Bay oysters in peril again Return of parasites renews threat to Chesapeake crop

'Not a very pretty picture'

More than half of population killed in lower bay already

September 21, 1995|By Timothy B. Wheeler | Timothy B. Wheeler,SUN STAFF

In another blow for Maryland's beleaguered watermen, scientists say that the Chesapeake Bay's oysters are sick and dying again, less than a year after they seemed to be recovering from a seven-year bout with parasitic diseases.

Spurred by the summer's drought, which made the bay's water much saltier than usual, the oyster diseases MSX and Dermo have returned with a vengeance.

Oysters throughout the bay are infected with one or the other disease. Hardest hit is the lower bay, where MSX already has killed off more than half of the population, scientists say.

"It's not a very pretty picture," said George E. Krantz, an oyster researcher at the state-federal biological laboratory in Oxford.

The microorganisms MSX and Dermo do not harm people who may eat infected oysters, but they kill young shellfish before they can grow to legally harvestable size.

The die-off comes six months after Maryland watermen reaped their biggest oyster harvest in three years.

Although the 1994-1995 harvest of 164,538 bushels was only about 10 percent of what the bay yielded just 15 years ago, it nonetheless fostered hope that the disease-ravaged shellfish industry was on the mend.

Now, the parasites' return is a bad omen for the oyster season, which begins Oct. 2.

Watermen are already bracing for a 20 percent reduction this fall in their most valuable catch, blue crabs, because of new state restrictions intended to protect that species from overfishing.

"We've been fearful of this," said Larry W. Simns, president of the Maryland Watermen's Association.

Until the die-off this summer, watermen had hoped to double last year's harvest on the strength of rebounding shellfish populations in the lower bay.

The two parasites thrive and spread when hot, dry summers reduce freshwater flows into the bay. First detected in the Chesapeake in the 1950s and 1960s, the diseases devastated oysters during a prolonged dry spell that began in the late 1980s.

Heavy spring rains and snowmelt in 1993 and 1994 almost flushed the parasites out of the bay with record-high river flows. Watermen reported last winter seeing young oysters growing in places where no live shellfish had been found in five or six years.

But this summer, with the Northeast and mid-Atlantic in the grip of a moderate drought, the bay's salinity climbed to levels rarely seen in the past 50 years.

"Given the high salinities we've had this year, we should expect some more mortality," said Steven Jordan, director of the Oxford lab, which is run jointly by Maryland's Department of Natural Resources and the National Marine Fisheries Service.

MSX, which can kill oysters within months of infecting them, has struck the resurgent oyster populations in the lower bay. In Tangier Sound, more than half the oysters checked about a month ago were dead, according to Dr. Krantz.

"And the oysters that are not dead yet are in very bad condition," he added.

In nearby Pocomoke Sound, "of the oysters that had survived so far, more than 60 percent were ready to die," he said.

Most of the oysters elsewhere in the bay are infected by Dermo, a slower-acting parasite that may take two to three years to kill its host.

Sampling has detected Dermo in 80 percent to 100 percent of the oysters in the Chester and Choptank rivers.

Dr. Krantz predicted that watermen still would be able to harvest oysters, even though most are already infected, in the Chester River, in mid-Shore rivers and in the Wicomico River.

In Virginia, where oysters never really rebounded from the diseases, MSX infection is widespread, and the outlook for harvest this fall and winter is "pretty bleak," said James Wesson, oyster repletion coordinator for the Virginia Marine Resources Commission.

He said there were so few oysters left alive that the state was mulling continuing last year's moratorium on harvests from publicly owned reefs in the bay.

"We had the worst MSX we've ever had this year," said Eugene M. Burreson, an oyster researcher at the Virginia Institute of Marine Science.

To make matters worse, the one major refuge from disease in Virginia, the upper James River, was hit by localized but heavy flooding in June, which killed off otherwise healthy shellfish.

"We just can't seem to get a break," Dr. Burreson said.

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