Salmon may have been too tired to navigate Whitehorse fish ladder, research suggests

The chair of an advisory group on managing salmon stocks in Yukon says there are lots of questions to be answered about why fewer salmon seem to be reaching and passing through the Whitehorse fish ladder.

Al von Finster, chair of the Yukon Salmon Sub-committee, says the numbers have been down in the last few years and 2020 was a particularly tough year for spawning salmon in the Yukon River.

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.

von Finster said the water was high in the river all of last summer, making it harder for salmon to travel upstream to reach Whitehorse, and then have enough energy to navigate the fish ladder around the Whitehorse hydroelectric dam.

"So first, the fish just simply weren't there. Secondly, the fish had to fight against the current going up and I think some of them probably were just exhausted when they hit the dam," he said.

"But what it does show is that there is something going on, and it should be looked into in 2021 and in succeeding years."

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.

Running a marathon, then climbing a mountain 

William Twardek, a Carleton University PhD student who's been studying Yukon River chinook salmon, says his four-year research project has found that some fish simply can't make it past the fish ladder to reach their spawning grounds.

He tagged some fish downstream from the fish ladder to see how they fared.

"Some of the salmon that approached the fish ladder would swim partly up the fish ladder, maybe leave, come back in, and some of them would basically turn around before making it all the way upstream to Schwatka Lake and the rest of their migration," Twardek said.

Twardek says the fish ladder is inherently challenging for fish that have just swum hundreds of miles upriver.

"It's sort of like running a marathon and then being asked to climb a mountain or, you know, run a really fast sprint," he said.

Twardek said some fish ladders elsewhere seem to be very successful, with high numbers of fish seeming to make it through — so it might be worth taking a closer look at those.

"Perhaps there's some opportunity to look at how those fish ladders are designed to see if maybe there are some changes that could be made," Twardek said.