Scientists Find Mussels Thought to Be Over 100 Years Old in Wisconsin River

Researchers have identified mussels in a Wisconsin river that are estimated to be more than 100 years old.

Biologists from the Wisconsin Department of Natural Resources (DNR), University of Minnesota and the National Park Service found the spectaclecase mussels (Cumberlandia monodonta) upstream from the St. Croix Falls dam in the St. Croix River in August, according to a statement.

The spectaclecase mussel is a species of freshwater mussel that is native to the United States, although it is now listed as endangered by the U.S. Fish and Wildlife Service (FWS) and the International Union for Conservation of Nature.

The large mussels, which can grow up to 9 inches in length, were historically found in at least 44 streams of the Mississippi, Ohio and Missouri River basins across 14 states, according to the FWS. But the species has disappeared from three of these states and is now only found in 20 of the aforementioned streams.

Today, spectaclecase mussels can be found in Alabama, Arkansas, Illinois, Iowa, Kentucky, Minnesota, Missouri, Tennessee, Virginia, West Virginia, and Wisconsin, although populations tend to be fragmented.

When biologists found the cluster of spectaclecase mussels in August in the St. Croix River, they were not able to determine their age on site by counting growth rings due to the eroded state of the animals' shells. Instead, the scientists estimated that the mussels were more than a century old based on the date that the river was dammed—1907.

"Native mussels can live a long time, but these mussels were pushing the limits," Lisie Kitchel, a conservation biologist with the DNR, said in the statement. "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."

When female spectaclecase mussels mature, they expel larvae known "glochidia" that must attach to the gills or fins of specific fish in order to continue developing into a juvenile mussel.

Eventually, the juvenile mussels are dropped off and, if they land in a suitable area, they will mature into adult mussels. In this way, the mussels use fish to move upstream and populate habitats that they would not be able to reach otherwise.

Any living spectaclecase mussels that the biologists collected were placed back in their original habitat. Meanwhile, the team saved shells from dead mussels so that they can be analyzed in a lab in order to determine the true age of the animals.

Jesse Weinzinger, another conservation biologist from the DNR, told Newsweek it was "certainly a possibility, and likely a high possibility" that the mussels will turn out to be the oldest ever recorded for their species.

"Known populations of spectaclecase mussels in the St. Croix River are regularly aged between 20 and 30 years old by the Wisconsin DNR, when counting external growth rings," she said. "Other known information on the species suggests a maximum age of 56 years, however a specimen from the St. Croix River was estimated—based on external growth ring counts—to be approximately 70 years old."

Spectaclecase mussels have suffered drastic declines due to various factors related to human activity, including the damming of rivers, increases in river sedimentation, pollution, dredging and channelization, and the introduction of non-native species, such as zebra mussels that compete for space and resources.

According to the FWS, the damming of rivers has contributed more to the decline and potential extinction of this species than any other factor, isolating upstream and downstream populations, and blocking the passage of fish species that the mussels depend on, among other issues. Damming creates, small, more unstable populations that have lower chances of survival.

Recent research has identified mooneye and goldeye fish as host species for these mussels. These fish are not found upstream from St. Croix Falls dam, but they are present downstream, meaning that the mussels can reproduce there.

Scientists are now working on strategies to help the spectaclecase population in the St. Croix River.

"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," Weinzinger said in the statement.

Wisconsin is home to 50 native mussel species, 24 of which are endangered, threatened or in need of conservation. Native mussels play a key role in the river ecosystem, helping to keep waters clean by filtering out pesticides, mercury and other pollution, while also providing food to several animal species.

"Mussels function as ecosystem engineers by filtering and cleaning vast volumes of water, cycling nutrients, and forming a basis for aquatic food webs by capturing and depositing organic matter on which other organisms depend," Weinzinger told Newsweek.

"As sentinels of ecosystem health, freshwater mussels have experienced dramatic declines and are considered the most imperiled animal group in North America. Widespread habitat destruction, pollution, stream fragmentation and inundation by dams have caused many mussel assemblages to decline or disappear.

"As a result, about 30 North American species are extinct, and 65 percent are considered endangered, threatened, or vulnerable."

Update 12/13/21, 8:52 a.m. ET: This article was updated to include additional comments from Jesse Weinzinger.

Spectaclecase mussels found in St. Croix River
Biologists display spectaclecase mussels found in the St. Croix River that are thought to be more than 100 years old. Marian Shaffer/National Park Service