Biologist David Baldwin pours a mixture of copper, zinc, lead and other pollutants into a large tank of water at the Suquamish Tribe’s Grovers Creek Hatchery, then slips four adult coho salmon into the dirty brown liquid. The poisonous soup he creates is aimed to simulate the kind of stormwater runoff to which salmon are frequently exposed, especially in urban streams.

Suquamish project biologist Anja Huff and USFW biological scientist Steve Damm take water samples at Grovers Creek Hatchery.

The tribe is working with Baldwin, a National Oceanic and Atmospheric Administration research zoologist, and Steve Damm, a U.S. Fish and Wildlife biological scientist, to figure out if toxins in stormwater runoff are killing adult coho salmon. Vehicle exhaust, brake pads, oil and gasoline are among the main contributors to polluted stormwater.

Scientists have observed adult coho dying within 24 hours of returning to urban streams. In most cases, death occurs before the fish can spawn. Known as pre-spawn mortality, it is commonly seen in streams near large urban areas such as Seattle.

“In urban streams, we are finding 60 to 90 percent of coho salmon dying before they spawn,” Baldwin said. “We want to figure out first what contaminants, if any at all, are causing the mortalities, then figure out how much of it actually kills them.”

At the hatchery, the coho are exposed to the chemicals for 24 hours and then monitored for changes in their behavior. Liver, gill and bile samples are then taken for analysis. The contaminated water is filtered then disposed of at Kitsap County’s wastewater treatment plant in Kingston.

For comparison, another group of coho is placed in a tank of clean fresh water for 24 hours. Like those in the polluted tank, the coho are watched closely and the same tissue samples taken.

Biologists chose Kitsap County as the site for the project because it is an area where development is rapidly turning healthy rural streams into polluted urban creeks because of increasing population and development.

For more photos, go to go.nwifc.org/cohoexperiment