Walleye surveys completed

NOXON - FWP recently completed spring walleye surveys in Noxon Reservoir. These surveys were conducted to determine optimal capture techniques, population demographics, reproductive potential, dietary habits and PCB concentrations within edible portions of walleye. Prior to initiating fieldwork, FWP developed a study plan to assure that our data needs were met. This plan was distributed to FWP’s Citizen Advisory Council and other interested individuals and sportsman’s groups. For 2014, the plan called for lethal samples to be collected from up to 101 walleye and stated that nonlethal samples would be collected from a target of 200 – 250 fish. We anticipated that less than 101 fish would be lethally sampled because few large and small walleye are captured. Walleye that were not killed were fin clipped, measured for length and weight, and tagged prior to release.

During 2014 spring surveys, FWP captured a total of 69 walleye. Of these, 35 were killed to collect biological and toxicological samples. The remaining 34 fish were released following data collection. Lengths of captured walleye ranged from a 17 inch male to a 30 inch female. About 38 percent of captured fish were female and the average length of all fish was just over 20 inches. Catch rates in 2014 were lower than anticipated likely due to cold water temperatures prior to high flows.

“Noxon Reservoir walleye remain a focus of FWP because they are an illegally introduced fish that pose a serious threat to the lower Clark Forks sport and native fish,” Lower Clark Fork Fisheries Biologist Kenny Breidinger said in a press release. “Walleye introduced into other waters that were not suitable for them have resulted in substantial negative impacts to the existing fisheries.”

According to Breidinger, these negative impacts have been documented and could happen in the Noxon Reservoir as well.

”Yellow perch and rainbow trout were devastated along with minnow and sucker populations following a walleye introduction into Canyon Ferry Reservoir. It is likely that walleye will have similar effects on Noxon’s bass, perch and trout populations because physical and biological conditions are not suitable,” Breidinger said.

FWP will continue to investigate walleye management options to minimize negative impacts to Noxon’s valuable fisheries. This winter FWP will release a draft environmental assessment that will propose a project to investigate the feasibility of walleye suppression.

**Courtesy of MT FWP.