Fate and behavior of rotenone in Diamond Lake, Oregon, USA following invasive tui chub eradication.

In September 2006, Diamond Lake (OR, USA) was treated by the Oregon Department of Fish and Wildlife with a mixture of powdered and liquid rotenone in the successful eradication of invasive tui chub Gila bicolor. During treatment, the lake was in the middle of a phytoplankton (including cyanobacteria Anabaena sp.) bloom, resulting in an elevated pH of 9.7. Dissipation of rotenone and its major metabolite rotenolone from water, sediment, and macrophytes was monitored. Rotenone dissipated quickly from Diamond Lake water; approximately 75% was gone within 2 d, and the average half-life (t½) value, estimated by using first-order kinetics, was 4.5 d. Rotenolone persisted longer (>46 d) with a short-term t½ value of 16.2 d. Neither compound was found in groundwater, sediments, or macrophytes. The dissipation of rotenone and rotenolone appeared to occur in 2 stages, which was possibly the result of a release of both compounds from decaying phytoplankton following their initial dissipation. Fisheries managers applying rotenone for fish eradication in lentic environments should consider the following to maximize efficacy and regulatory compliance: 1) treat at a minimum of twice the minimum dose demonstrated for complete mortality of the target species and possibly higher depending on the site's water pH and algae abundance, and 2) implement a program that closely monitors rotenone concentrations in the posttreatment management of a treated water body.