It’s been a half-century since Maryland crowned clam queens in honor of a thriving wild soft-shell clam industry that, in some years, brought millions of dollars into the state. But the singular soft-shell could rise again — this time as a product grown and sold with the help of modern aquaculture.
Morgan State University scientists are more than a year into researching whether soft-shell clams could not only be harvested from Chesapeake Bay waters but also farmed in them. The state’s aquaculture industry has grown rapidly the last decade, but it currently consists of a single species: the Eastern oyster (Crassostrea virginica).
Making a viable alternative out of soft-shell clams (Mya arenaria) could help growers diversify their offerings while returning the oysters filter-feeding boost to the water.
“In Maryland, by law, we are only allowed to work with native species, so that’s a big limitation,” said Ming Liu, an oyster genomics researcher leading the project. “Local oyster growers always show an interest in alternative [aquaculture] crops, especially in the upper and middle Chesapeake Bay, where low salinity is a challenge.”
Those are the places where soft-shells could be a good fit. Although growing clams can be finicky, the researchers are working to breed a version that is custom-made for Maryland waters and ready to support regional markets.
Funded by Maryland Sea Grant, the Morgan State team has successfully produced hundreds of thousands of tiny soft-shell “seeds” out of a small shellfish hatchery at PEARL, the university’s Patuxent Environmental and Aquatic Research Lab. (The juvenile clams are referred to as seeds after they have developed shells.)
This fall, the team began taking the brood stock, grown from seed in the hatchery, to a nearby tributary of the Patuxent River to determine which growing methods will work best in wild waters.
Also called white clams, manos, longnecks and steamers, soft-shell clams are named for their comparatively thin and brittle shells, propped open by protruding leathery siphons. New Englanders, who call them Ipswich clams and are more accustomed to eating them steamed whole, use these rubbery siphons as a handle for dipping.
The market for soft-shells in the Chesapeake Bay region has come and gone over the decades alongside dramatic swings in wild harvest numbers. The invention of the hydraulic escalator dredge in 1951 made it possible to suction large quantities of soft-shells from the subtidal areas where they burrow into the sediment to grow.
The soft-shell fishery hit its stride in the 1950s and ’60s, with harvesters bringing in an average of 460,000 bushels per year until the early 1970s. That’s when a string of diseases, worsening water conditions and then Tropical Storm Agnes — which wiped out soft-shells in Virginia — devastated the Bay’s wild population. Harvest totals have never come anywhere close to their mid-’60s height. After a slight rebound in the 1980s, annual takes leveled out to a few hundred bushels a year.
In 2016 and 2017, harvests leapt inexplicably to more than 17,000 bushels. Then heavy rains in 2018 buried the fishery’s comeback, but not before generating fresh excitement about its potential. The recent reappearance also meant that Morgan State researchers could harvest soft-shells to see how well they would grow in a hatchery environment.
When soft-shell clams have been available, there’s been a strong demand for them. And if anyone is good at creating and sustaining a market for local shellfish, it’s oyster growers.
“The right entrepreneur or group of them might be able to create excitement around this product,” said Scott Knoche, an environmental economist and director of PEARL. “The verdict [on the potential market] is not in yet, but that’s part of what’s being researched.”
A good start
It can take years to genetically fine-tune a shellfish species so it can succeed as an aquaculture product, but the Maryland researchers think they’re off to a good start.
In a small hatchery space humming in the research center’s basement, the team successfully spawned approximately 300,000 soft-shell larvae. These were used to develop better methods for culturing and growing the clams to sizes that would be ready to continue growing in outside waters. Many of them were discarded “because we don’t have enough space,” Liu said.
Hatchery manager Brittany Wolfe-Bryant said she learned early on the big differences between growing oysters, which has been the lab’s exclusive focus until now, and growing soft-shell clams.
“We were learning as we went from the [scientific] literature and reaching out to colleagues in New England who have worked more with this species,” Wolfe-Bryant said.
While a more controlled process called “strip-spawning” works well for oysters, the hatchery has had more success propagating the clams by allowing them to broadcast their eggs and sperm into the water column, “how they would naturally in the wild,” she said.
Unlike oysters, the soft-shells don’t require pieces of shell, or substrate, to settle on once fertilized, which Wolfe-Bryant said “makes life a little bit easier.”
But the researchers have a feeling that growing soft-shells in the lab may have been the easy part. That’s because, once soft-shells get outside, they can be quite particular about water conditions and climate.
That’s one of the reasons their wild numbers have been subject to such highs and lows. But it’s also a problem that the genomics experts hope they can tackle with the tools they’ve developed over years of oyster breeding. Having hatchery space at PEARL and funding to support research on the soft-shell’s entire life cycle has made their project possible.
Genetic breeding technology will make it happen a lot faster than it would in nature. The natural selection that would, in theory, produce heartier, better clams over time can be sped up, Liu said, by genetic methods that find the connections between certain variations and desirable traits.
If they can engineer the clams they’re working with to be better suited to Maryland’s warming, changing water conditions, the species could have a leg up against those challenges.
“We’re in a race against climate change, to some extent,” Knoche said. “We’re going to need to continually improve these lines of soft-shell clams so that they’re ever more able to survive.”
Perhaps the biggest limitation for growing these clams is water temperature, followed closely by salinity. Warmer waters will cause the clams to grow more quickly, but water that’s too warm can kill off an entire community. Soft-shells can be better than oysters for some low-salinity waters, but they do need salinity. Heavy rains that water down salinity can be deadly.
Oyster geneticists like Liu are already accustomed to helping shellfish survive in such conditions. But there are challenges specific to soft-shells. In the wild, they grow submerged in the sediment, an environment that can be difficult to mimic while retaining the ability to find and harvest them easily.
Clam farming in Maine takes advantage of intertidal flats where clams can be scattered to grow under predator-exclusion nets and easily gathered later. Virginia has developed some best practices for farming hard-shell clam species, but many are suited for higher salinity and not all of the methods translate well to soft-shells.
“In Maryland, we don’t have an intertidal area to work with,” said Jon Farrington, an oyster grower, engineer and facilities manager at PEARL. But “anywhere you can grow oysters, you can grow these clams.”
Farrington is one of four oyster farmers who are working with the researchers to find growing methods that will work for Maryland waters. The project’s next stage involves trying six different methods for growing the clams.
That includes methods that work well for oysters, such as in floating cages at the top of the water column, as well as methods that work well for other clams — for instance, in mesh bags sunk into the bottom sediment. Soft-shells are more brittle than oysters, so methods that involve jostling or packing them together in high densities may not work as well.
Like any filter feeders, clams grow better with a good flow of water bringing them nutrients, or, as Farrington puts it, “more flow, more grow, more dough.”
To find optimal conditions for quick growth, the team also plans to experiment with the timing of when the clams go from a controlled environment to outdoor waters.
Soft-shells take about two years to reach market size in Maine, but the Chesapeake’s warmer waters could speed that up — unless they prove too warm.
The researchers speculate that placing midsize hatchery-grown clams outside at the end of summer might let them catch enough warmer waters to speed up growth while avoiding high-heat days. Harvesting early in the next summer could give the clams about 10 months to reach the 2-inch market size while avoiding the hottest weeks of the year.
“The warmer temperature outside is a double-edged sword,” Liu said. “It can facilitate more growth, but if it’s too high, it will kill the animals.”
Liu also plans to breed for clams that do better in warmer waters and lower salinity. “A heat-tolerant clam could be protected against an unexpected high-temperature event in May or September.”
The team doesn’t think that the current small cadre of clammers will soon be turning in their dredges in favor of farming soft-shells. For now, oyster growers will likely be the early adopters of whatever technology seems to give the clams the best chance.
“Oyster farmers are already out there doing something that nobody was doing at all before,” Knoche said. “They are innovators by trade, and they’re interested in something new.”