Mighty mussels surviving in post-flood Iowa River

Despite last year's catastrophic flooding of the Iowa River, researchers last week found six specimens they believe to be the endangered Higgins eye pearly mussel.

“We're pretty sure that's what they are,” though the samples' identity will be genetically tested, said an elated Scott Gritters, the Department of Natural Resources fisheries biologist who coordinates the DNR's annual mussel survey on Iowa's interior rivers.

The Higgins eyes, found between Hills and Iowa City on Thursday, were introduced through a propagation effort involving the stocking of smallmouth bass whose gills have been inoculated with the mussels' larva.

About 20 Higgins eyes had been found during last year's survey on the Wapsipinicon River near Anamosa and Central City, but none had been found in the Iowa River before Thursday.

The goal is to establish self-sustaining populations of the Higgins eyes outside the Mississippi River, where zebra mussels, a proliferating non-native species, threaten to render them extinct.

Gritters said he was pleased to learn that last year's catastrophic flooding on the Iowa River had not disrupted the propagation effort.

“The whole river bottom has been rearranged,” severely altering the mussels' habitat, said Gritters, who searched the river above, below and in Iowa City along with more than 20 other members of a multiagency task force on Wednesday and Thursday.

Gritters said he was surprised to find strong mussel populations below the Coralville dam's emergency spillway, where rampaging floodwaters in June 2008 crashed through at a rate of almost 40,000 cubic feet per second.

“We were amazed they didn't get blown out by the current,” he said.

That good news was tempered, however, by the researchers' discovery that a major mussel bed in downtown Iowa City could no longer be found.

“We're hoping they survived and will be found farther downstream,” he said.

The researchers were unable to find any sign of mussel reproduction in 2008, according to Gritters. “We lost a year class because of the flood,” he said.

Gritters said high post-flood bacteria levels could have also taken a toll on freshwater mussels, which are especially sensitive to pollution.

Gritters said last week's mussel survey - the DNR's fifth since 2005 - was one of the largest studies of the impact of catastrophic flooding on mussels.

The researchers spent Monday on the Wapsipinicon River near Anamosa and Tuesday on the Wapsi above and below Quasqueton. Attempts to find more Higgins eyes on the Wapsi were frustrated by high water, Gritters said.

Gritters said the annual surveys of mussels, which filter water for a living, have evolved into a method for monitoring the health of all aquatic species in Iowa's interior rivers.

“Mussels can't survive in degraded water. If we can keep them in our rivers, our rivers will support everything else we expect of them,” he said.