River may not be cold enough for fish
The Daily Inter Lake
Chilling out the Kootenai River in November and December to improve spawning conditions for burbot hasn't been easy, but there are plans to try it again this year.
The Technical Management Team, a committee that operates federal hydroelectric dams in the Northwest, plans to pursue temperature control using a "selective withdrawal" system in Libby Dam that works well in the summer but not so well in the winter.
The committee last week requested more information on past temperature control efforts from Vaughn Paragamian, a fisheries biologist with Idaho Fish and Game who specializes in the Kootenai River burbot.
"We want to provide the coldest water possible, and November would be a good month to start," Paragamian said in an interview this week.
But it is questionable whether selective withdrawal can be effective at that time of year, he said.
That's because Lake Koocanusa "turns over" before November, mixing water to a point where there is little temperature variation at different depths. During the summer, the deepest water is much colder than surface water, allowing the selective withdrawal system to effectively mix and control the temperature of water released from Libby Dam.
"The issue is, how cold can we make it in November through December?" Paragamian said.
Last year, early November releases were almost 4 degrees Fahrenheit above the temperature target.
Water temperatures are crucial for burbot, an inland cod species that spawns in the winter.
"It's essentially a marine fish that evolved to a freshwater form, so they still retain a lot of the marine characteristics of cod," Paragamian said.
And temperature profiles on the Kootenai River were vastly altered by the construction of Libby Dam.
"The water is much, much warmer than it was before the dam" during winter months, Paragamian said. "You have this enormous body of water that's been warmed over the summer and you release it over the winter for power generation."
Prior to the dam, water temperatures dropped to 5 degrees Celsius (41 degrees Fahrenheit) by early November. Since the dam was built, the river has not cooled to that temperature until late December, Paragamian said.
Idaho Fish and Game tagged 11 burbot with radio transmitters that allowed them to be monitored for three spawning seasons.
"We found that with six specific fish, the migration and movement for spawning didn't happen until temperatures started falling below 5 degrees Celsius," Paragamian said.
The "motivation to move" didn't come until late December, and that presents a conflict - the Kootenai River is running high because Libby Dam is being operated for winter power production.
A Canadian researcher did a study that found that burbot have the lowest swimming endurance out of 20 types of freshwater fish, Paragamian said.
"They aren't built for swimming against high-velocity flows for very long," he said.
Reproductive success was severely hindered when Libby Dam was being operated for peak power production, with widely varying flows, Paragamian said.
Flows would drop to 4,000 cubic feet per second and burbot would start moving, but then flows would suddenly rise well above 20,000 cfs.
"When they peaked flows, the burbot would stop swimming and drift downstream again," he said. Discharge and temperature changes "have complicated the life history cycle of burbot tremendously."
Paragamian said the Kootenai River burbot population has been in steep decline. "We've gone from 400 fish 10 years ago to maybe 40 now," he said.
And that has made it even more difficult to monitor the fish and how they respond to selective withdrawal and flow changes.
"It's getting more difficult to expect to get measurable biological effects with the fewer and fewer fish we have," he said. Only seven fish are currently tagged with transmitters and Paragamian said he'd be fortunate to catch and tag a few more this winter.
Reporter Jim Mann may be reached at 758-4407 or by e-mail at jmann@dailyinterlake.com