St. Croix River Infested?

?

From January, 1996 (Update #26)

When is a body of water truly "infested?" Minnesota DNR Ecological Service Section's Gary Montz recently wrote ZMU requesting help from the zebra mussel community to define the term. Montz wrote: "A number of agencies in Minnesota and Wisconsin are trying to keep the zebra mussel from spreading into the St. Croix National Scenic Riverway, which is home at last count to over 40 species of unionids, including the Winged Mapleleaf. The St. Croix is a tributary to the Mississippi River below the Twin Cities, and supports a tremendous amount of recreational boating traffic in the lower 26 miles. Above that area, the river becomes much shallower and boating traffic decreases. "The problem in trying to stop the zebra mussel arises from the boat travel between the Mississippi and St. Croix rivers. Additionally, this lower part of the St. Croix includes border waters managed by both Minnesota and Wisconsin, with federal agencies such as the USFWS, National Park Service and Coast Guard having additional responsibilities. "Actions the Minnesota DNR might take depend on whether the river is officially 'infested' or not. Certain laws apply to uninfested waters, while others only apply to waters infested with exotic species. We also have specific signs for access sites on infested waters. "Together with the other agencies working on the zebra mussel issue, we need to determine if the St. Croix River should be declared 'infested.' However, there are widely differing opinions on what determines infestation. "I would appreciate input from on some of the following issues:

1. How would you determine when a river (or lake) is 'infested' with zebra mussels? Do specific densities need to be reached? Do you need evidence of reproduction? Or is the presence of zebra mussels on multiple fixed substrates (bridge piers, rip-rap, etc.) sufficient to assu me infestation? What about multiple size classes attached to river substrate?

2. If evidence of reproduction is necessary, what level of sampling is necessary in a large river system to document this event? Should plankton samples or mesh samplers be used, or settling plates? Is any sampling likely to catch reproduction in the early stages?

3. Should we be looking at intermediate stages before calling something infested? For example, should we be telling people that we have found attached zebra mussels, but no evidence of reproduction, and that we are waiting for this to declare infestation?

4. What about remediation to prevent or slow the infestation of zebra mussels? Is having divers physically remove mussels from river substrates a viable option? Or is this a gesture as futile as trying to bail out the ocean with a bucket? Is there a density at which this might make sense? Has this been tried in any form elsewhere and, if so, what happened?

"Please send comments to me via email: gary.montz@dnr.state.mn.us. You can also fax me at (612) 296-1811, or call (612) 297-4888. I'd also like to try and organize an informal session at the 6th Zebra Mussel Conference to discuss these topics.".

ID: 199601-2.

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.