Scientists are finding signs of hope in efforts to reestablish native mussels in the Mississippi River downstream from the Ford Dam.
Federal divers waded into the Mississippi River Wednesday looking for signs of life. Finding the winged mapleleaf mussels that had been planted last fall downstream from the Ford Dam would give hope that even sensitive native species can once again survive there.
"Forty or fifty years ago you couldn't find anything alive in this section of the river, let alone think about reintroducing an endangered species here," said Byron Karns, biologist for the National Park Service.
Karns and another diver swam parallel upstream, feeling their way along the murky bottom about 25 feet from shore and towing a float with a bright orange safety flag. They were looking for two containers, each about the size of a salad-mixing bowl. Each held five winged mapleleaf mussels -- named for a small extension of the shell that resembles a wing -- that scientists had helped to propagate and nurture since late 2004.
Mussels require clean water to survive, and decades of pollutants and sewage wiped them out in dozens of locations. According to the Minnesota Department of Natural Resources, more than half of the state's native 48 mussel species are endangered or threatened. The St. Croix River contains about 40 species of native mussels, and hosts the nation's only population of winged mapleleafs known to be reproducing.
Scientists are trying to boost the mapleleaf's population, and to restore them to areas where water is now clean enough to support them again.
It isn't easy.
Baby mussels, or larvae, cannot survive unless they live on fish gills as parasites during a key part of their life cycle. The larvae, harmless to fish, grow for several weeks and metamorphose into mussels before dropping off to begin their lives in rive bottoms.
The juveniles near Hidden Falls came from mothers taken from the St. Croix River in 2004. Scientists took the mothers to the Genoa National Fish Hatchery in southwestern Wisconsin, harvested the babies and mixed them with channel catfish, the only species that will host them. They drove the catfish back to the St. Croix, and kept them in underwater cages until the babies formed shells and dropped off. Researchers raised the tiny-shelled mussels for three years in cages in the river, before taking half of the population to an area near Hidden Falls Regional Park in St. Paul last year to see if they could survive in the Mississippi.
The two divers located the mussel containers weighted by concrete and brought them ashore.
"The last time we saw these guys was October," said Phil Delphey, endangered species biologist for the U. S. Fish and Wildlife Service. He unscrewed the top of one container. Inside, mixed among sand, were five gold-colored mussels about the size of walnuts.
Delphey measured each mussel and pronounced them all healthy.
They need at least one more year in the containers before they are big enough to survive in the wild.
Other mussels rebound, too
The winged mapleleaf is only one endangered mussel species making a comeback, said Delphey. Thousands of Higgins' eye pearly mussels have been raised and distributed in parts of the St. Croix and the Mississippi.
Delphey said that human intervention is needed to restore mussels, because they can only move about 10 feet per year. He hopes to build self-sustaining populations in many of the areas where they once thrived. Research is funded by the Fish and Wildlife Service and the Army Corps of Engineers, he said. Minnesota's Department of Natural Resources is also working on mussel restoration.
"In a couple years we could have as many as four or five federally endangered mussels [reintroduced] in this area," Delphey said.
Tom Meersman • 612-673-7388