100-year-old mussels living in St. Croix River
The Wisconsin Department of Natural Resources says biologists have confirmed that endangered mussels first discovered in the St. Croix River more than three decades ago are still alive, and now estimated to be at least 100 years old.
The spectaclecase mussels (Cumberlandia monodonta), which can grow up to nine inches long, were first found above the St. Croix Falls dam in 1987. Biologists from the DNR, University of Minnesota and the National Park Service returned to the area and August and confirmed that the mussels are still there.
Biologists estimated that they must be more than a century old because a dam has prevented spectaclecase mussels from reproducing in the area for more than a century.
"Native mussels can live a long time, but these mussels were pushing the limits," said Lisie Kitchel, DNR Conservation Biologist, in a news release issued this month.
"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," Kitchel said.
The fish needed for reproduction are mooneye and goldeye fish, which serve as host species for spectaclecase larvae. Mooneye and goldeye fish are found downstream from the dam, where surveys have found younger spectaclecase.
"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 a news release.
The biologists retrieved some dead spectaclecase shells from the upstream site to be cross-sectioned to verify their age. The live spectaclecase mussels were returned to their habitat.
The U.S. Fish and Wildife Service says spectaclecase mussels are found in only 20 streams nationwide.