Picking Up in Pepin

From January, 1997 (Update #29)

Since 1995, zebra mussel densities in Lake Pepin - a widening in the Mississippi River just south of Red Wing, Minn. - have tripled in some locations to around 30,000 per square meter, according to Mike Davis, Minnesota Department of Natural Resources river ecologist. At the same time Davis observed water clarity changes in a rather peculiar way. During several dives this summer, he noticed that while the top 1.5 meters of water was normally turbid, the bottom 2 to 4 meters were clear. It has been widely reported that zebra mussels filter large amounts of water, but usually increased water clarity occurs throughout the entire column or in the top few meters. Since last year summer zebra mussel recruitment dramatically increased from 100 to 1,000 percent in the southern half of Lake Pepin, from Lake City to Camp Lacupolis, noted Davis. North of Lake City, however, the level of infestation and recruitment was much lower. Along with staff from the Army Corps of Engineers Davis has been monitoring the infestation to determine the density and depth distribution of zebra mussels in the lake. Monitoring conducted this season shows the density of juvenile and adult zebra mussels continued to follow the pattern observed in 1995 - a gradual increase in density from north to south. This year's recruitment of young zebra mussels also followed a similar pattern. Although density varied by location and depth, the greatest densities were generally found between 1 and 4 meters. Davis expects to see greater reproduction, higher densities and even greater impacts here next season, depending on overwinter survival.

by Doug Jensen, Minnesota Sea Grant.

ID: 199701-5.

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.