Biologists monitoring impact of high flows on sturgeon
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| A Kootenai Tribal Hatchery technician shows a young Kootenai River White Sturgeon ready for release. |
The U.S. Army Corps of Engineers operated the dam for pure flood control purposes this year, a change from past years when flows and temperatures have been adjusted in efforts to test and improve sturgeon spawning conditions.
This year, the dam was scheduled to conduct a spill test, releasing water over the spillway to boost flows so as to coax sturgeon into moving into prime spawning habitat in the stretch of river known as "the braided reach" just upstream from Bonners Ferry.
Unprecedented low elevation snowpack feeding Kootenai River tributaries led to high flows for weeks on the river, requiring restraint on the part of Libby Dam operators and negating the need for the spill test.
"The main thing was to keep Bonners Ferry from getting wet," said Brian Martoz, a Montana Fish, Wildlife and Parks biologist and a member of the interagency White Sturgeon Recover Team. "Just the way it came off, the water was just below flood stage at Bonners Ferry and stayed there for a month, and that allowed us to achieve the conditions that the spill test was going to produce without actually having to spill."
But the sheer duration of high flows was a bit different than a spill would have produced, and there were sustained cold water temperatures in the river, different conditions than sturgeon have experienced with the Libby Dam went in in the late 1970s. There hasn't been a detectably successful sturgeon spawn since.
Idaho Fish and Game biologist Pete Rust and others have been watching whether this years' unusual conditions have a noticeable affect.
"The spawning season was a bit delayed," he said, noting that the first eggs collected on adhesive mats in the river bottom didn't appear until May 31, when they're usually picked up in the middle of May. Even with the delayed season, though, Rust said he anticipated that more spawners would move in the the brtaided reach than in other years.
But only four female sturgeon tagged with transmitters were detected moving into the reach, down from six last year. This year 28 fish were tagged and monitored, whereas last year there were 36 fish, which may account for the difference, as well as the very length of time the water ran high.
"If you have high, cold, dirty water, it's hard to catch them, and that's what we had for awhile," Rust said.