This year, though, it’s getting attention from the Maryland Department of Natural Resources and a couple of biologists-- who value mussels for keeping water clean and giving life to other species --and are attempting for the first time to grow tens of thousands in a hatchery.
“They filter water. They remove nutrients and sediment. . . . They give other animals habitat and food. Fish and muskrats, raccoons, they eat mussels,” said Matt Ashton, a DNR biologist with a specialty in freshwater mussels. “We are hoping to help the ecosystem out by restoring a keystone species.”
On an early May morning, Ashton and Jennifer Tam went to the green banks of Deer Creek in Harford County and gathered mussels, some small enough to be held easily in the palm of a hand, and pried open the shells with pliers looking for females full of larvae. They collected about 100 female mussels.
“We definitely got more than enough mussels that looked pregnant and were developing larvae,” Ashton said.
After the mussel harvest, they headed for another stream in Harford where they knew there were American eels to capture and serve as a host fish. After shocking a small population of eels, they netted them and headed with a truck of eels and mussels to the hatchery near Brandywine in southern Maryland. The mussels can’t survive without a host to grow and launch their young.
In the hatchery, scientists again pried open the mussels’ shells and pierced their gills to extract the larvae, which they inspected under a microscope to make sure they were active and plentiful, Ashton said.
They poured the larvae over a vat with foot-long eels, hoping the eels would breathe in larvae that then would attach to their gills. When the baby mussels grow to about the size of a grain of sand, they will drop out of the eel’s gills.
The scientists hope to produce 10,000 baby mussels to plant in the Patapsco River, which may not have hosted a mussel in about 100 years. They’re hoping for a 25 percent survival rate.
“We really have no clue what to expect in terms of numbers,” Ashton said. “We have to produce as many as we can.”
The mussel is prized for its ability to filter water in freshwater streams, much as oysters do in brackish waters of the Chesapeake Bay, but they have disappeared from some rivers in the state due to damming, pollution, runoff and the loss of host fish.
The fisheries scientists chose the Patapsco for their reintroduction because other species needed for the Eastern Elliptio to survive are beginning to make a comeback there, said James McCann, a zoologist with Maryland’s Wildlife and Heritage Service. The work to reintroduce the mussels is being paid for with the help of federal funds administered through the wildlife agency.
All but two of the river’s 12 dams that kept fish species from migrating have been removed. American eels, which had been missing from the river for at least 50 years and perhaps as long as a century, are now beginning to travel it. American shad and hickory shad, two other migratory species, are also present, McCann said.
“As the mussel population recovers, we think the Patapsco River will be a little cleaner,” he said.
The federal and state governments, as well as nonprofit groups, have been working to restore the Patapsco for 12 years, said Serena McClain, director of river restorations for American Rivers, a conservation organization.
The river, which flows 39 miles from its origins in Carroll and Howard counties down into Baltimore to form the city’s harbor, was targeted because three of its dams could be removed easily, she said. Taking out the dams opens historic migratory corridors for such fish as American eel, hickory shad and alewife, among others, and will help increase their populations in the Chesapeake Bay eventually, she said.
By this time next year, fisheries scientists think they will have been able to place thousands of penny-size mussels in the Patapsco. Ashton isn’t exactly sure where they will be placed, but it will be upstream of the Daniels Dam north of Ellicott City.
The mussels grow slowly, but once established can live for 20 to 30 years. After a couple of years, the scientists hope they will have a population large enough to reproduce and sustain itself. In five years, they hope to have created several self-sustaining populations. With an increase in mussels, other species that feed on them also could grow, including great blue herons, mink and catfish, the fisheries biologists said.
There are 300 species of freshwater mussels in the United States, but 30 are now extinct. Two thirds of the remainder are endangered or declining, McCann said.
Maryland has 16 native species, said McCann, 14 of them uncommon, threatened, rare or endangered.
“What this speaks to is the state of our streams and rivers,” he said. “They are telling us something is amiss.”