstateuniv/FIS)
Exposure to copper, bad news for salmon
Friday, July 27, 2012, 15:20 (GMT + 9)
Trace amounts of copper from brake linings and mining operations undermine salmon’s ability to avoid predators, according to a study from the Washington State University (WSU). Researcher Jenifer McIntyre determined that the metal affects salmon’s sense of smell to the extent that they cannot detect a compound that ordinarily alerts them to predators.
"A copper-exposed fish is not getting the information it needs to make good decisions,” said McIntyre, a postdoctoral research associate in WSU’s Puyallup Research and Extension Centre.
Her research, conducted for a University of Washington doctorate with colleagues at UW and the National Oceanic and Atmospheric Administration (NOAA), appears in the latest issue of the journal Ecological Applications.
McIntyre combined earlier research which showed that copper impacts a salmon’s sense of smell and that when a salmon’s sense of smell is affected, its behavior is altered.
She exposed juvenile coho salmon to differing amounts of copper and placed them in tanks with cutthroat trout, a common predator.
Salmon are attuned to smell a substance called Schreckstoff -- German for “scary stuff” -- which is released when a fish is physically hurt, alerting nearby fish to the predator’s presence.
McIntyre used a 4ft-diameter tank and introduced fish that were not exposed to copper; these fish would freeze in the presence of Schreckstoff, which made it harder for motion-sensitive predators to detect them. On average, 30 seconds would pass before they were attacked.
Conversely, salmon in water with just five parts of copper per billion failed to detect the Schreckstoff and kept swimming -- they were attacked in about five seconds.
"It’s very simply and obviously because predators can see them more easily,” said McIntyre. "They’re not in lockdown mode.”
The fish exposed to copper were also more likely to be captured and killed in the attack. Unexposed fish managed to escape the first strike nearly nine times out of ten, probably because they were already cautious and ready to defend themselves.
McIntyre also noticed that the behavior of predators remained unchanged whether or not they had been exposed to copper.
Copper makes its way into water bodies from motor vehicle brake linings, pesticides, building materials and protective boat coatings, for example.
With testimony from McIntyre’s NOAA colleagues and others, the Washington State legislature in 2010 started phasing out copper brake pads and linings over the next 15-20 years. According to Washington’s Department of Ecology, brake pads are the source of up to half the copper in the state’s urban waterways.
"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 noted.
Alaska’s proposed Pebble Mine would generate tens of billions of lb of copper near Bristol Bay, the world’s largest sockeye salmon fishery.
By Natalia Real