Asian carp DNA not found in Mississippi, St. Croix rivers in Minnesota

The long-feared Minnesota invasion of two species of invasive carp apparently has not hit yet.

No DNA of silver and bighead carp, often referred to as Asian carp, was detected in the Mississippi or St. Croix rivers in Minnesota, according to a fresh analysis by federal, state and academic researchers, officials announced Thursday, April 4.

The fish still could be present, despite the lack of environmental DNA -- or eDNA -- officials cautioned. In fact, commercial fishing boats in Minnesota waters have caught live bighead carp. The fish are unlikely present in large numbers, officials said, but a leading researcher warned that he still believes the fish will eventually be able to breed here.

"These results support the conclusion that bighead and silver carp have not yet become established in Minnesota," said Steve Hirsch, director of the Ecological and Waters Division for the Department of Natural Resources. In a statement this morning, he added that "the threat of Asian carp is nevertheless an urgent issue for the state, requiring immediate action."

It's unclear how the results might affect efforts to erect or enhance barriers to the fishes' movements.

According to the DNR: "The new report documents what is considered to be the most rigorous study of Asian carp eDNA in Minnesota waters to date." The study, which examined water samples collected in 2012, was completed by the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota, U.S. Geological Survey and the DNR.

The negative results of the DNA testing might raise eyebrows among those who have followed prior tests, since eDNA of invasive carp was detected in 2011 tests. For example, in 2011, the DNR announced a positive eDNA test of silver carp, known for their leaping ability, above the Coon Rapids dam on the Mississippi River. That result raised alarms that the fish were marching upstream faster and with more ease than most had imagined.

However, since then, a host of analyses have shown that the sensitive testing, which seeks traces of carp secretions in the water, can have a sort of false-positive effect. In at least one study, eDNA was detected in a water sample from a lake where it's known with near certainty the fish are not present. Scientists have speculated that traces of the fish's DNA might exist in water without the actual fish -- perhaps from a source such as wastewater outflow from an area where commercial foods containing the fish might have been present.

The most recent study "used a large number of experimental controls and techniques recently developed by the U.S. Army Corps of Engineers for use in the Illinois River and Great Lakes that include DNA sequencing as a final verification step," according to the DNR.

Still, the new round of testing raises questions of eDNA reliability, too. For example, no bighead carp DNA was detected anywhere, including a location in Iowa where the fish are known to be present.

"The differences between the 2011 and 2012 eDNA testing results may be partly attributable to the evolving technology," said Peter Sorensen, director of the U's Invasive Species Research Center and leader of the research team. "As the bighead results show, this particular technique needs to be refined for detecting this species in open waters."

A news conference is scheduled for 11 a.m. Thursday.