Success! Common carp under control in Riley Chain of Lakes
Work in the Riley Purgatory Bluff Creek Watershed District culminated this fall with the exciting announcement that common carp in one of their sub-watersheds, the Riley Chain of Lakes, is under control. Work continues in the other sub-watershed, Purgatory Creek.
Nearly a decade of basic and applied research has gone into this project to understand common carp, a ubiquitous invasive species that infests many lakes, wetlands and rivers across southern and central Minnesota, including the metro area. This long-term project, which required cooperation from numerous partners, worked not just to understand common carp, but to use this knowledge to advance control efforts.
The common carp, which was originally introduced to the U.S. following citizen requests in the 1870s, was seemingly able to take hold due to its high fecundity, low mortality rates, resilience, and ability to exploit productive and degraded waters for reproduction. By uprooting plants and releasing nutrients from sediments, carp further degrade water quality and waterfowl habitat.
Despite the pervasive presence of common carp in Minnesota, it – like all species – has weaknesses. A team of researchers, led by Dr. Peter Sorensen and Dr. Przemek Bajer, has been researching how carp movement and distribution can be used for control.
Through the use of radio-telemetry to track individual fish, researchers found that carp are widely dispersed throughout lakes in the summer and fall, but begin aggregating in mid-December. These aggregations, which appear to be a social behavior, can be targeted with seine nets for removal. Researchers are still unsure how carp determine where to gather; there is no discernible difference in temperature or dissolved oxygen in the area they choose. As evidenced in Lake Riley, seining can be extremely effective: 90% of the carp population was removed this way.
During the winter, researchers use antennae and receivers (pictured) to track fish (known as “Judas fish”) that have been implanted with radio-tags. When conditions are appropriate and the fish are densely aggregated, the scientists then work with commercial fisherman to place nets under the ice, surround the fish, and remove them. Carp are highly sensitive to sound and will avoid the nets if targeting is imprecise or too noisy, or if the nets get caught on debris. They also seem to learn to recognize fishers, so the technique must be deployed strategically.
In order for seining to have long-term, sustainable effects on carp and water quality, Sorensen, Bajer, and their colleagues have determined that adult fish removal needs to be part of an integrated approach that also includes biocontrol using native bluegill sunfish that consume carp eggs and larvae, as well as aeration to prevent winterkills and keep bluegills alive. This approach – known as Integrated Pest Management – was developed and implemented for carp on the Riley Chain of Lakes and has successfully kept the carp population under control. It was the early success on that project that inspired the creation of the Minnesota Aquatic Invasive Species Research Center by Sorensen and will help guide future research and management plans for other Minnesota watersheds.
Congratulations to all the researchers and partners who have worked on the project, including the managers and staff of the Riley Purgatory Purgatory Bluff Creek Watershed District, Lake Riley Improvement Association, CH2M Hill Engineering, Barr Engineering, the City of Eden Prairie and private citizens. The Minnesota Environment and Natural Resources Trust Fund and the Riley Purgatory Bluff Creek Watershed District funded this critical work. Stay tuned to our website for more updates as we continue work on common carp in the Purgatory Chain of Lakes in 2015.