Mussel Blitz
Posted: 08/26/2014

From the adjacent sandbar, the scene looks like a diving school gone awry. Two shallow divers are connected to oxygen lines. A couple others have masks. Another four wade through the shallower sections. Every couple minutes, someone hoists another mussel; adding to the inventory.

“You are looking for coarser gravel, but not big cobblestones,” explains Vance Polton, DNR fisheries technician. He is standing knee deep in the Iowa River, below Iowa City; returning a Wabash pig toe to the sandy bottom.

“They have to push through the substrate where they are located,” says Polton. Onshore, small piles of live mussels are inventoried, measured for growth; and then returned to the water.

Iowa’s mussel dilemma is mirrored throughout North America. A dozen of 54 known Iowa species are gone. At least half of the remaining species are endangered or threatened. That wakeup call is what brings up to 50 biologists, students and volunteers for a week of wading and groping often muddy Iowa stream bottoms for elk toes, three-ridge, pocketbooks and fat muckets. If nothing else, freshwater clams have great names!

This summer, the target river was the Iowa; above and below Iowa City. Historically, it has been a good ‘mussel’ river.

“Fish and mussels have ‘co-evolved.’ They somewhat depend on each other,” underscores Scott Gritters, DNR fisheries biologist and annual ringmaster of Iowa’s Mussel Blitz. “The more mussel species; the better the mussel density; the better our fish populations; the better our water quality.”

The results this year?

"It’s one of those ‘glass half full, glass half empty,’ scenarios,” assesses Gritters. His long term concern is that populations cannot handle the cycle of water level highs and lows of past years.

“We really scoured some areas. We found 1,500 mussels; 20 species. We found some decent populations, but I had hoped for 3,000 or so. Mussels don’t react well to water level fluctuantions that change quickly.”

On the upside, the 2014 Mussel Blitz turned up another six Higgins’ eye pearly mussels; thought nearly extinct 40 years ago. Any Higgins’ eyes in the Iowa River were stocked there. Raised in hatcheries; they were inoculated as glochidia--larvae--into the gills of fish, stocked several years ago. No larger than grains of salt then, they hung onto their host for several weeks…before dropping off; hopefully into a hospitable gravel bed.

To have the nearly microscopic mussels show up now, as adults?

“It’s a pretty big deal,” applauds Gritters. “It is a way to reintroduce mussels into our rivers by stocking fish. We stock a lot of fish for our anglers and this way we can ‘double dip,’ so to speak.”

With floods, excess nutrients and sediment covering mussel habitat, even extreme cold affecting these inland mollusks, a few glimmers appear from year to year.

“People will like our rivers a lot more, if they can support mussels,” says Gritters.

For more information, contact Joe Wilkinson, Iowa Department of Natural Resources, 319-430-0325