Study: No DNA Evidence of Asian Carp in the St. Croix River; Scientists Urge Continued Action

There's some more good news on the invasive-species front in the St. Croix River.

Last month, the Minnesota Dpearptment of Natural Resources reported that the presence of zebra mussels are on the decline in the St. Croix River.

New analyses for Asian carp DNA in water samples from the St. Croix and Mississippi rivers show "little evidence" of bighead and silver carp, researchers announced in a report released today.

The joint effort by scientists from the new Minnesota Aquatic Invasive Species Research Center at the University of Minnesota (MAISRC), U.S. Geological Survey and the Minnesota DNR also concludes that while recent captures by commercial fisheries show these invasive fish are present in Minnesota, their numbers are likely still relatively low.

Studies in 2011 using this technique, which detects DNA fragments released to the environment (eDNA), showed positive results for silver carp eDNA in up to half of the samples collected from the St. Croix and Mississippi rivers.

The new report documents what is considered to be the most rigorous study of Asian carp eDNA in Minnesota waters to date, according to the DNR. It 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.

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According to the researchers, while the new study consistently detected silver carp eDNA in Iowa where the fish are abundant, it detected no silver carp eDNA in the sampling areas just above and below St. Croix Falls in the St. Croix River or in the sampling areas above and below the Coon Rapids Dam or below Lock and Dam No. 1 in the Mississippi River.

In contrast, no bighead carp eDNA was detected at any location, including in Iowa where this species is known to be present.

“The differences between the 2011 and 2012 eDNA testing results may be partly attributable to the evolving technology,” Peter Sorensen, MAISRC director, and leader of the research team stated in a news release. “As the bighead results show, this particular technique needs to be refined for detecting this species in open waters.”

Sorensen believes that despite the lack of eDNA evidence reported in this study, there are very good reasons to believe these fish are routinely entering Minnesota waters from the south and could eventually 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 DNR’s Ecological and Waters Division, adding that “the threat of Asian carp is nevertheless an urgent issue for the state, requiring immediate action.”

The research study was coordinated by the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota, and was funded by the Minnesota Environment and Natural Resources Trust Fund.

The complete report is online at http://www.maisrc.umn.edu/