Responses of invasive silver and bighead carp to a carbon dioxide barrier in outdoor ponds

Resource managers need effective methods to prevent the movement of silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) from the Mississippi River basin into the Laurentian Great Lakes. In this study, we evaluated dissolved carbon dioxide (CO2) as a barrier and deterrent to silver (278 ± 30.5 mm) and bighead (212 ± 7.7 mm) carp movement in continuous-flow outdoor ponds. As a barrier, CO2 significantly reduced upstream movement but was not 100% effective at blocking fish passage. As a deterrent, we observed a significant shift away from areas of high CO2 relative to normal movement before and after injection. Carbon dioxide concentrations varied across the pond during injection and reached maximum concentrations of 74.5 ± 1.9 mg·L–1 CO2; 29 532 – 41 393 μatm (1 atm = 101.325 kPa) at the site of injection during three independent trials. We conclude that CO2 altered silver and bighead carp movement in outdoor ponds and recommend further research to determine barrier effectiveness during field applications.