The raw and rugged beauty of Devon Lakes and the nearby Clearwater River first cast its spell over Charlie Pacas back in the 1980s.
Years later, in his belief that national parks are essentially the last bastions of wilderness, the Parks Canada aquatics specialist began thinking about a daunting environmental restoration project in this remote region of Banff National Park.
The goal was to wipe out destructive non-native brook trout from two of the Devon Lakes and the upper reaches of the Clearwater River – and return the ecosystem to a pristine state.
“The lakes presented an incredible restoration opportunity,” said Pacas at the 16th annual Parks Canada research update series last Thursday (May 4).
“This was once a fishless system. These fish were never supposed to be there and they had totally changed the ecosystem.”
It was not an easy task by any means, but, after almost a decade of work involving more than 50 people in the field, there are now thought to be no more brook trout.
More than 5,163 non-native fish were eliminated from the middle and lower Devon Lakes and from a 7.3-kilometre stretch of the Clearwater River and its tributaries.
In the beginning, crews caught big fish in gill nets and electrocuted them, but when it became apparent it would take too long to get rid of all the fish that way, talk turned to poison or draining the lakes.
But, in the end, Parks decided to exhaust every other possible option before tinkering with a delicate ecosystem in Canada’s flagship national park.
The last fish were electrofished – which delivers an electric current into the water to stun or kill a fish – in what turned out to be an unprecedented and monumental electrofishing effort.
Pacas said the removal of fish through electrofishing is a “significant scientific achievement” as the total elimination of fish by this method has never been documented before.
“Many experts would have declared this impossible to do. The efforts were without impacts on the native aquatic community, including amphibians and invertebrates,” he said.
“We’ve returned these aquatic systems back to their natural states. We achieved it without using a poison or de-watering the river, which are the only two proven methods.”
The Devon Lakes are a chain of four alpine lakes that form the source of the Clearwater system, about 80-kms north of the Banff townsite.
The lakes were traditionally fish-free, but non-native brook trout were introduced into the lower and middle lakes in the 1960s for sport fishing.
Over the decades, the brookies managed to escape from these two lakes and make their way into the Clearwater River – home to threatened native bull trout.
The upper Devon Lake, isolated from the other lakes by a series of impassable waterfalls, was never stocked with fish and has served as an ecological benchmark for the project.
It was a joint project involving Parks Canada and the University of Alberta. Park crews caught the fish and the U of A documented changes in the water chemistry, algae and the phyto and zooplankton communities as a result of eliminating fish.
The formidable work got off the ground in October 2002 with three days of using gill nets in the lakes under extremely cold temperatures, windy weather and snowy conditions.
Over a three-day period, 158 brook trout were caught.
“We quickly realized the challenge we would face working in this remote and cold landscape,” said Pacas.
Then from 2003 to 2005, they set gill nets in the two alpine lakes and electrofished the upper reaches of the Clearwater River.
By the end of 2006, they were catching far fewer fish with gill nets in the lakes; however, they were still regularly catching fish by electrofishing the river.
“If we stopped electrofishing, all it would take would be two fish – one male and one female – to find each other at spawning time and reverse the trend that we had worked so hard to eliminate,” said Pacas.
“We also knew that there were more fish in the river. It became readily apparent that to catch the remaining fish, we would have to expend a huge amount of effort.”
It was at that point that several aquatic and ecosystem specialists came together in 2007 to discuss the options for removing the remaining, stubborn fish.
The options at the top of the list were poisoning the fish with Rotenone or draining the lakes – both proven techniques for eliminating fish, particularly in the U.S..
After considerable discussion and debate, Parks decided against both techniques, amid concerns that neither was the right approach for Banff National Park.
Instead, they decided to go with a novel approach of stopping or severely restricting the flow of the water leaving the lakes, rather than draining them.
Convinced they had eliminated all the fish in the lakes, they set up portable dams, known as aquadams, which are similar to those presently being used in the Manitoba floodings.
The dams aimed to substantially reduce the flow into the river and concentrate the remaining fish into pools, where it would be easy to electrofish them.
But the dams broke, and Parks was back to the highly labour intensive electrofishing efforts. “It was too bad it didn’t work,” said Pacas.
Not wanting the project to fail after years of work, they put all their efforts into electrofishing the river. In total, 3,294 fish were electrofished from the river.
In 2008, only one brook trout was caught, and in 2009, there was none.
In 2010, Pacas and his team returned one last time just to make sure. No fish were caught in the upper reaches of the Clearwater or its tributaries.
“I feel pretty confident we got all the fish out of there,” said Pacas.
David Schindler, considered one of Canada’s leading aquatics experts, said the work at Devon Lakes over the past 10 years is a “good news story”.
Schindler, who is a professor in the U of A’s Department of Biological Sciences, said they have already documented the recovery of a number of invertebrate communities that had been suppressed by the non-native fish.
“There are many streams and lakes in Banff that have suffered from alien species introductions in a previous generation that did not realize that they could harm native species such as bull trout,” he said.
Schindler said he knows of no other system this large where a non-native fish has been eradicated without the use of poison, noting other jurisdictions throughout North America can follow.
“It will inspire similar efforts in the USA,” he said.
“Parks Canada should be commended, and in particular, the persistence of Charlie and his team in doing this field work, often under very unpleasant weather conditions, are admirable.”
Pacas said a fisheries survey was conducted last year of the Clearwater River below a waterfall that acts as a barrier to fish and prevents them coming back upstream.
He said four teams of electrofishers worked a section of the river and captured 104 brook trout in one day, similar to efforts years earlier in the upper reaches of the river.
“Our efforts that day generated many thoughts into the Devon Lakes sequel,” said Pacas.
“I think we could probably do a pretty good job in that section of the river, too. It’s doable from an electrofishing perspective.”
