Asian carp search enters new phase on Mississippi, St. Croix, Minnesota rivers

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Asian carp search enters new phase on Mississippi, St. Croix, Minnesota rivers
(Released September 8, 2011)

The search for Asian carp in the St. Croix and Mississippi rivers will continue next week with a new round of environmental DNA (eDNA) testing, the Minnesota Department of Natural Resources (DNR) has announced.

Also, the Minnesota River has been added to this round of testing because of its proximity to the Mississippi River.

The ad hoc Minnesota Asian Carp Task Force, made up of state and federal natural resource agencies and the University of Minnesota, will initiate a new round of sensitive eDNA sampling in four stretches of the St. Croix and Mississippi rivers. The testing will be done at 225 locations in those two rivers and 50 locations in the Minnesota River.

The process, which should begin Wednesday, Sept. 14, involves taking a liter of water from each location, filtering it, and analyzing it for the presence of DNA left by two species of invasive Asian carp, silver and bighead.

The testing is part of a multi-prong, long-term effort to determine the presence and distribution of invasive Asian carp in the rivers, and to identify and implement ways to slow their upstream spread.

The DNR recently completed a nine-day search of Asian carp in the St. Croix River using nets and electro-shocking gear, and no invasive carp were caught. The testing followed positive eDNA tests in June that showed the presence of silver carp DNA about 50 miles upstream from the river’s mouth.

In addition to its own netting and electro-shocking efforts, the DNR hired a commercial fisherman with experience netting Asian carp in Illinois. After four days of netting, the operator did not catch any carp in what he believed would be the fishes’ preferred backwater habitats in the St. Croix River.

“This is good news because it suggests Asian carp may be in low numbers in the St. Croix River, and perhaps only a few individuals,” said DNR Commissioner Tom Landwehr. “It also suggests we have some time to research and implement barriers that can help slow their spread.”

The next round of eDNA sampling will be done in previously untested sections of all three rivers; in addition, researchers plan to retest sections of the St. Croix and Mississippi rivers that were sampled in June.

The June results from the Mississippi River may have been unreliable because the river was near flood stage, researchers say, and they want to see if the St. Croix results come back positive again:

In the St. Croix River, new testing (30 water samples) will be done above the St. Croix Falls Dam, while 20 samples will be collected below the dam in the area previously tested.
In the Mississippi River, new testing will be done downstream of Lock and Dam 2 at Hastings (75 samples), and below and above the Coon Rapids Dam (50 samples total). Retesting will be conducted below Lock and Dam 1 in St. Paul (50 samples).
In the Minnesota River, which was not tested in June, 50 samples will be collected close to its confluence with the Mississippi River.
Results will be available as samples are processed. The first round of results should be available by mid-October.

All fish, including Asian carp, shed DNA material into the environment through mucus and excrement. DNA floats on the water surface and accumulates in eddies and backwater areas. The presence of individual fish species can be detected by collecting water samples in those areas and filtering them in the lab for DNA.

The testing is being coordinated by the DNR and the National Park Service, with assistance from the University of Minnesota and the U.S. Fish and Wildlife Service. The same company, eDNA Solutions of Indiana, that conducted the June testing will perform the next round of laboratory tests.

The DNR is continuing to investigate funding, feasibility and development of a diversionary sonic and bubble barrier for the St. Croix River. Fisheries managers are currently looking into the effectiveness of such barriers in other locations.

The barriers work by using sound and bubbles to divert fish away from river mouths. Such technologies are experimental, especially on a river as large as the St. Croix, DNR officials say, and would not provide a 100-percent deterrent to Asian carp, but might keep their numbers at a manageable level while long-term control methods are developed.