SUQUAMISH — Stormwater runoff from highways appears to contain one or more unidentified compounds shown to be highly toxic to coho salmon and perhaps other salmon as well. The problem has been studied only a few years. Now, experiments at Grover’s Creek Hatchery in North Kitsap have confirmed that polluted stormwater has the ability to kill adult coho before they can spawn. This “pre-spawn mortality,” as it is called, could pose a serious threat to the ongoing salmon populations in many urban areas, said Nathaniel “Nat” Scholz, a biologist with NOAA’s Northwest Fisheries Science Center.
An extensive forensic analysis ruled out everything but toxic chemicals, Scholz said. Further investigations revealed that the more polluted a stream became, the more likely the fish were to experience pre-spawning mortality. Up to 90 percent of the females were dying in some streams following a rainstorm.
Scholz said the answer is likely to be one of two things. Either the mystery compound is two or more known chemicals working together synergistically — which means together they are worse — or the mystery compound is a single chemical that has never been identified for its extreme toxicity.