Project background
Common carp (Cyprinus carpio), an invasive fish from Eurasia, dominates lakes of south-central Minnesota. The carp ‘flip’ shallow lakes into turbid, non-vegetated basins and by doing so destroy feeding and breeding grounds that were once used by waterfowl. The carp also reduce recreational use of lakes by increasing water turbidity. Attempts to control carp in Minnesota date back to 1930s when large seine nets, or rotenone were used to rid lakes of carp. Those simplistic efforts brought disappointing results, however, as they were not backed by solid science on processes that drive carp abundance.
MAISRC researchers have explored innovative methods to manage invasive common carp populations, starting with a study on the potential of bluegills as a natural biocontrol agent. Through whole-lake and pond experiments, researchers assessed the impact of bluegill presence on carp recruitment. In lakes stocked with bluegills, carp offspring were reduced by a staggering 11 times compared to lakes without bluegills. The experiments also revealed that bluegills prey on carp eggs and larvae, effectively curbing recruitment. Further analysis of Minnesota DNR data suggested that winter aeration could prevent fish kills in shallow lakes, supporting bluegill populations and enhancing their role as a biocontrol strategy.
Another promising approach involved the use of antimycin-A, a natural toxin, embedded in corn pellets to target carp selectively. Corn, naturally attractive to carp but not native fish, successfully baited carp in laboratory, pond, and field trials. While the toxin-laced pellets significantly reduced carp numbers with minimal impact on native fish, fathead minnows were also affected, underscoring the need for refinement. Field trials showed that corn attracted large aggregations of carp while native species remained disinterested, positioning corn-based baits as a dual-purpose tool for either direct removal or toxin delivery.
The social foraging behavior of carp presented another opportunity for targeted management. A study on a 258-acre lake found that a subset of carp, dubbed "superfeeders," repeatedly visited bait sites and dominated feeding activity. Although 54% of tagged carp were attracted to bait during the summer, inconsistent aggregation patterns limited removal efficiency, with only 27% of the carp population captured across three events. These findings underscored the need to synchronize aggregations, leading to trials in acoustic conditioning. By training carp to associate sounds with bait delivery, researchers aimed to improve synchronization and baited trap efficiency.
Acoustic conditioning trials showed significant potential. Laboratory studies revealed that carp retained conditioned responses to sound longer under partial reinforcement, while field trials demonstrated that combining bait with acoustic cues attracted 11% more carp and elicited a 30% faster response compared to bait alone. These findings highlighted the potential for reducing removal costs and enhancing efficiency. The research informs Minnesota’s carp management efforts, offering scalable, innovative strategies that combine natural biocontrol, selective baiting, and behavior-driven solutions to protect native ecosystems.
Phase I
Project manager: Przemek Bajer
Research team: Josh Poole
Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources
Project start date: 2015-2017
The first phase of this project tested whether bluegills can be used as a biocontrol agent for common carp through whole-lake experiments. Researchers conducted experiments on both moderately productive and very productive lakes, measuring carp and bluegill density over two seasons. Survival of carp eggs, larvae, and fry were monitored at appropriate intervals throughout the study. Water quality and zooplankton abundance (food for larval carp) was also measured as it might provide additional information about the survival of carp larvae and fry. This was tested in 6 small ponds. All lakes were stocked with adult carp and every other lake was stocked with bluegills. Carp offspring survival was assessed through electrofishing and mark-recapture.
At the end of the season, lakes with bluegills had 11 times fewer carp offspring than those without bluegills. This shows that biocontrol by bluegill is an important element of common carp management strategies. Researchers also analyzed previously collected MN DNR data to evaluate whether aerating shallow lakes in the winter affects carp recruitment. This showed that bluegill populations can be strengthened in many shallow lakes by winter aeration to prevent winter fish kills.
Phase II
Project manager: Przemek Bajer
Research team: Peter Hundt, Josh Poole
Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources
Project start date: 2017-2019
The second phase of the project explored using antimycin-A (a natural fish toxin) in corn pellets to selectively bait and kill common carp without harming native species. Carp, with their unique attraction to plant seeds like corn, can be trained to aggregate in baited areas. Researchers conducted a series of trials to test this approach. Lab and pond experiments showed promising results: the toxin-laced corn pellets effectively killed a significant proportion of carp while sparing native species like perch and bluegill. However, fathead minnows were also impacted, suggesting further refinement is needed to minimize non-target effects.
Field trials in natural lake settings reinforced the method's potential. Corn successfully attracted large numbers of carp without drawing native fish. Over 400 carp and 800 native fish were tracked using PIT tags, revealing that carp responded immediately to the bait while native species remained uninterested. This indicates that corn-based pellets could be used to either deliver toxins selectively or train carp to form aggregations for removal using nets. These findings, combined with the role of bluegill populations as a natural biocontrol, suggest innovative strategies for managing invasive carp while protecting native ecosystems.
Phase III
Project manager: Przemek Bajer
Research team: Peter Hundt
Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources
Project start date: 2019-2021
Previous research demonstrated the potential of bait to selectively attract carp, leading to an experiment designed to study their attraction mechanisms and removal efficacy. In a 258-acre lake with eight baiting sites and 300 carp tagged electronically, 54% of the tagged carp were drawn to the bait over the summer, with approximately 20% of the population visiting daily. A subset of carp, termed "Superfeeders," visited baited sites almost nightly and were notably larger than others. Feeding occurred primarily at night, with dynamic aggregations forming and dissolving over several hours. Despite the nightly activity, only 27% of the carp population (3,602 individuals) were captured across three removal events, with minimal native fish bycatch (<1%).
The results revealed that carp foraging is social, driven by species-specific bait, dominated by large-bodied individuals, and predictable. However, inconsistent visitation patterns among individual feeding groups limited the efficiency of removals. Synchronizing carp aggregations at baited sites is a promising next step, with acoustic conditioning trials beginning in January 2022. This research has already informed carp management efforts in Minnesota, often involving volunteers to bait the fish. Future optimizations aim to enhance removal efficiency, advancing this innovative approach to managing invasive carp populations.
Phase IV
Project manager: Przemek Bajer
Research team: Rebecca Bullers
Funded by: MAISRC and the Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources
Project start date: 2022-2024
Acoustic conditioning, where carp are trained to associate a sound with bait delivery, was investigated as a means to enhance this method by promoting larger, more synchronized feeding aggregations.
Two studies evaluated the potential of acoustic conditioning. In a laboratory experiment, carp trained to respond to an acoustic cue remembered the conditioned behavior longer under partial reinforcement than continuous reinforcement. In a field study at Lake Minnetonka, sites using both bait and an acoustic cue attracted 11% more carp and elicited a 30% faster response to bait compared to bait-only sites. These findings suggest that acoustic conditioning could improve baited trap efficiency and reduce removal costs. Discussions at the inaugural Common Carp Workshop in March 2023 emphasized the need for funding, legislative support, and streamlined permitting processes to advance carp control strategies.
Media
- Controlling the common carp, Echo Press, 2014