Natural resource officials in Minnesota and Iowa are advocating for the construction of two fish barriers on the Mississippi River that they hope willl stop the upstream migration of Asian carp.
These barriers, which would be placed below lock and dam 14 or 15 (just north of Davenport, Iowa) and lock and dam 11 (just north of Dubuque, Iowa), might use bubbles and sounds to stop the fish from entering the open locks. The fish could be directed into pools where commercial fishermen could harvest them. (Similar barriers are already used on a smaller scale to keep fish away from water intake pipes at power plants.) Minnesota Department of Natural Resources employees are looking at a variety of different technologies, trying to find one that's as selective as possible. The idea is to find something that will deter the carp, but not the paddlefish and other species that ecologists want migrating up the river, many of which are threatened or endangered.
How big is the invasive carp problem? That's a little unclear. So far, two species of the fish--bighead and silver carp--have escaped from southern fish farms and moved north along the Mississippi and its tributaries. A third species, black carp, has been caught in several areas, but scientists don't know if it's reproducing. One bighead carp was caught in Lake Pepin (south of the Twin Cities) in the fall of 2003, but no others have since been reported.
But the Upper Mississippi is one of the most pristine of American rivers, and officials are anxious to keep it that way.
Silver and bighead carp can reach more than 50 pounds, and out-compete native species for food such as plankton. Silver carp are also dangerous to recreational boaters and water-skiers, as they jump out of the water when disturbed; they've injured people and damaged equipment.
The University of Minnesota's Bell Museum of Natural History has an invasive carp feature on their "Hot Topic" website.
The Star Tribune has a special feature on invasive species in the Great Lakes.