AUSTIN — Minnesota’s freshwater mussels need some help.
While wildlife naturalists are doing their part to help some species gain a foothold in areas where they have disappeared, mussels also need a hand from wildlife in their habitat.
To reproduce, mussels need host fish to carry their larvae to maturity and them throughout their habitat.
Staff from the Minnesota Department of Natural Resources’ Center for Aquatic Mollusk Programs in Lake City did their part last week. They released captive-raised black sandshell mussels in the Cedar River near Austin.
The release was the first re-introduction of a mussel species into the wild by the center, also known as CAMP.
"It’s probably been a century since those mussels have been here," said Mike Davis, CAMP project leader. "And we think we can get this species going here again."
Some specially tagged mussels were carefully placed a couple of inches deep into the river bottom by staff in scuba gear. The release had been delayed due to high water and the Cedar was still somewhat high and moving swiftly when staff donned the gear in stifling heat.
The mussels they placed will be tracked for movement and survival rate.
Hundreds of other mussels, with DNR markings but not numbered, were placed in the river a bit less ceremoniously.
"We can just toss them," said Madeline Pletta, CAMP mussel biologist as she waded into the river and tossed the 2-inch shells into the water.
Overall, biologists and staff released nearly 1,500 of the mussels in three locations in the river.
Those tossed mussels will have a chance to find and establish their own spot in the river bank.
"If they don’t like where we put them, they’ll find a better spot," Davis said.
'Near and dear'
Although that portion of the release appeared nonchalant, the sandhill mussels have a special place in Pletta’s heart, she said.
"This is a big moment for me," she said. "These mussels are near and dear to my heart."
"They’re a pretty little mussel," Davis said.
Black sandshell mussels were native to that stretch of the Cedar River. However, pollution eradicated the population in that area. The river is cleaner now and the species has rebounded downstream in Iowa. However, the species faces obstacles for returning to the area in southern Minnesota. Downstream dams in the river prevent the fish the mussels use to propagate from moving upstream.
Biologists at CAMP collaborated with the Iowa DNR to propagate mussels at the lab in Lake City. Iowa officials helped CAMP staff collect pregnant female mussels in Iowa. Lab staff placed them in tanks with a mix of host fish — large mouth bass and bluegill.
The lab is home to hundreds of host fish of several species.
Catch a host
Pletta helped design the lab when she accepted her position there following working to raise mussels at the Virginia Fish and Wildlife Center. Davis has been a longtime Minnesota mussel researcher and historian.
In the wild, mussels ready to release larvae will put out a "lure" for their host fish. The lure is a fleshy part of the mussel that resembles fish food. When a fish goes to strike the lure, the mussel releases larvae that lodge in the fish’s gill. Once the larvae mature into juvenile mussels, they drop from the gills.
In the lab, a filter collects the 0.2 millimeter-wide juvenile mussels. Mussels are placed in tanks of river water and fed algae. Once they reach about an inch in size, they get "field trips" into freshwater environments for a season. The first round of growth takes a couple years in the lab. In the wild, the mussels more than double in size in one season in natural habitat.
The release last week was the first of two releases planned this year. Lab staff are currently working to help reintroduce eight endangered or threatened mussel species in three Minnesota watersheds including in the Mississippi River at St. Paul and in the Cannon River in Southeast Minnesota.
The sites were chosen based on mussel population surveys and water quality testing of 4,000 potential sites across the state. In Minnesota, 28 of the state’s 50 mussel species now are listed as either no longer found in the state, endangered, threatened or of special concern.
In the Cedar River, CAMP plans to re-introduce six mussel species — black sandshell mucket, elktoe, round pigtoe, flutedshell and monkeyface.
Mussels filter particles and bacteria out of freshwater but are also sensitive to habitat disturbance and pollution. That the CAMP lab is located in Lake City is a bit of history coming full circle. The first efforts in the U.S. to cultivate freshwater mussels were in Lake City more than a century ago when mussel shells were used to make buttons. The U.S. Fishery officials worked to set up a propagation operation in Lake Pepin to supply the riverside button industry. However, pollution killed off the mussels, Davis said.
Much of the work done there is funded by grants including from the Environmental Natural Resources Trust Fund.