After 50 years, westslope cutthroat trout are returning to a lake in Banff National Park

For the first time in 50 years, westslope cutthroat trout are swimming back into Secret Lake—a conservation feat that Parks Canada experts have worked to achieve for more than a decade.

High in Banff National Park’s Skokie Valley, experts have worked through trial and error to restore ideal habitat for trout on Alberta’s native and at-risk west slope. This summer, thousands of fish strong enough to survive in the wild are once again swimming freely in the lake.

“I can’t even believe we’re finally getting cutthroat trout back on the west slope, it’s like the pinnacle of our work,” said biologist Megan Goody. “One day I thought we’d never see, but here we are.”

Fertilized eggs are transferred from the incubator to downstream side incubators that protect them from predation. The buckets cradle the growing trout and simulate the nesting environment as the water flows through the pipes and the valve is set up in the moving stream.

Karly Upshall carries tubes that form streamside incubators that help trout grow in Hidden Lake. (Helen Pike/CBC)

For those walking by, it doesn’t look like anything other than an assortment of pipes you’d find at Home Depot. But for those working on the project, it means years of hard work are finally paying off.

If all goes well, in five years this small fishing population will be mature enough to reproduce.

“They were self-sufficient in this lake in the 50s,” said Shelley Humphries, a water expert. “So we expect them to do well in this lake in the future.”

Fertilized eggs are transferred from the incubator to incubators on the far side of the stream, where they are protected from predation. (Helen Pike/CBC)

The challenge began in the 1900s, when officials introduced non-native species to many of the lakes in the National Park to preserve them for anglers looking to catch interesting fish. The park stopped the practice decades ago, but the damage was done.

Brook and rainbow trout flourished and overwhelmed native species. Then the increase in water temperature made it difficult for the fish to survive.

Across the park, they now occupy less than 10 percent of their historic area.

Located in a remote corner of the Skokie Valley in Banff National Park, Hidden Lake is an ideal spot for trout reintroduction because it is cool and secluded. (Helen Pike/CBC)

“These feed the ospreys and the bears,” Humphries said. “It’s not the same time bears and birds spawn because bears and birds are here. We’re righting a mistake we made here about 50 years ago.”

To correct this error, Parks had to perform several high-profile battles:

  • Fish need cool lakes to thrive.
  • They had to find genetically pure trout because they bred for years with introduced populations.
  • Introduced species, namely non-native brook trout, were to be removed from Hidden Lake.

When the province first listed cutthroat trout at risk, Humphries said they began a spawning survey to find out where these fish were nesting.

Then a chance discovery helped establish Hidden Lake as the ideal habitat for this conservation project. They found a waterfall downstream.

A waterfall in Banff’s Skokie Valley protects at-risk fish. (Helen Pike/CBC)

“It’s not on our maps and you can’t see it from aerial photos,” Humphries said.

“We’re very happy to have that waterfall in the valley. It’s going to stop the trout from coming back here and undo this conservation project that we’re doing.”

Protected by nearby glaciers and a downstream waterfall to keep it cool, Hidden Lake became the refuge the team sought.

Then they set to work, first trying to manually remove the non-native species by netting, fishing and electrofishing. But it proved frustrating and ultimately unsuccessful.

Water treated with rotenone is pink, but the color disappears as the water flows down. (Provided by Parks Canada)

“After about four years, we realized it wasn’t really working,” Humphries said. “We were still getting a lot of reproduction of introduced brook trout, so we had to change methods.”

That’s when they decided to take a new path and introduce rotenone, a natural fish toxin derived from plant roots.

Humphries explained that the pink powder is added to the water and enters the fish’s system through the gills, preventing it from breathing at a molecular level. It is toxic only to fish and is not dangerous to humans, mammals or birds at the levels used.

“It rapidly decays spontaneously in the sun and decays together with the turbulent water that flows through it.”

It was more efficient, he said.

Two years later, that treatment offered Parks a blank slate—a lake free of any fish and ready to reintroduce cutthroat trout to the west slope.

Humphries added that a whole new process has begun: finding the hardiest fish that have the best chance of survival.

“They’re threatened. There aren’t that many of them and we can’t just go get them somewhere. We have to find them in the landscape,” Humphries said.

After training in the incubator and growing the eggs in a mobile incubator, the eggs are hardy enough to survive in the stream.

And these are alewives – newborn trout still carrying the yolk – swimming in buckets, inspected by Park rangers until they are ready to be released.

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