Factors Influencing Successful Eradication of Nonnative Brook Trout from Four Small Rocky Mountain Streams Using Electrofishing

We successfully eradicated nonnative Brook Trout Salvelinus fontinalis by electrofishing from 2.4- to 3.0-km treatment reaches of four Rocky Mountain streams in Montana to conserve sympatric populations of native West-slope Cutthroat Trout Oncorhynchus clarkii lewisi. At least 6, and as many as 14, removal treatments of two to four electrofishing passes per treatment were required to successfully eradicate Brook Trout from these treatment reaches. We increased success by modifying our treatment efforts during this study from single annual treatments to several treatments a year to take advantage of autumn spawning and winter aggregating behavior. Eradication by electrofishing cost US$3,500 to $5,500 per kilometer where no riparian vegetation or woody debris clearing was necessary, increasing to $8,000 to $9,000 per kilometer where clearing was needed. Treatment costs without stream clearing were similar to costs of eradication using piscicides. Eradication by electrofishing may be preferable where native fish occur in sympatry with nonnative fish in smaller streams (base flow wetted widths <3.0 m) because native fish can be salvaged during removal efforts and because electrofishing may be more acceptable to the public than use of piscicides.