Angelique Edgerton is the Invasive Species Coordinator for the St. Croix River Association. This article originally appeared in SCRA’s newsletter, “River Time.”
Zebra mussels (USGS photo)
Zebra mussel prevention efforts began on the St. Croix in 1992. None were found living in the river (over the years, a few were detected on boats) until 2000. At that time, the MN DNR declared the river from Stillwater south to be infested and over the next several years, zebra mussel populations established and formed colonies more numerous as you headed downstream. While zebra mussel numbers have fallen from their peak in 2007, they are still found throughout the river south of the Stillwater Lift Bridge. Since 1996, the National Park Service has instituted annual boating restrictions to protect zebra mussel-free stretches of the river. Today, these aquatic invasive pests remain a significant threat with the potential to drastically alter the river ecosystem and devastate native mussel populations.
During this past fall, the SCRA assisted the National Park Service in conducting zebra mussel inventories on dry docked boats at local marinas. The proportion of boats with zebra mussels attached was lower further upstream; 46% of boats in Prescott, 30% of boats in Hudson, and 5% of boats in Stillwater had attached zebra mussels. This trend is consistent with previous years, and indicates that zebra mussels are still very much a threat to the lower watershed.
The SCRA will continue assisting partners with aquatic invasive species (AIS) management on the St. Croix in an ongoing effort to protect the wild and scenic riverway. Over the next year, SCRA will expand current partnerships, as well as forge new relationships with businesses, communities, and riverfolk throughout the watershed. These partnerships will allow all of us to make more informed decisions and work collaboratively, and will enable us to achieve larger results in the prevention and control of AIS in the St. Croix basin.
Zebra mussels were most likely brought to America as larvae, in water used as ballast aboard ships that traveled from fresh water Europe to the Great Lakes. They are reproductively mature within 1 year, and females can produce up to 30,000 eggs in their first year of life. The shells of their trochophore larvae form within 2 to 9 days of fertilization. Zebra mussels are the only freshwater mollusks that can firmly attach themselves to solid objects.
Byron Karns of the Saint Croix National Scenic Riverway contributed to this article.