On my walks around Landen Lake this week (a small suburban lake north of Cincinnati), I have been repeatedly reminded that the Asian carp invasion is a significant problem throughout the Mississippi River watershed. Introduced in the 1970s to control aquatic vegetation and to filter sewage water, they escaped containment areas during floods and have spread throughout most of the U.S. Favoring shallow, sluggish waters, they often attract our attention as they thrash about, their dorsal and tail fins breaking the surface.
Represented by four species (grass, black, silver and bighead carp) these large fish are very prolific and soon dominate the aquatic ecosystems that they colonize; black carp, which feed on mollusks, threaten native snail, mussel and clam populations while the others reduce the availability of plankton and vegetation vital to native fish, amphibians and aquatic reptiles. As video enthusiasts know, silver carp also pose a threat to boaters, jumping into the air (and into boats) in response to the sound of outboard motors.
Concerned that Asian carp will enter the Great Lakes and disrupt the ecology of their fisheries, efforts have been made to block carp migration along canals that connect those Lakes with streams of the Mississippi watershed; "electric fences" have been used with some success but carp also spread as eggs or fingerlings on boat hulls, via the use of live bait, during floods and perhaps even on the legs of wading birds. Taking advantage of the carp bonanza, some companies are culling them to produce pet food or fertilizer; vultures also partake of the bounty, feasting on dead carp that were stranded by shrinking lakes or rivers.