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Wild Side: River monster appears again in the St. Croix

Take a good look at this bighead carp, the kind that was found recently in the St. Croix River. U.S. Geological Survey photo.

With lips only a mother could love and eyes set low in the head, bighead carp are not pretty fish. Bighead carp is an invasive species from Asia that poses a threat to native fish and aquatic ecosystems in North America.

You may have already heard that commercial fishermen seining in the lower St. Croix near Prescott caught a 27- pound bighead carp on Monday April 18. The fish was 37 inches long and about 5 years old. An individual bighead carp was first found in the St. Croix in 1996 and more recently others were captured in Lake Pepin and at other locations in the Mississippi River along Wisconsin and Minnesota.

Plankton-feeding bighead and silver carp were imported from Asia in 1972 to improve water quality in fish ponds in Arkansas. By the early 1980s, both species had escaped from aquaculture facilities and had established reproducing populations in the Mississippi River. Both species have now established populations in the Upper Mississippi, Illinois and Missouri Rivers.

The Asian carp are invading northward. Both bighead and silver carp have established reproducing populations in the Mississippi upriver of the high hydropower dam at Keokuk Iowa. Large individual Asian carp are able to swim upriver through the Mississippi River navigation dams during floods when the dam gates are raised out of the water.

Asian carp are abundant in the Illinois River and threaten to invade the Great Lakes at Chicago. Three electrical barriers have been constructed and are energized now to deter Asian carp from passing through the Chicago Sanitary and Ship Canal into Lake Michigan.

Silver carp are the notorious ones that have a behavior of swimming near the surface and leaping high out of the water when startled. Recreational boating is dangerous where silver carp are abundant. It's no fun to get smacked in the kisser by a 60-pound carp.

Where Asian carp are abundant, they crowd out native fish species. They compete for plankton and particulate organic matter with native fishes like paddlefish, emerald shiners, gizzard shad and buffalo.

Unfortunately, there are no "silver bullet" technologies available to stop the spread of Asian carp. Although state and federal agencies have discussed the potential for electrical or acoustic-bubble barriers to deter fish movements, they probably won't work in big rivers like the St. Croix and Mississippi. Physical barriers like high dams and waterfalls prevent them from swimming upstream. Care must be taken to avoid people transporting young Asian carp in bait buckets.

A federal ban on interstate transport of live silver carp was enacted in 2007. A ban on transport of live bighead carp was added in March of this year. The ban on live transport of Asian carp may serve to further limit their spread through intentional or inadvertent stocking.

It won't be pretty if those river monsters become abundant in our local boundary waters.

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Bighead carp. U.S. Geological Survey photo.