Westslope cutthroat trout reintroduced to Cascade Creek near Banff

It's a project that's been in the works for decades but in June 2024, Parks Canada reintroduced westslope cutthroat trout (WSCT) into Cascade Creek just north of the Banff townsite.

"We introduced 18,000 eggs into Cascade Creek, which is quite a lot," said Nicole Sulewski, Parks Canada field biologist.

"Through checking our incubator units, we saw about 97 per cent hatch success, which was far more than we even thought we would see. We were expecting maybe 80 per cent."

Sulewski has been on the Cascade Creek restoration team for more than five years and says the eggs came from adult WSCT in Marvel Lake, fertilized onsite and incubated in a portable hatchery in Field, B.C., for about three weeks.

"They reached what's called the eyed egg stage, so you can see the little eyes on the eggs," she said.

"At that point, they are a lot more resilient in there and ready to be moved, so then we moved those eggs into incubator units, right into the stream right here in Cascade Creek."

Dan Struthers, Cascade Creek project manager, says the eggs have been in the creek for close to 10 weeks and now the fish are small, measuring about 70 to 80 millimetres.

"At this stage, they're hiding from predators," he said.

"They don't like to come out during daylight hours, they're more nocturnal at this stage, so they're in amongst all those large cobbles and boulders, kind of waiting for it to get darker. If we were to snorkel this at night, we would see all kinds of fish schooling about looking for food but during the day, they're kind of hunkered down."

Struthers says the 2013 flood worked to their advantage by hitting the reset button on Cascade Creek.

A large volume of water rushed down, cleaning debris and years of silt from the creek bed.

"We consider it a catalyzing event, so without that flood, we wouldn't have had improved infrastructure at the dam to provide more flow coming through," he said.

"So there's a bunch of variables at play there."

Over the past few years, Parks Canada has worked to improve the aquatic habitat by building riffle pools and adding boulders and woody debris for the fish to hide.

"A riffle provides all kinds of good services for fish," Struthers said.

"It provides oxygen because it turns up the water, it makes it very turbulent and that mixes oxygen in the water. If you don't have the oxygen, you don't have fish, you don't have bugs, so you provide a food source. It's a conveyor belt for a food that comes right into the face of the fish that are hanging out just below those riffles, waiting for their meals."

Westslope cutthroat trout are a native species but hold "threatened" status in Banff National Park.

That's likely because in the 1960s, Parks Canada stocked a variety of fish to attract anglers. Those other species of trout dominated and WSCT were hard to find in the park.

"We've since learned a lot more about the science of fish ecology," Sulewski said.

"We've learned that some of the fish species that were introduced, like brook trout, which were introduced here in Cascade Creek, that they're actually invasive and they can outcompete a lot of our native species."

Parks Canada will continue to stock Cascade Creek for the next two years, creating different age classes of fish in the habitat.

"They'll start to spill over downstream into the Bow River and start to colonize other little tributaries and we might have cutthroat in a larger extent in the park and in the Bow River watershed in general," Struthers said.

"Then, we can use this creek to take fish from eventually and stock other places in the park, because we'll know that they're genetically suitable and they're free of diseases."