Common carp management using biocontrol and toxins
This project will test whether common carp can be baited and killed using corn pellets with antimycin-a, a natural fish toxin, without harming other species. Although other biocontrol strategies – such as using bluegills to consume carp eggs – are successful on some lakes, they are unsuccessful on lakes which are prone to winterkilling. 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 will first determine the concentration of antimycin-a needed and the species-specificity of the approach. They will then conduct trials to test this “bait and switch” concept with carp of different sizes in experimental ponds.
This project will also test through whole-lake experiments whether bluegills can be used as a biocontrol agent for common carp. Researchers will conduct experiments on both moderately productive and very productive lakes, measuring carp and bluegill density over two seasons. Survival of carp eggs, larvae, and fry will be monitored at appropriate intervals throughout the study. Water quality and zooplankton abundance (food for larval carp) will be also measured as it might provide additional information about the survival of carp larvae and fry. Researchers will also analyze previously collected DNR data to evaluate whether aerating shallow lakes in the winter affects carp recruitment.
Researchers tested two new methods to control common carp. First, they tested biocontrol, which is the ability of native bluegill sunfish to control carp reproduction by consuming their eggs and larvae. 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. Bluegill populations can be strengthened in many shallow lakes by winter aeration to prevent winter fish kills.
Second, they tested if toxic bait could be developed to target carp without impacting native fish. This is important in lakes where biocontrol is unlikely. 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. Additional research into carp personality traits and social learning strategies, and how those could be used to optimize baiting strategies and maximize carp removal efficacy, is ongoing.