New research findings support use of biocontrol for common carp
A team of MAISRC researchers recently completed first-of-their-kind experiments on the use of bluegill sunfish for the biocontrol of common carp. They found that bluegill predation had a significant effect on common carp recruitment and that bluegills could be harnessed to reduce carp’s reproductive success. While previous evidence had suggested this possibility, it had never before been tested experimentally in natural lake systems.
Bluegills already naturally control carp in some lakes by consuming their eggs and larvae. But because bluegills often don’t live in marshes due to winterkill, carp have learned to migrate there to spawn. This research set out to evaluate whether increasing bluegill populations throughout the year, using tactics like aeration, would limit carp populations.
To conduct this research, MAISRC graduate student Josh Poole, led by his advisor Dr. Przemek Bajer, selected six small experimental lakes in 2016 and 2017. Each lake was big enough to have natural properties like a littoral zone with vegetation and internal food webs. They stocked bluegills in half of the lakes, waited until the carp had spawned and for their young to hatch and become free-swimming, and then sampled for carp during three different life stages.
The results indicated that bluegill predation had a significant effect on the abundance of post-larval carp, which were approximately nine times fewer in lakes with bluegills than those without.
“To our knowledge, this is the first experiment on the biocontrol of an invasive fish conducted using whole-lake manipulations over multiple seasons,” said Poole. “These results are applicable to the management of carp in shallow, productive lakes – like many found in southern Minnesota. It highlights the usefulness and benefits of winter aeration to keep bluegills alive in shallow marshes.”
“While biocontrol has many benefits, it is not a silver bullet,” added Dr. Bajer. Its applicability will vary among lakes. For example, some extremely shallow marshes may not be able to support abundant bluegill populations. Nevertheless, the use of biocontrol and winter aeration could and should be considered in many locations.”
Several tactics are currently in use to control common carp, such as winter seining for aggregations and electric barriers – both of which have benefits and major drawbacks. Researchers have been searching for a method to control carp that will be less labor-intensive and more successful. This team also completed a complementary set of preliminary tests to evaluate integrating a toxin into carp-specific bait. This project, which has now been tested in the lab and small, man-made ponds, will be moving to larger, more natural ponds and lakes later this year.
Common carp are one of the country’s most ubiquitous invasive species, but MAISRC has made significant strides toward controlling them. They cause damage to the ecosystem by rooting around in the bottom sediment for food, which reduces water clarity and contributes to harmful algal blooms, eutrophication, and habitat loss. Learn more about common carp and additional MAISRC research here.