Libby Dam flows increased for sturgeon
Libby Dam releases started ramping up last week under a plan with different approaches toward helping endangered white sturgeon in the lower Kootenai River.
A System Operation Request from the U.S. Fish and Wildlife Service was approved by a multi-agency panel in Portland, Ore., last week and was immediately implemented at Libby Dam, said Greg Hoffman, the U.S. Army Corps of Engineers biologist stationed at Libby Dam.
As with past years, the spring releases are aimed at increasing velocities to give sturgeon a better chance of reaching suitable spawning areas.
But this year's flows are also designed to assist a U.S. Geological Survey team that is conducting studies associated with sturgeon habitat in a stretch of river known as "the braided reach" upstream from Bonners Ferry, Idaho.
And as an intentional side benefit, Hoffman said, the peak flows are expected to "clean out" an algae problem that has developed through much of the Kootenai River below the dam over the last year, Hoffman said.
"It's something that we considered, because it has to do with the general health of the river," he said.
The spring sturgeon flows are being coordinated with a new plan to deliver fertilized sturgeon eggs to river stretches where they are expected to survive.
Biologists believe that the main reason for sturgeon declines in the river since the construction of Libby Dam can be traced to degradation of prime spawning areas.
"The theory is this: They are not spawning over appropriate substrate. They are spawning over sand right now. Those eggs hit the sand, they roll up and they suffocate," Hoffman said.
Through higher flows and other methods, biologists have been trying to get sturgeon to spawn in areas where the riverbed is made up of cobbles and gravels.
Last year, biologists pursued a "set and jet" program, in which adult hatchery-reared sturgeon were hauled in boats and released upstream from Bonners Ferry, in hopes that they would successfully spawn.
"This year, we're skipping the middle man, if you will, and we will be fertilizing eggs by hand," Hoffman said.
Biologists will first strip milt from male sturgeon. When they are ripe with eggs, female sturgeon will once again be transported upriver. "When they are ripe, you rub their bellies and the eggs will come out," Hoffman said.
Right on the river, the eggs will be mixed with the milt and strategically scattered in areas where they will have a chance to survive.
"Sites have been chosen where we think there is appropriate velocity, where predators won't get to them, and where the river bottom is composed of gravel and cobble," Hoffman said.
That is expected to happen in early June, well after next week's peak flows.
"But we will still be providing higher velocities for those eggs to survive," Hoffman said.
Libby Dam releases were scheduled to ramp up from 9,000 cubic feet per second this week to 20,000 cfs by Saturday, and a peak of 25,000 cfs by Monday. Those peak flows will be maintained for a week, and then they will be gradually reduced, reaching 15,000 cfs by June 2.
This year's sturgeon releases are being carried out over a three-week period, while last year's were carried out over four weeks.
Low-water conditions have classified this year and last year as "tier 2" water years, in which 800,000 acre feet of water is available for sturgeon releases. In a "tier one" water year, no water is made available for sturgeon.
This year's inflow forecast at Lake Koocanusa, projected for April through August, is about 5.2 million acre feet, compared to average inflows of 6.2 million acre feet.
The reservoir is projected to rise within four feet of its full-pool elevation of 2,459 by July 19, and it is expected to drop to 20 feet below full pool by the end of August. There were similar projections last year, but timely August rains kept reservoir levels higher than expected.
Lake Koocanusa did not drop to 20 feet below full pool until Nov. 15 last year.
Reporter Jim Mann may be reached at 758-4407 or by e-mail at jmann@dailyinterlake.com