After a five-day search, Minnesota Department of Natural Resources (DNR) fisheries staff did not capture any Asian carp in the St. Croix River, but efforts to locate them continue this week.
Last week, DNR fisheries biologists used trawling techniques and electro-shock fishing methods to sample fish populations in two stretches of river. On Aug. 15 and Aug. 16, crews sampled sections of the river below the St. Croix Falls dam. This is where 22 out of 50 environmental DNA (eDNA) samples taken in June suggested the presence of silver carp, an invasive species.
From Aug. 17 to Aug. 19, fisheries crews searched the lower reaches of the river near Prescott, Wis., where a bighead carp, another Asian species, was caught by a commercial fisherman in April.
No Asian carp were caught during the searches.
“This is good news because it suggests that if Asian carp are present, the population could be very low, perhaps only a few individuals,” said DNR Commissioner Tom Landwehr.
Starting Tuesday, Aug. 23, a commercial fisherman hired by the DNR will begin using large nets to try to capture Asian carp in the St. Croix. The gear is larger than what DNR fisheries crews typically use. The fisherman may also use large seine nets. Both techniques have been effective in catching Asian carp. The contract for the commercial operation was expedited in response to the positive eDNA results announced earlier this month.
This week, the DNR will also present information to the Lessard-Sams Outdoor Heritage Council (LSOHC) about a proposed sonic bubbling system that would discourage Asian carp from entering the St. Croix River. The LSOHC recommends spending to the Minnesota Legislature for a portion of the Land, Clean Water and Legacy Amendment approved by voters in 2008.
The system would use a combination of bubbles and sound to direct the invasive species away from the river’s mouth. Asian carp are sensitive to noise, and the device would be calibrated to target Asian carp.
Scientists believe the barrier would not be a 100-percent deterrent to Asian carp, but it could keep populations low while other control methods are developed.
Bighead and silver carp are voracious eaters, capable of eating 5 to 20 percent of their body weight each day. Asian carp feed on algae and other microscopic organisms, often outcompeting for food with native fish. Scientists believe the fish could severely disrupt the aquatic ecosystems of Minnesota waters.