Following the early closure of the scalloping season in Aquinnah, town officials and shellfish biologists are trying to understand the unexpected decline in the number of adult scallops this year.

The town shellfish committee, along with the natural resources department of the Wampanoag Tribe of Gay Head (Aquinnah) finished reseeding Menemsha Pond with about 1.4 million seed (young scallops) this week, and are hoping for a stronger harvest next year.

The season closed Nov. 15 in response to a lack of adult scallops since continued dredging for the adults would likely disturb the juveniles that may not be harvested until next year. A black algae was also observed growing on many of the scallop shells. Samples were sent to the Woods Hole Oceanographic Institution for testing and town officials are awaiting results.

Bret Stearns, natural resources director for the tribe, said it was not uncommon for algae to be found growing on the shells. He added that the pond’s water quality and food supply, as well as the presence of eel grass (an important element in shellfish habitat) were relatively normal.

3,500 bushels were harvested last year in Aquinnah. — Albert O. Fischer

Following an early closure of the season in 2011, the next two seasons were highly successful. “We are following sort of a cyclical pattern of a banner season and then a closed season,” Mr. Stearns said. But like other officials, he was unsure what may have led to the decline this year.

Many scalloping areas see a similar cycle, said Rick Karney, director of the Martha’s Vineyard Shellfish Group, which runs a hatchery and nursery and supplies scallop seed to Island towns. Because scallops typically live for only two years, the size of each year’s adult population depends heavily on the number of juveniles the year before.

Buddy Vanderhoop, chairman of the town shellfish committee, said people raking for quahaugs in the pond this summer were finding many adult scallops. “That was really puzzling to everyone, because it looked like we were going to have a banner year,” he said.

He said “a huge amount” of empty shells were later discovered in the pond.

A few of the dead scallops were sent to Mr. Karney for analysis. He said they had likely died from old age, supporting his suspicion that many of the adults this year were left over from last year.

There were so many adult scallops in Menemsha Pond last year that the commercial season in Aquinnah was extended. With so many adults in the pond, Mr. Karney said, the younger scallops could have been out competed for food, contributing to the poor season this year.

Mr. Vanderhoop said Menemsha Pond “is pretty choked up,” and that dredging the pond’s inlet to the sea would improve the flow of water and also the distribution and abundance of plankton, which the scallops feed on. He said the lack of flow may also have contributed to the poor season.

The Army Corps of Engineers was expected to dredge the inlet this fall, but their dredge was unavailable, Mr. Vanderhoop said. After the pond was dredged in 1972, he said, Aquinnah had five banner years in a row for scalloping. “It was the best five years we ever had in the pond,” he said. He expected the dredging to happen next fall. (Chilmark town leaders are opposed to the dredging.)

Last year about 3,500 bushels were harvested in Aquinnah. Mr. Stearns said there were years when the harvest was as high as 4,000 bushels, but that even 3,000 bushels would mark a “great year.”

Aquinnah shellfish constable Brian Vanderhoop was also baffled by the poor season this year. Last year he had closed the eastern two thirds of the pond to scalloping for the last several weeks of the commercial season to help protect the seed. “I thought for sure these animals would make it through,” he said. “In the past that’s worked out perfectly for us, but not last year.”

In Chilmark’s portion of Menemsha Pond, the scalloping has been good, Mr. Stearns said. But he pointed out that the water there is slightly warmer and has better circulation. He said officials in both towns would meet this winter to address the problems in Aquinnah.

Mr. Karney said that he believed that Chilmark’s success this year indicated that toxins were not to blame for the poor season in Aquinnah. “If it was toxic, we would see other things on the Chilmark side also,” he said. Mr. Karney himself had examined the black algae and sent a sample to a specialist at Roger Williams University. He said the specialist found no indication that the species of algae could be deadly.

One option for Aquinnah is to improve predator control in the pond, Mr. Stearns said. Shellfishermen already work with the town and the tribe to control the number of green crabs, which prey on the scallops. Juveniles are also kept in sanctuaries for a year before being added to the harvest area. “It’s a smart way that costs no money to protect your harvest,” Mr. Stearns said.

But people this year did not report seeing cracks in the shells of dead scallops, Mr. Karney said, which suggests that the scallops did not die from predation.

Town administrator Adam Wilson said the town usually has about 30 commercial scallopers, each paying $200 for a license. He said the town loses about $6,000 when a commercial season is cancelled.

Scallops sell for about $12 per pound, with a bushel yielding about eight pounds of meat. That would suggest that about $336,000 worth of scallops were harvested in Aquinnah last year.

Roxanne Ackerman, a longtime scalloper and oyster farmer in Aquinnah, estimated that at least 30 families will be affected by the absence of a commercial season this year. “It trickles down,” she said, explaining that some people harvest while others shuck, and others sell the scallops.

“This was another scalloping season that we counted on,” Ms. Ackerman said.