Just how deadly could a parasite be to Yukon River chinook salmon?

Above are a series of logs with moss growing on them.
A chinook salmon rests beneath some deadfall along Michie Creek, south of Whitehorse. (Julien Greene/CBC)

By RCI, CBC News

U.S. biologists are studying how deadly a parasite that’s afflicting Yukon River chinook salmon could be, with the hope that one day the research is factored into decision-making on both sides of the border.

Zachary Liller, with the Alaska Department of Fish and Game, told CBC News there’s no method to account for natural mortality that’s associated with disease, especially ichthyophonus, which, under the right conditions, can prove fatal, because of the distances the imperilled chinook must travel to reach their spawning territory.

“Nobody is annually monitoring for disease and, and certainly nobody is interpreting those disease metrics,” Liller said.

All that information would be rounded up and punched into a statistical tool, which would allow scientists to sample the population in future years and make formal estimates of the number of chinook that die from diseases like ichthyophonus.

“It’s not currently factored into our stock assessment programs and therefore it’s not currently factored into any of our fisheries management decision making frameworks. And we wanted to rectify that by building a new tool,” said Liller, noting this could in turn influence whether to keep the harvest closed.

“If we’re successful with that, it will … fundamentally and in perpetuity change the face of our assessment program on the Yukon [River].”

Over the last several months, biologists in Seattle-area laboratories have been feeding fish flesh riddled with the parasite to young chinook, or inoculating them. Then, they wait, monitor and wait some more for any signs of infection.

In a process some researchers suspect can be accelerated in warmer water, the fungal-like parasite first targets the heart, then blooms across the muscles, affecting movement. Eventually, it can cause death.

The parasite could be one of the biggest problems behind chinook dying en route to their spawning grounds, some swimming roughly 3,200 kilometres from the Bering Sea to reach areas upstream of the Whitehorse dam.

But to what degree ichthyophonus is ravaging the fish remains an open question. That’s what the team, a partnership between Alaska Department of Fish and Game, the U.S. Geological Survey and Alaska Pacific University, is seeking to get a clearer picture of, with potential to expand that work in the years to follow.

What the research looks like

Under special permit, biologists have removed four wild chinook — two males, two females — from a tributary of the Yukon River. Then, Liller said roughly 2,500 juveniles were shipped to the laboratories, where they were separated into about four different tanks, set with different water temperatures — mainly freshwater — to see whether the parasite thrives in fish found in warmer water, a symptom of climate change, which is particularly acute in the North.

Scientists planned to continue running the experiment through September, but they hit a roadblock. Now things could be pushed back, said Paul Hershberger, who’s the chief of the fish health section at the U.S. Geological Survey’s fisheries research centre in Seattle.

“We did not get as many fish infected as we would have liked for our temperature study,” he said. “We were hoping to start seeing mortalities by now.

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Hershberger said Yukon Energy, which operates the Whitehorse hatchery, has sent older fish used for breeding down to Seattle, and biologists are out on the Bering Sea collecting pollock infected with ichthyophonus.

“We should be doing a second exposure to get a much higher infection prevalence in these experimental fish,” Hershberger said.

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“From a practical perspective, this research, I think, is really important for informing how much take — how much harvest can happen.”

This article is republished from RCI.