Bay Creatures: The American Oyster

 

                          BAY CREATURES: THE AMERICAN OYSTER

 

It’s hard to explain our hunger for oysters. How could we possibly crave something that looks as though it was dredged from the depths of a spittoon? The first person to sample an oyster must have been uncommonly brave—or famished.

          But humans have been eating oysters for eons. Prehistoric shell heaps rim coastlines worldwide. By the late 19th century, when the legendary gourmand, Diamond Jim Brady, was reportedly devouring several dozen oysters a day, Americans had a huge appetite for these bivalves. Chesapeake Bay’s oyster landings averaged 25 million bushels a year and both demand and supply seemed inexhaustible.

          Those days are gone, and not just because of Diamond Jim. Bay watermen now bring in less than 1 percent of peak landings a century ago. What happened? Overharvesting, pollution, disease and habitat destruction have all played a role in the mollusk’s demise. Today the local oyster fishery seems to be on life support.

          But there are signs that oyster populations may be on the rebound. More about that later. First, a little background about this popular seafood.

          Chesapeake Bay’s signature shellfish, the American or Eastern Oyster (Crassostrea virginica), is fundamentally a hardy creature, able to withstand wide ranges of temperature, salinity and oxygen levels. It can survive long periods out of the water (oysters in the shell may be refrigerated for up to a week and still be good to eat if still lively).

          Oysters reproduce prolifically. In early summer fertile females release successive clouds of eggs, producing 100 million eggs or more in a single season. The eggs, fertilized by discharged sperm from adult males, soon become free-swimming larvae. In two to three weeks larvae grow a “foot,” settle on a hard surface (oyster shells are preferred), and secrete a substance that cements them in place. The sedentary juvenile oysters are known as spat.

          Seemingly sexually conflicted, oysters start out as males but, by the second year, when most oysters are mature, half or more have become female. Sex inversion can continue as oysters grow older. When males are scarce, some females may switch back to the opposite sex.

          Oysters feed by pumping seawater through their gills, straining out food particles. A single adult can filter up to 50 gallons of water daily. In their heyday the Chesapeake’s teeming oyster populations could filter the entire bay volume—ten trillion gallons—in less than a week.

          So these mollusks are hardy, adaptable, well-armored, prolific breeders and prodigious eaters. Small wonder that they have survived, almost unchanged, for 200 million years. Still, very few larvae make it to adulthood. The developing shellfish are done in by predators (notably crabs, snails, starfish, fin-fish, marine worms and humans), disease (especially the parasites, MSX and dermo), pollution and extreme weather conditions. In the last several decades, overharvesting and deteriorating water quality have accelerated the decline of oysters in the Chesapeake.

          But it is not yet time to write the bivalve’s obituary. Though the jury is still out, our local stocks may be recovering. For one thing, they seem to be developing natural resistance to MSX and dermo—mortality from diseases has recently declined significantly. And the Bay’s water quality is gradually improving, even if the changes are frustratingly slow.

          Equally important, programs to rebuild the Bay’s oyster populations are beginning to bear fruit, especially in Virginia. Restoration efforts include reef-building, hatcheries and aquaculture. Reefs, consisting of accumulating layers of oyster shells, are critical for the survival of the species. Shells provide suitable settling areas for spat, and the elevated surfaces help keep growing oysters above smothering sediments. But the Bay has lost 90 percent of its oyster reefs since the 19th century. Using recycled oyster shells, Maryland and Virginia are trying to establish new reefs in sanctuary areas temporarily closed to harvesting.

          Hatcheries produce juvenile oysters in carefully managed facilities. The young shellfish are later seeded into the Bay. The University of Maryland’s Horn Point Laboratory in Cambridge is the world’s largest oyster hatchery with the capacity to produce two million oysters a year.

          Aquaculture—farming the sea—has particular promise for rejuvenating the Bay’s commercial oyster industry. Worldwide, farming produces more than 4 million tons of oysters annually, worth more than $3 billion, but the enterprise is still in its infancy in Chesapeake Bay. That is changing. Virginia is actively promoting oyster cultivation by streamlining the permitting process, providing grants and supporting the development of sterile oysters that grow to market size in one year, two years faster than in the wild. Virginia oyster farmers now lease more than 100,000 acres of Bay bottom. Maryland recently passed legislation to facilitate permits for this emerging business opportunity.

          It is too soon to judge the effectiveness of these efforts. But two things seem certain. Restoration of Chesapeake Bay’s threatened oyster populations will help revitalize the region’s maritime economy and improve the quality of the Bay’s fertile waters.

          For more information log onto www.OysterRecovery.org

~ Henry S. Parker

 

 

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