CHAMPAIGN, Ill., 4/5/22: In the summer’s heat, an Illinois Natural History Survey (INHS) aquatic biology team can be found in shallow rivers or streams under bridges slated for reconstruction, wading in water and sliding their fingers through the rocks and sediment below, searching for the edge of mussel shells. They’ll move the mussels they find out of harm’s way of construction equipment that will soon roll into the area.

“It’s difficult to track the survival of the population of mussels in an area to know if we are making a difference,” said Alison Stodola, INHS aquatic biologist. “But as we’re collecting them, we like to say that we’re making a difference to this one. We know that this one won’t get squished.”

INHS mussel surveys and relocations are funded by the Illinois Department of Transportation (IDOT), which manages road and bridge construction projects. A project that is in the vicinity of any protected natural resource will likely be subject to restrictions under the Illinois Endangered Species Protection Act, including mandatory surveys in the area prior to construction.

The field surveys aim to confirm the presence or absence of threatened and endangered species and to minimize the impact of IDOT bridge and roadway projects on these species. Besides mussels, INHS biologists survey a wide variety of plants and animals.

Unlike birds that have specific migration and breeding seasons that can dictate when construction may begin, mussels are present year-round, so it’s difficult to avoid adverse effects on mussel populations. Sometimes they must be relocated further downstream.

There are approximately 60 mussel species remaining in Illinois, and all have unique preferences for different parts of the river. They are also difficult to find since they bury themselves in the sediment at the bottom.

“Freshwater mussels can be sneaky, and sometimes species go undercover for many years,” Stodola said.

For relocations, the team uses weighted ropes mapped out across the stream. Each person searches all the way across and back, making several passes until they no longer find any mussels. The team measures each mussel, identifying the species and examining its condition.

The mussels are then moved downstream, far enough outside of the silt plume created by construction equipment. Once they move to their new location, mussels use their foot to get a toehold and work their way back into the substrate.

At least two follow-up surveys are required after construction to measure the impacts of the project. Surveys taken before and after project completion are important since there is no statewide monitoring program for mussels, as there is for fishes and macroinvertebrate insects.

To find populations threatened or endangered species, “we use what we know about the different species to target certain areas” Stodola said. “There’s an art to surveying, so it’s helpful to have people on the team who are familiar with mussel biology and search techniques.”

The surveys provide a community assessment of mussels in a location and extensive data that are stored at INHS. Stodola, who is the curator at the INHS Mollusk Collection, keeps a catalog of the shells of different species in case there is a question about the species identification or an unusual find.

“Mussels can live for 40 or 50 years, which is why it’s critical to be cognizant of the endangered species that might be destroyed,” Stodola said. “The mussels are going to live awhile, so it’s important to take care of the ones that are there.”

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Media contact: Alison Stodola, 217-300-0969, alprice@illinois.edu
news@prairie.illinois.edu