Diseases killing fewer bay oysters

The Baltimore Sun

Maryland's oysters, though ravaged by disease and loss of habitat, are showing some signs of resilience, state biologists reported yesterday.

A survey last fall of Maryland's part of the Chesapeake Bay indicates that while most oysters are infected, fewer are dying from the parasitic diseases that have devastated them over the past 25 years, according to the Department of Natural Resources.

"They're not out of the woods," said Chris Dungan, who tested the oysters for diseases at a joint state-federal laboratory in Oxford. "But at any rate, there are some hopeful signs."

The bay's oysters have been infected by Dermo and MSX, parasites that have killed off up to 90 percent of the oysters in some areas of the bay. The organisms, which are not harmful to humans, tend to thrive when dry weather causes the salinity of the bay to rise.

Only about 17 percent of the oysters sampled last fall had died recently, according to Mitch Tarnowski, who runs the annual state survey. The decrease was remarkable, he said, because the diseases usually spread and intensify when the bay is saltier than normal, as it has been for the past two years.

The diseases' reach shrank last year, the survey found. Dermo infected 56 percent of the oysters checked last fall, down from 68 percent the year before. MSX, which becomes virulent only when the bay is very salty, infected only about 2 percent, mainly near the Virginia line.

The improvement in oyster survival has not resulted in any real rebound in the population or in the commercial harvest, the biologists caution. The survey found that reproduction was poor throughout the bay, with the exception of some areas along the lower Eastern Shore, such as in Tangier Sound and in the Honga and Little Choptank rivers.

Watermen reported harvesting just 22,700 bushels of oysters through the end of December, about half as many as were caught by the same time the year before. The total harvest reported in 2008 was about 83,000 bushels, far below annual catches of more than 1 million bushels logged in the 1980s before the diseases set in.

Nonetheless, biologists are intrigued by the uptick in the oysters' fortunes. The bay has had reprieves from the diseases before, only to see them storm back after two or three years. Last year marks the fourth straight year of below-average die-off, said Mike Naylor, assistant state fisheries director.

"Something's going on," he said.

Biologists are not sure whether oysters are becoming resistant to the diseases, he said, or are simply benefiting from environmental conditions.

"We're certainly going to keep an eye on this," he said.

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