Mussels in the Mighty Miss'

From January, 1996 (Update #26)

Since zebra mussels were first found in the Mississippi River near La Crosse, Wis., in 1991, the population has grown much denser and become more widely distributed. Densities in the Minnesota stretch of the Mississippi River are highest at the southern end of Lake Pepin, near Red Wing, Minn., according to Minnesota Department of Natural Resources fisheries biologist Mike Davis. The highest densities approach 5,400 per meter square, averaging well over 1,700 per square meter at some locations. Zebra mussels are found everywhere downstream from there, according to Davis. "I've found specimens up to 50 mm long, with many about 20 mm long," he said. "In many areas, the average size of last year's cohort is about 10 mm." Zebra mussels are also found at every lock and dam north of Lake Pepin. Infestations are not as dense because veligers drifted farther downstream before settling, Davis speculated. What impacts are zebra mussels having in the river? First, the infestation is causing industries using Mississippi River water to implement on-line control strategies. In addition, a team of natural resource agencies, led by the U.S. Fish and Wildlife Service, has moved hundreds of unionid mussels from the river to save them from becoming encrusted with zebra mussels. The unionids will be temporarily held in experimental ponds at the Genoa Fish Hatchery south of La Crosse. If unionids can be successfully maintained in hatchery ponds, more river specimens will be moved; if an effective control can be developed or if the infestation eventually subsides, the native unionids will be returned to their native habitat. At least five recreational boats suffered problems during the 1995 boating season because zebra mussels clogged their engine cooling systems, according to John LaRocque of Northport Marina in Alma, Wis. "Two engines were wrecked completely," LaRocque said. "Three others experienced overheating, but suffered no damage. Another boat that came up river from Iowa had so many zebra mussels on the outdrive it couldn't be turned to the right." Mussel-caused nuisances weren't exclusive to boaters, either. Anglers reported that their lines had been cut by the mussels' sharp shells, the Minnesota DNR's Davis said. - Doug Jensen, Minnesota Sea Grant.

ID: 199601-13.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.