Md. tries to replenish its freshwater mussels
Nearly-vanished shellfish are ‘a keystone species,’ scientists say
Perhaps it isn’t surprising that the Eastern Elliptio — and other varieties of freshwater mussels — have disappeared from many streams and rivers in Maryland without a flicker of notice from the public.
The little-known or -appreciated mussel lies in stream bottoms for most of its life, out of sight and growing slowly for decades.
This year, though, it’s getting attention from the Maryland Department of Natural Resources and a couple of biologists who value mussels for their role in keeping water clean and giving life to other species and are attempting for the first time to grow tens of thousands of them 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,” he said.
On an early May morning, Ashton and Jennifer Tam went down to the green banks of Deer Creek in Harford County and gathered up 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 of the 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 County where they knew there were American eels to capture. 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 fish — in this case an eel — to grow and launch their young.
In the hatchery, scientists again pried open the mussel shells and pierced their gills to extract the larvae, which they then 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 that the eels would breathe in the mussel larvae, which 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, which they will 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 the brackish waters of the Chesapeake Bay, but they have disappeared from some rivers in the state due to the damming of rivers, pollution, runoff and the disappearance of host fish.
The fisheries scientists chose the Patapsco River for this reintroduction because other species that are needed for the Eastern Elliptio to survive are beginning to make a comeback there, said James McCann, a zoologist with Maryland’s Wildlife & Heritage Service. The work to reintroduce the mussels is being paid for with the help of federal funds administered through the DNR’s Wildlife & Heritage Service.
All but two of the river’s 12 dams — some as old as the Colonial era — that kept fish species from migrating up the river have been removed. American eels, which had been missing for at least 50 years and perhaps for as long as a century from the river, are now beginning to migrate up 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 nonprofits, have been working to restore the Patapsco River 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 up 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.
The ongoing removal of the Bloede Dam, which is owned by the state, was not difficult to gain support for, McClain said, because nine people had drowned there since the 1980s. When it’s gone, she said, there will be 65 miles of river reopened to migration.
By this time next year, fisheries scientists believe they will have been able to place thousands of penny-sized mussels back into the Patapsco. Ashton isn’t exactly sure where they will be placed in the river, but it will be upstream of the Daniels Dam, which spans the river just north of where U.S. 29 runs into Interstate 70 in Ellicott City.
With most of the dams gone, the eel population is making a comeback, Ashton said. The two remaining dams are not preventing eels from migrating. Small eels can use a fish ladder at the dams, while large eels are able to wriggle up and over their sloped structures.
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 that is large enough to reproduce and sustain itself in one place. 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, catfish and other fish, the fisheries biologists said.
There are 300 species of freshwater mussels in the United States, 30 of which are now extinct. Two-thirds of the remainder are endangered or declining, McCann said.
But scientists are well aware of places where they were once found because Native Americans ate them, used them to make tools and even crushed them to put in their pottery to make it stronger. Thousands of shells can be found in early Native American settlements.
Mussels are sensitive creatures that only survive in clean water and need host species to reproduce. Maryland has 16 native species, said McCann, 14 of which are 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.”