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Chesapeake Bay oysters make a remarkable recovery

After being decimated by disease, pollution, and overharvesting, the Chesapeake Bay’s renowned oysters are thriving once again, thanks largely to a selectively bred oyster that grows rapidly and is more resistant to pathogens.

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    An oyster recovery partnership boat works on Harris Creek, Md., in 2013. A combination of overfishing, disease, pollution, silting, and runoff devastated oyster numbers in North America's biggest estuary. But a number of steps, including cleaning up the waters and introducing a hardier oyster, have reversed the trend.
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[This article originally appeared at Yale Environment 360, a publication of the Yale School of Forestry & Environmental Studies.]

If the world is our oyster, where are the oysters in our world? Not in the places we’re used to finding them.

Louisiana once supplied most of the United States’ oysters, but Hurricane Katrina and the Deepwater Horizon oil spill have slashed the state’s oyster production. The Pacific Northwest was the U.S.’s second-largest oyster supplier, but ocean acidification is hurting those populations. In Florida, Apalachicola Bay oyster production has fallen by two-thirds because of freshwater diversions. Globally, oyster populations are in serious trouble, with more than 90 percent of the world’s oyster reefs having been lost in the past century, according to a 2011 study.

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But there is one oyster that can claim it is better off today than it was a decade or two ago. It is Crassostrea virginica, of the Chesapeake Bay. Last year, Maryland and Virginia reported their best oyster harvests in three decades, gathering a combined 900,000 bushels. And that number doesn’t include the oysters in both states that are raised in floats and cages, which is rapidly becoming a multimillion-dollar business.

The oyster most of the world had written off just a decade ago is making a rousing comeback thanks to a brilliant oyster geneticist, improved state and federal management, the expansion of private hatchery operations, the cleanup of the Chesapeake Bay, and a little bit of help from Mother Nature in the form of average rain years and excellent reproductive oyster classes.

How long can it last? Where does it go from here? It’s hard to say, but for now the Chesapeake — the U.S.’s largest estuary — has found its Holy Grail oyster. It tastes good, it grows fast, and it doesn’t easily succumb to the diseases that have devastated previous generations of Chesapeake oysters. The biggest surprise is that this new super-oyster was there all along.

“I didn’t think I’d live long enough to see the oysters come back,” said Casey Todd, 60, the owner of MeTompkin Bay Oyster Company, a shucking house in Crisfield, Maryland. “I was getting resigned to the fact that they would never come back in my lifetime, but it looks like they might.”

The Chesapeake Bay’s oysters were long the pride of what Native Americans called “great shellfish bay.” A vital part of the Chesapeake’s ecosystem, oysters can filter 50 gallons of water a day, create marine habitat, encourage bay grasses, and provide excellent homes for organisms at the bottom of the food chain. When they are farmed, oysters are a net benefit to the waters where they live, unlike other farm-raised species such as fin-fish, which pollute waters with fecal material.

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Over the last two centuries, Chesapeake Bay oysters have suffered from overharvesting, pollution, and parasitic diseases like Dermo and MSX. The latter scourge killed so many oysters in the 1970s that several farmers decided to grow clams instead. Cherrystone Aquafarms was one; it soon grew into a $15 million clam company.

By 2004, a Maryland oyster harvest that reliably yielded 16 million bushels a year in the 1970s produced only 26,000 bushels. Oystermen hung up their dredges. Shucking houses shuttered their doors. The few remaining brought in trailers of oysters from the Gulf of Mexico so workers had something to shuck.

Just a decade later, those tractor-trailer loads are going the other way. For the first time that anyone can remember, Marylanders and Virginians are sending their oysters to shucking houses in Louisiana.

What is responsible for this turnaround? Many factors have played a role, but none has been as important as the development of a kind of super-oyster called a triploid that grows rapidly and is more impervious to disease. Triploids have three chromosomes instead of two, and because they do not reproduce, they put all of their energy into growth. A wild diploid oyster can reach market size in three years — about an inch a year. A triploid can get there in 18 months or less. 

Many scientists worked on the development of triploid oysters over numerous decades, but the person who perfected its creation in the native Chesapeake oyster, Crassostrea virginica, was Standish K. Allen of the Virginia Institute of Marine Science. Allen had developed triploid oysters in Maine and the Pacific Northwest, creating the first triploids in 1979. In 1997, Virginia hired him to find a genetic fix for its oyster woes.

At that time, oyster harvests were plummeting in Maryland and Virginia and state officials and oyster growers were desperate to find a heartier oyster. The two states and the federal government spent five years and nearly $15 million investigating whether to seed the Chesapeake with Crassostrea ariakensis, a Chinese native. Virginia’s original plan was to create C. ariakensis triploids and compare their growth to native reproductive oysters, a contest the natives would surely have lost.

But Jamie King, a scientist with the National Oceanic and Atmospheric Administration, convinced Virginia to conduct the trials In recent years the federal government and the states have spent billions of dollars cleaning up the Chesapeake Bay. with triploids from both species. 

As it turned out, those tests in the early 2000s showed that the native C. virginica species was superior in virtually all respects, from its knack for building oyster reefs to its ability to outrun disease with its rapid growth. Allen turned his brood stock over to Virginia’s private hatchery managers, who bred triploids that could grow in 10 months.

That was the beginning of the turnaround for Chesapeake Bay oysters. Virginia already allowed oyster aquaculture and King began pushing Maryland to legalize it, too. That occurred in 2009. Today, Maryland has 4,000 acres under lease and 474 people working in shellfish aquaculture. Its dockside value for aquaculture in 2014 was more than $3 million; the wild harvest exceeded $14 million.

Virginia has 104,000 acres under lease, five private hatcheries to raise seeds, processing houses to shuck the meat, and an infrastructure to send its oysters all over the world. In 2014, the value of the Virginia farm-raised oyster and clam harvest topped $55.9 million.

“With oysters, things are completely different now — you almost don’t worry about diseases anymore,” said Mike Peirson, the former head of Cherrystone Aquafarms, which raises millions of oysters and seed.

Eyeing the success of Chesapeake Bay oysters, officials in neighboring Delaware last fall legalized shellfish aquaculture, the last coastal state in the U.S. to do so. The Delaware Bay Oyster Restoration Project also aims to employ oyster shell planting and transplantation programs to boost wild oyster production in Delaware Bay and other coastal waters.

Maryland’s decision to legalize oyster aquaculture in all its counties has fulfilled the dreams of many watermen and oyster processors who wished they could grow their own oysters, but dared not try.

Mike Lindemon, an oyster farmer who dreamed of having just one small plot, now has 500 acres under lease with his partner in the Nanticoke River. Oyster harvesting in the wild is a dangerous job; watermen must contend with unpredictable winds, high tides, and icy days that prohibit working at all. But oyster farming? One farmer said that even on his worst day, he can still make it to the bus stop to pick up his children.

The stunning reversal of the Chesapeake Bay oyster owes much to environmental factors, such as average rain years instead of droughts. In addition, over the past 25 years the federal government and the states have spent billions of dollars cleaning up the Chesapeake Bay.

Those efforts have resulted in sewage-treatment plants that discharge far less nitrogen and phosphorus into the Chesapeake than in the past, and better agricultural practices that help absorb fertilizer before it runs off the land. Oysters do filter pollution, but too much of a good thing will stifle their growth. Plus, over-sedimentation can smother their reefs and prevent them from delivering their many habitat benefits. Oysters are among the many beneficiaries of a cleaner Chesapeake Bay, and so are the creatures that depend on them to thrive.

But the oyster revival also owes something to new management techniques — large oyster sanctuaries instead of small, postage-stamp ones; more shell replenishment in the Chesapeake; an active plan to clean oyster reefs so the sediment doesn’t cover oysters; and an aggressive plan to plant hatchery seed.

Previously, oyster sanctuaries were small and in the least productive areas. But former Maryland Gov. Martin O’Malley began the push to make whole rivers sanctuaries and off-limits to watermen. The decision has proven unpopular with oyster harvesters, but it has been terrific for local oyster populations. In restoration areas, the waters are teeming with oysters — some planted, but many recruited because of the population already there.

The oysters bring life with them — not just the grass shrimp and the bay grasses, but the rockfish and the crabs. Those species are coming for the cleaner water and the protections from predators that oyster reefs offer. And when the sanctuary-planted oysters spawn, they create more oysters that help clean the water, create habitat, and recruit other fish even more effectively.

Aquaculture oysters do their part for restoration, too, even if they’re sterile and unable to build reefs because they’re in cages or floats. These oysters are still recruiting marine life. Cages are teeming with critters, and the water around oyster farms is clear as gin in some places.

What can other oyster-depleted regions learn from the Chesapeake Bay’s resurgence?

Perhaps the greatest lesson is not to give up on native species, be they watermen who harvest oysters or the oysters themselves. Some of the greatest innovations have come from watermen who have spawned improvements like better cages. It takes a precise set of conditions to grow an oyster. But changing laws and policies — such as making it easier for small operators to enter the oyster aquaculture business — can help resurrect or launch an oyster industry.

• Rona Kobell is a staff writer for the Chesapeake Bay Journal and the co-producer of "Midday on the Bay," a radio show on WYPR out of Baltimore. A former environmental reporter for the Baltimore Sun, she has been recently published in Slate, Modern Farmer, The Boston Globe, and Grist.

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