Telemetry evaluation of carbon dioxide as a behavioral deterrent for invasive carps

Abstract

Carbon dioxide (CO2) mixed into water is being explored as a possible management strategy to deter the upstream movements of invasive carps through navigation locks and other migratory pinch-points. This study used two-dimensional acoustic telemetry to assess the effectiveness of dissolved CO2 as a chemosensory deterrent to two carp species in a large U-shaped pond. Free-swimming movements of telemetered bighead carp (Hypophthalmichthys nobilis) and grass carp (Ctenopharyngodon idella) were documented 24 h before treatment and 24 h during treatments at 60, 121 and 213 mg/L CO2 (mean concentrations in pond water). Several behavioral endpoints were then quantified and compared to evaluate deterrence efficacy. In general, results showed that both carp species responded similarly to CO2 treatments. Carps consistently relocated into areas away from the injection site and made fewer attempts to re-enter CO2 treated areas. On average, CO2 treatments reduced mid-line crosses between untreated and treated sides of the pond by 58% at 121 mg/L CO2 and 78% at 213 mg/L CO2 relative to normal swimming movements recorded before treatment. Fish swim speeds increased significantly when inside the CO2 plume during treatments during 213 mg/L CO2 trials relative to swim speeds outside the plume, possibly indicative of active searching and avoidance responses. Overall, this study found that CO2 altered the behavior of bighead carp and grass carp. Natural resource agencies could consider the CO2 concentrations identified in this study to inform future applications to deter invasive carps from locations where they are at-risk to move upstream.