A serious oyster disease that has afflicted Edgartown Great Pond for years is now in Tisbury Great Pond and it is expected to cause a major die-off in the months ahead.

The disease known as Dermo is not harmful to humans in any way but it is responsible for having caused the collapse of the oyster fisheries from Cape Cod to the Gulf of Mexico. The only cure, according to Rick Karney of the Martha’s Vineyard Shellfish Group would be a frigid winter. The parasite that causes the disease can’t stand bitter cold water.

Dermo has been linked to global warming for years. It is a southern shellfish disease, which during the last decade has made its way up the coast from the Chesapeake Bay. Dermo was found in Edgartown Great Pond in 1997 and there is little sign of recovery for years to come.

“We are looking forward to a real cold spell this winter, which will knock the disease down,” said Ray Houle, the West Tisbury shellfish constable. The oyster fishery in Tisbury Great Pond has been an important economic benefit for at least seven shellfishermen in town. Chilmark also has a few oyster fishermen. For years, if you wanted to eat an oyster, in most cases it came from the Tisbury Great Pond. There are still a few Island fishermen who remember when Tisbury Great Pond had a highly productive oyster fishery supporting many families.

In response to the expected die-off in the coming year, West Tisbury town officials agreed to open the oyster fishery in the pond on Nov. 13,  increasing the daily limit to five bushels per day instead of three. Fishermen will be allowed to fish three days a week. With the anticipated collapse of the fishery, Mr. Karney said, there is nothing one can immediately do but bring what remains to market.

Mr. Karney said he learned about traces of the disease in Tisbury Great Pond a year ago. Only a small amount of the disease was present and so Mr. Karney said: “I thought it was a fluke. There was only a little bit. The selectmen knew and the shellfish constable. There wasn’t any reason for alarm.”

“These results now are certainly more alarming,” Mr. Karney said. The sampling of the pond was done last month. “A total of 75 mature oysters were sent off to Woods Hole for analysis,” he said, noting that he had learned on Wednesday from Roxanna Smolowitz, a veterinarian with the Marine Biological Laboratory, that the disease was throughout the sampling. “We found that 30 per cent were moderately to highly infected and the other 30 per cent were mildly infected,” Mr. Karney said. If the Vineyard has a really cold winter, the Woods Hole scientist believes the mildly infected oysters might survive through the winter, he said. Otherwise, he should expect a significant die-off of oysters in the coming year.

Dermo is not in residence in either Edgartown’s Oyster Pond or Squibnocket, which is in Aquinnah and Chilmark. There is no evidence of the disease in Katama Bay. None of the cultured oysters that are being grown in Katama Bay has evidence of the disease.

Dermo is caused by a parasite named Perkinsus marinus. It infects all the tissues of the oyster. The parasite cannot handle low salinity rates and low temperatures. The disease only spreads during the warmer months of the year, which is why the scientists do their samplings in the fall.

Dermo has infected oysters in the Gulf of Mexico and the Atlantic Coast for the last 45 years. It was first discovered in the Gulf of Mexico in the 1940s. “Since we have milder and milder winters, the disease has moved up the coast,” Mr. Karney said.

While there appears to be no human way to limit the spread of the disease, one key way to protect uninfected oysters is to keep them away from those that are infected. There are strict state laws prohibiting the relaying of oysters from one pond to the next. Shellfish constables have been highly conscious about trying to keep Dermo out of uninfected ponds.

Now there will be a shift in the fight to protect the oyster fishery. Mr. Karney said he is going to move in the direction of finding ways to raise Dermo-resistant oysters. “There will always be nature’s own oysters on Martha’s Vineyard. It may be necessary for us to tweak our efforts. We will look at coming up with Dermo-resistant stock. The shellfish group is committed to restoring and preserving the public and private effort to grow oysters,” Mr. Karney said.

There has already been a significant amount of work in southern states to find a disease-resistant oyster. The oysters is one of the most valuable commercial shellfish species on the eastern seaboard.

Yesterday, Mr. Karney was making arrangements to have more oysters from the Great Pond sent up to Woods Hole for analysis. He said, “We want to get an even better handle on the extent of the disease.”

Mr. Houle said, “We have thought all along that we were the next one to get it.”