A temporary ban on harvesting oysters, clams and other bivalve shellfish that went into effect Sunday is expected to last until Wednesday or Thursday, according to a scientist at the Department of Marine Resources.

More than 2 inches of rain fell Sunday morning, causing runoff containing bacteria from fecal matter to enter Casco Bay, triggering the shellfish harvesting closure stretching from Freeport to Harpswell.

It is the eighth rain-caused closure of 2024. Last year, the department enacted 24 such closures.

Oyster farmers, from left, Shae Hemburger, Jesse Devereaux, Noah Hebert and Sam Deggett, with Mere Point Oyster Company, make their way back to the docks Tuesday. Despite the harvesting closure in the Freeport-Harpswell area, the crew was out working on gear maintenance and other tasks. Shawn Patrick Ouellette/Staff Photographer

The closures can force restaurants to look elsewhere for fresh shellfish, and prevent aquafarms from doing any work that involves removing oysters or other bivalves from the water, even if only temporarily.

The department closes areas to shellfish harvesting every time there is over 2 inches of rain within 24 hours. At that threshold, oysters, clams and mussels risk absorbing enough bacteria to give food poisoning to anyone eating them raw.

Department scientist Bryant Lewis said DMR measures contamination levels in the ocean every time it rains and uses that data to inform how long its closures will last.

“We identify specific stations within all the different coastal water bodies, and then we’ve gone out to them every time it’s rained on, starting approximately 48 hours after, and then each day following, to build up a data set,” Lewis said.

The Shop by Island Creek Oysters, which normally sources about a third of its oysters from the Freeport-Harpswell area, has had to buy more oysters from farms in other areas, according to manager Kit Paschal.

“This happens – this is normal,” Paschal said. “Fortunately, here in Maine, there’s a large variety of places where people grow oysters. So in the event of something like the areas in Harpswell being closed, the areas in the Damariscotta River are open. … You just end up buying from different areas more.

“It’s tough on the farmers when they can’t harvest and make their income, but I don’t think any farmer gets into this not realizing that it’s a possibility,” he added.

Cam Niven, operations manager at Mere Point Oyster Company, a Brunswick oyster farm affected by the closure, said the ban is broader than it needs to be.

“We’re not allowed to bring any product onto land to process or do any husbandry tasks with,” Niven said. “Even if it’s not going to market, nothing can be landed, which is kind of a huge monkey wrench in the flow of work.”

Niven thinks the closure shouldn’t prevent farms from doing work such as seed separation, when a farm brings seed oysters ashore, separates them by size, and returns them to the water. Since it only takes a few days for oysters to purge themselves of bacteria, there is no risk that the seed oysters would retain harmful bacteria when they get larger and go to market.

“A big part of our process is working with oyster seed, and we can’t even bring that out onto land to shake it and separate sizes, even though it’s not going to market for human consumption … (for) a year, a year and a half,” Niven said.

He doesn’t oppose the closure but thinks the restrictions should be narrower.

Jesse Devereaux, right, hands supplies to Noah Hebert as they unload a boat at Mere Point Oyster Company in Brunswick on Tuesday. Shawn Patrick Ouellette/Staff Photographer

“I understand why (the closure) is so broad, just for overall safety of the Maine aquaculture,” Niven said. “We don’t want anybody to get sick, but I do feel like there could be some more leniency.”

But Lewis, the DMR scientist, wrote in an email that it would be too difficult to allow aquafarms to conduct certain land-based tasks, but not others.

“All shellfish harvesting activity that would move product off leases is included in the closure due to the enforcement complexity that would be associated with permitting the transportation of seed during these closures,” Lewis wrote.

Farms are allowed during closures to tumble oysters – putting them through a tube in the water to remove any sediment or growth.

“(Tumbling oysters) chips off the new growth and forces them to grow deeper … instead of skinnier, so it grows a higher quality oyster,” Niven said. “And that can be done through a closure because we’re not harvesting or landing any shellfish.” 

The rain-related closures are not the only kind to affect shellfish harvesting this summer. The FDA also recalled oysters harvested over a monthlong period stretching from June into July, saying they may be contaminated with bacteria.