McKinleyville man helps save salmon — with math

Formula predicts habitats of a key player in salmon parasite's life cycle

The life cycle of Ceratonova shasta and Parvicapsula minibicornis (J. Bartholomew, Oregon State University)
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A McKinleyville man recently created an equation to better target tricky parasites linked to Klamath River salmon deaths.

“I study salmon because I love statistics, I love rivers, and I love fish,” Nicholas Som, a statistician with the United States Fish and Wildlife Service, said in an email to the Times-Standard. “I was never interested in some of the more traditional statistics jobs like working for insurance companies or banks.”

Ceratonova shasta is a microscopic parasite worm that is about a third of the size of a grain of salt. It’s been linked to the infection and increased death of salmon populations. In 2015, local tribes sued two federal agencies after more than 90 percent of juvenile salmon were infected with the parasite and likely died as a result of the infection.

The life cycle of ceratonova shasta

To understand the importance of Som’s formula, it’s important to understand the life cycle of the parasite. Much like the chicken and egg debate, the origin of ceratonova shasta does not yet have an established starting point. Instead, the parasite’s life is understood in terms of a cycle that has four stages during which it is inhaled, digested and expelled, consumed again, and then re-expelled.

In the first stage, called the actinospore stage, the parasite is in a triangular form and is floating through the water. The actinospore is inhaled through the gills of salmon, and then infects the salmon as it is digested. During this time, the actinospore changes form into a different type of spore called a myxospore, which is shaped like a kidney bean. The myxospore makes its way back into the water  by being expelled as waste from the salmon, or in severe cases of infection, through the decomposition of the salmon’s body after it dies. As the myxospores float around in the water, they are then consumed by the polychaete worms. After the worms eat the myxospores, the spores change from kidney bean-shaped myxospores to the triangular-shaped actinospores and burst through the skin of the polychaete worms, re-entering the water stream.

Predictions with precision

Som’s formula specifically targets the parasites by creating an accurate way to predict where in the Klamath River the worms are likely to inhabit. Som and Nicholas Hetrick, who also works for Fish and Wildlife, said in a statement that suitable habitats for polychaetes consist of stable areas with moderate depths, lower velocities, and a supply of nutrients. By first identifying the habitats of the worms, they are able to measure how effective river management strategies are in reducing the prevalence of the worms.

“The polychaete worms are an integral component of the C. shasta life cycle, and high infection rates by C. shasta have been linked to infection and increased mortality of Chinook salmon,” Fish and Wildlife said in a statement. “We are very excited about the applied management aspects of our work, and its potential to minimize disease impacts to Klamath salmon.”

Coalition building

Both Som and Hetrick were adamant in acknowledging the results of their work are derived from a broad coalition involving local tribes, out-of-state researchers, and other parties.

“We had a very limited understanding of the complexity of the problem, and little to no funding to do any of the work,” Hetrick said in an email. “I know on behalf of the [Fish and Wildlife] Arcata Office and [California-Nevada] Fish Health Center, much of the work we have done couldn’t have been completed without our partnerships with the tribes.”

Michael Belchik, a senior water policy analyst for the Yurok tribe said that Som’s equation translated into the real world with great accuracy. He said the Yurok, Hoopa, and Karuk tribes created a guidance document for river management strategies based off  technical memorandums that Som and Hetrick helped write. Several suggestions in the document were ultimately implemented as a result of the litigation the tribes brought forward in 2015, he said.

“Using science the tribes were able to obtain a prelim injunction and obtain the flows necessary to reduce the disease,” he said.

Belchik said the most effective guidance measure implemented to reduce the prevalence of polychaete worms has been flooding the river in a manner which causes the river bed to move — which disturbs the ideal conditions for the worm colonies.

The case for dam removal

Belchik said although disturbing the river bed is an effective way to reduce the number of polychaete worms, the task is getting harder because the dams interfere with the amount of sediment on the river bed.

“There’s a direct tie between dam removal and what it’s going to do to the river and how much more movable the bed will be,” he said. “The more mobile bed resulting from dam removal means that bed is going to move a lot easier — the science is very clear about the connection. We are looking forward to that.”

Philip Santos can be reached at 707-441-0506.

 

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