Environmental drivers of rotenone persistence in stream fish eradications

Abstract Objective Although rotenone has been used to remove nonnative fish populations in the United States since 1934, the factors influencing its persistence remain unclear, even though under- and overapplication have substantial social, financial, and ecological consequences. Here, we quantified the variation in rotenone persistence across streams and evaluated the environmental drivers associated with rotenone loss during treatments. Methods We measured physical and chemical stream characteristics that are hypothesized to impact rotenone persistence across 21 montane streams and collected rotenone mass flux measurements every hour for a 7-h treatment. We then fitted generalized linear models to quantify the influence of stream characteristics on rotenone persistence. Results Physical, chemical, and stream bed characteristics varied widely across the 21 sample reaches. Patterns in rotenone mass flux at our lowest measurement location showed high variability compared with upstream measurements. Vegetation, conductivity, and gradient were the strongest predictors in the generalized linear models and were all negatively associated with rotenone persistence. Conclusion The variability in rotenone persistence and the relatively strong influence of factors that influence rotenone persistence emphasize the need for practitioners to carefully consider rotenone treatments in streams. We suggest a framework and working model to help guide pretreatment surveys and bioassays that can greatly increase the potential for successful rotenone treatments.