Editor's Note

From September 16, 1993 (update #18)

After a record-setting mid-July peak, veliger (mussel larvae) densities and recently settled veligers declined in southern Green Bay. High densities (20,000-40,000 per cubic meter) showed up in water samples collected in early August. But by the end of the month, densities were moderate (1,000 per cubic meter). Moderately high densities (8,000 per cubic meter) turned up in mid-August for the first time at Marinette harbor. Lower densities (4,000 per cubic meter) were found at Sturgeon Bay. Low veliger levels (less than 1,000 per cubic meter) were found at Oconto. Fox River samples taken downriver from the DePere dam were also low (200 per cubic meter). Zebra mussels continued their rapid expansion in Green Bay and several Lake Michigan harbors north of Milwaukee throughout August. Moderately high veliger (mussel larvae) densities (around 10,000 per cubic meter) were found in Manitowoc harbor in late July and early August. Slightly lower densities (7,000 per cubic meter) were found in Sheboygan harbor in early August. At other Lake Michigan sampling sites, similar veliger densities signaled thriving local zebra mussel populations. From July 1 to September 1, veligers were detected in 95 of 109 (87%) Lake Michigan harbor samples. Recently settled post-veligers were found on 36 of 82 (44%) substrate samples. From July 1 through September 1, no veligers were found in any of 12 Superior harbor samples. No recently settled post-veligers were found on 30 substrate samples taken from Superior harbor, nor were zebra mussels seen in any of 33 plankton tows examined from Lake Winnebago this summer.

ID: 19930916-1.

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.