Scientists Finally Find Reason For Mysterious Salmon Deaths On West Coast

by : Niamh Shackleton on : 04 Dec 2020 17:49
Scientists Finally Find Reason For Mysterious Salmon Deaths On West CoastPA/Pixabay

After years of research, scientists think they may have found the reason for masses of salmon dying every year.

Each year, coho salmon travel from the Pacific Ocean to America’s West Coast to spawn in its rivers. However, for several years, large numbers of the fish have been turning up dead before they had a chance to deposit eggs.


The strange phenomenon had left researchers stumped for years, but they now think they may have discovered a key piece to the puzzle in a study released yesterday, December 3.

PA Images

It’s thought the reason for the salmon’s population decline is down to a chemical known as 6PPD, which is reportedly used in tires to make them last longer, reported CNN.

Sceintists have found that deposits of 6PPD go on to react with ozone, as the tires begin to wear down and leave behind pieces of microplastics on roads.


Once 6PPD reacts with ozone, it becomes a different chemical known as 6PPD-quinone, which is said to be toxic to coho salmon. Researchers found evidence of this chemical in roadway runoff samples from across the West Coast, causing them to link it to the masses of salmon deaths.

PA Images

Part of the study reads, ‘Retrospective analysis of runoff and receiving waters indicated that detected environmental concentrations of this toxicant often exceeded acute mortality thresholds for coho during URMS events in the field and across the U.S. West Coast.’

Waterways closest to the roads have been the worst affected by 6PPD-quinone.


Following the discovery, scientists now hope they can start making steps towards saving the coho salmon.

As per CNN, Ed Kolodziej, the lead investigator for this study, said:

We believe that 6PPD-quinone is the primary causal toxicant for these observations of coho salmon mortality in the field. It’s exciting to start to understand what is happening because that starts to allow us to manage these problems more effectively.

PA Images

Kolodziej further explained that in a healthy stream, fewer than 1% of adult coho salmon die before spawning, but the mass deaths in recent years as seen up to 90% of the fish die in affected streams.

Study co-author Jen McIntyre added, ‘We’ve been documenting these mortality events since the early 2000. We suspect they’ve been going on for much longer than that, but nobody was looking for it.’

In response to the findings, Sarah Amick, the US Tire Manufacturer’s Association vice president of environment, health safety and sustainability, has said the industry is ‘deeply committed’ to creating sustainable products and ensuring they don’t negatively impact the environment.

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Niamh Shackleton

Niamh Shackleton is a pint sized person and journalist at UNILAD. After studying Multimedia Journalism at the University of Salford, she did a year at Caters News Agency as a features writer in Birmingham before deciding that Manchester is (arguably) one of the best places in the world, and therefore moved back up north. She's also UNILAD's unofficial crazy animal lady.

Topics: Animals, Deaths, News, Now, US News


  1. CNN

    Salmon have been dying mysteriously on the West Coast for years. Scientists think a chemical in tires may be responsible