Trout Eggs Destroyed

Missouri River

A Montana biologist suspects most brown-trout eggs in a 35-mile stretch of the Missouri River were killed when a power outage and other problems at Holter Dam cut the river’s flow by more than 80 percent.

“We did impact the brown trout in that part of the river,” said Jon Jourdonnais, environmental sciences director for Montana Power Co. “But we don’t want to paint the picture that it was a total loss.”

However, George Liknes, a fisheries biologist for the Montana Department of Fish, Wildlife and Parks, said the impact on brown trout could be extensive, including residual effects from losses of aquatic insects.

Liknes said the area affected by the drawdown probably includes the Missouri from Holter Dam downstream to the town of Cascade.

The malfunction at the dam shut down three working turbines. The dam’s spill gates, frozen shut, could not be opened for 1-1/2 hours, dropping flow to 17 percent of normal.

The result was a flow reduction over a six-hour period exposing to freezing temperatures the eggs laid by the fall-spawning brown trout.

Impacts of the event could become most apparent in four or five years with a marked decrease in large brown trout available for fishing and for spawning, Liknes said.

But he said the entire age class of brown trout should not be lost, because there probably was no effect on eggs lain in tributaries of the Missouri River.