A four-year project to rid Rainbow Lake in Banff National Park of non-native rainbow trout and introduce threatened westslope cutthroat trout has come to an historic end.
Over two days last week, Parks Canada crews and volunteers from Trout Unlimited caught about 100 cutthroat trout from Sawback Lake – one of only 10 water bodies in Banff National Park with pure cutthroat trout populations.
The cutthroat, both adults and juvenile, were then flown by helicopter to nearby Rainbow Lake, where Parks Canada had removed more than 500 non-native rainbow trout in the previous few years in preparation for reintroducing the at-risk species.
Parks Canada officials say rainbow trout were first introduced into Rainbow Lake in the 1930s and again in the 1960s for sport fishing and, over time, they made their way into the Cascade River watershed, competing with native cutthroat trout.
They say last week’s introduction of cutthroat was an historic moment.
“The objective of the recovery strategy is to protect existing pure populations of cutthroat and establish new populations in their historic range,” said Mark Taylor, an aquatics specialist for Banff National Park.
“It’s like if you have 100 golden retrievers with one black lab and let them all breed, and over enough generations you lose the black lab genes. We’re hoping to lose the remaining rainbow in the Cascade watershed over time by introducing cutthroat to Rainbow Lake.”
Westslope cutthroat trout were listed as threatened under the Species At Risk Act (SARA) in 2013, primarily because of habitat loss, too much fishing and competition with non-native fish species.
They now exist on the edges, fringes and margins of their former range. Populations are disconnected from one another and are small enough some are at significant risk of winking out of existence.
In Alberta, they now occupy less than 10 per cent of their historic range, and populations in the protected lands of Banff National Park have also seen their historic range shrink in size.
Taylor said genetic research showed the main stem of the Cascade watershed still had pure populations of cutthroat trout, but there were still rainbows and hybridized trout there, too. Both Rainbow Lake and Sawback Lake feed into the Cascade River watershed.
“We were seeing mostly pure fish in the watershed, except for a few bad apples and we knew the cause of that was Rainbow Lake,” Taylor said. “When you have a population of non-natives at the top of the watershed, it’s a problem for all of the watershed all the way down.”
“Overall, the Cascade watershed is one of the best watersheds in the entire park, though it’s obviously impacted below the reservoir, and the rainbow were infiltrating the entire watershed.”
In 2011, Parks Canada started removing rainbow trout from Rainbow Lake by electro-fishing and gillnetting. In total, 528 rainbows were captured – the last fish was caught in September 2013.
Parks was confident they could remove all the rainbows in the four-hectare lake with nets and electro-fishing based on a previously successful aquatic restoration project at Devon Lakes, where non-native brook trout were removed from the once fishless system.
“It’s a lot of grunt work and it probably takes longer than what some agencies do where they just go out and poison a lake,” said Taylor.
“But based on Devon Lakes, with that experience, we were confident we could go into Rainbow and remove the entire population of rainbows.”
After the last fish was caught, Parks Canada left the nets in Rainbow Lake for another year, until fall of 2014, just to make sure there were no more rainbow trout. “We didn’t catch any more fish and we declared the lake fishless,” Taylor said.
Another step in the recovery strategy involved finding a pure source of cutthroat trout. It was found in nearby Sawback Lake.
Other lakes, creeks and rivers with pure populations include Elk Lake, Little Fish Lake, Big Fish Lake, Cutthead Creek, Upper Spray River, Upper Bow River, Babble Creek, Helen Creek and Outlet Creek.
“These are all pure populations in places where they were historically found,” said Taylor. “You can find pure fish in other areas, but they were stocked somewhere where they were never supposed to be.”
Last week, crews caught about 100 of an estimated 2,500 cutthroats from Sawback Lake.
The fish were kept in net pens in the lake for just a short time while waiting for a helicopter to arrive, and then flown in a bucket used for fighting fires slung beneath a helicopter to Rainbow Lake.
Rainbow Lake was historically a fishless lake, but Parks Canada made the decision to put cutthroat trout in Rainbow, believing the ecological benefits for the entire Cascade watershed far outweighed leaving the lake fishless.
“The pure fish that we’ve now put in Rainbow Lake will trickle down, much like the rainbow did, and have a top down effect, in a positive direction,” said Taylor.
The $160,000 Rainbow Lake project was initially led and initiated by Charlie Pacas, a renowned aquatics expert for Banff National Park, who passed away in 2013.
Bill Hunt, resource conservation manager for Banff National Park, said Pacas would be proud.
“He would be really happy to see we carried it though,” he said.
Hunt said the lake has been teeming with invertebrates since the rainbows were removed.
“As soon as we put them in last week, the fish were already rising,” he said. “Literally, as the chopper pulled away after the first load of fish, we all gave each other high fives and yahoos, and just as we did that, two little fish jumped out and did double flips.”
