Emily Robbins measures and takes detailed information on mussels removed from an area near the new piers for the I-74 Bridge on the Illinois side of the Mississippi River.

Kevin E. Schmidt, QUAD-CITY TIMES

The first phase of relocating tens of thousands of freshwater mussels from the Mississippi River as part of the construction of a new Interstate 74 bridge has been completed. And while another phase remains to be done, officials say they don't expect to collect nearly as many mussels as they initially thought.

An official from the U.S. Fish and Wildlife Service said that work on the first phase, which began in August, was completed in early November. Heidi Woeber, a fish and wildlife specialist, said about 140,600 mussels were moved, including 886 that are federally protected.

The relocation involved teams of divers combing the bed of the Mississippi River for mussels, which then were identified and, in some cases, tagged for future identification. The mussels then were returned to another part of the river.

A second phase will take place before demolition of the existing span, which is expected in four to five years. The initial work, mostly near the Illinois shoreline, was done in the area where a new I-74 span will be built. There also were removals near the Iowa side of the river, but the numbers were smaller.

Construction of the new bridge is expected to begin in 2017, with the installation of piers in the Mississippi River.

Initially, officials said, they expected to relocate approximately 450,000 mussels. An Iowa Department of Transportation official said Tuesday they're not likely to reach that figure.

"I don't think we'll get close to that 400,000 number," said Mary Kay Solberg, senior environmental specialist with the state DOT.

Surveys were conducted to locate mussel beds and estimate their density before work began. But officials say that while those surveys, which used random sampling techniques, accurately located the areas where there were the highest number of mussels, the density estimates were high.

Solberg did not have a new estimate for how many mussels would be collected when all the work is done. But Woeber said they did not expect to relocate as many mussels in the second phase as the first.

Of the 140,600 mussels relocated during the first phase, 755 were Higgins eye pearly mussels, 107 Sheepnose and 24 spectacle case mussels. Those three species are federally protected.

The relocation of the mussels has so far cost about $1.6 million. Overall, the estimated expense of the removal is expected to be between $3 million and $3.5 million, Solberg said. The I-74 project itself is estimated at $1.2 billion.

Solberg initially said the relocation would be the largest in U.S. history. Even while it appears the final figures will fall below initial estimates, she said it still will likely rank among the largest. Solberg said there was a relocation in Pennsylvania that was roughly the same size.

Regardless of the number of mussels removed, officials say the exercise will yield lessons for future relocations. Officials expect to track the mussels they tagged for several years. In addition: Before construction begins on the new span, crews are expected to go out next spring to do another sweep of the area. Woeber said one of the things they expect to learn is whether, and how quickly, mussels move back into an area.