In the face of growing opposition to a major expansion project at the Martha’s Vineyard Shipyard, Tisbury selectmen voted Wednesday night to send a letter of support to the owners of the shipyard.

More than 75 people attended the meeting at the Katharine Cornell Theatre, filling seats and perched along stairways.

Most were there to urge selectmen not to back the shipyard expansion plan, which includes a 48-vessel marina on Lagoon Pond.

Selectmen have no regulatory authority over the project, but shipyard owners Phil and James Hale had asked the board earlier this month to write them a letter of support before the project goes in front of the Martha’s Vineyard Commission for review as a development of regional impact (DRI). An exhaustive review is expected by the commission, which has the plan but has not set a hearing date yet. The plan will further require review by a large number of state and federal agencies.

A letter of support from the selectmen that had been drafted earlier by town administrator John W. (Jay) Grande was made available at the meeting.

“The selectmen are pleased to see your investment and confidence in Tisbury’s and the Island’s future,” it reads in part. “The project is under review by no less than nine local, state and federal agencies and we expect them to find a net improvement over existing environmental conditions,” it continues. “Your success is critical to preserving a viable and prosperous working waterfront for the Island.”

On Wednesday critics were many, but selectmen had limited the number of speakers to four.

Lagoon Pond Association president Doug Reece said while not every member of his organization was against the plan, the group’s petition opposing the development has gathered 1,900 signatures.

Mr. Reece said he applauded the Hales for responding to earlier concerns from environmental groups by adding mitigation measures to their plan.

But he also cited a November letter from the Massachusetts Division of Marine Fisheries recommending the Hales consider relocating the project to the Vineyard Haven inner harbor, in order to protect shellfishing in what’s called the west arm of Lagoon Pond.

“That’s one pretty impressive statement,” Mr. Reece said.

“Secondly, it’s our opinion that adding another marina in the west arm will forever alter the health of the pond,” he said.

Emma Green-Beach of the Martha’s Vineyard Shellfish Group also expressed strong concern for the health of the fishery in the west arm.

“It’s one of the most productive areas in Tisbury and in the Lagoon,” she said, citing the shallow waters where families can dipnet for bay scallops.

Even the most meticulously maintained vessels and vehicles shed toxins that threaten the way shellfish develop, she said.

“In supporting this project . . . you’re making

a choice,” she told selectmen. “If we have to make a choice to support private business and recreational boats, then we are choosing these things over traditional shellfisheries and the hard-working watermen.”

Gerard Hokanson of Tisbury Waterways Inc., a nonprofit concerned with clean water in the town’s estuaries and harbor, suggested the proposed stormwater mitigations — permeable gravel pavement and waterside plantings — are insufficient to protect water quality.

“They simply don’t work well near the water’s edge because of the high water table along the shoreline,” Mr. Hokanson said.

Shelly Edmundson, executive director of the Martha’s Vineyard Fishermen’s Preservation Trust, added her concerns.

“I wanted . . . just to say a few things for all the fishermen in the room,” Ms. Edmundson said, reading from a letter that echoed concerns expressed by earlier speakers.

“We believe this project is a direct threat to the diversified occupations that make up our working waterfront tradition and our community at large,” Ms. Edmundson said.

“We do not want to see the many livelihoods endangered for the benefit of one business and the convenience of a collection of recreational boaters.”

There was no public discussion of the matter, and selectman Melinda Loberg reminded the group that a full public hearing will eventually be held in front of the MVC.

“The board of selectmen does not review this project,” she said. “As soon as they [the shipyard owners] apply for a permit they are sent to the Martha’s Vineyard Commission,” she continued.

“That is why we are not holding a public hearing, because public hearings will be a matter of course.”

Mrs. Loberg thanked the audience members for coming.

“I encourage you to attend the [Martha’s Vineyard] commission hearing,” she said.