Officials aim to understand eDNA
St. Paul — Highly sensitive water tests conducted last year on the Minnesota, Mississippi, and St. Croix rivers turned up what appeared to be evidence of silver carp.
While the fish have been found in the Mississippi River in the southern part of the state, a live fish hasn’t been found in the areas where testing – known as eDNA testing – was conducted.
And now there are questions anew about the accuracy of the eDNA.
Earlier this year – in April – 20 water samples were collected from a metro lake where it was unlikely Asian carp could be. All the samples were sent to a U.S. Army Corps of Engineers lab and a private lab, which tested all of the more than 400 samples collected last year in Minnesota – many in the Twin Cities area.
While all samples tested at the Army Corps lab were negative, one of those tested at the private lab was positive.
“There is a high likelihood this is a false positive, which creates uncertainty about previous results,” according to a Minnesota Asian Carp eDNA Update. “The percentage of positives in the 2012 samples was much lower than previous samples, suggesting there may have been a mix of real and false positive samples in 2011.”
Though there’s doubt about the accuracy of last year’s samples, there are plans to move ahead with additional eDNA testing this year. The University of Minnesota’s new Aquatic Invasive Species Research Center will spearhead the effort, using funding it received from the Environment and Natural Resources Trust Fund.
The U.S. Geological Survey in La Crosse, Wis., will analyze the samples; the Minnesota DNR and National Park Service will collect them.
“The bottom line is we are still catching fish every once in a while in the river,” said Steve Hirsch, director of the DNR Division of Ecological and Water Resources. “We’re trying to use the eDNA to get an early warning signal. But the live fish are the most definite test you can have, and we are getting those.”
Officials hope this year’s water sampling regime sheds more light on what positive eDNA results mean.
Beginning in September, they plan to collect 150 samples from two metro lakes and from well water. These are “negative control sites” where they don’t expect to find Asian carp DNA.
They will collect 100 samples from “positive control sites,” including a water tank with Asian carp present, where they expect to find Asian carp DNA.
Finally, they will collect 250 samples from five sites – below the Ford Dam on the Mississippi River; above and below the Coon Rapids dam on the Mississippi; and above and below the St. Croix Falls dam.
“It will be interesting to see how the results from this year compare to the results from last year,” Hirsch said. And the addition of the positive and negative control sites will add to the body of knowledge. “All of those pieces together will give us a better idea of what a positive eDNA result might mean.”