Endangered mussels found in St. Croix River believed to be more than 100 years old

A group of researchers discovered a group of native mussels believed to have been in the St. Croix River for more than 100 years, an especially long livelihood for the endangered species important to healthy rivers.

The spectaclecase mussels were discovered in August by biologists from the Wisconsin Department of Natural Resources, the University of Minnesota and the National Park Service. The group was trying to relocate the endangered native mussels after they were first discovered in 1987 above the St. Croix Falls dam.

The mussels showed signs of shell erosion, so biologists weren't able to determine the mussels' age on-site, according to a DNR release, but estimates put the water-dwellers at around a century old, based on when the river was dammed.

The live mussels were returned safely to their habitat after inspection, but dead shells were saved and will be inspected this winter to verify their age.

“Native mussels can live a long time, but these mussels were pushing the limits,” Lisie Kitchel, DNR conservation biologist, said in the release. “Finding some alive was amazing since the host fish species needed for their reproduction have been prevented from getting upstream as a result of the St. Croix Falls dam built in 1907.”

The mussels were located as a part of a collaborative partnership to recover the spectaclecase. The Wisconsin DNR is working alongside the Minnesota DNR, the University of Minnesota, the U.S. Geological Study, the U.S. Army Corps of Engineers and the U.S. Fish and Wildlife Service to gather data on where to find the mussels and how to conserve and restore the population.

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The mussels can grow up to nine inches long and are named for the shape of their shells, which are elongated and curved, much like a case for spectacles. Spectaclecase were historically found in at least 44 streams of the Mississippi, Ohio and Missouri River basins in 14 states, but the mussel has vanished completely in three states and is rarely found in 20 streams, according to the Fish & Wildlife Service.

Spectaclecase mussels reproduce through the use of larvae, known as "glochidia," which then attach to the gills or fins of a specific fish to continue developing. Eventually, the juvenile mussels will drop off of the fish and continue growing. Using fish as a host allows spectaclecase to move upstream and populate habitats it otherwise wouldn't reach, the DNR said.

Recent research has shown mooneye and goldeye fish as hosts for the mussels. Those species are not found above the dam in the St. Croix River but are found downstream, meaning reproduction can occur there.

The biologists that discovered the endangered mussels over the summer are now working to preserve the genetic stock while they're still alive.

“Now we can implement strategies to propagate and augment the spectaclecase population there or reintroduce mooneye or goldeye above the dam to allow the spectaclecase to reproduce,” said Jesse Weinzinger, DNR conservation biologist, in the release.

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Mussels such as the spectaclecase are important to keeping Wisconsin rivers clean by filtering pesticides, mercury and other pollution out of the water and fish. They provide food for otters, raccoons, muskrats, ducks, fish and other wading birds. They also can help to indicate issues within water that can affect the whole lake or river ecosystem, according to the DNR.

The Wisconsin DNR is working to introduce more native mussels across the state and has placed more than 1,200 hatchery-raised mussels where water quality issues have taken a toll on the creatures.

“Propagation and reintroduction are a useful conservation strategy to increase the abundance and distribution of native mussel populations,” Weinzinger said. “We’re thankful for the partnerships that made it possible to augment mussel populations in these streams and provide research going forward to help us shape recovery efforts.”

Laura Schulte can be reached at leschulte@jrn.com and on Twitter at @SchulteLaura.

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This article originally appeared on Milwaukee Journal Sentinel: Endangered mussels in St. Croix River believed to be 100 years old