High water expected to have some impacts on migratory fish

The flood-swollen Okanogan River at Shellrock Point on May 11.

Photo by Al Camp
The flood-swollen Okanogan River at Shellrock Point on May 11.



— High water flows in the Okanogan River system are expected to impact migratory fish, but it’s not yet clear how much.

State Department of Fish and Wildlife infrastructure at the Similkameen and Omak hatcheries are operating as intended, said Ryan Fortier, District 6 fisheries biologist.

The Omak Hatchery, on Jasmine Street, is fairly far from the river and is not likely to be threatened, he said. The Similkameen Hatchery is being monitored, but there is not an immediate concern to the facility.

High flows of the Okanagan River in British Columbia are likely to scour sockeye redds dramatically before the juveniles fully mature and depart the gravel, Fortier said.

“It is anticipated to result in very high mortality of the natural spawning populations,” he said. “We will not be able to fully understand the full magnitude until the juveniles return as adults in a few years.”

Steelhead have been known to suffer reduced spawning success in their traditional spawning locations as water dynamics reduce survival through scouring flows. However, it has been shown that steelhead move from their traditional spawning locations at higher proportions to seek out water conditions that are preferred, he said.

“This can result in steelhead moving to smaller tributaries - currently flowing like bigger tributaries - (where) we do not traditionally see them,” he said.

Summer Chinook juvenile survival is not completely clear.

“The redds are dug deeper than sockeye redds, which provides more protection,” he said. “They are also located in traditionally less depositional areas of the stream, which can reduce smothering. The timing of exit from the redds by the juveniles is occurring currently so one cannot tell if this flooding provides a benefit or hindrance to overall survival for the species.”

Water flows on the Similkameen River are not high enough to permit passage of anadromous fish past Enloe Dam, though there is no limitation to passage above Coyote Falls (Similkameen Falls), he said.

“In general, much of the fate for anadromous species is determined by the hydropower systems (migration) and ocean survival,” Fortier said. “We can do our best to create as many juveniles as possible here in the breeding areas, but if they encounter the same survival situations that have been driving them toward extinction, then the benefits are dramatically watered down.”

Resident fish should do fairly well, as they have adapted to these conditions historically and are not suffering the same life history pressures as the anadromous species from their migration - hydropower dams, he said.

“ I suspect they may flood up into the flood plains to avoid high water and take advantage of new food sources, but they should follow the same flows down into the historic channels as it recedes,” he said. “In general, too much water is less of an issue for fish than not enough.”



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