Researcher looks at why some chinook salmon don't make it up the Whitehorse fish ladder

William Twardek, a PhD student who's been studying chinook salmon migration in Yukon, says there's ample reason to be concerned about how the fish will survive a changing environment — but he's optimistic.

"They are pretty resilient animals. They've been around for a long, long time and there's been changes in the climate in the past and they've been able to adapt," Twardek said.

"So hopefully they're a flexible enough animal that they're able to stick around in the future. But you know, it's not going to be easy for them."

Twardek just received a $10,000 grant to continue his research on chinook in Yukon. Specifically, he and his research team are looking at how well the spawning fish manage to navigate around an unnatural barrier — the Whitehorse hydroelectric dam — using Yukon Energy's fish ladder.

It's a project being done in partnership with Yukon Energy as well as some local First Nations. 

Twardek, who studies at Carleton University, said the seed for his research was planted by a former supervisor who suggested looking at how well the fish ladder works.

"He told me all about this project and this amazing run of chinook salmon that comes up through the Yukon River to Whitehorse, and really painted this beautiful picture of what this project could be," Twardek said.

The four-year project has Twardek tagging salmon downstream from the fish ladder, to monitor and track their movements. So far, he's found that some fish just can't seem to find their way.

"We do see circumstances where fish are unable to find the entrance, or they may enter the fish ladder and spend a few hours in there before turning around and going back downstream," he said.

"It's mixed. Sometimes it works fairly well and at other times fish don't make it through."

Fewer chinook reaching the fish ladder

The fish ladder was built in 1959, soon after the hydroelectric dam was finished. According to Yukon Energy, it's the longest wooden fish ladder in the world.

Chinook reach the ladder after a long journey up the Yukon River from the Bering Sea. It's one of the longest upstream salmon migrations in the world. 

But the number of chinook reaching the fish ladder has dropped in recent years, and it's not clear why. Last year, it saw the lowest number of spawning chinook in more than 40 years — just 282 fish, compared to 690 in 2018, and more than 1,200 in 2017.

Twardek says his research is aimed at helping as many chinook as possible make it through the fish ladder to spawn upstream. That means figuring out why some fish don't make it.

"We're hoping with this that we'll be able to provide some information to hopefully make the fish ladder even better, so more salmon are making it upstream," he said.

"If you don't provide a way for them to get around that dam, you're going to lose that salmon population."

Sometimes it works fairly well and at other times fish don't make it through."- William Twardek, researcher

If the fish ladder represents a challenge for some fish, a changing climate can make that challenge even more difficult, Twardek says. He says the warmer the water, the faster a fish's metabolism is.

"So as the water gets warmer, the salmon are burning up the energy reserves a lot quicker. And that's going to make it tougher to get around the hydro dam," he said.

"Unfortunately, sometimes climate change makes a lot of the other challenges that salmon face a lot worse."

He hopes to be able to present some of his findings within a couple of years.

He says even if the number of chinook reaching the fish ladder is relatively small — they're an extremely important resource for many local communities.

"So I'm hopeful that this work will allow salmon to at least improve in their abundance over the coming years," he said.