Common carp are an invasive species and are prevalent in Upper Prior Lake and previously in Spring Lake (prior to a very successful seine in 2017 where roughly 70% of the population (17 tons) was removed). Carp can live over sixty years and grow to a length of more than 3 feet! They mature when they are 2-3 years old at which time they are roughly 1 foot in length.
Carp adversely impact water quality by uprooting aquatic plants, stirring up sediments from the lake bottom, and releasing harmful phosphorus, which can lead to algae blooms as well as reduced water clarity. Studies estimate the carp population in Upper Prior is approximately 3.5 times higher than the management level (recommended ecological threshold value for carp is 100 kg/ha).
After the successful seine of Spring Lake, the current carp biomass was calculated at 84.9 (±27.3) kg/ha, which is below the ecological threshold value of 100 kg/ha. Based on electrofishing by the Watershed District, the estimated carp population for Upper Prior is 342.45 kg/ha carp biomass and the estimate for Lower Prior is 9.72 kg/ha carp biomass.
Several important methods are underway to control carp including barriers, physical removal and biological control.
Barriers:
In 2016, the Watershed District began a Passive Integrate Transponder (PIT) tagging project that helped track carp movement. The small, coded wire PIT tags have been implanted in approximately 300 carp. PIT tags allow the District to track carp at all times of day and varying size/age of fish as they travel into or out of specific areas where receivers have been placed. The tags have also allowed the District to identify key areas carp enter during spawning season. The District now installs seasonal barriers in these areas to prevent carp congregation for spawning.
Adult Carp Removal with Seine Nets:
The PIT tagging project has helped to identify carp favorite hangouts during ideal seining seasons. The District anticipates that it will have one or two seine events in Upper Prior Lake over the next year in an effort to remove a significant portion of the population. This should help provide some significant water quality improvements in Upper Prior Lake.
Biological Control:
Young carp survive poorly in lakes that have abundant bluegill population. In fact, the Minnesota Aquatic Invasive Species Research Center (MAISRC) has identified that bluegills can control carp populations by consuming carp eggs and larvae, and thus limiting survival of offspring. The University of Minnesota is conducting studies on the relationship between bluegill and carp in hopes of determining appropriate bluegill stocking levels as an ongoing potential carp management tool.
Carp Management is a multi-level and multi-organizational effort. The Watershed District hopes to successfully seine carp during the winter months. Barriers will be in place during spawning season and, ongoing research will provide us with data regarding the appropriate levels of bluegills for ongoing efforts of keeping carp levels well managed. Data from water quality monitoring of a nearby wetland area shows that the water going into this body is cleaner than the water going out during carp spawning season. The Prior Lake Association will continue to provide the community with updates on this massive effort as well as others that are implemented with the goal of improving the quality and clarity of our waters.
Sources: Minnesota DNR, Minnesota Aquatic Invasive Species Research Center and the Prior Lake-Spring Lake Watershed District