Aquatic Ecologist Dr. Mark Taylor works with a contractor to set gill nets in Johnson Lake Reservoir in Banff National Park. Photo Credit-Bill Hunt, Parks Canada
Breaking the Life Cycle-Eliminating Whirling Disease from Banff National Park’s Johnson Lake.
Banff National Parks has begun removing fish from Johnson Lake in an effort to eliminate whirling disease. Whirling disease is caused by an invasive, microscopic parasite called Myxobolus cerebralis. The parasite requires two hosts to complete its life cycle: an aquatic worm (Tubifex tubifex) and a salmonid fish (e.g. trout, char, or whitefish). Whirling disease can have serious impacts on some species of trout and salmon including physical deformities and in some cases mortality rates reaching up to 90%.
In August 2016, whirling disease was detected in Johnson Lake in Banff National Park; the first time this fish disease had been confirmed in a Canadian waterbody. This immediately triggered a response by both provincial and federal government which included testing other sites in the wild for whirling disease. Although there remains a backlog of samples collected in Fall 2016 which still need to be tested for whirling disease, the disease has been confirmed in the Bow River and some tributaries, as well as the Crowsnest River. The Canadian Food Inspection Agency has also declared the Bow and Oldman watersheds as “infected”.
Although whirling disease was just recently detected in Canada, much can be learned from fisheries managers in the U.S. as some states have had to deal with this disease in the wild for several decades. Recent work on managing whirling disease in the U.S. has included controlling “hotspots” for the disease. Although it was previously understood that myxospores (one of the life stages of the parasite) could remain viable in the sediment of a waterbody for as long as 30 years, recent research indicates the long-term survival of myxospores is actually much shorter. Additionally, tubifex worms can only become infected by ingesting the myxospores released when an infected fish dies – they do not pass the disease to the next generation without the fish host. In Placer Creek in Colorado, fishery managers successfully eliminated all evidence of the parasite by removing all of the fish from the reach of stream they were concerned about. Without the fish host, the lifecycle of the parasite was broken. Rio Grande native Cutthroat Trout have since been reintroduced and a barrier installed to protect the population from downstream Brook Trout invaders.
Aquatic Ecologists Dr. Mark Taylor and technician Colby Whelan use an electrofisher to capture fish in Johnson Creek as part of a fish removal effort underway in Banff National Park. Photo Credit-Bill Hunt, Parks Canada
Historically, Johnson Lake was home to a population of native suckers but was stocked with non-native Rainbow Trout, Brook Trout, and Brown Trout. Following removal of fish from Johnson Lake, Parks Canada will re-stock the lake with native White Suckers. This aligns well with Parks Canada’s policy to remove non-native species when practical to do so, in an effort to help native species. Thus, removing the fish from Johnson Lake is not only a big step towards breaking the lifecycle of Myxobolus cerebralis and therefore whirling disease, it will also be a positive move forward in efforts to help native species persist and an excellent test case in Canada for innovative treatments to deal with whirling disease.
Banff National Park is home to two at-risk salmonid fish species: Westslope Cutthroat Trout and Bull Trout. Protecting these species from whirling disease is extremely important, requiring action to reduce risk to these populations. Johnson Lake is considered a hotspot not only because of the prevalence of whirling disease but also due to its proximity to Lake Minnewanka and the Cascade watershed (which are currently whirling disease free). The Cascade watershed is of significance because it is home to four of only 10 core populations of Westslope Cutthroat Trout in Banff National Park. Johnson Lake is also a very popular recreation area so the potential for the movement of the parasite via boats, boots, and birds is high.
Historically, Johnson Lake was home to a population of native suckers but was stocked with non-native Rainbow Trout, Brook Trout, and Brown Trout. Following removal of fish from Johnson Lake, Parks Canada will re-stock the lake with native White Suckers. This aligns well with Parks Canada’s policy to remove non-native species when practical to do so, in an effort to help native species. Thus, removing the fish from Johnson Lake is not only a big step towards breaking the lifecycle of Myxobolus cerebralis and therefore whirling disease, it will also be a positive move forward in efforts to help native species persist and an excellent test case in Canada for innovative treatments to deal with whirling disease.
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