New Sightings in Wisconsin

From July 28, 1992 (update #14)

TREMPELEAU - Colonies of zebra mussels were found in July clinging to three navigation locks on the Mississippi River near here, according to U.S. Army Corps of Engineers biologist Tim Peterson. Divers doing routine maintenance and inspection first found clusters of zebra mussels in early July at Lock & Dam #6 near Trempeleau. A subsequent inspection at Lock & Dam #5A, just north of Winona, Minn., turned up 40 to 50 mussels. On July 17, mussels were also found at Lock & Dam #5 near Merrick State Park. The mussels were attached to the concrete walls of the lock chambers, which are the structures that allow towboats, barges and other watercraft to pass around the adjacent dams. Lock and dam structures on the Mississippi River have water-intake tunnels up to 14 feet in diameter, with smaller connecting water channels. Wisconsin DNR biologist Ron Benjamin, La Crosse, described the mussels retrieved from Lock & Dam #6 as "full-blown adult colonies." He noted that maintenance dive teams work at these locks under conditions of zero visibility and can only retrieve what they feel through neoprene gloves, so it is unlikely that they would discover small zebra mussels under these conditions. Benjamin also noted that a recent drop in commercial clam prices has greatly reduced commercial clam harvests on the Mississippi River, reducing potential reports from clammers of zebra mussel sightings.

STURGEON BAY - Veligers were found for the first time in a water sample taken on July 16 from the Sturgeon Bay Ship Canal by UW Sea Grant Zebra Mussel Watch personnel.

RACINE - Veligers were first found on June 9 at a density of about one per quart (1/L) in a water sample taken from the Racine Water Utility wet well, according to plant superintendent Herb Schmidt. Water sample analyses conducted two or three times per week regularly turned up veligers at that density throughout June and early July, with an increase in density to about four per quart (4/L) on July 14 and another increase to 15 per quart (16/L) on July 23. This is approximately the peak density reached in August 1991 at the same location. Schmidt also noted that a storm washed up large numbers of zebra mussels on shore for the first time in late July. The "thumbnail-sized" mussels were tangled in mats of green algae, making them look like "beaded mats," Schmidt said. A diving inspection conducted in late May of an intake line that had been sealed in January to produce anaerobic conditions turned up no zebra mussels. A few mussels were found in the Racine Water Utility shore well at that time.

ID: 19920728-2.

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.