Effect of rotenone treatment on alpine stream invertebrate communities in Colorado

Objective Introduction of nonnative salmonids to western United States streams has resulted in extirpation of native cutthroat trout. Once thought to be extinct, a genetically verified population of Greenback Cutthroat Trout Oncorhynchus virginalis stomias was identified and used for population reestablishment efforts. To restore native trout habitat, stream reaches above a dispersal barrier are typically treated with a piscicide (i.e., rotenone) to remove nonnative salmonids before reintroduction of natives. One concern with this method is the possible effect to nontarget invertebrates, which are an important food source for salmonids, and a drastic disturbance to invertebrates following rotenone treatment could negatively affect native salmonid establishment. Methods Two alpine streams were treated with liquid rotenone via drip stations during two consecutive days. Invertebrate communities were sampled for 6 years in two streams where Greenback Cutthroat Trout was reintroduced. Pre- and posttreatment sampling allowed for examination of short-term, intermediate, and long-term responses to invertebrate communities. Results Negative short-term (1–2 months) responses were detected for total taxa richness; Ephemeroptera, Plecoptera, and Trichoptera richness; and percent Heptageniidae density immediately following rotenone application. However, most community metrics returned to pretreatment values within 1 to 2 years posttreatment. Invertebrate community changes between pretreatment and 3 to 5 years posttreatment were observed with increased percent Chironomidae density and decreased percent Ephemeroptera, Plecoptera, and Trichoptera density. Conclusion This study provides insight into invertebrate community response to rotenone treatment in high alpine streams and adds to the current literature, which displays short-term declines in invertebrates following rotenone and recovery of most aspects of the initial invertebrate community within 1 year posttreatment.