The Mayo B rearing channel: ‘thinking fish first’

In 1952 the Mayo hydro power project began supplying electricity to Elsa, Keno City, the United Keno Hill mine and the community of Mayo.

In 1952 the Mayo hydro power project began supplying electricity to Elsa, Keno City, the United Keno Hill mine and the community of Mayo.

The dam and power house on the Mayo River were sufficient for the needs of the day … and for years after. However, engineers knew that the territory would inevitably require more power to meet residential and business demands.

What experts of the 1950s might not have foreseen was just how great an impact juvenile chinook salmon would have on that future project, the one we call Mayo B.

“Mayo B was always an option, it was first discussed back in the 1950s, but the need for the power wasn’t there yet,” says Travis Ritchie, staff biologist and manager of environment, assessment and licensing for Yukon Energy. And 21st-century needs did catch up with Mayo hydro. “In 2008 we started planning Mayo B; we began the process of assessment and permitting,” says Ritchie. But Mayo B might have remained on the shelf for many more years had the federal government not covered most of the cost, through the Green Infrastructure Fund.

Thus recharged, Yukon Energy engineers, EDI Environmental Dynamics Inc. biologists, territorial and federal fisheries experts, and the First Nation of Na-cho Nyak Dun combined their visions and their expertise to undertake a fish habitat-enhancement initiative unprecedented in the Yukon.

“As part of the Mayo B project, we understood that we were going to be making slight changes to the flow patterns of the lower Mayo River,” recalls Ritchie. “We saw an opportunity to both address the potential effects of the project but also an opportunity to enhance the ecological values of the river.”

Adding to infrastructure in place since 1952, Yukon Energy designed and built a one-kilometre juvenile chinook salmon-rearing channel parallel to the Mayo River.

“Beyond being just necessary, this was a unique opportunity to do something that hadn’t been done in the Yukon before, in terms of fish habitat,” says EDI fisheries biologist Ben Snow. “Basically what we had with the Mayo B project was an opportunity to try out a number of fish-habitat enhancement measures.”

Enhancement efforts were given a welcome boost by a pre-existing strip of local geography, says Snow. The new rearing channel followed the path of an abandoned side channel of the Mayo River.

“It was part of the ancient flood plain reclaimed by the land,” recalls Ritchie.

The remnant of that natural channel “basically didn’t look like much of anything,” says Snow. There was a slight depression covered by poplar and shrubs.

The first step in construction was to flag the path of the channel. Biologists walked its length keeping their eyes open for other creatures that could be displaced or harmed by construction work.

A Mayo-based contractor, “an artist with an excavator” as Ritchie and Snow describe him, then cleared the brush and cut the fresh channel. Then the task was to make the channel as fish-friendly as possible. This meant creating sections of shallow, fast water interrupted by calmer, deeper pool sections. The channel also follows a winding course, just like a natural stream, allowing for cut banks and other hiding, resting and feeding spots for juvenile fish.

Branches, root masses, logs and other pieces of forest debris were carefully placed through the channel to attract nutrients and create hiding places for juvenile chinook from pike, burbot, kingfishers and other predators.

The channel bed is made of the same material found in the natural side channel of the Mayo River: cobbles, boulders, sand and gravel.

EDI biologists, including Snow, had previously spent years studying the environment around Mayo. They learned from nature’s own designs for streams, and speculated on how best to connect these with manmade technology.

Flow from Mayo B can be controlled with a valve at the top of channel; this ensures the channel has a constant, but adjustable flow of water.

Fish are, of course, cold-blooded animals; their metabolisms benefit when water has been warmed on its passage through the powerhouse. The channel is further warmed by groundwater seeping up from beneath the bed.

The channel, which began flowing in 2012, is monitored during the summer and winter to ensure the tiny chinook are thriving, and that their habitat remains clean and healthy. Minnow traps allow biologists to take a closer look at the young fish.

“Think of it as a kindergarten for juvenile chinook,” says Snow. In this class, rather than adults of the species doing the rearing, the entire habitat takes charge.

Chinook spawn along the Mayo River in late summer. The eggs hatch in late winter. The juveniles move up into the channel for the following spring. After spending a few months to a year in the channel, they head back down the channel to the Mayo River, down the Mayo River to the Stewart – about eight kilometres away – and then down into the Yukon River and on to the sea.

Though the biologists had expected a longer wait before juvenile salmon took to the channel, the earliest fish showed up during the first autumn, says Ritchie.

Snow adds that they have been present ever since, and it appears from population numbers and fish size that they are thriving as well as – and sometimes better than – chinook elsewhere.

“This is really a prime example of thinking fish first,” says Snow. But, he adds, there is another very human component to the rearing-channel initiative. The public is encouraged to visit, walk the adjacent interpretive trail, and observe how young chinook behave and how the new channel functions. The Mayo B habitat-enhancement project provides exciting educational opportunities.

“And we’d love to build more of them,” says Snow.

This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at research/publications/your-yukon