MINNEAPOLIS -- Scientists have found evidence that invasive Asian carp have spawned much farther north in the upper Mississippi River than previously recorded, the U.S. Geological Survey said Tuesday.
Asian carp eggs, including late-stage embryos nearly ready to hatch, were recently identified in samples collected as far north as Lynxville in southwestern Wisconsin, which the agency said is 250 miles upstream from previously known reproducing populations. And it said the spawning would have occurred somewhere upstream from that site.
"The presence of eggs in the samples indicates that spawning occurred, but we do not know if eggs hatched and survived or whether future spawning events would result in live fish," the service's Midwest regional director, Leon Carl, said in a statement.
Scientists are still awaiting the results of genetic tests to try to confirm whether the eggs are from either bighead or silver carp, as visual analyses suggested, though it's possible some of the eggs are from grass carp, the statement said.
Researchers discovered the eggs two weeks ago while processing samples collected last May and June as part of a larger project to identify Asian carp spawning habitats. The eggs were found in samples taken at seven locations between Pool 19 near Keokuk, Iowa, and Pool 9 near Lynxville. Scientists plan to collect additional samples this year as part of the ongoing research project, which is being coordinated by the USGS in collaboration with Western Illinois University.
Bighead and silver carp have infested much of the Mississippi River basin since escaping from southern fish farms in the 1970s. They're threatening to reach the Great Lakes through rivers and canals, leading the federal government to spend more than $200 million to try to stop them. They've been a menace to the aquatic food chain because they eat enormous amounts of plankton needed by native species.
Adult bighead carp have been found in Minnesota as far north as Lake Pepin on the Mississippi, as well as in the St. Croix River north of where it joins the Mississippi. Silver carp have been found as far upstream as Winona, Minn. There's been no indication so far that either species is reproducing that far upstream. Still, there have been calls for closing the Upper St. Anthony Falls Lock and Dam in downtown Minneapolis to keep them from advancing farther north.