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Iowa Mussel Blitz

  • 9/12/2017 2:21:00 PM
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The upper Cedar River was the focus of this year’s annual research project to inventory and map the distribution of Iowa’s mussels, often called clams. 

More than 50 biologists, students and volunteers collected 18 species of freshwater mussels in the Cedar River during the three day event held each August since 2005.

“We had excellent participation from our conservation partners, volunteers and county naturalists with this year’s survey,” said Scott Gritters, fisheries biologist with the Iowa Department of Natural Resources (DNR).

Live mussels were inventoried, measured for growth; and then returned to the water. Most of the mussels were found using a technique known as pollywogging, as researchers and volunteers crawl along a stream bed, probing the bottom with gloved hands.

“These studies help us learn more about mussels and the areas where they live and thrive,” said Gritters. “We knew this area is biologically diverse, but we wanted to study the impact of the many dams on this stretch of the Cedar River. We are also working with the Minnesota Department of Natural Resources to determine the best methods to restore some lost mussels or declining mussel species in our respective stretches of the Cedar River.”

The Iowa DNR, the U.S. Fish and Wildlife Service and the U.S. Army Corps of Engineers started researching the disappearance of native fresh-water mussels in Iowa 12 years ago, including the federally endangered Higgins-eye pearly mussel. Once ranging across most of the upper Midwest, this species has been eliminated from most of the river systems it once thrived in.

"Historically, there were maybe 54 species of native mussels in Iowa,” Gritters said. “Now, it's about 42. Of those, nine are endangered. Another six are threatened and several more species are very hard to find any more in Iowa.”

Over the past several years, stretches of the Cedar, Wapsipinicon and Iowa rivers have been stocked with walleyes and bass whose gills had been injected with the mussels’ larvae.

“Stocking fish, something we commonly do anyway, is one way to reintroduce mussels into our rivers,” he said. “We stock a lot of fish for our anglers and this way we can ‘double dip’, so to speak.”

This year’s Mussel Blitz documented some very rich and diverse mussel beds, mostly in the free flowing and wild stretches of the Cedar River. Mussels (and fish) flourish in this type of habitat.

Native mussels do not do well in soft substrates in our rivers, he said. The stretches immediately above the low head dams were nearly empty of native mussels. Impoundments block migrating fish, which are the main way native mussels move (hitchhiking) and the habitat above dams usually has silt and sand. 

Mussels are a good indicator of the health of a river. The better the water quality, the more mussels there are in that water. Mussels compact the algae they filter then kick out the crushed pellet to waiting fish; much like how fish are fed at a fish hatchery.

Many of the major fish spawning areas are in mussel beds on the Mississippi River. That may hold true on the Cedar River as well. The abundant crayfish populations observed were using old dead remnant mussel shells for their homes. Crayfish are a vital food source for predatory fish including smallmouth bass.  

“The whole river ecosystem runs better with native mussels living in it. Fish and mussels have ‘co-evolved.’ They depend on each other,” said Gritters. “Our fish populations, water quality and the opportunities people have to enjoy the water improve with more mussel species in Iowa waters.”