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Research Suggests Pesticides Disrupt How Salmon Smell by Lisa Stiffler Seattle Post-Intelligencer - August 1, 2000

More elusive threat could endanger the survival of the fish

Low levels of pesticides can disrupt the ability of salmon to smell, potentially diminishing their survival, new research from scientists at the National Marine Fisheries Service indicates.

The findings underscore what many experts are beginning to believe -- we could spend millions of dollars on habitat restoration, dam removal and other measures designed to save salmon. But if this new research is correct, the fish could remain threatened unless pesticides are reduced or eliminated in the water.

In the shadowy, murky Northwest waterways, friend or foe can be difficult to distinguish. Is the shape up ahead a female looking to mate or a predator looking for lunch? Is this the right stream for spawning or was it the creek half-mile back?

To navigate in their aquatic world, salmon rely heavily on their sensitive nose. But pollutants -- including pesticides -- can plug their noses worse than hay fever on a sunny afternoon in the country.

With 25 species of West Coast salmon and trout listed as threatened or endangered, negative impacts on the fish are facing increased scrutiny.

About 750 pesticides and 8,500 products sold to kill bugs, weeds and fungus are approved for use in Washington. Surveys have found dozens of these chemicals in urban and rural waterways.

The new research, conducted by Dr. Nat Scholz and other Seattle-based researchers, looked at one of these compounds, diazinon, commonly used in backyards and farms to kill insects. Other research recently conducted in Britain showed low levels of four pesticides, including diazinon, impaired the salmon's mating behavior.

In response to such findings, a group of state and federal scientists here, including Scholz, have joined to study the effects of pesticides on salmon.

"The task force is very much looking at any effect pesticides might have on salmon," said Phil Millam, a special assistant with the Environmental Protection Agency in Seattle and founder of the 4-month-old group that also includes state Ecology and Agriculture departments.

The researchers are reading published data to try to understand how pesticides might impact recovery efforts.

In the past, safe pesticide levels for fish have been determined with lethality tests -- in short, if the fish died because of the dosage, it was too much.

"To make sure that pesticides aren't harming salmon, the EPA needs to look at the subtler effects," said Erika Schreder, staff scientist at Washington Toxics Coalition, a group working to reduce pesticide use.

Using behavioral tests and experiments that measure brain activity, Scholz studied the impact of pesticides more carefully by looking at its impact on smell.

In the wild, salmon detect predators by compounds given off skin of mammals and from alarm-pheromones given off by other fish. When salmon detect these odors, they stop, drop in the water and wait for danger to pass.

And there is strong evidence that scented cues are the primary way a salmon "imprints" or memorizes their stream of birth. Pacific salmon leave their home stream, swim out to sea and return one to six years later to spawn.

But only if they can smell.

Scholz is testing the effect of diazinon on hatchery salmon. The levels of pesticide are in a range similar to what might be experienced in nature.

In tests, the insecticide, which is used to kill crane flies and other bugs, is squirted into the water, followed by a signal that normally triggers the predator response. The fish exposed to diazinon do not respond to alarm pheromones.

Similar experiments show that the fish are impaired in their ability to find their home stream after exposure to pesticides.

Scholz also is doing research that taps right into the brains of the fish. Electrical signaling can be measured with and without exposure to pesticide.

Mirroring the behavior response, a salmon's response to odors is reduced when the fish has been exposed to diazinon. Without pesticide, a signal travels from the nose to the brain, detected as an electrical signal that triggers a behavioral response.

In the United Kingdom, sheep have been bathed in diazinon to treat ticks and lice. The sheep are near streams and tributaries that are home to salmon, and diazinon has been detected in these waterways.

British researchers examined the effect of the insecticide on mating.

"It's very important," said Dr. Andrew Moore, a researcher with the Centre for Environment, Fisheries and Aquaculture Science in England.

"What you're really trying to determine is what effect these pesticides are having on the behavior level."

Moore, who presented his research yesterday at a meeting in Seattle, has tested the effect of four pesticides on spawning.

Signals sent by females inform males that they are ready to lay eggs, which are deposited in stream or river beds. The message that salmon eggs are on the way is detected by nose, attracting males and triggering the spawning response.

The British researchers found that exposure to diazinon at low levels reduced the ability of male fish to smell an ovulating female and elicit the appropriate behavior.

While the dose of diazinon was not lethal, the scientists concluded that dulling the salmon's ability to smell could reduce reproductive success. The British research also looked at brain signaling, again with results supporting the behavioral response.

Environmental groups, including Seattle-based Washington Toxics Coalition, have filed an intent to sue to force the EPA to directly address the effect of pesticides on salmon.

The federal agency has 60 days to respond to the notice, which was filed Wednesday, or be sued. An EPA spokesman yesterday declined comment on the suit.

"The EPA has not looked at the subtle effects of pesticide on salmon, such as the effects that Nat Schloz is seeing," Schreder said. However, Heather Hansen, executive director of Olympia's Washington Friends of Farms and Forests, a non-profit organization promoting responsible use of pesticides, urged caution in proceeding with the pesticide and salmon issues.

"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 (caused to the salmon)," Hansen said.