Coho salmon, known scientifically as Onchorhynchus kisutch, are native to the US, Japan, and Russia. They average 8 lbs. or 3.6 kg, but they can weigh up to as much as 35 lbs. or 16 kg, while their oldest recorded age is about 5 years. They regularly are known to be "anadromous," meaning they spend most of their adult life in salt water and migrate into freshwater regions to spawn. Their appetite reflects their life stage: they graduate from insects to planktonic (free-floating) crustaceans when they move from fresh water to salt water with age, and finally they begin to prey upon other fish, squid, and jellyfish at their most mature. Historically, they supported thriving commercial, tribal, and recreational fisheries from Point Hope in Alaska all the way down beyond California and into Mexico. Unfortunately for the US, that is no longer the case as many of its populations in different regions are considered to be of "threatened" or "endangered" statuses.
On left: Photo credit to Bureau of Land Management, Public domain, via Wikimedia Commons
On right: Photo credit to Oregon Department of Forestry, CC BY 2.0 https://creativecommons.org/licenses/by/2.0 via Wikimedia Commons
Seattle, Washington's government spent millions of dollars restoring the creeks of Pudget Sound starting in the 1990s, from tending stream vegetation to reducing mud in the stream beds. Why did they do this? To build better homes for various species of fish, one being the coho salmon. And Seattle's hard work restoring Pudget Sound's creeks paid off--with time and their newly restored native habitat, Washington state's coho salmon began making a comeback. Seattle wasn't the only location to show that far-reduced and highly-pressured fish populations such as coho salmon could make a comeback, either--government branches including NOAA, the U.S. Fish and Wildlife Service, the California Dept. of Fish and Wildlife, business corporations turned from environment-degraders to environment-restorers, and even individual scientists and landowners proved it too.
A photo of restored coho salmon habitat on Lawrence Creek in northern California, created by joint cooperation between a private landowner and NOAA. It was highly successful! Photo credit to Bob Pagliuco, Public Domain under NOAA Fisheries Dept.
The habitat of the above photo was created to be complex, meaning it is filled with logs, other natural plant debris, and rocks for shelter from predators and constant water currents; such an environment is essential for juvenile coho salmon to grow in before migrating to the ocean.
However, Seattle's officials noticed that every time it rained, anywhere from 50-100% of their coho salmon would suddenly die out, and other major cities along the West Coast were noticing it in their native coho salmon habitats too. This phenomenon persisted as a miserable occurrence throughout the entire restoration process of Pudget Sound's creeks, and for decades, no one fully knew what the elusive killer was.
Finally, after 20 years of research, Washington state, San Francisco, and Los Angeles proposed the prime suspect for the mysterious die-offs of coho salmon. The reason it took so long to figure out was because coho salmon are already very sensitive to different environmental pressures, and there were so many possible chemicals to test for. With the hard work of scientists who specialized in the study of rising unknown contaminants, and a lot of time, they narrowed down their suspect list to one major figure. So what was the proposed coho killer? A chemical called 6PPD-quinone. This chemical is formed from 6PPD, a chemical that tire companies apply to their tires as a preservant to keep the tires from breaking down quickly. When 6PPD wears off onto roads and reacts with ozone, the chemical can transform into multiple new chemicals--one of which is 6PPD-quinone. Worn-off tire pieces, such as microplastics, and the chemicals tires release are often carried into by factors such as wind and rain into surrounding water bodies, where they inflict damage to multiple fish species, and to varying degrees of seriousness depending on the species of fish.
The good news of this discovery is that scientists, government officials, and the manufacturers of these tires and chemical preservants can now begin working together to find different solutions that benefit both the coho salmon and people's car tires. These different parties have had conflicts in the past, but that's no reason to believe they won't work together to find much-needed solutions. In this situation, the USTMA (US Tire Manufacturers Association) made a response within a day or two of the scientists' Science Magazine publication, communicating their commitment to the benefit of the environment through proven science. We're going to need these collaboration efforts between multiple parties if we want our fisheries to last for future generations of people after our own!
Sources:
About the study connecting car tire chemicals with coho salmon deaths
About the Coho Salmon Itself
A response by the USTMA (US Tire Manufacturers Association) to the discovery of 6PPD-quinone and its effects on coho salmon:
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