CHAMPAIGN, Ill. – Relocating freshwater mussels from the path of a bridge construction site to a safer zone upstream is proving to be a time- and cost-effective conservation practice. Mussel survival rate after relocation is high, according to new research from the University of Illinois’ Prairie Research Institute (PRI).
Temporary dams erected for bridge construction alter silt and water levels in the river, and mussels are crushed from large equipment. Both common and endangered mussel species are at risk.
Historically, about 80 freshwater mussel species inhabited Illinois streams. Only about 55 species remain today. Populations have declined largely because humans have changed river habitats.
While relocation of mussels over short distances is preferred to minimize damage to mussel communities, its effectiveness in terms of recovery and survival is not well known.
In a three-year study, aquatic ecologist Jeremy Tiemann and colleagues at the Illinois Natural History Survey, a division of PRI, relocated 100 mussels upriver during a reconstruction project on the Interstate 90 bridge over the Kishwaukee River in northern Illinois.
The team tagged individuals of two common mussel species, the Mucket and Plain Pocketbook, with microchips, and used an underwater radio receiver to locate the mussels without disturbance. Tagged mussels were monitored monthly in the spring and summer months of 2013–2015.
The team lost the signals of 17 mussels, which may have moved or been swept out of the study area. Overall, the survival rate was high, with most deaths occurring during the first two months after relocation, Tiemann said.
“The mortality we recorded in 2013 may have resulted from stress following the recent drought when the river started to return to its normal levels, as well as relocation to an unfamiliar habitat,” he said.
The researchers used a statistical model to predict survival rates, which indicated that 93 percent of the relocated Mucket species and 71 percent of the Plain Pocketbooks remained alive three years after relocation.
“Our data suggest that short-distance relocation is a viable tool for mussel conservation,” Tiemann said.
Mussels can live more than 50 years and play a vital role in improving river conditions.
“We call them livers of the rivers because they purify water, removing bacteria, particles, and pollutants,” Tiemann said. “Their filtering capacity can be compared to a water treatment plant, because a single mussel can filter 8 or more gallons of water a day. They do their part to clean up the environment.”
Considering that mussels occur in aggregations, the amount of water being filtered increases exponentially. Some sites in the Mississippi River support millions of mussels in a small area.
This study was funded by the Illinois State Toll Highway Authority and was published in the journal Freshwater Mollusk Biology and Conservation.
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Media contact: Jeremy Tiemann; jtiemann@illinois.edu; 217-244-0802
