Evaluating carbon dioxide and sound as an invasive bigheaded carp (Hypophthalmichthys molitrix and H. Nobilis) deterrent in a model lock and dam

Abstract

Bighead (Hypophthalmichthys nobilis) and Silver (H. molitrix) carp, collectively referred to as bigheaded carp, are aquatic invasive fish that present a significant ecological threat to freshwater ecosystems across the United States. Since the wild establishment of invasive bigheaded carp in the early 1970s, their population and habitat ranges have grown exponentially throughout the Mississippi River and many of its connected tributaries (Kolar et al. 2007; Buck et al. 2010). Established populations have caused extensive ecological damage through resource exploitation, which has negatively impacted native planktivorous fish such as gizzard shad (Dorosoma cepedianum) and bigmouth buffalo (Ictiobus cyprinellus) (Irons et al. 2007; Sampson et al. 2008; Sass et al. 2014; DeBoer et al. 2018). The continued dispersal of bigheaded carp raises concerns about their potential establishment in habitats across the Upper Mississippi River (UMR) and the Laurentian Great Lakes (Larson et al. 2017; Ivan et al. 2020). Managing invasive bigheaded carp populations primarily relies on two strategies, capturing and removing established populations as well as using anthropogenic barriers to restrict movement. Preexisting dams on the Mississippi River act as a physical barrier that has fragmented the ecosystem and provided a buffer against unimpeded range expansion (Zielinski et al. 2018; Turney et al. 2022). However, their adjoining lock chambers provide fish with the opportunity to move upstream when lock gates are opened during vessel transit (Fritts et al. 2021; Vallazza et al. 2021; Turney et al. 2022). Because of this, multiple deterrent strategies are currently being investigated to restrict the movement of bigheaded carp through contained environments such as lock chambers. Previous studies have shown that broadband sound and CO2 can effectively modify bigheaded carp swimming behavior (Murchy et al. 2017; Vetter et al. 2017; Cupp et al. 2018; Borland et al. 2020). In this study, both stimuli were combined to create a multimodal deterrent for restricting the upstream movement of bigheaded carp. The deterrent strategy was evaluated within the lock chamber of a 10,000L recirculating model lock and dam system. Initially, schools of 10 bighead or silver carp were classically conditioned to associate broadband sound with the simultaneous injection of CO2 in the lock. After two days of conditioning, broadband sound alone was evaluated for deterring bigheaded carp from transiting upstream through the lock chamber during standard operations consistent with vessel traffic. For each school, a total of 28 sound trials were conducted over a seven-day experimental period. Bigheaded carp schools were tested under two different environmental scenarios to assess the deterrent’s efficacy under varying levels of motivational pressure to move upstream. First, bigheaded carp were provided food in the downstream pool throughout the experimental period and access to food was never restricted (Frett et al. 2025). Next, a new subset of food-motivated bigheaded carp were evaluated. Food was exclusively provided in the upstream pool throughout the experiment, and schools were trained to associate the upstream area with food availability. During experimental trials, access to concentrated food was only possible by transiting the lock and moving upstream despite acoustic deterrence (Chapter 2). Overall, broadband sound alone was 100% effective in restricting the upstream passage of conditioned bigheaded carp under standard lock operations, as fish were deterred from entering and transiting the lock chamber for 28 consecutive trials over a seven-day period. Avoidance behaviors remained consistent throughout the experimental period and conditioned bigheaded carp did not show habituation to the sound deterrent. The presence of food upstream did not impact deterrent efficacy, as food-motivated bigheaded carp remained deterred from transiting the lock during sound trials. These results build on previous experiments and highlight the potential of using a multimodal stimulus to deter the upstream movement of bigheaded carp through lock chambers.