How Baby Oysters Get From Spat To Flat

By: Doreen Leggett

Topics: Commercial fishing and shellfishing

Bags of baby oysters attached to sea clam shells are removed from vats at A.R.C. in Dennis. DOREEN LEGGETT PHOTO

In a greenhouse off a long, sandy road in Dennis, concrete pools are filled every spring to offer millions and millions of oysters a swim.

Before the budding bivalves took the plunge this year, about 4,000 mesh bags of mostly sea clam shells, originally from a processing facility in New Bedford, were placed inside two of the empty pools at A.R.C. Hatchery.

“After we put the bags of shell in the tanks, we fill the tanks full of seawater and algae – food for the baby oyster. The (oyster) larvae permanently attach themselves to the shell (called setting) inside the bags,” said Rick Sawyer, president of the hatchery. “It is quite a process.”

The baby oysters spawn inside the hatchery, which got its start growing clams in the 1960s and now spawns, grows and sells a variety of shellfish. Once they get big enough, no bigger than a flea, the oysters are released into the tanks and go right for the shells, or cultch.

“Calcium carbonate is really what the oysters are looking for,” said Ashley Fisher, Mashpee’s Director of Natural Resources.

The baby oysters set on the shells to begin their journey to adulthood, but about two weeks into it they are transported into the wild.

Mashpee has been participating in A.R.C.’s remote set program since 2004. Fisher said they first got involved to help clean up the Mashpee River; oysters filter a lot of water — up to 50 gallons a day. Sometimes the town takes up to 2,000 bags (that’s about 20 million oysters).

The remote set program, so named because the oysters “set” at A.R.C. and then are brought to communities across the Cape and beyond, is one of many ways the hatchery — renovated in 2015 — helps power the blue economy.

“A.R.C is the largest producer of shellfish seed in New England and a unique resource in the region, able to provide shells that have baby oysters growing on them,” said Melissa Sanderson, chief operating officer of the Cape Cod Commercial Fishermen’s Alliance, an investor in A.R.C. “This helps jumpstart oyster beds and other restoration projects, which provide important seashore erosion control against storms and wave action, as well as cleaning the water.”

There were no oysters in the Mashpee River when the remote set program began. The filter feeders went to work, removing nitrogen, eating algae and slowly pushing up the oxygen levels.

The Mashpee River is still pretty degraded, but we haven’t seen fish kills since we put them in,” Fisher said.

Staff from Mashpee were among representatives from towns across the Cape — Barnstable, Chatham, Dennis, Eastham, Truro and Yarmouth — and even Rhode Island that descended on A.R.C. one day in June to pick up their oyster bounty.

Mashpee, which took the most bags, sent down DPW trucks to load and drove them right to the river to put on boats and take out to the drop spot.

“It is a very big day for us,” said Fisher.

Chatham does much the same thing.

“We put them down at Mill Creek,” said Chatham Shellfish Constable Renee Gagne. “We make a little assembly line, fill up two Jon boats and we walk them out and keep them in the bags. We put them in cages, cover them and buoy them off to make sure no one takes a boat and hits them.”

The shells’ on-Cape journey actually started more than a year earlier. While the landscape industry has pretty much cornered the market on clean shells, cultch for the Cape gets trucked to the transfer station in Dennis and set out behind the landfill. Fisher says Dennis staff nicely turns them over so the remaining meat gets baked off.

“They have to be out and toasting for at least six months before you put them back in the water,” Gagne said, to avoid any possible organic contamination.

Early in June towns show up and put the shells into however many bags they need.

“It’s a community event,” said Sawyer.

“This year was especially interesting because of social distancing,” said Gagne.

The bulk of the oysters support various recreational shellfish programs.

In Chatham, once the oysters get big enough they are taken out of the bags and moved to a spot where the town creates a bank of oysters people can harvest. Hopefully they’ll spawn and help the wild population as well.

“We have really nice product. They look beautiful,” Gagne said. “Anything you can put in the water to help recruitment is a good thing…and it is just another opportunity for people to experience oyster harvest.”

Fisher said that until oysters from A.R.C. arrived there were none in Mashpee, and even now there are no wild oysters. Townspeople love when the larger oysters are moved to the recreational areas for harvest come Nov. 1, she added.

“They get really excited about it.”