Infrared Imagery and Inert Media Used in Treating Upwelling Groundwater with Rotenone

Abstract Untreated upwelling groundwater from seeps and springs in and adjacent to surface water bodies has been long suspected of causing failed rotenone treatments by providing a refugia of nontoxic water. A possible solution involves the use of an inert media to carry the liquid rotenone to the source of upwelling groundwater and release rotenone over an extended period of time sufficient to affect the mortality of the target fish. In our initial study to address this problem, we used thermal infrared imagery (FLIR One) on a smartphone to locate groundwater that was subsequently treated with mixtures of the liquid rotenone formulation CFT Legumine (3.3% rotenone) utilizing two commercially available inert carriers: (1) CatSan Hygiene Litter (mixture of quartz sand and calcite) and (2) Vectocarb (fine powder of modified CaCO3). Trials on the mixtures were conducted in 2015 in upwelling groundwater areas of the Skibotn River drainage, Troms County, Norway, the site of previously failed eradication efforts. Following application, mean concentrations of 75.6 to 131 μg/L rotenone were present at 0.5 h in the pools and the brooks downstream of the upwelling groundwater that decreased and stabilized to 11.5 to 16.8 μg/L rotenone at 3 h. Both carriers have large surface areas (porosity) that transport (through sorption) the rotenone liquid to the source of upwelling groundwater and release (through desorption) concentrations of rotenone over at least 3 h. Both mixtures show promise in treating upwelling groundwater to eradicate fish from those areas and were used successfully in the 2016 retreatment of Skibotn River for the eradication of Atlantic Salmon Salmo salar infested with the ectoparasite Gyrodactylus salaris.