The Minnesota Department of Natural Resources and the U.S. Fish and Wildlife Service have been using environmental DNA (or eDNA) technology to detect invasive carp in the St. Croix, Mississippi and Minnesota rivers. May sampling in the St. Croix River showed silver carp eDNA about four miles north of where invasive carp have been confirmed in the St. Croix.
eDNA is DNA released from an organism into the environment that is detectable at very low concentrations. USFWS screens for three markers: one for silver carp, one for bighead carp and one general invasive carp marker.
“While eDNA results are not conclusive evidence that invasive carp were present, eDNA is another helpful tool the DNR and partner agencies are using to learn more about invasive carp movements,” DNR Invasive Fish Coordinator Grace Loppnow said.
Due to the nature of eDNA and of invasive carp movements, caution must be taken in interpreting these results. eDNA analysis detects DNA in the water but cannot determine whether the DNA came from a living fish or another source such as bird feces or a fish carcass. It also does not determine when the DNA was deposited in that area. Invasive carp are highly mobile, so it is not unexpected that they would range throughout the open stretch of the Lower St. Croix River. For example, since 2017 the DNR has been tracking a tagged bighead carp on the St. Croix that has a home range of about 23 river miles. Tracked invasive carp in other states are known to range more than 60 miles.
USFWS staff notified the DNR last week that eDNA samples from May showed a small percentage of positive samples in the St. Croix River at Andersen Bay near Bayport and the Boom Site just upstream of Stillwater, a priority invasive carp surveillance area. Of the 100 samples taken in Andersen Bay, five tested positive for bighead carp DNA and three tested positive for a general marker for invasive carp DNA. Of the 100 samples taken at the Boom Site, three tested positive for silver carp DNA and one tested positive for the general invasive carp marker.
The DNR regularly samples for invasive carp in Andersen Bay and has removed several bighead and silver carp from the bay and the adjacent portion of the St. Croix River in years past. No invasive carp have been captured in Andersen Bay thus far in 2022. Andersen Bay is one of the locations that the DNR-tagged bighead carp frequents, making this area a target for surveillance and management.
The Boom Site detections are approximately four miles north of the farthest upstream capture of invasive carp in the St. Croix River, and approximately one and-a-half miles upstream from the farthest detection of a tagged invasive carp. In response to these detections, additional sampling at the Boom Site is planned for this fall.
The DNR believes continued eDNA monitoring in both Andersen Bay and the Boom Site is important as part of a proactive approach to invasive carp monitoring and response. Changes in the eDNA detection rate over time can be used as a tool to assess potential changes in the invasive carp population. eDNA may also be used to identify locations to target for management. To that end, the DNR is working with USFWS to explore how eDNA can be used to inform targeted removal efforts, including the Modified Unified Method the DNR, USFWS and other agency partners piloted on the Mississippi River in 2021-2022.
Invasive carp have been progressing upstream since escaping into the Mississippi River in Arkansas in the 1970s. These large fish compete with native species and pose a threat to rivers and lakes. Thus far, there has been no evidence of reproduction or spawning populations in Minnesota waters.
Individual invasive carp have been caught as far upstream as Pool 2 of the Mississippi, near the Twin Cities (bighead, grass and silver), the King Power Plant on the St. Croix River by Oak Park Heights (bighead and silver), and just downstream of Granite Falls in the Minnesota River (bighead). Invasive carp have also been captured in the Missouri River drainage in southwest Minnesota, where control structures are in place to prevent invasive carp movement into Minnesota waters.
The DNR is actively engaged with several other prevention efforts:
- The DNR is an active partner in the Upper Mississippi River Invasive Carp Workgroup. The group includes representatives from Minnesota, Wisconsin, Iowa, Illinois, Missouri, and several federal agencies.
- The Minnesota Aquatic Invasive Species Research Center at the University of Minnesota, in partnership with the DNR, is testing and evaluating carp deterrents in Mississippi River locks and dams.
- The DNR leads a program to monitor fish population changes and impacts of management actions.
- The DNR leads Modified Unified Method events to capture and remove invasive carp, in partnership with the USGS, Wisconsin DNR, USFWS and other agencies.
- The DNR is working closely with stakeholders to update the Minnesota Invasive Carp Action Plan.
State and federal funding sources, including the Environmental and Natural Resources Trust Fund and Outdoor Heritage Fund, have provided key funding for deterrent actions and the DNR invasive carp detection and response program.
Invasive carp captures must be reported to the DNR immediately by calling 651-587-2781 or emailing [email protected]. Take a photo and transport the carp to the nearest DNR fisheries office or make arrangements for it to be picked up by a DNR official. Do not release captured invasive carp. A permit can be requested to keep captured invasive carp for consumption or disposal.