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

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.