Disease that kills salmon and trout detected in B.C. waterways

A disease known for decimating salmon and trout populations has been detected in B.C. for the first time.

Whirling disease is caused by the parasite Myxobolus cerebralis, which can kill up to 90 per cent of young salmon and trout in affected bodies of water, according to a study in the Canadian Journal of Fisheries and Aquatic Sciences. The disease is named for the “whirling” swimming patterns it can cause in fish due to underdeveloped tails. It does not pose a risk to humans.

The country’s first case of whirling disease was detected in 2016 after Parks Canada submitted a sample of a Banff National Park brook trout to the Canadian Wildlife Health Cooperative. On Sept. 20, 2023, Parks Canada found B.C.’s first suspected case by testing bodies of water in Yoho National Park.

“To limit the spread of whirling disease, Emerald Lake, Peaceful Pond, Lone Duck Pond, and the Emerald River shorelines, water bodies, and tributaries were closed until further notice,” Parks Canada said in an email to Cottage Life. Further tests found more suspected cases in Kootenay National Park. All water bodies in both parks are closed until at least March 31, 2024.

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Gail Wallin is the executive director for the Invasive Species Council of British Columbia. She says these closures are the “first line of offense” to stop the disease from spreading further. Parks Canada is “taking proactive action, which is the right thing to do,” she says. “The problem with whirling disease is there’s not any management treatment that we have for it right now.”

It’s not yet known how the disease arrived in B.C. Wallin says it’s easy for someone to spread it if they’re handling fish from infected waters. The affected bodies are connected to Banff’s waterways through the Columbia River, so she says the disease likely came from Alberta.

It may have also been caused by someone catching a fish in an infected river and releasing it in another: “It’s illegal to release anything outdoors, but we also know people do that, and we have lots of examples like goldfish.”

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Dave Burns has been a fly-fishing guide in Golden, B.C. for eight years. He says people are quick to blame anglers for transporting parasites across water bodies when there are many other ways diseases can be transmitted.

“Boats, kayaks, stand-up inflatable paddle boards, even the fur of a dog that goes for a swim in one place can hold it on their surface for a day or two,” he says. “Wherever (the dog goes) for their next swim, they can be transmitting the disease without knowing.”

Since many of his clients come from Banff’s Bow Valley, Burns has always been concerned about the disease coming to B.C.’s waterways. He makes sure anglers booking sessions have taken measures to prevent transmission, like cleaning boats and clothing. He checks again before the anglers arrive, and a third time before boarding.

“We’ve been very careful,” he says. “I ask ‘When was the last time (your) boots were sanitized?’ I carry extra boots with me if people are like ‘Oh, I forgot to do that.’”

Now that the disease is in the Emerald and Kicking Horse Rivers, Burns says it’s “pretty fair to say there’s traces” already in Columbia River. Wallin agrees, saying predators like eagles and bears rely on salmonids as a source of food, so the increased death of these fish could cause ecological imbalance. She adds that certain infected fish species are also important to local Indigenous communities.

Whirling disease has had varying impacts on rainbow trout populations and other salmonids in Alberta, says Elliott Barnes, the manager of the fly-fishing retailer Bow River Troutfitters, and a board member for the Bow River Chapter of the conservation group Trout Unlimited. In the Bow River and Crowsnest River, he says a few factors have influenced the disease’s lethality, including spawning habits and temperature.

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“The infectious spores (triactinomyxon) that infect the young trout are most prevalent when you get to a temperature of 14 degrees Celsius,” he says. Rainbow trout in Crowsnest spawn in early spring, and the temperature becomes ideal for the release of infectious spores in May, when young fry emerge from streambeds. Their smaller sizes make them more vulnerable to the spores. Not as many young Bow River rainbow trout are in danger, however, because they spawn in cooler areas.

Lethality also depends on streambed deposits, he says. The parasite that causes whirling disease lives in an intermediary host, the tubifex worm, which thrives in waters rich in mud or sedimentary deposits like those of Crowsnest. When young fish die from the infection, they release spores that re-infect the worms, creating the “second infectious stage of the whirling disease cycle.” Rainbow trout spawn in Bow River’s less sedimented streambeds, so Barnes says their young may be less impacted by the disease.

Wallin and Burns say more research needs to be done to determine how exactly B.C.’s waterways and fisheries will be impacted. To that end, Burns says Trout Unlimited has been raising money to fund biological studies and redd surveys seeking to understand their wild fish populations.

Burns has also spent the last two years advocating for the provincial and federal governments to conduct research on certain parts of the Columbia River.

“The governments should do more to study the headwater region of this very large, international water body,” he says. “This area has been ignored and overlooked for too long.”

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