Effects of Rotenone on Columbia Spotted Frogs Rana luteiventris during Field Applications in Lentic Habitats of Southwestern Montan

Fisheries managers are restoring native populations by removing nonnative fishes worldwide. Increasingly, the piscicide rotenone is used to accomplish this. Fish introductions and removals change the aquatic environment, and it is important to consider the impacts of these actions on nontarget species, including amphibians. Laboratory experiments have shown that rotenone can negatively affect tadpoles. We therefore assessed the effects of rotenone used on two wild amphibian populations. The commercial piscicide formulation CFT Legumine (5% rotenone) was applied at 1 mg/L (50 μg/L rotenone) to a lake containing nonnative trout in Yellowstone National Park (YNP) in 2006 and two fishless wetlands on private lands in southwestern Montana in 2008. Amphibian surveys were conducted immediately prior to and after the rotenone treatments to obtain tadpole population estimates. Follow-up surveys were conducted 1 year posttreatment to estimate tadpole recovery. In YNP, additional surveys were conducted 2 and 3 years postapplication to observe longer-term effects of fish removal and the subsequent introduction of native fish. Within 24 h following application of rotenone, there was 100% mortality in gill-breathing tadpoles, but nongill-breathing metamorphs, juveniles, and adults were apparently unaffected. In the years following, tadpoles repopulated all waters and population levels were similar to, or, in the case of YNP because of concurrent fish removal, higher than pretreatment levels. In YNP, tadpole abundance and distribution decreased after westslope cutthroat trout Oncorhynchus clarkii lewisi were stocked in the treated lake.