Use of Explosives to Protect a Native Westslope Cutthroat Trout Population In the South Fork Madison River, Montana

摘要

Westslope Cutthroat trout have declined in distribution and abundance across their range andcurrently occupy about 59% of their historic habitat. Due to hybridization with non-nativespecies such as rainbow trout, genetically pure populations persist in only 10% of that range. Awestslope cutthroat trout population with relatively high genetic purity (97%) and conservationimportance persists in less than two linear stream miles in the headwaters of the South ForkMadison River in southwest Montana. The relative purity of this population has been maintainedthrough the presence of a downstream intermittent reach. However, spring flows fill theintermittent reach, creating a connection between occupied westslope cutthroat trout habitat inthe headwaters and the habitat of competing trout species downstream.To prevent continual invasion of non-native trout during spring runoff and the associatedhybridization and competition risks to cutthroat trout, it was proposed to create a fish barrier byblasting the granite ledge rock of the stream channel and excavating the blasted material. In sodoing a four foot waterfall could be created which was deemed sufficiently high to preventupstream passage of fish.This paper will further describe the challenges presented by the terrain, the remoteness of theproject, the close proximity of an abandoned railroad culvert of historic significance, as well as anearby 400 kva power transmission line owned by the Bonneville Power Administration. Thispaper will further describe the ways in which these challenges were met, and how somefavorable geologic structure of the rock ledge proved to be highly beneficial to the project.