Is the Mystery of Mass Salmon Die-off Solved?


Scientists have been concerned for many years that something was happening in the waterways of the Pacific Coast when the salmon return from the ocean.

After heavy rains, large numbers of fish have been found dead just before they can spawn. Now, scientists think they may have found the clue that will help solve this mystery.

According to the new study, the cause is more common than you would think. The cause is scattered all over the roadways of America.

“It starts with a chemical antioxidant known as 6PPD, used in tires around the world to make them last longer.”

As tires break down they leave behind little pieces of the microplastics on the surfaces of roads. “The 6PPD in them reacts with ozone to become a different chemical — a previously unreported byproduct called 6PPD-quinone, scientists say. This chemical is toxic to coho salmon.”

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When heavy rains occur the runoff from the roadways are entering the watershed and introducing the chemical into the habitat of the salmon.

“We believe that 6PPD-quinone is the primary causal toxicant for these observations of coho salmon mortality in the field,” said Ed Kolodziej, the lead investigator for this study. “It’s exciting to start to understand what is happening because that starts to allow us to manage these problems more effectively.”

We still have many challenges ahead even with the chemical being identified. ‘The scale of the problem could make saving the fish difficult”. The focus of the solution may be treatment and handling of the runoff before it enters the watershed. Maybe we should also look to a “green” for the chemical?

This news was originally reported on CNN.

Justin Townsend

Justin (Choctaw) is an avid hunter, angler, and chef whose passion for the outdoors lead him to create Harvesting Nature in 2011. He continues to hunt, fish, and cook all while sharing his experiences with others through film, podcasts, print, and with recipes. He also proudly serves in the United States Coast Guard.

One thought on “Is the Mystery of Mass Salmon Die-off Solved?

  • Brad T.

    Interesting read, thanks for sharing! This is one of a hundred or more puzzle pieces affecting salmon and steelhead survival and reproduction in PNW.


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