Invasion Progress Report

From January, 1995 (update #23)

GREEN BAY, Wis. - No zebra mussels were found on navigational buoys retrieved in late November from the Fox River between the DePere Dam and the bay of Green Bay, according to U.S. Coast Guard Aids-to-Navigation personnel stationed here. Moderate numbers of veligers were found for the first time this summer in this heavily used stretch of the river. Green Bay city personnel reported no zebra mussels on floating docks retrieved from the area, though mussels were found on anchors attached to floating buoys near the docks. For the second year in a row the Coast Guard found dense mussel concentrations on buoys retrieved from the mouth of the Suamico River.

LADYSMITH, Wis. - No zebra mussels were found this summer in Dairyland Reservoir, a hydropower impoundment on the Flambeau River where recently settled mussels were found in August 1993. Dairyland Power Environmental Biologist John Thiel said that "nothing at all turned up" on substrate samplers collected every two weeks throughout the summer of 1994 and into late November. These were the same samplers on which mussels were found last year. Nor were any mussels found in a "bio-box" monitoring device that receives untreated reservoir water used for cooling hydropower plant generating equipment. In an attempt to kill zebra mussels in nearshore areas, the reservoir water level was lowered seven feet late last February and in early March during a period of sub-freezing temperatures, Thiel said. Lowering the water level exposed the area where mussels had been found on substrate samplers. In an additional effort, DNR malacologist Dave Heath conducted dive surveys in July. He found no zebra mussels along the wall of the reservoir dam, nor any upstream or downstream from the dam while examining unionid mussels. Both Thiel and Heath said they hoped last summer's discovery meant the reservoir was "innoculated" but not successfully "colonized" by zebra mussels. Further inspections will continue next summer.

LA CROSSE, Wis. - The zebra mussel population has risen dramatically in the upper Mississippi River, according to studies conducted by the National Biological Survey (NBS) and U.S. Army Corps of Engineers (COE). For the past three years, NBS biologists have examined the density and growth of zebra mussels in Pool 8 near here. Each year, standard concrete blocks were put in the water and analyzed monthly over a six-month period. In 1992, three zebra mussels per square meter were found on the NBS samplers. The same density was found the following year. However, 284 zebra mussels per square meter were found on these samplers in 1994. The 1994 growth rate was 0.15 mm per day - similar to the estimated growth rate in the previous two years of the study. Seventy-eight percent of the zebra mussels were collected in main channel border habitat rather than in backwater habitat. Between June and September 1994, COE divers inspected 12 upper Mississippi River locks and dams. Fourteen one-square-meter plots were surveyed in each lock chamber. (Unfortunately, water conditions were murky, and only zebra mussels larger than five mm were collected, leading to a probable low estimate of true mussel densities.) Estimated mussel densities ranged from less than 0.1 per square meter at a lock near the Twin Cities to 68 per square meter at a lock near Winona, Minn. The Winona lock was surveyed later in the year than some of the other locks, perhaps contributing to higher density readings there. Compared to 1993, densities increased at all locks surveyed in 1994. Finally, on Dec. 13 COE biologists found zebra mussel densities up to 4,000 per square meter in the lock chamber for Lock and Dam 7, located a few miles north of La Crosse. Maximum densities of seven per square meter were found in the same lock chamber in 1993. For more information, contact Upper Mississippi Science Center Director Jan Riffe at (608) 783-6066 or COE biologist Tim Yager at (612) 290-5277.

ID: 199501-4.

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.