Rare mussels came up for air from the bottom of the Mississippi River on Thursday, boosting hopes that their endangered population may be able to rebound eventually in the now-cleaner water.
It's part of an experiment to learn whether winged mapleleaf mussels can survive in a stretch of river where they thrived historically, but were wiped out many decades ago by sewage, sediment and other pollution.
U.S. Fish and Wildlife Service biologist Phil Delphey said that the nation's only known population of mapleleafs that reproduces in the wild is in the St. Croix River. That population could be at risk from a pollution accident or invasive zebra mussels, he said, so biologists want to know where else the species might be able to live, and how to propagate and spread them out.
"We decrease the risk of extinction by having more populations out there in more places where they face minimal threats," Delphey said.
Nick Rowse, another biologist working on the project, said that the stretch of the river downstream of the Ford Dam has few zebra mussels, and is a haven for mussels that require clean water. "There's good aeration and lots of natural food," he said.
The area already has one success under its belt. Hundreds of Higgins' eye pearly mussels, another federally endangered species, have been re-introduced and are reproducing successfully.
Rowse and Tamara Smith waded into the river near Hidden Falls Regional Park in St. Paul where the winged mapleleafs have been living for the past two years. The biologists first used GPS information, but then had to feel their way, crablike, along the murky bottom about 25 feet from shore until they located two containers, each about the size of salad bowls. The housing protects the mussels while allowing flow-through of nutrient-rich river water.
After bringing the containers ashore, the scientists unscrewed the tops and immediately noticed that the shells of two mussels were open, showing that they had died. They quickly rinsed mud and sediment off the others, revealing the golden hue of their bumpy shells.
Delphey measured each carefully, compared the results with last year's sizes, and declared that they are healthy and growing at normal rates.
Rich Baker, endangered species coordinator for the Minnesota Department of Natural Resources, said he was pleased that the winged mapleleafs are surviving. Of the nearly 50 species that are found in Minnesota, he said, more than half are threatened or endangered.
"We just don't list a species and say, 'Now we're done,' " Baker said. "That's just the beginning. The purpose is to recover these populations so we don't need to worry about them anymore."
Tom Meersman • 612-673-7388