Sightings

From March 7, 1994 (update #20)

PETERBOROUGH, Ont. - Few inland sightings of zebra mussels have been reported to date in Ontario, according to Beth MacKay of the Ontario Federation of Anglers & Hunters (OFAH).

MacKay said that provincial budget limitations have eliminated most systematic sampling of inland Ontario lakes for the presence of veligers or settled mussels. Current maps of zebra mussel distribution are largely based on previous surveys and informal observations called in to OFAH's Invading Species Hotline.

Of the noteworthy inland sightings during 1993, all were in canal systems connected to already infested waters. One was in Rice Lake, which is the first lake inland from Lake Ontario on the Trent-Severn Waterway, according to MacKay. Other sightings were in lakes that make up part of the Rideau Canal System near Ottawa. Although veligers were detected by Ontario of Natural Resources personnel at Rice Lake in 1991, no adult mussels were reported at that location until the summer of 1993.

ST. PAUL, Minn. - Zebra mussel densities at Mississippi River locks and dams increased downstream from here, according to a 1993 U.S. Army Corps of Engineer (USCOE) survey.

Estimated densities ranged from less than one per square meter at the lower St. Anthony Falls Lock and Dam near the Twin Cities to 6.5 per square meter at Lock and Dam 7 near LaCrosse, Wis., which is located about 130 miles down the Mississippi.

Densities observed at Lock and Dam 9 were lower than at neighboring locks. The report also noted that Lock and Dam 9 was dewatered in 1992 for major maintenance, and "that the dewatering operation appears to have substantially affected colonization of lock chamber surfaces by zebra mussels."

For further details, contact USCOE biologist Tim Yager at (612) 290-5277.

TREMPEALEAU - In early December, Lock and Dam 6 on the Mississippi River was dewatered for major maintenance and repair work.

At that time, zebra mussels were observed to be sparsely attached to lock walls and hard surfaces throughout the lock chamber, according to USCOE personnel. Estimated mean density was 7.9 mussels per square meter along the lock floor; 19 per square meter along lock intake ports.

A USCOE report stated that "considering all surfaces available for attachment in the lock chamber, it can reasonab ly be estimated that 120,000 zebra mussels existed in the lock chamber prior to de-watering...reported densities...are relatively low and currently causing no problems in terms of lock operation."

Finally, the report said that "dewatering during cold weather periods is an effective method of killing zebra mussels within lock chambers."

ST. CROIX FALLS - No zebra mussels were found in the St. Croix or Namekagon rivers during 1993, according to Sue Jennings, Resources Management Specialist for the Saint Croix National Scenic Riverway.

As part of an "active" sampling program, five survey dives were conducted at monthly intervals in 1993. Bridges, buoys, native mussel beds, docks, breakwalls and other suitable substrates were inspected. A "passive" monitoring program included bi-weekly inspections of 65 sampling stations throughout the river-way.

To prevent upstream passage of boats exposed to infested waters, an interception station was staffed from daybreak to dusk, May 24 - Oct. 11. Of 2,955 boats "contacted" by station personnel, 138 were refused upstream passage. Of the 611 individuals who completed survey forms, 92 percent were judged as "Friendly/Supportive" of boater restrictions, while three percent were deemed "Resistant" or "Hostile.".

ID: 19940307-3.

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.