Home Biologist Scientists discover that century-old “stranded” mussels survive in the top of Sainte-Croix

Scientists discover that century-old “stranded” mussels survive in the top of Sainte-Croix

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Biologists from the DNR, the University of Minnesota and the National Park Service present spectacle mussels over 100 years old found in the St. Croix River. Photo credit: Marian Shaffer, National Park Service

The Wisconsin Department of Natural Resources (DNR) today announced that threatened native mussels first found above the St. Croix Falls dam in the St. Croix River in the St. Croix River in 1987 were discovered by the federal and state governments for the first time. are still alive and are believed to be over 100 years old.

In August 2021, biologists from the DNR, the University of Minnesota and the National Park Service excavated a stretch of river upstream of the St. Croix Falls dam where spectacle mussels (Cumberlandia monodonta) was discovered 34 years ago and found a cluster of native mussels.

Spectacle mussels (Cumberlandia monodonta} can grow up to 9 inches long and are named after the shape of their shells, which are elongated and sometimes curved. Spectacle cases are on the federal and state lists of endangered species. . (Photo by Marian Shaffer / NPS)

Due to the erosion of the mussel shell, biologists were unable to determine the age of the mussels on site by counting their growth rings. Instead, biologists estimated the specimens to be over a century old based on when the river was dammed.

The living spectacle mussels have been safely returned to their habitat. Shells of dead glasses cases have been rescued and will be cut this winter to verify their age.

“Native mussels can live a long time, but these mussels were pushing the boundaries,” said Lisie Kitchel, MNR conservation biologist. “Finding them alive was incredible, because the host fish species necessary for them to reproduce were prevented from moving upstream because of the St. Croix Falls dam built in 1907.”

Once the female scopes have reached maturity, they expel their larvae, called “glochidia,” which must attach themselves to the gills or fins of a specific fish to continue developing into a juvenile mussel before dropping and falling. become an adult mussel. Using fish as a host allows the spectacle case to move upstream and populate habitats that it might not otherwise be able to reach.

Recent research has identified moon-eyed and golden-eyed fish as host species for spectacle cases. These species are not present upstream of the dam but are found downstream. This means that reproduction can take place downstream, and studies have found younger glasses downstream.

Due to the advanced age of mussels, biologists take steps to preserve their genetic stock while they are still alive.

“Now we can implement strategies to propagate and increase the spectacle population there or reintroduce moon eyes or gold eyes above the dam to allow the spectacle box to breed,” said Jesse Weinzinger, conservation biologist at DNR.

Collaborative partnership aims to restore eyeglass molds

The St. Croix River investigations are part of a collaborative, multi-state, multi-agency effort to help recover the eyeglass cases. The DNR, the Minnesota Department of Natural Resources, the University of Minnesota, the US Geological Survey, the US Army Corps of Engineers, and the US Fish and Wildlife Service are working to provide the data necessary for the recovery of cases at glasses and the implementation of conservation, restoration and propagation priorities.

Spectacle mussels can be up to nine inches long and get their name from the shape of their shells, which are elongated and sometimes curved. Historically, the spectacle case has been found in at least 44 rivers in the Mississippi, Ohio, and Missouri river basins in 14 states. It has completely disappeared in three states and is now rarely found in just 20 rivers, according to the US Fish & Wildlife Service.

Little was known about their current distribution and status in the Mississippi and St. Croix rivers until recent surveys by MNR and other partners in 2019, 2020, and 2021.

Wisconsin has 50 native mussel species, including 24 endangered, threatened, or in need of conservation. Native mussels are important in keeping Wisconsin rivers clean. They filter pesticides, mercury and other pollutions from the water and prevent them from entering the fish. They provide food for otters, raccoons, muskrats, ducks, fish and other wading birds. They also help indicate problems that may affect all lake or river ecosystems.

Students and bolunteers help place hatchery-raised mussels in rivers

MNR has partnered with partners across Wisconsin to deliver and place more than 1,200 hatchery-raised mussels in several rivers in Wisconsin where past water quality issues have taken a toll on mussel populations. .

“Propagation and reintroduction is a useful conservation strategy for increasing the abundance and distribution of native mussel populations,” Weinzinger said. “We are grateful for the partnerships that have increased mussel populations in these streams and provide future research to help shape recovery efforts.” ”

Weinzinger said the Genoa National Hatchery has bred thousands of fatmuckets (Lampsilis siliquoidea) as part of an experiment to find optimal water quality parameters and feeding rates for better survival.

Students at the University of Wisconsin-Stevens Point worked with conservation biologists from MNR to place more than 700 mussels in two streams in Portage County to monitor animal growth and survival. The results of this student-led project will help determine the feasibility of future reintroduction efforts.

In southern Wisconsin, MNR has partnered with the Upper Sugar River Watershed Association to place an additional 500 muckets in the Sugar River to increase existing populations.

To learn more about how MNR and its partners are working to conserve our native mussels, visit the MNR Wisconsin Mussel Monitoring Program webpage. Read the Clam Chronicle newsletter to see how MNR is working with volunteers to create projects, programs and tools for citizen-focused monitoring efforts.