In a troubling sign about the spread of invasive Asian carp, scientists have found evidence that Asian carp have spawned much farther north in the upper Mississippi River than previously recorded.
Asian carp eggs were recently found in the Upper Mississippi River near Lynxville, Wis., about 20 miles south of the Minnesota border, the Star Tribune reported. That's 250 miles upstream from previously known reproducing populations, and the spawning would have occurred even farther upstream, the Associated Press reports.
Some of the eggs were in later stages of development and nearly ready to hatch. The U.S. Geological Survey collected the samples last year and reported the findings Monday.
"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," Leon Carl, USGS Midwest Regional Director, said in a news release.
According to the release, the eggs were discovered two weeks ago while researchers were processing samples collected last year.
Scientists are still trying to confirm whether the eggs are from bighead or silver carp, though it's possible some of the eggs are from grass carp, according to the Associated Press.
Asian carp are voracious eaters and once established in a particular waterway, they crowd out native species. They've gradually been moving northward in the Mississippi River. The USGS, the Department of Natural Resources and other entities are trying to slow down the carp's move into Minnesota's lakes and rivers.
"Invasive Asian carp could pose substantial environmental risks and economic impacts to the Upper Mississippi River if they become established," Carl said. "Further research will help us to better understand their habitat requirements and inform integrated control efforts."