Salmon harmed by copper fail to avoid predators

I guess it’s common knowledge among fish biologists that fish can smell death.

It’s a survival mechanism. When the skin of a fish is damaged, a substance is released into the water. Other fish smell the substance and instinctively take evasive action.

When juvenile coho salmon smell death, they tend to stop moving and become more wary of predators, according to a new study by Jenifer McIntyre and colleagues at the University of Washington and National Oceanic and Atmospheric Administration.

But the most important finding is that the coho exposed to minute levels of copper lose their sense of smell. Their brains don’t register the smell of death, and they get eaten at a much higher rate than coho not exposed to copper. For details, check out the story published today in the Kitsap Sun.

The video shows the response of coho salmon when ground-up fish skin is released into the water. Coho not exposed to copper freeze, as you can see in the upper tank. Coho exposed to copper keep on moving, as if unaware of the danger, making them prime targets for predation.

These are interesting findings, but more research is needed to determine what levels of toxic copper may actually be found in urban streams, where copper typically comes from brake pads and pesticides, and rural streams affected by mining operations.

For further reading, check out the slideshow called “Impacts of copper on the sensory biology and behavior of salmon” (PDF 9.2 mb), which reports on findings by the research group of which McIntyre is a member

Other reports:

“An Overview of Sensory Effects on Juvenile Salmonids Exposed to Dissolved Copper: Applying a Benchmark Concentration Approach to Evaluate Sublethal Neurobehavioral Toxicity”

“Effects of Copper on Aquatic Species: A review of the literature” by Phyllis Weber Scannell.

“Control of Toxic Chemicals in Puget Sound: Assessment of Selected Toxic Chemicals in the Puget Sound Basin, 2007-2011”

Some previous blog entries in “Watching Our Water Ways”:

Nov. 4, 2011: “More results, more questions found in toxic studies”

May 18, 2011: “New study refines Puget Sound pollution issues”

March 10, 2010: “Washington is first to tackle toxic copper in brakes”

June 7, 2009: “Barnacle-free hulls would be a dream come true”

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