Comparative Effects of Rotenone and Antimycin on Macroinvertebrate Diversity in Two Streams in Great Basin National Park, Nevada

We used rotenone and antimycin A to eradicate nonnative rainbow trout Oncorhynchus mykiss and brook trout Salvelinus fontinalis as part of a program to reintroduce Bonneville cutthroat trout O. clarkii utah in two streams in Great Basin National Park, Nevada. These treatments followed standard protocols for piscicide application and provided a unique opportunity to compare the effects of the two piscicides on macroinvertebrate diversity over a short spatial and temporal window. Antimycin A had minimal effects on macroinvertebrate diversity. Total species richness and that of Ephemeroptera, Plecoptera, and Trichoptera (EPT); total and EPT density; and Simpson index values were reduced significantly more with rotenone than with antimycin. The Hilsenhoff biotic index increased with rotenone but decreased with antimycin A. Rotenone also had greater effects on species composition. The proportions of EPT taxa, shredders, and filterers were less than expected when rotenone was used, whereas scraper proportions were greater than expected. The proportions with antimycin A did not differ from those expected. No taxa were lost from antimycin A-treated sites, but four taxa were still missing from rotenone-treated sites 1 year posttreatment. Of these four taxa, however, two were collected 3 years posttreatment. We suggest that antimycin A be used rather than rotenone if minimizing the effects on macroinvertebrates is important. Recovery was relatively rapid with both piscicides, however, and if the short-term impacts on macroinvertebrates are not a concern, the use of rotenone may be appropriate.