MADISON, Wis. -- Additional tests for Asian carp environmental DNA in the Lower Fox River have come back negative, Wisconsin Department of Natural Resources officials said.
Bob Wakeman, aquatic invasive species coordinator for DNR, said the additional tests were requested after one out of 200 sample collected in June and July from the Lower Fox River tested positive for silver carp. The latest round of testing - by the U.S. Fish and Wildlife Service - included collecting 200 additional samples from the Lower Fox River on two days of sampling in the weeks following the initial results.
"We're pleased that the results came back negative and it's a good indication there are no live silver carp in the river," Wakeman said. "We're particularly grateful to the U.S. Fish and Wildlife Service for their work in carrying out the water sampling and analysis. Through continued monitoring and the preventive efforts of Wisconsin anglers, waterfowl hunters, recreational boaters and commercial partners, we hope to keep Asian carp out of Lake Michigan."
Asian carp pose significant ecological and economic threats to the Great Lakes region and its fishery because they eat voraciously and compete directly with valuable native fish for food. Asian carp species including bighead and silver carp were introduced into the southern United States in the 1970s.
The tests for eDNA are extremely sensitive and can detect genetic material shed in mucus or excrement from fish as well as from birds that have eaten the fish elsewhere. Contaminated bilge water also can carry traces of the fish and the latest negative results suggest the source of eDNA from the summer sampling originated from a temporary source.
While the genetic fingerprints are clear enough to identify specific invasive carp species, the eDNA testing program relies on multiple positive samples over time to indicate the likelihood of live fish. The single positive result among 1,950 samples from Wisconsin tributaries to Lake Michigan in June and July followed by the negative results returned this week recalls a similar situation in 2013. Then, a single positive sample from the Sturgeon Bay area was followed by all negative results.
In addition to the federal eDNA monitoring, DNR fisheries team members conduct a variety of netting, electroshocking and trawling operations in state waters. To date, these efforts have not captured any Asian carp in any waters of the Lower Fox River, Green Bay or Lake Michigan.
DNR encourages anglers and others to review Asian carp identification materials, to report any sightings of Asian carp and to make sure that bait buckets don't inadvertently contain the fish because young Asian carp resemble popular bait species. Photo identification tools and more information on Asian carp can be found on DNR's website, dnr.wi.gov, by searching "Asian carp."