Car pollution causing rapid die-off of coho salmon
SILVERY coho salmon are as much a part of Washington state as its flag. The fish has a sacred place in the diets and rituals of the state’s indigenous peoples, beckons to tourists who flock to watch its migration runs, and helps to sustain a multi-million dollar Pacific Northwest fishing industry.
So watching the species die in agony is distressing: Adults have been seen thrashing in shallow fresh waters, males appear disoriented as they swim, and females are often rolled on their backs, their insides still plump with tiny red eggs that will never hatch.
“Coho have not done well where a lot of human activity impacts their habitat,” said Nat Scholz, research zoologist, a research zoologist for the National Oceanic and Atmospheric Administration. That’s to say the least.
A recent study traced a major coho salmon die-off to contaminants from roads and automobiles – brake dust, oil, fuel, chemical fluids – that hitch a ride on stormwater and flow into watersheds. The contaminants are so deadly, they kill the salmon within 24 hours.
“Our findings are... that contaminants in stormwater runoff from the regional transportation grid likely caused these mortality events. Further, it will be difficult, if not impossible, to reverse historical coho declines without addressing the toxic pollution dimension of freshwater habitats,” said the study, published last Wednesday in the journal Ecological Applications.
This sort of point source pollution from antiquated sewer systems is a problem across the nation, including the Chesapeake Bay region, as rain overwhelms storm drains, commingles with human waste and surface road garbage, then flushes into ponds, creeks, streams and rivers.
In Seattle and large cities across the Pacific Northwest, those waters are stocked with salmon. The finding could be a breakthrough in a mystery that has vexed scientists for years. But it fell short of explaining another mystery: why are coho the only affected family in five salmon species.
Chinook, sockeye, pink and chum don’t remotely experience the same mortality. “This is the great mystery that we are working on,” Scholz said.
The future for a species the experiences up to 40 percent mortality before spawning in the Puget Sound is no mystery. “The population will crash,” said Jay Davis, an environmental toxicologist for the US Fish and Wildlife Service who coordinated field research for the study.
In separate interviews last Thursday, Davis and Scholz estimated that it could happen in as few as six years. “We have to act now,” Davis said. — WPBloomberg