A little more than two years ago, on a sunny weekday morning, divers set upon the Mississippi River near the Moline riverfront to remove tens of thousands of mussels from the footprint of the Interstate-74 bridge construction zone.
Now that construction of the span is well underway, the mussels haven't been forgotten -- not the ones that were moved, nor the habitat from which they were relocated.
Approximately 140,000 mussels were relocated two years ago. It was a significant undertaking that included divers, as well as people on shore who were charged with sorting and cataloguing the mussels.
Of the mussels that were removed 3,470 were Higgins eye pearlymussels, 407 spectaclecase mussels and 856 sheepnose mussels, according to the U.S. Fish and Wildlife Service.
Those three species are federally protected.
The removal was just the first step in a lengthy monitoring process.
So far, according to an official from the U.S. Fish and Wildlife Service in Rock Island, the news has been good.
"As far as mortality, I think we're in an expected comfort zone," Heidi Woeber, a fish and wildlife biologist, said.
Monitoring is done in each of the first two years after a relocation. One round took place in 2017, and Woeber said she believes that this year's monitoring will likely occur before the end of September.
To some extent, the timing depends on water levels, which have been high on the Mississippi River this year.
Monitoring involves divers examining a quadrat, or search area, to identify mussels with markings, as well as resident mussels that have not been marked, Woeber said.
The examination tells officials not only if the mussels survived the move, but whether they've continued to grow.
"We hope that the monitoring study will result in greater knowledge of the success of mussel relocation methods for future transportation projects," Woeber said.
After the first two years of a relocation, monitoring is done in years 5, 10 and 15.
A 2014 survey estimated that there were over 850,000 mussels living in a 22-acre area likely to be affected by construction of the new I-74 bridge. The number of mussels moved, 140,000, was less than originally expected. But it was still one of the largest in the country, according to the I-74 project team.
Construction of the span also is done with a range of protected species in mind, said Danielle Alvarez, I-74 project manager for the Iowa Department of Transportation.
"It doesn’t stop at mussels. There are a lot of protected species we need to be cognizant of," she said.
That includes bats and migratory birds, which affected tree clearing.
In addition, she notes, steps have been taken to accommodate the surrounding environment, particularly the Mississippi River. When shafts were drilled to support the bridge's piers, chemicals were used to help filter sediment from the water.
That also had some benefit for mussel habitat. "This is part of the stewardship of the water body," said Alvarez.
Another survey will be conducted soon of the area where mussels were removed two years ago, she said. And prior to removal of the existing bridge, which is expected in 2021, there will be another examination of areas with protected species of mussels.