Field evaluation of carbon dioxide as a fish deterrent at a water management structure along the Illinois River
Construction of a water management structure (WMS) in the levee surrounding The Nature Conservancy’s Emiquon Preserve (Havana, Illinois, USA) created a new hydrological connection and potential aquatic invasive species pathway between the Illinois River and a large conservation wetland complex. Site managers need a control tool that deters the upstream passage of non-native fishes into the wetland lakes, but does not interfere with normal gate operation and water discharge. This short field study evaluated carbon dioxide (CO 2 ) injected into water as a non-obstructive method to reduce fish abundance near the WMS culverts. We quantified relative fish abundance using underwater sonar with and without injection of CO 2 into culverts during three discharge events: no flow (0 m 3 /s), restricted flow (0.9 m 3 /s), and unrestricted flow (3.2 m 3 /s). Overall, CO 2 reached or exceeded our target concentration of 100 mg/L during no flow and restricted flow, and fish abundance was 70–95% lower at culvert entrances relative to untreated control days. The target CO 2 level was not reached during unrestricted flow and fish abundance was not reduced during CO 2 injection. Atmospheric CO 2 concentrations were inconsequential and unaffected by CO 2 treatments throughout testing. Results from this initial field study provide several considerations for CO 2 as a fish deterrent in natural environments.