Detecting a population of mussels up to 100 years old on the American River

A team of researchers identified upstream mussels in Wisconsin as more than 100 years old based on the time it took to build the dam.

Biologists from the Wisconsin Department of Natural Resources (DNR), the University of Minnesota and the National Park Service discovered a population of spectaclecase clams (Cumberlandia monodonta) in the upper reaches of the St. Croix at the St. Croix in August 2021. The spectaclecase clam is a freshwater mussel native to the United States and is listed as Endangered by the US Fish and Wildlife Service (FWS) and the International Union for Conservation of Nature.

The team took pictures with the population of perennial mussels on the St. Croix. (Photo: NPS)

Large mussels that can grow up to 23 cm are found in at least 44 streams in the Mississippi, Ohio and Missouri river basins in 14 states, according to the FWS. But spectaclecase oysters are disappearing in these three states and only exist in 20 streams. Today, spectaclecases exist in the states of Alabama, Arkansas, Illinois, Iowa, Kentucky, Minnesota, Missouri, Tennessee, Virginia, West Virginia, and Wisconsin.

When biologists found the spectaclecase mussel population in August in the St. Croix, they were unable to determine their age in situ by growth ring counting due to shell erosion. Instead, they estimated mussels to be over 100 years old based on the date of the river's dam construction in 1907. "Native mussels can live for long periods of time," says Lisie Kitchel, a conservation biologist at the DNR. , said. "Finding a viable population of mussels is an interesting discovery because the fish, the hosts that mussels need to reproduce, cannot swim upstream due to the St. Croix waterfall dam built in 1907."

As female spectaclecase clams mature, they release larvae called "glochidia". Larvae must attach to the gills or fins of fish to continue to develop into young clams. The young clams then separate and if they land in the right area, they will develop into adults. In this way, mussels use fish to move upstream and settle down. The biologists put the live spectaclecase clams back to their original environment. The team also collected the shells of dead mussels for laboratory analysis to determine their true age.

The spectaclecase oysters are declining due to a variety of factors related to human activity, including damming on rivers, increased river sedimentation, pollution, dredging and canal construction. According to FWS, dam construction Rivers contribute more to spectaclecase mussel decline and extinction than any other activity. This activity isolates populations upstream and downstream, blocking the swimming path of many of the fish species that mussels parasitize. Dam construction creates small, less stable populations with a lower chance of survival.

Wisconsin is home to 50 native mussel species, 24 of which are endangered, threatened, or in need of conservation. Native mussels play an important role in river ecosystems, helping to clean the water by filtering pesticides, mercury and pollutants, and providing food for some animals.