Project background
Invasive bigheaded and silver carp continue to threaten Minnesota waters as they attempt to move north through the Mississippi River. While dams can block fish movement, navigation locks remain a pathway that allows invasive carp to swim upstream. Building on earlier research that successfully prevented carp from passing through a model lock and dam, this next phase focuses on refining deterrent strategies that can be used in real-world navigation systems.
MAISRC researchers are working with a custom-built scale model lock and dam designed and constructed by the Applied Research and Engineering team at the St. Anthony Falls Laboratory (SAFL). With design input from researchers, SAFL created a tank that included features like lock and miter gates, a spillway, and systems to manage water flow.
In this next phase of this project, MAISRC researchers will use this model lock and dam to evaluate whether combining carbon dioxide (CO₂), sound, and strategically generated water currents can stop invasive carp while minimizing impacts on native fish. Previous research showed that carp could be conditioned to associate elevated CO₂ with a specific sound, allowing sound alone to deter their movement with remarkable success. This project will test whether that same approach affects native fish species, providing important information for designing barriers that selectively target invasive carp while allowing native fish to move freely.
The project will also investigate how bigheaded carp respond to water currents. Early observations suggest these fish are strongly attracted to certain flow conditions. By better understanding this behavior, researchers hope to develop methods that draw carp away from navigation locks, reduce their chances of moving upstream, or even concentrate them in areas where they can be more easily captured and removed.
All experiments will be conducted at the MAISRC containment lab, where researchers can safely test fish behavior under controlled conditions before applying the findings in the field. The results will help inform the design and operation of proposed invasive carp deterrent systems at locations such as Lock and Dam 5 on the Mississippi River and other high-priority navigation structures throughout the region.
This research can provide state and federal resource managers with practical, science-based tools to help prevent the spread of invasive carp while maintaining river navigation and protecting native fish communities. By improving selective deterrent technologies, this project moves Minnesota closer to effective, long-term strategies for keeping invasive carp out of vulnerable waters.
Phase I
Project title: Increasing effectiveness of bigheaded carp deterrents by carbon dioxide integration
Project manager: Allen Mensinger, Swenson College of Science and Engineering at University of Minnesota Duluth
Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources
Project timeline: 2021-2023
Research findings:
Researchers found that adding carbon dioxide (CO₂) to existing fish deterrent systems can improve their ability to prevent invasive bigheaded carp from moving upstream. In laboratory experiments, bubble curtains infused with CO₂ were more effective at blocking common carp than bubble curtains using air alone, while having only limited effects on a native fish species. This suggests that CO₂-enhanced barriers could help target invasive carp while minimizing impacts on non-target fish.
The team also tested a combined sound-and-bubble barrier, known as a Bio-Acoustic Fish Fence (BAFF). Adding CO₂ increased the barrier's effectiveness, raising blockage rates for both common carp and bighead carp. Although the improvement was modest, researchers concluded that even a small increase in effectiveness could make a meaningful difference in slowing the spread of invasive carp at critical locations such as locks and dams.
Researchers also demonstrated that bigheaded carp can learn to associate sound with rising CO₂ levels. After conditioning, the fish moved away from the sound source more quickly and stayed away longer than unconditioned fish. While this learned response weakened over time, the findings show that pairing sound with CO₂ has the potential to strengthen acoustic deterrents and could improve future barrier technologies.
The research shows that integrating CO₂ into existing deterrent systems is a promising strategy for reducing the spread of invasive carp. Future studies will evaluate these technologies in larger experimental systems and real-world lock and dam settings to determine how they perform under field conditions.
Phase II
Project title: Evaluating CO2/sound bigheaded carp deterrents in model lock/dam
Project manager: Allen Mensinger, Swenson College of Science and Engineering at University of Minnesota Duluth
Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources
Project timeline: 2023-2024
Research findings:
Researchers tested eight schools of bigheaded carp in a model lock and dam and successfully conditioned them to associate sound with carbon dioxide release. The deterrent system achieved a 100% success rate in preventing upstream carp passage through the lock during more than 200 trials. Before conditioning, the fish freely swam through the lock chamber and generally preferred the upstream pool. After conditioning, carp rarely approached the lock entrance and almost never entered the lock chamber. This is the first carp deterrent system to achieve a 100% success rate under these experimental conditions.
Phase III
Project title: Evaluating CO2/sound bigheaded carp deterrents in model lock/dam
Project manager: Allen Mensinger, Swenson College of Science and Engineering at University of Minnesota Duluth
Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources
Project timeline: 2024-2026
Research findings:
Researchers continued to advance a promising non-physical deterrent that combines sound and carbon dioxide (CO₂) to prevent invasive bigheaded carp from moving upstream through navigation locks and dams. Building on earlier work that achieved 100% success in laboratory trials, the team confirmed that the deterrent remained fully effective even when carp were motivated by a food reward, with no fish passing the barrier during testing.
The project is now focused on understanding how the deterrent could perform under real-world conditions. Recent experiments found that just three conditioned fish were able to influence the behavior of seven unconditioned fish, resulting in a 98.8% deterrence rate for mixed schools. Researchers are also studying how water flow, sound propagation, and CO₂ dispersal affect barrier performance, generating data that will help guide future field deployment in navigation locks and other waterways.