BANFF – Non-native fish have been killed in a remote alpine lake in Banff National Park this summer – but it’s all for a good cause.
In August, Parks Canada used rotenone to poison all the introduced eastern brook trout in Helen Lake, a small alpine lake north of Lake Louise that historically had no fish.
The next step is to kill Yellowstone cutthroat trout, an American sub-species that does not belong in Canada, in nearby Katherine Lake.
Parks Canada aquatics experts say it’s all part of a bigger plan to save west-slope cutthroat trout, a federally listed threatened species in Alberta that has disappeared from all but 10 per cent of its historic habitat in the province.
“Over the next two years, we’ll treat both of those lakes and remove all the non-native trout,” said Shelley Humphries, an aquatics expert with Lake Louise, Yoho and Kootenay National Parks.
“We will restore the valley stream – Helen Creek – with west-slope cutthroat trout when we’re ready, but not the lakes because they were historically fish-less.”
The outlet stream eventually feeds into the Bow River between Hector Lake and Bow Lake.
“Helen Lake has brook trout and Katherine Lake, unfortunately, has Yellowstone cutthroat trout, which is an introduced species to Canada,” said Humphries.
“We collected genetic data that shows Yellowstone cutthroat mixing with the west-slope cutthroat DNA in the outlet stream.”
This summer’s work at Helen Lake follows on the heels of a pilot project using rotenone at Hidden Lake in Skoki Valley, where approximately 5,000 non-native fish were killed in 2018 and 2019.
Rotenone, a naturally occurring compound derived from the roots of a tropical plant of the bean family, easily enters the bloodstream of fish and leads to reduced cellular uptake of oxygen, essentially suffocating the fish.
“At Hidden Lake, we spent a lot of time trying to use manual removal methods to remove fish and it wasn’t successful,” said Humphries.
“It took us about a day with rotenone to do what we couldn’t get done in six years there with nets and electro-fishing.”
It’s hard to know how many fish were killed in Helen Lake last month because most sunk.
But Humphries said a few hundred were picked up along the edge of the lake and in the outlet stream.
“Fish-eating birds that can dive picked up some on the bottom,” she said.
“We like to leave them in the lake if we can because it’s the best thing to get productivity going again and reinvigorate zooplankton and phytoplankton.”
American agencies have had such great success with rotenone and fish restoration projects that certain jurisdictions are looking to de-list some of their at-risk fish species, according to Humphries.
Humphries said here in Alberta, west-slope cutthroat are listed as threatened under the federal Species At Risk Act (SARA) because of concerns that they now occupy less than 10 per cent of their historic distribution in the province.
“Through our stocking practices, we’ve caused terrible problems for them,” she said, noting brook trout out-compete them, and rainbow and Yellowstone cutthroat trout hybridize with them.
“This is an important part of our restoration and recovery efforts to try to re-expand the range of this fish closer to its historic distribution.”
Part of those recovery efforts means Parks Canada must be careful about the genetic integrity of the west-slope cutthroat trout being reintroduced.
In eastern Montana and Yellowstone National Park in the U.S., aquatics experts have used a method whereby they take eggs and milt – the semen of a male fish – from cutthroat trout stream-side and fertilize them on site.
“They let the adults go back to the stream that they came from, and then the eggs harden for a couple of hours, and then they go to the hatchery where they stay for about three weeks,” said Humphries.
“They do about three-quarters of the maturation at the hatchery, and then they get them back, and they build simulated incubators or nests in the stream and put the eggs in there and then they finish their maturation in the stream.”
Parks Canada has never done this before.
But with the help of the Allison Creek Brood Trout Hatchery in the Crowsnest Pass, the agency tested a pilot at two locations in Banff National Park to learn how to do it – which was successful.
Humphries said this is a great method if the donor fish population is threatened and can’t take loss of any adults, which in this case is threatened west-slope cutthroat trout in Banff.
“We don’t think that we’ve got enough fish in some of these places that we can successfully take adults and not crash populations,” she said.
“It’s a great way to take eggs and milt from the location, and have good control over the genetics that we’re using, but leave the parent population in good shape,” she added.
“It’s one of three or four methods that we’ll be using, but this is the one we think that is going to be really useful for trying to preserve some of the historic genetic integrity.”
The restoration work at Hidden Lake, Helen Lake and Katherine Lake is thanks to special federal funding of $2.2 million.
With the money, there is also a plan in a couple of years to restore Margaret Lake, which is located near Hector Lake off the Icefields Parkway.
“It’s one of the original cutthroat trout lakes that was described in the early explorer reports in the early 1900s and it had really robust populations of cutthroat trout,” said Humphries.
“It probably fed cutthroat into Hector Lake as well, and now Hector is dominated by non-native lake trout and Margaret Lake is dominated by brook trout. It will be the last lake that we will work on under this current funding.”
Parks is excited to get all projects completed.
“We really need to use this landscape level tool so that we can start working on a scope and scale that’s going to allow us to work on de-listing this fish,” said Humphries.
