Parks to fight whirling disease by removing fish

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Aquatic specialists with Parks Canada are looking at removing all fish from Johnson Lake over the next two years as a method of combating whirling disease which was confirmed to be in the water body last August by the Canadian Food Inspection Agency.

Banff National Park aquatic specialist Mark Taylor said the agency is currently undertaking an environmental impact assessment (EIA) for its response to whirling disease in the lake.

Taylor said the plan is to eradiate the disease from Johnson Lake by removing all fish, and thus removing the host for the disease – Myxobolus cerebralis.

A recent case study in Colorado where aquatic managers removed fish in an infected creek watershed with branching tributaries were able to demonstrate the approach worked.

“For the first time they realized that if you eradicate the fish host, you can eradicate the disease,” Taylor said. “That is because the worms themselves cannot pass the disease to each other; so if they don’t have the fish hosts to pass it to, the disease doesn’t follow the lifecycle.”

The lifecycle of whirling disease is complex, because it is actually a worm that is present in aquatic environments that eats the spores from myxobolus cerebralis and then turns them into triactinomyxons, which then attach to fish and allow the parasite to inject cells into the fish, thus infecting it.

Taylor said in Colorado at Placer Creek they eradicated all fish and were able to prove they eradicated the disease as well and “in the small world of fisheries management, it is quite cutting edge.”

As to the plan for Johnson Lake, removal of fish is expected to take place in spring using mechanical methods like electrofishing and nets. Taylor said to use chemical methods to eliminate all fish in the lake would not be “Parks Canada’s style.

“We do not really believe the national park is a place for using chemicals, even though you can accomplish your task a lot faster,” he added. “It just does not make sense to us and there are still unknowns.”

Parks Canada has removed invasive fish from two of its lakes, Rainbow and Devon. Taylor said those high elevation lakes demonstrate that Parks can successfully remove all fish from a waterbody using mechanical means.

Johnson Lake is different, however, as it is a montane water body with an irregular shoreline and more plants along it than Devon or Rainbow at higher elevations.

Taylor said aquatics staff will begin removing fish from the lake in spring, but only until the Canada Day long weekend. He said the lake should be closed to public access until that time, and for summer it will be accessible for residents and visitors. The only exception, he added, is that there will be no access for watercraft such as boats, kayaks and standup paddleboards.

“That helps us, because the whole issue of boat washing is pretty hard to manage,” Taylor said.

The Labour Day long weekend, he continued, would be when he expects public access to be shut down again to continue to collect fish from the lake. In fall as well, crews would use pumps to remove water from Johnson Lake to restrict the area fish have to swim and assist in catching them. Taylor said the timing of the de-watering is also done to protect amphibian species in spring and these are the types of considerations being looked at as part of the EIA.

“That is a great tool for us to dig deep,” he said about the EIA preparation. “One of our challenges is amphibians, as much as possible, we do not want to impact them.

“We are confident our nets are not going to hurt amphibians, but we wouldn’t want to shrink the lake when they are in the water in spring.”

As for the rest of the water bodies in Banff National Park, Taylor said the federal agency is committed to protecting healthy aquatic ecosystems and a four point action plan has been created to respond to whirling disease in the park.

That response plan includes testing of lakes and rivers to understand what areas have been affected by whirling disease; prevention through closure of Johnson Lake; education of the public about the situation and how it is spread through contaminated recreational and commercial equipment and protection of waterbodies that contain populations of westslope cutthroat trout, which are listed under the Species at Risk Act as threatened.

When whirling disease was first detected, Parks responded by closing high elevation lakes that contain westslope cutthroat trout to public access. Taylor said in retrospect, the knee jerk reaction to close those lakes was a good idea to protect those fish populations.

“We didn’t know that much about (whirling disease), so it took us literally months to learn from the literature and talk to experts in Colorado,” Taylor said. “Now that we are more confident with our knowledge of the disease and management options … we are still keeping those lakes closed.”

Another aspect of the response plan for Parks is determining where tubifex worms are present in the national park. The worms eat the whirling disease spores and pass them along to infect fish species. Taylor said there isn’t enough knowledge about the species or worm or where they are even present in the Banff.

“There may be parts of Banff that are not susceptible to whirling disease because we simply do not have those worms,” he said. “We are out now in winter taking sediment cores from different lakes.”

The analysis of the different water bodies for the presence of the worms is part of the risk assessment Parks Canada is undertaking to better understand how to best respond and manage the situation.

The worms need organic sediment to live, said Taylor, which is why Johsnon Lake has seen a high prevalence of the disease.

“It is a higher prevalence and that is probably related to the abundance of the tubifex worm and the habitat there,” he said. “It is the wetland uphill and north of the lake that feeds it where we are finding the largest concentration of worms.”

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