Tag Archives: pesticides

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”

Speaking of poisoned waters and salmon…

The National Marine Fisheries Service has been studying the effects of chemical pesticides on threatened and endangered salmon species, and I have to say that I’m impressed with the thorough approach to this scientific challenge.

Not everyone is so impressed, however, and pesticide manufacturers have filed a federal lawsuit to block implementation of protection measures proposed by NMFS, but more about that in a moment.

Risk analysis is always a tricky subject, but it appears that the NMFS researchers have taken a step-by-step approach, turning over every stone.

The latest “biological opinion” (PDF 11.7 mb) is a 600-page report covering pesticides containing carbaryl, carbofuran and methomyl. Like the previous biological opinion (PDF 11 mb) on diazinon, chlorpyrifos and malathion, the agency has determined that the pesticides pose a significant risk of extinction for listed salmon and outline further restrictions on their use.

Read my story in Wednesday’s Kitsap Sun and a well-written piece by Associated Press reporter Phuong Le.

NMFS scientists have been looking at how much of each pesticide can get into a stream under various kinds of applications. In the water, these neurotoxins can affect a fish directly — if not by killing them, by impairing their response to predators, their ability to get food, their ability to find their natal streams or their ability to connect with a mate.

Even if a fish is not harmed directly, these insecticides can affect fish simply by doing their job very well — killing off all or a significant portion of the insects that a fish needs to eat, grow and survive.

As if measuring all these effects are not enough, now we learn that chemicals may exhibit synergistic effects — making it necessary to look not just at the effects of a single chemical but how multiple chemicals in the water work together.

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