High water temperatures and low stream flows prompted Montana Fish, Wildlife & Parks officials to close northwestern Montana’s Thompson River and its tributaries to angling from noon to midnight daily until conditions improve.
With little relief in sight from Montana’s record-breaking heat, drought conditions threaten the Thompson River’s popular wild rainbow trout and native westslope cutthroat trout fisheries and its federally protected native bull trout population. The order takes effect today.
On the Thompson River, the flow Monday was 199 cubic feet per second (cfs), near an all time low for July 21. In addition, water temperatures in the Thompson River above the confluence of Fishtrap Creek have exceeded 73 degrees for five consecutive days, a combination that can turn lethal for trout.
"Flows do not usually drop to this level until September," Laura Katzman, FWP fisheries biologist in Thompson Falls, said.
FWP closes streams to fishing when low water conditions, and high temperatures combined with fishing pressure would lead to an unacceptable level of stress on fish. Fish are stressed by low flows, high water temperatures and competition for space and food. When fish seek refuge in pools, where the water is deeper and cooler, they become more vulnerable to anglers and predators. Fish can die from the higher water temperatures, lower oxygen levels and reduced resistance to disease. These threats can affect adult trout numbers in future years.
If conditions deteriorate, the river may be closed to all fishing. Biologists will continue to monitor the river, Katzman said.
The mandatory angling closure, which follows FWP’s Drought Contingency Plan, was approved by FWP Commissioner Mike Murphy based on the recommendation of Dan Vincent, FWP Region 1 supervisor, and Jim Vashro, FWP fisheries manager, both of Kalispell.
Under FWP’s drought plan, angling restrictions are called for on streams that provide habitat for bull trout when stream flows reach 1-in- 20-year lows and maximum daily water temperatures equal or exceed 60 degrees for three consecutive days. Water temperatures in areas inhabited by bull trout in the lower portion of the Thompson River have periodically exceeded 60 degrees since late June and recently exceeded 65 degrees for five consecutive days.
For all other trout, the water temperature to trigger angling closures is 73 degrees for three consecutive days.
The Thompson River drainage provides important bull trout spawning habitat. The bull trout spawning migration begins during spring run-off and continues through September when spawning occurs. Bull trout migrate from the Clark Fork River or Thompson River to Thompson River tributaries. Although it is not legal to fish for bull trout because they are listed as a threatened species under the Endangered Species Act, the closure will help reduce stress on the species, Katzman said.
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