Thousands of fish in Johnson Lake have been caught and killed as part of Parks Canada’s ambitious plan to eradicate whirling disease to protect a threatened native trout species in the nearby Upper Cascade watershed.
In an intense effort over the past few weeks, roughly 5,000 fish have been caught as Parks teams electrofish in shallow areas and catch fish with gill nets in deeper parts of the 18-hectare lake.
The plan is to halt work in time to open the popular lake for the July long weekend, then resume in fall when the lake closes again. There’s also a plan to drain the lake later in fall so remaining fish are stranded or able to be caught easily.
Parks officials say they are confident they can rid the lake of all fish within the year, and have the worm that’s needed to spread the fish parasite to die off in one to three years, thereby reducing risk to threatened westslope cutthroat in the Upper Cascade.
“We have experience with fish eradication projects,” said Mark Taylor, an aquatic ecologist with Banff National Park, noting two successful projects at Devon Lakes and Rainbow Lake, both in Banff’s backcountry.
“I don’t think we’d tackle something like this without the experience in our back pockets.”
Johnson Lake was the first place whirling disease was detected in Canada. It was discovered last year, prompting widespread testing to see where the disease may or may not be.
It has since been found throughout the Bow River watershed and several creeks and rivers both in Banff National Park and the province of Alberta, as well as commercial fish hatcheries in the province.
Whirling disease can affect several fish species found in Alberta, including provincially threatened bull trout and federally threatened westslope cutthroat, as well as rainbow trout, mountain whitefish, brown and brook trout.
Whirling disease is not spread directly between fish, but a parasite is spread through contact between fish and a freshwater worm, known as tubifex.
People can spread whirling disease by moving infected live or dead fish, or infected equipment as well as contaminated sports and fishing equipment or contaminated water. Birds such as loons and ospreys can move fish from one water body to another, too.
Named whirling disease after the circular swimming patterns of infected fish, the parasitic disease has decimated fish populations in the United States since first being introduced from Europe in the 1950s.
It is primarily a cause of death in the young, susceptible freshwater fish, with overall deaths of infected fry and fingerlings known to reach 90 per cent in some cases.
The budget for removing fish in Johnson Lake is $450,000 over two years.
Bill Hunt, resource conservation officer for Banff National Park, said nearby Two Jack Lake and Lake Minnewanka reservoir thankfully tested negative for whirling disease, noting the Upper Cascade River drains into Minnewanka.
“That was very promising to us because the Upper Cascade is home to several core populations of threatened westslope cutthroat trout,” Hunt said, noting if whirling disease persisted in Johnson Lake the risk is too high for the threatened species.
“It’s a huge challenge and a very onerous task – and it’s probably not practical on a large scale – but in situations like this where we have a small water body with potentially a significant risk on a species at risk, we felt it was worth doing.”
After whirling disease was discovered at Johnson Lake, Parks Canada was quick to put a closure in place in the Cascade watershed, and other areas, to prevent people acting as a vector to introduce the disease and put westslope cutthroat at greater risk.
In early May, work began to catch fish in Johnson Lake, home to non-native brook, rainbow and brown trout, as well as native suckerfish. It was stocked with brookies and rainbows decades ago, but never with browns.
“They either came up the channel, which is very steep, or somebody may have helped them get in here,” said Hunt, noting it will likely never be known exactly how whirling disease ended up in the park.
Parks Canada has five approved techniques to euthanize, but in this case, fish are given “an overdose of electricity” from the electro-fishing unit than would normally be given. The larger fish then have their heads cut off.
Electro-fishing is essentially where an electric current is delivered into the water, stunning the fish. Scientists and biologists commonly use it as a non-lethal way to capture fish.
Taylor said fish caught and killed are potentially contaminated, so they are all put in a freezer at Banff’s resource conservation office until they can be sent to an approved landfill and disposed of.
“In the past, theoretically, you could use them for the purpose of bear management, but we don’t want bears tracking them around the park and to other water bodies,” he said.
Parks Canada plans to stop electro-fishing and netting in time to open Johnson Lake up for the July long weekend, then resume after the September long weekend when the lake will again be closed to public access.
A fishing ban is in place at Johnson Lake.
The lake will also be drained, for the most part, later in fall, which Taylor said would make it much easier to get at the remaining fish, particularly smaller ones that are more difficult to get with nets.
“Fish are pretty good at following the water, and so as the water declines, it’s likely a lot of them will end up in a small concentrated area in the deepest part of the lake,” said Taylor.
“That will present an opportunity for us to go into a nice contained area and then remove fish. Some of those fish will get stranded in the dry as well.”
Once Johnson Lake begins to freeze, the pumping company will leave and the shallow lake will start to recharge.
The plan is to reopen the lake as soon as possible in 2018. “By then, we hope all the fish will be gone,” said Hunt.
