Biologists discover rare mussels in St. Croix River

1 10 Mussels
DNR, University of Minnesota, and National Park Service biologists display 100-plus-year-old spectaclecase mussels found in the St. Croix River. (Marian Shaffer, National Park Service)

MADISON, Wis. —Biologists discovered a cluster of rare mussels that could be more than 100 years old in the upper St. Croix River this past summer.

Wisconsin Public Radio reported last week that biologists from the University of Minnesota, the Wisconsin DNR and the National Park Service discovered eight spectaclecase mussels in the river in August.

Spectaclecase mussels rely on mooneye and goldeye fish to serve as hosts for their larvae. But a hydroelectric dam built in 1907 has prevented the fish from swimming upstream and reaching the mussels in the upper St. Croix. Younger spectaclecase mussels have been found downstream of the dam, but researchers stopped looking for them upstream in 1987. They were surprised to find any still alive in the river’s upper reaches, DNR officials said in a news release.

“Native mussels can live a long time, but these mussels were pushing the limits,” Lisie Kitchel, a DNR biologist who was on the team that discovered the cluster, said in the news release.

She told WPR that the cluster will probably die off but biologists will keep monitoring them to see how long they live.

DNR officials said in the news release that biologists will try to preserve the cluster’s genetics before they perish in hopes of growing the population in the upper St. Croix or reintroduce mooneye or goldeye above the dam to encourage reproduction.

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