Dying before spawning sucks as reproductive failure. Sockeye and pink salmon are susceptible to prespawning mortality (PSM) in the interior Fraser and Columbia River drainages and on the southeastern-Alaska coast from too much summer heating which is worsening with climate change. It also happened in the Klamath River to Chinook and coho over 2 decades ago, when irrigation took precedence over instream-flow protection. (1)
But that’s not what’s going on in Puget Sound. What’s alarming is that the lower segments of most mainland streams around the Sound are vulnerable to PSM for in-migrating-adult coho, particularly in the greater Seattle area. Fish are dying full of eggs (females) or milt (males) before they reproduce and make salmonid fry. This could also be a concern in the lower Columbia River drainage (especially in the Portland/Vancouver area), the last bastion of native-coho runs in that basin.
When the Rubber Meets the Road
More-recent studies show that organic chemicals in rubber tires are the cause of the problem, which impact coho adults, not their young (2,3,4,5) with resultant harm to imperiled, salmon-eating Southern Resident orcas (6,7) that is leading to lawsuits.
Notably, rubber leaches whether it’s recycled or not, and the City of Olympia’s call for using AstroTurf in its future Yelm Highway Park is concerning because such cushioning contains recycled-tire debris that could leach out in stormwater runoff. Although AstroTurf reduces both watering and maintenance costs, the latter potentially including machinery that contributes to climate change, there could be increased coho PSM in the nearby Deschutes River basin, as well as lost grassland habitat for pollutant filtering, carbon sequestration, and insect (e.g., bee) pollination. Keeping grass/clover longer where possible enhances those benefits, too.
Urbanization and Stormwater – Aquatic Killers and Possible Solutions
Why coho are so vulnerable is still a mystery. They survive worse as adults than (a) young coho and (b) adult chum and Chinook salmon that may even be nearby in such urbanized streams, so it appears adult coho really are more sensitive to toxins. (8)
Could their relatively long freshwater rearing (as juveniles) lead to more toxin buildup that carries into adulthood? A NOAA-Fisheries seminar by Nat Scholz explained how coho adults are dying from stormwater-runoff impacts after the first winter flushing in the Salish Sea (WA/BC) catchment and as far south as California freshwaters. It could be an osmoregulation problem, in which case better estuarine protection might reduce impacts (not tested yet).
What has been tested is a stormwater filter that has been shown to keep coho adults alive. Filtration through a mix of soil, bark chips, and gravel was effective as mitigation, so innovative stormwater management is needed here. Hence, the building of a new stormwater facility in the Central Sound could help reduce such PSM in future years, if it can keep up with human-population growth that puts more cars and their leached pollutants on the road.
Permeable pavement can also reduce stormwater toxicity for coho and other aquatic animals. Such pavement allows water flow-through and is strengthened using Boeing’s surplus carbon fiber, which has the added benefit of further reducing stormwater toxicity. But permeable pavements, which are now being used in Olympia, do require more landowner maintenance than impervious pavement, which creates the worst stormwater runoff. Dennis Thireault (Seattle biochemist) notes the high levels of chlorinated hydrocarbons in asphalt, too.
Timing is Everything
But why is PSM higher for coho than coastal cutthroat, such that coho are absent from many urbanized creeks throughout the Sound? Perhaps coho aren’t more sensitive to toxins than spring-spawning trout, but rather because their spawning-run is earlier, it puts adults at more risk for toxin exposure and thus PSM. This follows from the commonly observed hysteresis shown by streams, in which the 1st big storms often carry more sediments, toxins, etc. This includes reduced pH (higher acidity) too, as emphasized by Hal Michael of the Sustainable Fisheries Foundation. Additionally, the in-migration of fall-spawning coho may be at a higher water temperature than for spring-spawning cutthroat, further exacerbating coho PSM. Because coho spawn well before cutthroat do, the latter likely have less contamination and heating issues to deal with.
Because coho PSM especially occurs during early cold-weather freshets when the winter snows melt, keeping instream-flows stable and filtering pollutants at stormwater outfalls should help reduce this problem. The more cars there are on roads near streams, the more car brakes are leaching toxins like heavy metals, and tires will leach into the water. Certainly, the Central Sound has the worst coho PSM because of greater riparian-habitat damage, including more impervious surface coverage, than elsewhere around the Sound.
We greatly need riparian and wetland restoration! That should also benefit coho because it, along with Olympic mudminnows and amphibians, rear extensively in off-channel habitats away from mainstream currents.
Coho PSM is high both near SeaTac and closer to Seattle, notably for Longfellow Creek. (9) For the latter stream, Steve Boessow (WDFW-Habitat) noted the heavy industrialization downstream and urbanization upstream, as well as past culverts, none of which have been good for Pacific salmonids (in cumulative fashion). The creek formerly had its own inlet to Elliott Bay, but now runs north into the polluted, Duwamish River inlet via downstream channelization. Ironically, fish-passage improvements there have increased coho in-migrations and thus PSM.
Something smells wrong
Let me summarize results of research done on impaired sense of smell, fish-olfactory impairment, that may be relevant to coho PSM for Seattle-area streams. Indeed, car-leached heavy metals cause fish problems in the eastern USA (e.g., studies at Virginia Tech). Runoff of pesticides and heavy metals, especially copper from mines, pesticide byproducts, and zinc from brake pads, can impair olfaction in Pacific salmonids, other fishes, and aquatic bugs to impair (a) detection of food, mates, and home streams and (b) avoidance of predators It has even been shown that zooplanktonic water fleas’ ability to grow armor is impaired to worsen predation on them.
What can we do to help?
Save car errands up for 1 day of “trap-lining” and use alternative transportation more often, like I do. Also drive more smoothly, by taking one’s foot off the gas pedal with less start-stop acceleration and breaking. That will reduce greenhouse gases, too! This should also help keep coho from becoming federally imperiled (and listed) in Puget Sound.
Robert Vadas, Jr. is an Olympia resident and aquatic ecologist
Footnotes
(1)Environmental impact assessments should include rigorous scientific peer review –
https://www.sciencedirect.com/science/article/pii/S2772735124000301
Stormwater:
(2) http://www.cleanwaterkitsap.org/Pages/The-stormwater-problem.aspx
EPA criteria:
(4) https://www.epa.gov/wqc/aquatic-life-criteria-and-methods-toxics
(5)https://www.epa.gov/chemical-research/6ppd-quinone
Orcas:
(6)https://wdfw.medium.com/orca-action-month-what-the-heck-is-bioaccumulation-2b56cbd5535b
(7)https://wdfw.medium.com/orca-action-month-clean-waters-healthy-futures-2173bee0c892
Trout Unlimited newsletter:
(8)https://issuu.com/wcturadio/docs/final_wctu_newsletter_april_2015_ed
(9)Turning Homeward: Restoring Hope and Nature in the Urban Wild by Adrienne Scanlan; https://www.thirdplacebooks.com/book/9781680510621
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