Common carp are a widespread, invasive fish that negatively impacts habitat and water quality in lakes. Practical and selective removal strategies are needed for carp. Previous research showed that bait can be used to selectively attract large numbers of carp in lakes.
An overarching goal of this project is to develop a new way to effectively and selectively remove invasive common carp from Minnesota lakes. Selective, effective, and safe methods are needed to remove large numbers of carp from lakes to restore water quality and ecological services. One method shows exceptional promise: carp can be selectively attracted with food to form large foraging aggregations that can be removed with specialized nets with high precision. However, to make these nets effective, researchers need to understand how to maximize carp foraging aggregations using two key social learning strategies: increasing access to bait to allow both frequent visitors (often “bold”) and infrequent visitors (often “shy”) to participate in foraging aggregations, and releasing individuals that might bring other carp to the aggregation.
A Phase IV was recently announced. Read more about it below! As of August 2021, whole-lake experiments were conducted as planned. In the first summer, researchers conducted experiments in two lakes, setting up two baiting stations in each. In the second summer, the team decided to focus on one lake (Parley) where they set eight baiting stations. 300 carp were tagged in each lake with PIT tags and PIT detection antennas were set at each feeding station and operated the whole season; 100,000s of detections were recorded. To examine social feeding behaviors of wild carp, the team analyzed this high resolution, spatio-temporal data using a Gaussian mixture model (GMM) approach to detect group associations. Based on these associations, researchers analyzed group size, feeding bout duration, and the heterogeneity and connectivity of carp social networks at foraging sites. The team found that wild carp foraging is social, easily induced by bait, dominated by large individuals, and potentially predictable, which suggests social behaviors could be leveraged in management of carp. Next efforts should focus on synchronizing carp aggregations at the bait so that more of them can be removed from baited sites.
Also of note, while the leader-follower hypothesis might offer some management benefits, a larger obstacle needs to be addressed first – overall, methods for capturing carp that already aggregate at the bait need to be improved to increase capture success. While many tagged carp are attracted to the bait daily, only a fraction of them are captured. This is because different carp visit the bait at different times of the day and for various periods of time while the removal (lifting nets), even if conducted during peaks of carp activity, is conducted instantaneously capturing only the carp that are present at the bait at that particular time. Synchronizing carp aggregations at the bait (focus of the next phase of this work) should ameliorate that problem to a significant degree.
Phase IV: Acoustic conditioning in common carp to accelerate removal and reduce cost
Researchers will test if the invasive common carp can be conditioned (trained) to associate sound with bait so that more of them aggregate at the bait and from larger areas to enhance physical removal strategies. There is a need for effective, safe, selective and scalable technologies for removing common carp from lakes. Currently, simple bait- and-remove strategies can remove 20-40% of carp in one season. However, the efficacy of these strategies may be significantly increased by using acoustic conditioning to ensure that carp aggregations at the bait are more synchronized and that more carp are attracted to the bait from larger areas. Acoustic conditioning has been shown to be effective in the lab and researchers will now test it in the field. Acoustic conditioning is easy to implement, inexpensive and will have minimal effects on native wildlife. This research will result in an effective, selective and easy to implement management strategy for carp in Minnesota and elsewhere. Management methods developed through this research proposal may be most applicable in situations where winterkill/drawdown to manage carp populations is not desired or possible, in small to medium sized basins where carp re-entry can be managed and especially in systems where carp recruitment is limited to seasonally unstable peripheral basins.
Phase III: Social learning and carp removal
The third phase of this project is researching carp personality traits and social learning strategies, and how these could be used to optimize baiting strategies and maximize carp removal efficacy. Research has shown that carp can be selectively attracted with food to form large foraging aggregations that can be removed with specialized nets with high precision. However, to make these nets effective, we need to understand how to maximize carp foraging aggregations using two key social learning strategies: increasing access to bait to allow both frequent visitors (often “bold”) and infrequent visitors (often “shy”) to participate in foraging aggregations, and releasing individuals that might bring other carp to the aggregation. We will examine these strategies in four natural lakes. This work combines basic and applied research and will result in implementation-ready management strategies.
Phase II: Bait and switch
The second phase of this project tested whether common carp can be baited and killed using corn pellets with antimycin-a, a natural fish toxin, without harming other species. Carp have a unique diet (plant seeds, such as corn, which native fish are not attracted to) and can be trained to aggregate in baited areas. Researchers first needed to determine the concentration of antimycin-a needed and the species-specificity of the approach. They then conducted trials to test this “bait and switch” concept with carp of different sizes in experimental ponds.
Researchers incorporated an EPA-approved toxin antimycin-A (ANT-A) into corn pellets, which the carp consume with high specificity and performed 4 experiments: 1) gavage trials which showed that the bait was toxic at 8 mg/kg; 2) leaching trials which showed that <1% of ANT-A leached out of the bait and did not cause mortality among native fish; 3) lab trials where carp were stocked with three native fish which showed that 46% of carp and 76% of fathead minnows perished after one application of pellets, but perch and bluegill were not impacted; and 4) pond trials with carp, bluegills and perch which showed that 37% of adult carp perished after 6 days of pellet application, while no perch and bluegill did. These results suggest that corn-based toxic pellets could be developed to selectively target carp but more work is needed to minimize impacts on native minnows.
By summer 2018, researchers had found that carp do not show the ability to avoid bait that contains antimycin-A. This is an important precursor to using this technology for control. Researchers designed and tested three different corn-based pellets in ponds, and found that common carp are attracted to and consume corn, while white suckers do not. Carp mortality was increased by introducing the antimycin-A-laced corn-based pellets.
During fall 2018, researchers moved to experiments in a natural lake, starting with dummy pellets that are not laced with antimycin-A. This was done to evaluate how carp can be trained in a lake, what percentage can be trained, if there are differences among individual carp in response to bait, and whether any native fish might be attracted to the pellets. Over 400 carp and 800 native fish were implanted with PIT tags, a site was baited with corn for over a month while an electronic antenna positioned at the bait continuously monitored which fish visited the bait and when (check out footage from the underwater camera here). Carp responded to the baiting immediately; roughly 1,600 carp were attracted to the carp each day. Native fish were not attracted to the bait. This tells us that corn can be used to selectively attract large numbers of carp. Toxins could be incorporated in corn-based food pellets, or the carp that aggregate at the bait could be captured in nets.
Overall, this phase of this project showed that a) maintaining healthy bluegill populations in lakes could serve as an important biocontrol strategy for carp in Minnesota; b) common carp readily consume corn pellets that contain a toxin and cannot distinguish between pellets with or without the toxin; c) only carp were attracted to the corn-based pellets. This means that toxins could be incorporated or corn could be used as bait to train carp to form large feeding aggregations that could be targeted using simpler and safer means than toxins, such as nets.
Phase I: Biocontrol using bluegills
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 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.
Dr. Bajer is the founder and owner of Carp Solutions, which develops management strategies for invasive fish. These interests have been reviewed and managed by the University of Minnesota in accordance with its Conflict of Interest policies. If you have concerns that your employment or academic efforts are being improperly directed due to his interests in Carp Solutions, you can contact MAISRC Director Nicholas Phelps, or Associate Director of the Conflict of Interest Program Jon Guden at [email protected] or (612) 626-4727.