Oyster diseases coming back Warm weather, drought took heavy toll on shellfish.

October 31, 1991|By Timothy B. Wheeler | Timothy B. Wheeler,Evening Sun Staff

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.

Those same conditions also have helped produce good oyster reproduction in the past couple of years. "We had good hatches in the lower bay," noted Larry Simns, president of the Maryland Watermen's Association, "and in September 90 percent died from MSX and Dermo."

Watermen, many of whom began the season working oyster bars along the western shore in Southern Maryland, have now moved northward and are concentrating their tonging off Annapolis and along the Eastern Shore from the Chester River south to the Choptank, Jensen said.

The loss of the oysters has had little impact so far on watermen, who have been complaining that slack demand for oysters has kept prices low. Simns said he and others have been on strike for the past five days because buyers have been trying to lower the price, which began the season at a depressed $13 to $14 per bushel, down from $20 to $30 last year.

"Watermen wonder what we would do if there were lots of oysters in Chesapeake Bay because we can't sell what we have today," Simns said. He blamed the drop in demand on publicity about oyster contamination in the Gulf of Mexico, where discovery of a strain of Peruvian cholera has closed all shellfish beds in Alabama.

MSX and Dermo, though deadly to oysters, present no health threat to humans who eat the bivalves, officials say.

The oyster industry is suffering throughout the rest of the East Coast and in much of the Gulf of Mexico, according to fisheries scientists attending a two-day oyster conference in Annapolis.

Virginia's oyster harvest last year was at an all-time low of 52,000 bushels, prompting officials to convene a task force seeking ways of reviving the industry. One controversial response being considered is importing Japanese oysters from the West Coast, which some scientists warn could spell the demise of what is left of the bay's native oysters.

In the gulf heavy rains, pollution and disease have depressed oyster harvests. Even on the West Coast, the only region where harvests have continued to climb, oyster beds are being contaminated by runoff from coastal development, according to Ken Chew, a fisheries scientist with the University of Washington.

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