Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

We tested our ability to eradicate nonnative Brook Trout Salvelinus fontinalis by electrofishing from 1.7 to 3.0-km treatment reaches of six streams to conserve sympatric populations of native Westslope Cutthroat Trout Oncorhynchus clarkii lewisi. Brook Trout were successfully eradicated from treatment reaches in four of these streams. Eradication success was related to stream size, distribution and abundance of Brook Trout, years of treatment, number of treatments per year, amounts of instream and riparian cover, cover reduction efforts, and beaver ponds. At least 6, and up to 11, removal treatments of two to four passes per treatment were required to successfully eradicate Brook Trout. Brook Trout were suppressed in two other streams, but dense riparian vegetation, beaver dams, and abundant woody debris in and along channels prevented eradication. Eradication by electrofishing cost US$3,500 to $5,500 per kilometer where no riparian vegetation or woody debris clearing was necessary, but US$8,000 to $9,000 per kilometer where clearing was needed. These treatment costs were similar to costs of eradication using piscicides. Eradication by electrofishing may be preferable where native fish still occur because they can be saved during removal efforts and because electrofishing may be more acceptable to the public than piscicides, thus requiring less time and effort to prepare environmental assessments.