POPULATION PROJECT

An Avista facility near Thompson Falls is being touted as a success in helping grow local bull trout populations. Avista has been capturing and tracking bull trout at the mouth of Graves Creek since 2002 using weir traps. In 20 years of improving the process to capture more fish, company representatives have also seen an increase in bull trout population.

"It's nice to see that it's working and succeeding," Sanders County Commissioner Claude Burlingame said during a tour of the Graves Creek permanent weir trap last week. Eric Oldenburg, Fisheries Biologist with Avista, provided the tour last Tuesday to county commissioners.

At the Graves Creek facility along Blue Slide Road west of Thompson Falls, Oldenburg explained how juvenile bull trout are caught and tagged. The fish are then transported by truck and released below Cabinet Gorge Dam so that they can make their way to Lake Pend Oreille, which Oldenburg said is optimal water for bull trout to grow. "Pend Oreille is warmer and there is more food for the fish, so they grow bigger," Oldenburg noted. Because of the difference in temperature from the stream to the river, the fish are acclimated in tanks for 24 hours as the water temperature rises before they are released. Oldenburg said the mortality rate in the transportation process has been minimal.

When Avista started the bull trout project in 2002, they were using conventional weir traps and screw traps that were not very efficient. From 2002 until 2012 when a permanent weir trap was built, an average of 52 juvenile bull trout were captured and transported each year, Oldenburg said. "The permanent weir trap basically tripled our capture efficiency, so from 2013 through 2018 we averaged 164 per year."

Bull trout has been listed as a threatened species with the U.S. Fish and Wildlife Service since 1998. Avista, as part of its licensing process with the Federal Energy Regulatory Commission, developed the Clark Fork Settlement Agreement (CFSA) that brought together 27 entities - including government agencies, tribes and other organizations - to develop projects that help mitigate the effects of the Noxon and Cabinet Gorge dams on the local landscape and watersheds. One of several goals of the CFSA management committee has been to increase fish passage and restore native salmonid fish populations, including bull trout.

The CFSA management committee and entities such as Montana Fish, Wildlife & Parks, U.S. Fish and Wildlife Service and Idaho Fish and Game have worked for decades to develop the Graves Creek project and increase the bull trout population in the area. "The CFSA is a great collaborative process. The contributions of agencies and partners have greatly helped shape the success we have found in Graves Creek," Oldenburg noted.

Oldenburg explained the behaviors of bull trout and how, like salmon, they prefer to spawn in the same streams they were born. With that, the bull trout captured at Graves Creek will work to get back to the stream once they mature in Lake Pend Oreille. Avista also aids in the process and transports adult bull trout back to Graves Creek to spawn. A trap recently finished at Avista's Cabinet Gorge Dam allows the company to study the adults coming back upstream to spawn. These efforts have also helped increase bull trout numbers at Graves Creek. From 2019 through 2021, an average of 442 juveniles were caught at the Graves Creek weir trap.

"This trap is working amazingly well," Oldenburg said. "The juvenile bull trout density in Graves Creek has been higher than any other stream in the area. We have seen growth at every step in the process. We're getting more fish up here than the stream can handle and that's a big win." Avista also is working to increase bull trout populations in Vermilion River and the East Fork of Bull River. Oldenburg said main stream connectivity has always been a problem for the bull trout. Avista's efforts to help get the juveniles to Lake Pend Oreille, bypassing two dams and countless predators, is helping. "Some juveniles do make it to Lake Pend Oreille on their own," he noted.

Improvements to the permanent weir trap at Graves Creek were completed last fall. Oldenburg said Avista worked with the management agencies and engineers for several years to implement the best design. Some of the problems addressed in the final design included fish escaping from the trap, issues with high water in the spring, and mink getting into the traps and eating the fish. The permanent structure is built with concrete and the metal traps have screens to help keep the fish safe in the trap and allow Avista more control over the water going through the trap. "The shore-based trap keeps the fish safe and is working really well," Oldenburg said. Avista visits the facility each day to tag and transport the fish.

Ten antennas placed in the creek capture data as fish approach the trap and the Clark Fork River. With the data collected, both in location and with genetics, Avista can pinpoint where a fish originated and where it needs to return for spawning.

Oldenburg said a forthcoming proposed project the CFSA management committee is developing is to transport some juvenile bull trout above Graves Creek Falls to evaluate whether it is feasible to expand the range of bull trout within the stream. If successful, the expanded range would likely also increase the overall abundance of this population, he added.