SEATTLE -- Low levels of pesticides can keep salmon from smelling properly, blocking their ability to detect predators, catch prey and return to their native streams, new research suggests.
The research, done by the National Marine Fisheries Service, is scheduled for publication in the Canadian Journal of Fisheries and Aquatic Sciences in September. It suggests reducing or eliminating pesticides and other pollutants in fresh water may be an important factor in restoring salmon, said John Stein, director of the service's Environmental Conservation Division.
``We need to be cognizant of the possible effect pesticides have,'' Stein said Tuesday.
Salmon rely heavily on their sense of smell. Pesticides can plug up their noses, Stein said.
When a salmon's skin is punctured - such as when one is eaten - it releases a scent into water that alerts nearby salmon to the presence of danger. The natural response of the other salmon is to freeze in the water and slowly sink until the danger passes, Stein said.
But when salmon have been exposed to low levels of pesticides, which can be found in many Northwest waters, they do not respond that way. They simply continue feeding, making them more likely to be killed by a predator, Stein said.
Researchers compared the reactions of Pacific salmon exposed to diazinon with those not exposed. Diazinon is commonly used in back yards and on farms to kill insects, and can reach streams when washed away by rain. Levels of pesticide used in the tests were comparable to levels the U.S. Geological Survey has routinely found in Western streams, Stein said.
The Seattle-based researchers focused on salmon's antipredatory behavior, but the evidence also suggests pesticides could affect other survival instincts, Stein said. The fish rely on their noses to feed, mate and possibly to find their way back to their native streams, where they spawn.
Their research was prompted by British studies of Atlantic salmon that showed four pesticides, including diazinon, impaired the fish's mating behavior, he said.
One of the British researchers, Andrew Moore of the Centre for Environment, Fisheries and Aquaculture Science, presented findings at a meeting in Seattle this week. He said pesticides inhibit a male salmon's sense of smell, and thus its ability to detect that a female is ovulating and ready to reproduce.
Environmental groups, including the Seattle-based Washington Toxics Coalition, have filed papers saying they intend to sue the federal Environmental Protection Agency unless it directly addresses the issue. The EPA has 60 days to respond. An agency spokesman declined to comment.
Previously, officials determined safe levels of pesticides by seeing what concentration would kill the fish.
``The EPA has not looked at the subtle effects of pesticide on salmon,'' Erika Shreder, staff scientist at the Toxics Coalition, told the Seattle Post-Intelligencer.
But Heather Hansen, executive director of Washington Friends of Farms and Forests, said people should not jump to conclusions. Her group promotes the responsible use of pesticides.
``From what we do know, I don't know anybody in the scientific community that really feels like they can conclude there's been some harm'' that pesticides have caused to salmon, Hansen said.