![]() Once the ravenous and prolific mussels get carried upriver, there’s not much anyone can do except watch their numbers rise and fall. Preventing their spread is why boats are not allowed to travel upstream past the Soo Line Arcola High Bridge. Native mussels use fish to carry their juveniles until the larvae-like organisms (called “veligers”) are old enough, but zebra mussel veligers float free in the water for a few weeks before latching on somewhere.Įven though numbers have risen in the known infestation zone, zebra mussels have still not been found on any cinder blocks upstream of the Boom Site boat landing. Unlike native mussels, which are large and heavy, have a muscular “foot” to hold onto the bottom and move around, and usually avoid the strongest currents, zebra mussels are native to lakes in Eurasia, and not well adapted to rivers. Protection possible Zebra mussels cover a rock found in the St. Croix before they can grab hold of something.īut the reverse is also true: periods of low water may make it easier for the invasive species to proliferate. During high water years, the river pushes zebra mussels, especially their helpless larvae, out of the St. The working theory is that zebra mussel juveniles get washed downstream when there is high water on the river, before they can grab onto something solid. Croix 360 about seeing the spike in numbers this summer. “We have higher temperatures, much lower water levels, lower flow than normal in previous years.”īoaters and beach users in both Prescott and Lake St. “The conditions must have been just right,” said Marian Shaffer, aquatic biologist for the Saint Croix National Scenic Riverway. ![]() The numbers increased by up to 1,000 percent. Then, last year, the blocks were covered in the little striped shells again. (Courtesy Marian Shaffer/National Park Service) It left more food for native fish and other aquatic creatures, helping the whole ecosystem.Ī monitoring cinder block from the St. The reprieve reduced the chances a boat motor would be destroyed by the mussels clogging its intakes, or that someone wading in the water would cut their foot on the sharp little shells. Very few of the invasive mussels, if any, were found on the blocks, year after year. In 2012, there was a sudden drop in the numbers, a trend that continued over the next two years. Ups and downs Zebra mussel numbers at monitoring sites on the lower St. The cinder blocks and boat checks helps scientists estimate the degree of infestation. In the fall, the agency visits marinas along the lower river and inspects boats which have been removed from the water, again counting how many zebra mussels they find. Divers retrieve them each spring, and scientists count the number of zebra mussels. The agency has placed cinder blocks on the river bottom at several points. ( Learn more on the Saint Croix National Scenic Riverway zebra mussels page.) To help monitor the population, the National Park Service began taking an annual zebra mussel census in 2004. In this program, we will treat once a month from May through August and from November through February (8 months total) concentrating on boat slips, bulkheads, lifts, jet ski ramps, ladders, irrigation water intakes and other structures.To reduce the chances of the invasive clams from getting farther upriver, boaters have been prohibited from traveling north past the Soo Line High Bridge since 1997. We used this product this past year and have had good success killing established adult colonies. We are offering a new program to treat zebra mussels with the only molluscicide approved in all 50 states. If left untreated, the cost of maintenance to repair damaged infrastructure can be extremely high and the danger of cut swimmers reduces your access to the lake. We are seeing the results of all that plant growth on the lakes now. This clearer water allows nuisance aquatic vegetation to grow in much deeper water than it could before. This deprives other marine live from the food and clears the water. Once done, they start to filter water to obtain nutrients. These quickly attach to structure, almost any type of surface, and begin to grow hard shells. When zebra mussels spawn in the Spring and the Fall they release millions of free floating larvae called veligers.
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