Massive mussel die off in Clinch River sparks investigation by researchers

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KYLES FORD, Tenn. (WJHL) – One of the most biologically diverse rivers in the world, the Clinch River, flows through Tennessee and Southwest Virginia.

It is home to more than 130 species of fish and more than 40 species of freshwater mussels.

Now, one of its most important species of mussels is in a rapid decline.

In 2016, biologists with the U.S. Fish & Wildlife Service started finding thousands of dead pheasant shell mussels in the river. Since then, they’ve been researching the cause and are hoping to determine an exact diagnosis.

“The Clinch River is really amazing,” said U.S. Fish & Wildlife Biologist Rose Agbalog. “It’s a biodiversity hot spot, over 100 species of freshwater fishes, 46 species of freshwater mussels and it really is a gem.”

Agbalog has helped research the cause of the die off of pheasant shell mussel since 2016.

The mussels are filter feeders and provide a number of services to the ecosystem.

“One of the most important is that they are cleaning our water, so large-bodied animals, like the pheasant-shelled, can filter 15 to 20 gallons of water a day and they pull out things like algae, and bacteria and organic matter,” she said. “They can also pull out heavy metals and toxins.”

In one 200-meter stretch of the Clinch River in Kyles Ford, Tennessee, the pheasant shell population dropped from an estimated 94,000 mussels in 2016 to less than 14,000 in 2019.

“At the same time we started seeing these patterns of mortality in the Clinch River, researchers in Washington State and Spain started seeing similar patterns or mortality in their species,” said Agbalog.

Agbalog’s colleague, Jordan Richard, said the team of researchers has seen a number of viruses, bacterium and parasites statistically associated with the dying mussels.

“The proximate cause could be that there’s some sort of infectious disease that’s killing them, but then the ultimate cause could really be something bigger,” said Richard, “so they could be sick and dying from a disease, but they only got that disease because something has changed with climate change or changing rivers or pollution, something else sort of triggered it.”

However, Agbalog says more lab work is needed to pin-point an exact cause.

“Unfortunately at this point, we don’t really have a smoking gun,” said Agbalog.

Richard said they hope to be close to a definitive diagnosis of the cause by the end of the year.

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