F&G working with Forest Service, Idaho Power on Crooked River bull trout restoration project

A small, isolated population of bull trout in west-central Idaho is in peril due to rapid brook trout expansion, and Fish and Game, Idaho Power Company and the U.S. Forest Service are working together this summer to help prevent this population from blinking out. 

The bull trout restoration project will take place between Aug. 5 and Aug. 12. Idaho Fish and Game staff will treat the uppermost 2.8-mile stretch of the Crooked River drainage with rotenone to halt the upstream expansion of non-native brook trout and reduce competition for the native bull trout population. The treatment area will span from the headwaters near Summers Grave, downstream to the upper extent of Forest Service Road 50772 (Long Saddle).

A native fish population in peril

Crooked River, which feeds into Wildhorse River (a tributary of the Snake), is located about 16 miles west of Council in the Payette National Forest in Washington County. Bull trout are native to the drainage, but in recent years their distribution and abundance has been shrinking. In 2018, Idaho Power Company biologists found that bull trout occupied the upper 2 miles of Crooked River, but when they went back just a few years later they estimated that only 60 bull trout are occupying about half of that former habitat. 

“We suspect that increasing abundance and distribution of non-native brook trout in the upper end of Crooked River is pushing this bull trout population to the brink of elimination,” said Fish and Game’s Regional Fisheries Manager, Jordan Messner. “Without intervention, we would probably lose this bull trout population within a couple of years.” 

Fish and Game staff, Idaho Power Company staff, and US Forest Service staff are springing into action this summer to hopefully prevent the loss of this headwater, native bull trout population. 

Pressing the "reset button"

One of the objectives listed in Fish and Game's current statewide Fisheries Management Plan is to, in some locations, develop and implement management actions to reduce or eliminate non-native trout where necessary to protect native species. And that is exactly what will be taking place in Crooked River this summer. 

To kick off the project, US Forest Service staff are installing an upstream migration barrier in Crooked River (about 3 miles downstream of the headwaters) so brook trout will not be able to recolonize the newly restored habitat from downstream after the treatment takes place. Following installation of the barrier, Idaho Power Company crews will lead an exhaustive effort to collect all bull trout from the treatment area and temporarily relocate them to an instream holding pen on a nearby creek. 

Once the bull trout are safely out of the area, Fish and Game crews will treat the 3-mile reach of stream with rotenone to remove all brook trout from the treatment reach. After approximately a week in streamside tanks, and once the rotenone in Crooked River has been deactivated, the bull trout will be returned to Crooked River – free from the risk of continued competition and hybridization with non-native brook trout. 

“We’re hopeful that by removing the current threat of competition and hybridization with non-native brook trout in the treatment reach, this bull trout population can thrive and expand,” said Messner. “Crooked River has really good, cold, clean water, and that’s exactly what bull trout need to thrive.”

Using rotenone as a management tool

Rotenone is a chemical that blocks the exchange of oxygen across the gills of fish and essentially suffocates them, and it works in very low concentrations. When properly applied to ponds, reservoirs, and streams, rotenone is an extremely effective tool for fish control. 

While it is very effective at removing unwanted fish, it’s not selective — meaning it targets all fish in the treatment area, and not just the species that managers want to remove. In cases like Crooked River, biologists often use nets or electrofishing to remove nontarget fish before using rotenone so those fish can be restocked after the rotenone treatment. 

Rotenone degrades quickly, and it quickly starts to break down after it’s exposed to sunlight and organic matter. This characteristic makes rotenone very safe for human use. In fact, exposure to rotenone has never been linked to acute or chronic medical conditions in people. 

Nonetheless, an abundance of caution is still taken to make sure the public is not exposed to rotenone during treatments. That includes closing access to treated waterbodies until rotenone is neutralized. Applicators also use personal protective equipment and undergo training and certification through Idaho State Department of Agriculture to ensure the safe and legal use of this product.

During the treatment, there will be no public access to the treatment areas on Crooked River. All entry points into the treatment area will be signed with placards denoting access restrictions, and the public should expect heavy use of the following roads and trails for the duration of the project: Forest Service Roads 50772, 50654, 50061, 51820, and Trail 235. 

Past mistakes and changing philosophies

The Crooked River bull trout restoration project is one of several in the works throughout the state that will use rotenone to help restore native fish populations, like bull trout and cutthroat trout. 

These treatments are intended to eliminate nonnative brook trout in some areas that were introduced nearly 100 years ago. Using rotenone to address past stocking mistakes is a way fish managers can help native fish to thrive and improve fishing opportunity.