Spatial Analysis of Forestry Related Disturbance on Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi): Implications for Policy and Management

Abstract

A landscape scale analysis of anthropogenic and natural disturbance indicates a significant negative relationship between the cumulative effects of forestry-related activities and the relative abundance of westslope cutthroat trout (Oncorhynchus clarkii lewisi, cutthroat trout) in southeastern British Columbia. Cutthroat trout abundance within 6 Kootenay River headwater streams ranged from 0.00 to 0.0325 fish/m2. Univariate analyses within a blocked regression design resulted in statistically significant (p < 0.05) negative relationships between cutthroat trout abundance and road density, roads on erodible soils, roads within near-stream zones and two measures of logging to the stream bank. There was no statistically significant relationship between cutthroat trout abundance and equivalent clear-cut area (km2/km2). Roads over erodible soils within near-stream zones emerged as the most significant individual variable. A multivariate model to predict cutthroat trout abundance included roads within near stream zones and recent logging adjacent to streams. Evidence from this study indicates that logging of non-fish bearing perennial and ephemeral streams is likely a key factor that has negative downstream effects on cutthroat trout abundance. Contrary to many conventional forest management approaches, this study suggests that considering the spatial distribution of disturbance is at least as important as the total amount of disturbance and that disturbance types can accumulate to produce negative effects on cutthroat trout abundance. The forestry-fish relationships that result from this project provide guidance for forest policy and planning, fish habitat monitoring and cutthroat trout conservation management.