ST. PAUL, Minn. — Scientists have found disappointing DNA evidence that invasive Asian carp are present in the scenic St. Croix River as far upstream as the dam at St. Croix Falls, Wis., the Minnesota Department of Natural Resources announced Thursday.
DNR Commissioner Tom Landwehr also told reporters he was "very surprised" that similar testing found no traces of Asian carp in the Mississippi River between Minneapolis and St. Paul, and more testing is planned while agencies scramble to try to stop the further spread of the large nonnative fish.
Scientists tested for environmental DNA, also known as eDNA, from silver carp, looking for small traces of DNA shed by the fish through their excrement and other means. The tests are highly sensitive, but do not indicate how many of the fish are present, their size or whether they're reproducing. Landwehr said 22 of 50 sites tested positive for silver carp in a 4.3-mile stretch of the St. Croix below the dam at St. Croix Falls.
While no silver carp DNA was found at the 50 sites tested in the 3.6-mile stretch of the Mississippi between the Ford Dam south to the confluence with the Minnesota River, DNR planner Tim Schlagenhaft said that doesn't prove they're not present because the river was high and turbid when the samples were collected in late June. Neither river tested positive for bighead carp, another Asian carp species.
Only a few Asian carp have been caught in Minnesota and its border waters before, and fishery officials weren't sure if those catches were just strays or a signal that the fish have established a permanent presence.
Asian carp have devastated native fish populations since they began spreading up the Mississippi River basin after escaping from southern fish farms several years ago. They outcompete native fish for the plankton that forms the base of the aquatic food chain. They've also attracted attention because of their propensity to jump in the air when startled, injuring boaters. They can leap 10 feet and swim 20 mph. So their advance up the St. Croix or Mississippi could do serious harm to many popular recreational rivers and lakes in Minnesota and Wisconsin.
There's also fear, based on similar DNA testing, they may soon enter the Great Lakes via a canal in Chicago if they haven't already.
"They quickly become the most dominant organism in the system. ...They definitely will chop you off at the bottom and topple the system in ways we don't want to see," said Byron Karns, an aquatic biologist with the National Park Service.
As for how long it might take for that to happen to the upper Mississippi and the St. Croix, Karns could only say, "Who knows?"
The DNR now plans to contract with commercial anglers to net the affected area of the St. Croix and to use electric shocking technology to try to capture live Asian carp to get a better idea of how many might be present. The agency also plans to install an air-bubbling barrier at the mouth of the St. Croix River at Prescott, Wis., to try to temporarily stop the spread of the fish until a more permanent solution can be found. The agency also will order new testing, this time above the St. Croix Falls and Ford dams, to see if the fish have managed to breach those barriers, as well as more testing to rule out the low possibility that the silver carp DNA came from fish hatcheries or other sources.
Minnesota and Wisconsin officials have discussed bubble barriers, which discourage fish movements with the underwater noise they make, but there are concerns about whether they work, Landwehr said. Some studies suggest the technology is only 95 percent effective, he said.
Minnesota's announcement came the same day that Wisconsin announced an angler's catch in southwestern Wisconsin of a bighead carp in the lower Wisconsin River, a tributary of the Mississippi. Bob Wakeman of the Wisconsin DNR's aquatic invasive species program said high water levels on the Mississippi are allowing more Asian carp to move upstream. No young Asian carp, nor other signs of reproduction, have been documented in any Wisconsin waters, fisheries researcher John Lyons said in the same statement.
And the Iowa DNR announced Thursday that two bighead carp were caught in East Okoboji Lake in northern Iowa. Officials said they weren't sure how the fish got there, but it might be a result of flooding on the Little Sioux and Missouri rivers, which eventually flow into the Mississippi.
One proposal advanced for stopping Asian carp at Minneapolis is to close the locks in the Ford and St. Anthony Falls dams, since they carry little commercial traffic, but that would take an act of Congress, said Russel Snyder, a project manager with the U.S. Army Corps of Engineers.
Both of Minnesota's U.S. senators issued statements pledging their support for any steps necessary.
The Minnesota Legislature last month approved $16 million for improvements to the Coon Rapids Dam above Minneapolis. Landwehr said that should make the dam 99 percent effective in stopping the northward migration, but the work won't begin until next year.—Copyright 2011 Associated Press