Highway runoff may cause pre-spawn mortality in coho salmon

A coho digs herself a hole to spawn in (or is that a male fertilizing eggs which have already been laid? Surely a reader will set us straight!) New research suggests that toxic compounds in stormwater runoff from roads and highways entering streams and rivers is killing coho before they get a chance to spawn.

Add this one to the long list of things we don’t know about salmon and human impacts on them.

Research in Washington State shows something in stormwater runoff from roads and highways is linked to pre-spawn mortality of coho spawners in rivers and streams nearby.

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.

The problem was first suspected in Seattle’s Longfellow Creek, which receives a rush of stormwater whenever it rains. Observers noticed that many of the female coho that made it home to their natal streams were dying before they could lay their eggs, often within a few hours of a rainstorm. Leading up to their deaths, researchers noticed that the fish seemed confused, often going in different directions and turning onto their sides while swimming.

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 and his team investigated this back in 2002 at the Longfellow Creek in Seattle. They have some interesting videos showing the difference between the affected fish and a normal fish in a different creek.

At first, they suspected heavy metals such as copper could be causing the sickness and death they witnessed. However, coho exposed to heavy metals at 10 times the amount found in the stormwater runoff showed no ill effects.

Meanwhile, other studies demonstrated that 65 percent of coho embryos exposed to this toxic stormwater had severe physical abnormalities, such as malformed fins, bleeding on the brain and swelling around the heart, according to Julann Spromberg, who discussed the findings at a recent meeting of the Kitsap Poggie Club, a local fishing group. Typically, the malformed fish die at an early age, she said.

Scholz partnered with a Washington Indian tribe to continue research. They collected stormwater runoff from a highway after a four-day dry period, and took numerous samples as the rain continued. They found that after only an hour of exposure to any of the water samples, coho started exhibiting the symptoms of illness, rolling around and bumping into the aquarium walls, and dying.

Scholz said typical highway runoff contains an enormous number of different compounds, and it is extremely difficult and costly to narrow down which ones may be affecting the fish. Because death comes so quickly, the cause must be a physiological or metabolic pathway, not any kind of disease progression, he said.

We confess, we had to bold that to contrast with what Alexandra Morton likes to suggest, that pre-spawn mortality on the Fraser River MUST be linked to mysterious diseases on salmon farms. However, she is not a toxicology expert; that’s Scholz’s job. He cannot pinpoint any particular compound yet, but has a few ideas.

Many tissues were taken from fish in the Grover’s Creek experiments in hopes of finding a problem in the heart, gills or perhaps other essential organs. The method involves testing for genetic markers to determine which organs are under stress. Results are still pending.

“The fish are telling us what is going on, given the high rates of mortality across many streams,” Scholz said. “But, scientifically, this is a tricky challenge. We have to look at target organs and try to figure out why they are dying.”

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 β€” which means together they are worse β€” or the mystery compound is a single chemical that has never been identified for its extreme toxicity.

“We don’t have evidence for either one,” Scholz said. “It could be an unmonitored chemical contaminant or a group of chemicals working synergistically. We have chemists at the Northwest Science Center looking at what they can find in tires.”

This is very interesting and disturbing. The Fraser River is surrounded by roads and highways, and many bridges spanning its waters. And it rains a lot here; no doubt there is an awful lot of stormwater entering the Fraser, likely containing this same mystery compound. Hopefully, whatever is causing these symptoms can be pinpointed, and removed from the construction of roads, car tires and car parts.




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