More bay oysters, but ripe for disease

Drought left bivalves vulnerable to Dermo, MSX, sample shows

October 01, 1999|By Joel McCord | Joel McCord,SUN STAFF

Maryland's watermen, whose oyster season begins today, are caught between the good news of a fast-growing oyster population and the bad news of the summer drought, weather perfect for diseases that kill oysters.

The oysters produced in the near-record spat set of 1997 are reaching marketable size, and they are producing even more oysters, said Chris Judy, head of shellfish programs at the Maryland Department of Natural Resources. The saltier water in the Chesapeake Bay resulting from the lack of rain encouraged oyster reproduction.

It also encourages Dermo and MSX, diseases that are not harmful to humans but kill oysters.

Signs of the diseases have shown up in the bay.

Many dead oysters were found in a sample taken from Tangier Sound on the lower Eastern Shore last month, and all of the dead ones were infected with Dermo, said Chris Dungan, a research scientist in the laboratory that the University of Maryland and the National Oceanic and Atmospheric Administration (NOAA) operate in Oxford.

Dungan said the sample was too small and too localized to consider it significant, but he called it "a warning to us."

"We're worried that we'll see more samples like that," he said.

Though acknowledging that conditions are ripe for the diseases, scientists in Maryland and Virginia would not predict the bay's oyster harvest until they complete surveys scheduled for the next two weeks.

"The indications are present, but it's not a certainty until we've done the surveys and have the results," said Richard Takacs, fisheries biologist with NOAA's Chesapeake Bay office.

The scientists also said it is too early to tell whether Hurricane Floyd, which deluged Maryland with millions of gallons of rain and sent tons of sediment and debris down bay tributaries Sept. 16, affected the oysters.

The torrent of fresh water decreased bay salinity by about three parts per thousand, said Judy, not enough to damage the oysters or enough to stave off Dermo and MSX.

"If we could have seen [the salinity] go down five to six parts per thousand a month earlier, that would have been better. It was too little rain a little too late," he said

Because state crews have not conducted their surveys, they don't know whether oysters were buried under the sediment.

Oysters are not only an integral part of Maryland's seafood industry, they also help restore the health of the bay. Oysters filter out pollutants, improving water clarity and allowing the penetration of light that is crucial to the growth of underwater vegetation. Their reefs provide habitats for them and other organisms.

Chesapeake Bay oyster landings, once legendary at about 24 million bushels a year, have been ravaged in recent decades by over-harvesting and disease, reaching a low of 79,618 bushels in the 1993-1994 season. The figures have rebounded, partly because of oyster-restoration efforts.

Maryland has rebuilt oyster bars throughout the bay and the tidewater areas of its tributaries since the 1960s by planting up to 2 1/2 million bushels a year of empty oyster shells on the bottom to provide places for spat -- baby oysters -- to attach themselves and by planting seed oysters in areas that need more oysters.

The state also has programs to develop disease-resistant oysters and plant their spat in beds throughout the bay. More than 10 million spat have been hatched in those hatcheries this year.

In 1997, scientists found an average of 277 naturally occurring spat per bushel of mud dragged from the bottom of the bay, the second-most since they began keeping records in 1939 and almost 140 times the naturally occurring spat in 1996.

Those oysters, if they survived the diseases, are maturing now, Judy said. Some will have reached market size of 3 inches long this year. More importantly, they have spawned at least once and sometimes twice, adding to the oyster population.

Scientists are "excited about the 1997 set because it is an established population that can contribute to the stock of oysters in the bay and the industry," Judy said. "But it remains to be seen how many have survived. Our survey will give us more information on what we can expect."

Pub Date: 10/01/99

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