Are our tires killing the Coho?


Active Member
Here's an interesting article about storm-drain pollution in Puget Sound. This article is from The StreamTeam organization located in Thurston County. They are stewards, working hard to reduce the stream pollution in the sound. They are a great bunch, so get out and help them.

The population boom in the Pacific Northwest has caused a large influx of people and development over the last 30 years. Communities are expanding at increasing rates as more and more land is transitioned from forest to subdivisions. With this growth comes unintended consequences, particularly for some of the Pacific Northwest’s oldest inhabitants, our iconic Coho salmon. Coho salmon, Oncorhynchus kisutch, have been an important part of Pacific Northwest life for thousands of years. These salmon, also known as silver salmon, used to range across the Pacific Ocean from Japan to southern California. Now these amazing fish face deadly challenges as humans have encroached on their habitat. Coho salmon are anadromous, meaning they migrate from the ocean to freshwater rivers to spawn. They usually spawn in small lowland streams from October to December. Eggs incubate in gravel nests called redds, until spring when fry emerge. The juvenile salmon spend about a year rearing in freshwater before migrating the following spring. The Coho then spend at least one full year in the ocean, eating and growing, before returning to their natal watersheds to spawn, restarting the incredible journey over again. However, in recent years, more and more Coho salmon have been dying in these streams before they can spawn. Streams around the Puget Sound have been the focus of many habitat restoration projects since the 1990s. The streams Coho spawn in were becoming increasingly urbanized and degraded as treed riparian areas were replaced with houses and roadways. The goal of these restoration projects was to restore natural spawning and rearing habitat for Coho, which would hopefully help increase falling population numbers. Many of these sites required post-project monitoring to determine how successful the restoration efforts were. But what surveyors found was baffling. Coho salmon returning to these streams to spawn were exhibiting unusual behaviors. Surveyors found salmon swimming at the surface of the water, gasping for air with their fins splayed as they appeared to be losing orientation and equilibrium. The alarming behaviors didn’t stop there, many Coho salmon died within a few hours. Salmon death isn’t an unusual occurrence, salmon usually die after spawning in their natal streams, but Coho were dying before spawning, females were found dead still full of eggs. In fact, over the last 30 years, pre-spawn mortality (PSM) was affecting 60–100% of the fall Coho salmon runs in urban streams. While non-urban streams were seeing PSM levels of less than 1%. Something in the urban environment was causing mass causalities to Coho salmon populations. In 2011, Washington State University began intense research on PSM to try to determine its cause. Pre-spawn mortality in itself wasn’t an uncommon occurrence; fish hatchery staff have been reporting it Urban stormwater runo, on average, contains more than 2,400 distinct chemical features (DO) levels, and low flows as common causes of PSM. In these situations, fish health often deteriorated over a matter of weeks, not hours. When researchers began testing the water quality in the streams where the Coho were dying, there was little evidence that temperature, DO, or low flows were causing the PSM seen in Coho salmon. Researchers next sought to determine if disease or injuries were causing the deaths. Yet stricken Coho were generally in good physical condition, showing little to no signs of major disease or wounds. They also found that Coho salmon from hatcheries were just as likely to die prematurely as their wild counterparts. To add even more to the mystery, it appeared that whatever was causing the PSM was only affecting Coho salmon. Chinook and Chum salmon spawning in the same water during field and laboratory tests appeared to show milder symptoms and were not dying at the same rate. In an attempt to learn more about what was causing PSM in Coho, researchers began working to determine the biological impacts of being exposed to the water. They tested blood pH, blood gases, lactate, plasma electrolytes, hematocrit, and glucose in exposed Coho. The physical symptoms and biological reactions of these Coho were similar to that of hypoxia, a condition where the body is deprived of oxygen. Preliminary results indicate that the water Coho are exposed to disrupts their osmorespiratory function, their ability to breathe and use oxygen. The vast majority of the large prespawn mortality die-offs were seen in urban streams, with less than one percent of nonurban streams seeing similar salmon die-offs. Researchers began assuming that some contaminant or combination of contaminants in stormwater runoff is causing PSM in Coho. The question then became, what are the responsible chemicals? Urban stormwater runoff, on average, contains more than 2,400 distinct chemical features, making the task of determining the exact chemicals responsible for PSM extremely difficult. A group of researchers from the Center for Urban Waters, University of Washington, Southern California Coastal Water Research Project, Northwest Fisheries Science Center, and National Oceanic and Atmospheric Administration began working on this problem in 2018. They started by taking stormwater runoff samples from areas where PSM was occurring around Seattle. By crossreferencing the chemical signatures from each sample, they were able to create a “Coho mortality signature”, a mix of chemicals that were always present in the water where PSM was occurring. After researchers were able to identify this “signature” they then started testing known stormwater pollutants to find matching chemical signatures. After testing things like brake pads, pesticides, car soap, fertilizers, pet waste, and other pollutants, researchers discovered that tire dust particles had an almost identical chemical make up as the “Coho mortality signature”. During normal driving wear and tear, up to 14% of the diphenylguanidine (DPG) used in the manufacturing of vehicle tires can be released. Current research suggests that this tire wear particle leachate might be the major reason for the PSM occurring in Coho salmon around Puget Sound. Continued research is needed across the board to understand more about pre-spawn mortality in Coho salmon, but preliminary results indicate that our everyday driving could be significantly contributing to declining Coho salmon populations. The good news is that preliminary findings have successfully shown that filtering urban stormwater runoff can significantly increase Coho survival. Laboratory studies have shown that running stormwater runoff through a mixture of 60% sand and 40% compost with a mulch bark top coat has been improving Coho survival from 0% to 100% in both adults and juveniles. The Coho pre-spawn mortality syndrome represents an expanding threat to Coho populations, especially in areas of increased human development and encroachment. Increasing our understanding of the factors causing PSM will be an important part of restoration efforts in the future. Research continues to determine the reason for this chemical contamination as well as ways stormwater can be treated before it is discharged into local creeks and waterways. Coho salmon remain an important indicator species for watershed health and will help future restoration efforts to improve not only habitat quality but water quality as well.
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Active Member
A few years back, the Suquamish Tribe did a little experiment at their Hatchery near Indanola. As I recall it involved placing Coho in a holding pond and washing road debris into the pond with a large hose. The results were alarming to say the least.The story appeared in the Kitsap Sun.


Active Member
Yes. The answer is yes. I am familiar with these studies.

In addition to adult and juvenile mortality (obviously important) in coho stormwater toxicant exposures also are likely affecting cardiac and immune function, growth, and lateral line development, among other effects, in coho and other species of fish.


The Tug Is The Drug
Just to add to this, when I was a member of another fly club, a speaker came and presented about how they have wondered and now think that brake dust off of your wheels( containing metals) is confusing salmons sense of smell and direction
His recommendation is that we reduce and/or stop washing our vehicles in a place where the dust will wash off and go down the storm drain. Try and take it to a self car wash( if you don't like the brushes like myself) or wash it over grass or gravel to filter on it way down.
If we all make some small changes here and there, it will certainly be better for the environment.


Steve Saville

WFF Supporter
True, true but to retrofit or build new filtration systems would cost more than our city/county governments are willing to engage in. Sad, but true, the almighty dollar controls everything. Can you imagine if your property taxes were increased to fund this, for example, the amount of screaming you'd hear? Those of us who fish understand but the vast majority would most likely jump off a bridge over it.


Active Member
The future is in public education. Little things can make a difference. A change in building codes to require rain gardens (runoff diverted through green area), no car washing in streets, fixing oil leaks in your car, etc. Quick fixes are not going to happen without the public getting involved and if they are not aware that there is a problem nothing will change...

Jim Darden

Active Member
I would sure like to see us do better with urban pollution but fear we may spend our time fixing a small problem and ignoring the major issues. We are killing most of these fish in less than two weeks out in the straight. Maybe we should ask if killing almost all of them before they return to the river has an impact on the run.

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