Sightings elsewhere

From December 17, 1993 (update #19)

ZION, Ill.-Zebra mussel growth slowed in southern Lake Michigan during 1993, according to a report by biologist Ellen Marsden of the Illinois Natural History Survey (INHS). Marsden's report also included information on zebra mussel effects on native snails and clams, including fingernail clams. If you would like a copy, phone Marsden at (708) 872-8677.

HAVANA, Ill.-Zebra mussels in the Illinois River increased downstream this summer, according to Doug Blodgett, an INHS biologist. Blodgett said he was surprised because zebra mussels initially colonized the Illinois River upstream via a barge channel that enters Lake Michigan. An INHS report on the summer's findings stated that the "most likely explanation for the upriver-downriver gradient is that larvae from populations in southern Lake Michigan or the upper Illinois River were released during the 'Great Flood of 1993' and carried far downriver before settling."

On a 176-mile stretch of the river, the densities increased from less than one to nearly 70,000 in a one square meter sample quadrant. At the downstream sampling site, divers found a mat of zebra mussels "carpeting" silty river bottom substrates.

For further information phone Doug Blodgett at (309) 543-6000.

GRAFTON, Ill.-Zebra mussels heavily colonized the Mississippi River this summer just south of where the Illinois River joins the Mississippi. INHS biologist John Tucker said the Illinois River was a major source of zebra mussels for that portion of the Mississippi. However, they remained relatively scarce in the Mississippi north of town.

Tucker saw one gravel bar on the Mississippi that was so completely covered by zebra mussels that native Unionid mussels could not move to safety when the bar became exposed by a river draw down. Under normal conditions Unionids could have moved to safety by pushing their muscular foot into a pliable substrate. But in this case, zebra mussels created a hard, impenetrable mat that prevented such movement.

Tucker also noted that some Unionids could not move due to the extra weight of the attached zebra mussels. The 740 Unionids Tucker examined carried an average of 40 zebra mussels per animal. He pointed out that this is a relatively low density compared with densities found on Unionids in Lakes St. Clair and Erie.

Results of a 1992 survey of zebra and Unionid mussels in the Illinois and Mississippi rivers by Tucker and three colleagues were published in the Journal of Freshwater Ecology, Vol. 8, No. 3, pp. 245-251.

LOUISVILLE, Ky.-"They're everywhere." That's how University of Louisville biologist James Alexander described the zebra mussel presence in the Ohio River in early November. "If you had asked me in July, I would have said they were rare," he said. "But everything has changed in the last three months." Alexander has been monitoring zebra mussels over a 70-mile stretch of the Ohio River near Louisville for the past three years. He said that a recent burst in reproduction has produced mussel densities of around 100 per square meter on all suitable hard substrates.

CLEVELAND, Ohio-Six power plants on Lake Erie reported fewer problems during the 1993 zebra mussel season, according to Louise Barton, environmental analyst for Cleveland Electric Illuminating. She said that the frequency and severity of mussel fouling problems at these plants were less serious than they've been in the past.

BINGHAMPTON, N.Y.-Very low numbers of zebra mussel veligers have been observed three years in a row at a power plant intake near here on the Susquehanna River, according to Ray Tuttle, senior environmental specialist for New York State Electric and Gas (NYSEG). No adult mussels have ever been found at this or any other location in the Susquehanna River system. Tuttle called these continuing low numbers "an anomaly" compared to the explosive growth of zebra mussel populations at many other North American locations. Monitoring efforts have been conducted regularly throughout the river system since the initial discovery of veligers here.

ID: 19931217-3.

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.