Invasion Progress Report

From September, 1994 (update #22)

SUPERIOR, Wis. - Despite the presence of a few large zebra mussels in Superior harbor, UW-Superior biologist Mary Balcer said that few newly settled mussels or veligers have turned up there. She characterized the situation as "nothing like we would expect" from a self-sustaining population. Balcer's Sea Grant-supported research this summer included analyzing plankton and substrate samples taken from Superior harbor, and conducting zebra mussel growth experiments to examine the impact of low calcium levels on zebra mussel growth.

MILWAUKEE, Wis. - Zebra mussel veliger numbers varied at Wisconsin Electric Power Company power plants this summer, according to technician John Babinec. Weekly veliger sampling was conducted at three of five Lake Michigan facilities. The Pleasant Prairie power plant averaged 8,000 veligers per cubic meter, up from an average of 5,000 last summer. The Point Beach power plant averaged 8,000 per cubic meter, about the same as last year, and veliger densities at the Oak Creek facility were down from 3,400 last year to 2,900 this year. Season highs were observed August 10 at Pleasant Prairie (55,000 per cubic meter) and Point Beach (34,000). Veliger densities at Oak Creek never exceeded 10,000 per cubic meter. Babinec said divers cleaned up a massive infestation in the pumphouse forebay at the Oak Creek power plant this summer. This area of the plant intake system currently must be treated manually. The mussels are under control, but continue to be a nuisance, Babinec said.

OSWEGO, N.Y. - Quagga mussels (Dreissena bugensis) are beginning to displace zebra mussels in western Lake Ontario at depths greater than 25 meters, according to National Biological Survey fishery biologist Randy Owens. Owens said between 50 to 100 pounds of quagga mussels were collected this summer in 10-minute tows using a bottom trawl. By comparison, only a half dozen mussels were found in 1991 using the same collection method. Owens said quagga mussels are abundant at depths up to 55 meters in the western part of the lake. They have not yet completely colonized the eastern end.

HAVANA, Ill. - Zebra mussel numbers dropped dramatically this summer at an Illinois River location near Grafton, Ill., where zebra mussels carpeted the bottom in 1993, according to biologist Doug Blodgett of the Illinois Natural History Survey (INHS). High densities of 61,000 per square meter in 1993 near Grafton dropped to 4,000 per square meter in similar 1994 surveys. Blodgett said that extremely high water conditions in 1993 closed the river to commercial barge traffic and could have produced unusually favorable settlement conditions. Based on surveys here and at other Illinois River locations, Blodgett said he believes that river populations are "very variable." Other surveys this summer also indicate that Mississippi River zebra mussel populations and Unionid mussel infestation rates remain much lower than in the Illinois River. Blodgett reported finding no zebra mussels in a mussel survey on the Mississippi River in Pool 25, several miles upstream from its confluence with the Illinois River. Farther upstream near Moline, INHS divers surveyed native Unionid mussel beds near Campbell Island in Pool 15 on Sept. 14 and 15. Of 1,000 native mussels examined, on average at least one zebra mussel was attached to every Unionid found, according to INHS biologist Helen Kitchel. A zebra mussel density of 48 zebra mussels per square meter was estimated in another mid-August INHS survey in Pool 15.

ID: 199409-4.

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.