Oysters Are on the Rebound in the Chesapeake Bay

Henry Fountain, The New York Times 3 Aug 09;

After decades of overharvesting of oysters in the Chesapeake Bay and many fruitless efforts to replenish them, scientists have re-established a significant population of the shellfish along the Virginia shore.

Researchers from the Virginia Institute of Marine Science at the College of William & Mary say that large experimental reefs created five years ago are now home to more than 180 million native oysters. That is still a far cry from the late 1880s, when the bay held billions of the oysters, Crassostrea virginica, and watermen harvested about 25 million bushels annually. But more larvae have been settling on the new reefs every year, the researchers said.

The results, they added, suggest there is a potential for further restoration in the bay by creating additional reefs where harvesting is prohibited.

“What we need are thousands of acres of permanently restored sanctuary reefs to turn this situation we have with the oyster around,” said David M. Schulte, a doctoral student at the institute and an author of a paper published in Science last week that describes the work. The sanctuaries would aid the oyster harvest by helping to seed nearby areas, but the overall effort would benefit the bay in other ways, by helping to clean the water and providing more habitat for fish, crabs and other marine life.

Mr. Schulte said that when he began the experiment, he assumed there would be only a 10 percent survival rate among juvenile oysters on the reefs, which are near the mouth of the Great Wicomico River, just south of the Potomac. Throughout the bay, high mortality due to disease, as well as overfishing, had reduced the population to about 1 percent of 19th-century levels.

The current harvest is less than 200,000 bushels a year, and the situation has become so dire that there is an elaborate proposal to introduce the Asian oyster, C. ariakensis, as an alternative.

But Mr. Schulte said that in the first year of the study there was about a 30 percent survival rate on the reefs. “I was really surprised,” he said. “That’s really what helped this project become what it has.”

“We’re hoping that the population in the Great Wicomico is stable,” he added.

A Virginia fisheries official said he was optimistic that the restoration technique was working, but that the next several years would be critical.

“The looming question is whether what we’re seeing is just a short-term effect or long-term restoration,” said Jack Travelstead, chief of the fisheries management division of the Virginia Marine Resources Commission. “Enormous numbers of oysters are thriving in that area, but oyster diseases are still present.”

He noted that in 1996 there was a very good spawn of oysters in the same river, but that as they grew most eventually died from disease. “We’re a little bit concerned that we might experience that here,” he said.

A key to the success of the new reefs, Mr. Schulte said, is their height and extent. The reefs, which were created by the United States Army Corps of Engineers by dumping oyster shells, are 10 to 18 inches high and cover more than 80 acres, with the largest about 20 acres.

In earlier restoration efforts, most of the reefs were lower, so the oysters had to cope with stirred-up sediment. Oysters are filter feeders, and filtering out sediment expends energy they could use for growth and makes them more susceptible to disease. Having the shellfish higher in the water column — they tend to grow on top of the reef, in thick layers — appears to keep them healthier.

Most of the earlier reefs were also smaller, usually about an acre in size. Mr. Travelstead said the new effort had shown that “it’s not just build it higher, but build it larger and inundate it with healthy broodstock that is showing some signs of disease resistance.”

“This is a first attempt at altering the scale,” he added. “But scale means money, and that’s pretty hard to find these days.”

Scott McGuire, a volunteer with the Coastal Conservation Association of Maryland, a sport fishing group, said that his organization supported the creation of more sanctuaries like the ones in the study. “This type of research is what we’ve been asking for a long time,” he said. Oysters, he said, are a keystone species in the bay. “They filter the water and provide all kinds of ecological niches for other organisms. And they create lots of good fish habitat.”

Ken Smith, president of the Virginia Watermen’s Association, said he was not surprised by the results of the study. He said watermen had been putting oysters in cages and raising them off the bottom, “and we have gotten the same results that the scientists have gotten.”

Mr. Smith said his group, too, would support more sanctuaries if they would contribute to the health of the bay and indirectly to the watermen’s livelihood. Harvesting oysters used to be his primary source of income, he said, “but for 20 years, it’s been dead.”