Why Do at Least Half of All Adult Coho Salmon Returning to Urban Streams in the Seattle Area Die Each Fall Before Spawning?

Why Do at Least Half of All Adult Coho Salmon Returning to Urban Streams in the Seattle Area Die Each Fall Before Spawning?

According to the article below, a chemical used to stabilize automobile tires is washing into streams where silver salmon spawn, and killing them.


Many of the chemicals, fertilizers, hormones and other additives that are routinely used in food production also wind up in these marine systems, where they also cause harm, even though this is not as obvious as dead salmon.


NOTE: this post was originally shared to Instagram by Wild Fish Conservancy on December 5, 2020.


In this new study, researchers from the University of Washington Tacoma, UW and Washington State University Puyallup compared stormwater runoff samples from creeks where coho pre-spawn mortality occurs to look for trends in the chemicals present.


Narrowing down a mix of 2,000 chemicals, the study found one common factor, 6PPD, a chemical used to keep tires from breaking down too quickly. When this chemical is exposed to ozone it transforms into multiple other chemicals, including the highly toxic one this study found is responsible for killing our wild salmon.

These results were especially meaningful to WFC’s science staff that have been involved in this effort for over two decades. In 1999, while conducting spawning surveys for the City of Seattle WFC’s Bill McMillan was the first to document and raise concerns about the alarming rates of coho salmon dying prior to spawning in urban streams, sometimes within minutes of stream entry. With support from the City of Seattle who helped secure funding through the Environmental Protection Agency and NOAA Fisheries, WFC launched a new research effort in King and Snohomish Counties to document and map the extent of this phenomena and to investigate potential patterns in land use and geographic characteristics that might explain this alarming rate of pre-spawn mortality. We’re proud these efforts could contribute to this groundbreaking new study.

We hope this new understanding will bring forward immediate solutions and conversations with the tire industry about how to address this issue facing wild fish moving forward. A huge thank you and congratulations to all who contributed to this study and effort over the years.


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