Parasitic oyster diseases, apparently aided by last winter's warm temperatures and the summer's drought, are again devastating shellfish beds in Maryland's portion of Chesapeake Bay, say watermen and state officials.
Preliminary surveys indicate that oyster bars in the lower bay, in the Patuxent River and in some tributaries of the Potomac River have lost the vast majority of their oysters, W. Peter Jensen, fisheries director for the Maryland Department of Natural Resources, said yesterday.
Some bars have lost up to 80 or 90 percent of their oysters, Jensen said, "or enough to make them unharvestable."
Laboratory tests are being conducted to determine which of two oyster diseases is responsible for the problem. Jensen said officials suspect much of the mortality was caused by Dermo, a relatively slow-acting parasite that had spread throughout much of the bay south of the Bay Bridge in previous years.
MSX, an even more virulent oyster disease that had been confined to Tangier Sound in the past few years, also appears to be spreading again, says George Krantz, director of the Oxford Marine Laboratory.
MSX has been found this fall in oysters at the mouth of the Little Choptank River on the Eastern Shore, Krantz said. It also has turned up, along with Dermo, among dying oysters in the waters off St. Mary's County.
The full extent of oyster mortality from the two diseases won't be known until DNR completes its survey of shellfish beds later this fall, Krantz said.
The discovery of disease mortality in the lower bay has confirmed the fears of state biologists and --ed the hopes of water-men, who had begun oyster season Oct. 1 predicting that their industry was finally beginning to rebound from the bay's previous bout with MSX in 1986-88.
Last year's harvest was 415,000 bushels, up slightly from the record low of 363,000 bushels in 1988.
"It was no surprise to us," said Krantz, who had predicted that conditions were ripe again for the diseases to spread and kill off oysters before they could be harvested. While MSX had receded from Maryland waters by last year, Dermo did not retreat.
MSX, which first appeared in the bay around 1960, can kill oysters within a year; Dermo often takes up to three years. Both tend to flourish in warmer, saltier water -- conditions produced by last winter's balmy weather and this summer's lack of rainfall.
