Sturgeon spill still planned at Libby

With a boost from recent precipitation, it appears that spilling water for Kootenai River white sturgeon is still on track at Libby Dam.

Although Kootenai Basin snowpack is just 68 percent of average, water availability for Lake Koocanusa is sufficient so far to allow water to be released over the dam’s spillway in June, said Brian Marotz, a Montana Fish, Wildlife and Parks fisheries official and a member of an interagency white sturgeon recovery team.

“Unless things change radically, we are moving toward a spill this year,” said Marotz, who met with anglers in Libby this week to discuss the matter. “We will lock it all in during the first week of May.”

The operation would involve releasing 25,000 cubic feet per second of water through the dam’s powerhouse, and an additional 10,000 cfs over the spillway.

The intent is to provide flows that will entice sturgeon to move into optimal spawning habitat upstream from Bonners Ferry, Idaho.

For the spill to proceed, Marotz said, adult sturgeon tagged with sonic transmitters need to be in position, the correct temperatures need to be available through the dam’s selective withdrawal system, and there needs to be sufficient water in the reservoir.

Lake Koocanusa is currently at an elevation of 2,402 feet, well shy of the full pool elevation of 2,459 and short of the 2,420 that is physically necessary to release water through the spillway. The reservoir is projected to reach 2,420 by mid-May, Marotz said.

There are also limitations on the spill specified in a permit issued by the Montana Department of Environmental Quality.

There are limits on gas levels in the river below the dam that will be elevated by the spill, and the spill cannot last longer than seven days.

The permit was necessary to provide exemptions from Montana’s Clean Water Act, which prohibits excessive gas levels that can cause gas-bubble trauma in fish.

Marotz said state fisheries officials will be on the river six hours during the day and six hours at night during the spill, monitoring for distressed fish. Thresholds have been set for numbers of bull, cutthroat and rainbow trout and whitefish that are detected with gas-bubble trauma.

If thresholds are exceeded, the spill operation will be stopped.

Based on observations from past emergency spill operations in 2001 and 2006, Marotz does not expect to see much of an impact on fish that inhabit waters below the dam. However, kokanee salmon that pass through the spillway will be impacted.

“People should expect to see a lot of kokanee,”  he said. “They come over the spillway and that’s a pretty wild ride. What happens is they are disoriented that they will turn up in shallow water, and they get gassed. Nearly 100 percent will have gas-bubble trauma.”

Marotz added that “a lot of those fish will survive.”

Marotz said sturgeon far downstream will be monitored closely to determine the effectiveness of the spill operation.

“What we’re looking for is a change in behavior in the adults,” he said, adding that if at least 40 percent of the sonic-tagged female adults move upstream from Bonners Ferry and stay there for at least five days, it will be considered a success.

Since Libby Dam was built in 1972, successful sturgeon reproduction in the river has been almost nonexistent because most spawning has occurred below Bonners Ferry, in sediment-covered riverbed that has inhibited egg survival.

The Kootenai Tribe of Idaho has an elaborate hatchery operation that has augmented the endangered sturgeon population, keeping it from the brink of extinction.

Reporter Jim Mann may be reached at 758-4407 or by e-mail at jmann@dailyinterlake.com