The DNR said the report reflects the most rigorous study of Asian carp DNA evidence in Minnesota to date.
Researchers looking for fragments of Asian carp DNA in the Mississippi and St. Croix rivers found little evidence of bighead and silver carp, according to a study released Thursday that concludes that while the invasive fish are present in Minnesota, their numbers are likely relatively low.
"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. "The threat of Asian carp is nevertheless an urgent issue for the state, requiring immediate action."
The DNR said the report reflects the most rigorous study of Asian carp DNA evidence in Minnesota to date, according to the St. Paul Pioneer Press (http://bit.ly/10zQ4eX ). The study was done by the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota, the U.S. Geological Survey and the DNR.
Researchers analyzed water samples for DNA fragments released to the environment, called eDNA. They found silver carp eDNA in Iowa, where the fish are abundant, but none near St. Croix Falls in the St. Croix, or near the Coon Rapids Dam or below Lock and Dam No. 1 in the Mississippi at Minneapolis.
In eDNA testing of samples taken in 2011, a year earlier, researchers recorded a positive eDNA test of silver carp above the Coon Rapids dam on the Mississippi River, raising alarm that the fish were heading upstream faster than anticipated. But since then, other analyses have shown the sensitive testing can sometimes have a false-positive.
The new round of testing also raises questions of eDNA reliability. For example, no bighead carp DNA was detected anywhere, including in Iowa where the fish are known to be.
"The differences between the 2011 and 2012 eDNA testing results may be partly attributable to the evolving technology," said Peter Sorensen, director of the Minnesota Aquatic 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."