Third time a charm? Sturgeon strategy altered
May 11, 2013
Flows sent down from northwest Montana’s Libby Dam with the intent of benefiting endangered Kootenai River white sturgeon will take a new shape this year in an ongoing attempt to lure the big beasts away from badly functioning spawning areas and onto gravelly river bottoms believed to be prime habitat for reproduction.

A double-peak strategy submitted this week by the U.S. Fish and Wildlife Service and approved for implementation by the U.S. Army Corps of Engineers will be the third flow manipulation strategy employed since the 2006 Kootenai River white sturgeon biological opinion was released in 2006.

Endangered Species Act BiOps assess whether federal actions, such as the existence and operation of Libby Dam, jeopardize the survival of listed species, such as the Kootenai sturgeon and bull trout in that river system.

BiOps often include prescriptions – reasonable and prudent alternatives – for improving the lot of the affected species. Among the requirements in the 2006 BiOp issued by the USFWS are requirements for minimum volumes of water to be released to augment flows for sturgeon in springtime, when natural flows historically rose to a peak called the freshet. That sturgeon volume depends on the anticipated volume of spring runoff.

Natural flows changed as a result of Libby Dam, which was built in the 1970s. Flood control and power production operations are believed to be one of the reasons for a considerable decline in white sturgeon reproduction and, as a result, the overall population.

Initial efforts to provide a several days-long “pulse” of water in 2008 and 2009 were deemed unsuccessful at changing the sturgeon’s spawning behavior, with most activity still taking place in silt-bottomed areas downstream of Bonners Ferry instead of gravel beds upstream more likely to produce successful spawning and production of juvenile sturgeon. Those operations stayed within the dam’s powerhouse capacity.

That lack of success triggered a three-year experiment called for in the BiOp that pushed the pulse volume up from powerhouse capacity of about 25,000 cubic feet per second to 35 kcfs, which included an additional volume of up to 10 kcfs sent through spill gates. The Corps operates Libby Dam.

“Telemetry data for spawning Kootenai sturgeon females from 2010-2012 indicate that the spill tests did not facilitate a change in Kootenai sturgeon spawning and migration behaviors. Given the results from 2008-2012 sturgeon operations at Libby Dam, a different approach to managing the sturgeon volume is warranted,” according to a system operation request presented by the USFWS’ Jason Flory Wednesday to the Technical Management Team.

The TMT includes representatives of federal, state and tribal hydro and fish management entities. They meet to consider dam operational operation that might be implemented to improve fish survivals.

“The objective of the 2013 sturgeon augmentation operation described in this SOR is to provide two periods of peak river stages/flows during the spring run-off period.

“The first peak, timed to low-elevation run-off below Libby Dam, is intended to provide sturgeon cues to begin upstream migration and staging.

“The second peak, timed to high-elevation run-off above Libby Dam, is intended to provide sturgeon cues to migrate further upstream from their staging areas and spawn towards the end of the second peak and/or on its descending limb.

“Overall, the goal is to provide conditions that will enable sturgeon to migrate to, and spawn over, rocky substrates that exist upstream of Bonners Ferry,” the SOR says.

“We’re tying other things, flow-wise, to see if we can affect a change” in sturgeon spawner behavior, Flory said.

“We need these fish to spawn in gravel,” whether that means bringing fish upstream, or bring gravel to the downstream areas where the sturgeon have been spawning, Flory said.

The placement of suitable spawning substrate in downstream spawning areas is part of an ambitious habitat restoration led by the Kootenai Tribe of Idaho and outlined in its Kootenai River Habitat Restoration Master Plan.

Each of the peaks is expected to last up to a week. The first would be triggered when a regional team of biologists determines that local tributary run-off at lower elevations downstream of Libby Dam is peaking.

Outflow volumes would be held at 20-25 kcfs for 5-7 days without using spill, which stirs up totaled dissolved gas that can be harmful to resident fish downstream of the dams.

Outflows would then backed off to levels that allow the maintenance of at least 18 kcfs at Bonners Ferry. The Kootenai River is nearly 450 miles long. Beginning in British Columbia, Canada, the river flows through northwest Montana and northern Idaho, and then turns northwest back into British Columbia.

Increased discharge from Libby Dam would begin again up to full powerhouse capacity when the team of biologists determines that the high-elevation run-off in the Kootenai Basin has begun.

“Actual peak discharge during this second peak will depend on local conditions (i.e. river stage at Bonners Ferry).

“Selective withdrawal gates at Libby Dam above elevation 2,326 mean sea level will be placed to within 30 feet of the surface of the reservoir prior to the end of the second peak, described above, allowing for release of warmer surface water as the receding limb of the hydrograph commences,” the SOR says.

“Release of warmer water from Libby Dam, in combination with lower volume of release, will allow the Kootenai River temperature to increase to appropriate spawning temperatures at Bonners Ferry (8-10 degrees C) during the receding limb of the hydrograph.”

The first pulse could start as early as this weekend, the Corps’ Adam Price said. Warmer than normal temperatures have prevailed and were forecast to continue. That has hastened snowpack meltdown.