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 and currently occupy about 59% of their historic habitat. Due to hybridization with non-native species such as rainbow trout, genetically pure populations persist in only 10% of that range. A westslope cutthroat trout population with relatively high genetic purity (97%) and conservation importance persists in less than two linear stream miles in the headwaters of the South Fork Madison River in southwest Montana. The relative purity of this population has been maintained through the presence of a downstream intermittent reach. However, spring flows fill the intermittent reach, creating a connection between occupied westslope cutthroat trout habitat in the headwaters and the habitat of competing trout species downstream.To prevent continual invasion of non-native trout during spring runoff and the associated hybridization and competition risks to cutthroat trout, it was proposed to create a fish barrier by blasting the granite ledge rock of the stream channel and excavating the blasted material. In so doing a four foot waterfall could be created which was deemed sufficiently high to prevent upstream passage of fish.This paper will further describe the challenges presented by the terrain, the remoteness of the project, the close proximity of an abandoned railroad culvert of historic significance, as well as a nearby 400 kva power transmission line owned by the Bonneville Power Administration. This paper will further describe the ways in which these challenges were met, and how some favorable geologic structure of the rock ledge proved to be highly beneficial to the project.