Clam harvester Mike Ashby holds up a green crab that was collected in the Harraseeket River in Freeport as part of a multi-year study by Downeast Institute and Maine Clammers Association on how predation is affecting softshell clam populations along the southern Maine coast. Credit: Photo by Sara Randall/Downeast Institute.

The future of Maine’s softshell clam industry may depend on farming them rather than harvesting the shellfish in the wild, according to scientists and clam diggers who collaborated on a recent research project.

A new study, conducted over two years at dozens of locations along the state’s southern coast, indicates that predators are the single biggest reason Maine’s softshell clam population has declined sharply in recent years. Raising clams in enclosures that protect them from being eaten by other creatures could go far in boosting the number of clams harvested in the state, according to researchers.

For over a month now, Freeport clammers have been trapping green crabs in the Harraseeket River of Casco Bay. In this video, MCA president Chad Coffin explains current green crab conditions.

Posted by Maine Clammers Association on Friday, 6 June 2014

“Clammers today are hunter and gatherers,” Brian Beal, a marine ecology professor at the University of Maine at Machias and co-author of the study, said Tuesday. “[The future of clamming] doesn’t look like hunting and gathering. It looks like farming.”

Beal, who also serves as director of the Downeast Institute for Applied Marine Research and Education in Beals, over the past few years has worked with clam diggers and the Maine Clammers Association to try to identify specific causes for the decline in softshell clams.

Softshell clams, which support a $12 million fishery in Maine, face a variety of challenges as the Gulf of Maine grows warmer as a result of climate change — increased temperatures and acidity, biotoxins and pollution among them. But what the researchers found is that the biggest culprit by far in the decline of of the bivalve shellfish species along Maine’s coast are green crabs and milky ribbon worms, which eat the clams by injecting toxins inside them and then sucking out their innards.

Milder winters resulting from climate change have allowed these predators to proliferate along the Maine coast, and the impact they have had on softshell clams has been severe. In some parts of Casco Bay, mud flats once known to produce clams have become known as “ dead muds” because of the absence of marine life.

According to Beal, the study showed mud flats can produce clams when predators are kept out. When he and other researchers placed square wooden boxes with mesh coverings on the tops and bottoms on the mud flats, tiny clams accumulated and grew in the boxes, often by the thousands. Water quality and other environmental conditions where researchers placed their boxes did not appear to be limiting factors.

“They are not deserts,” Beal said of open mud flats where diggers have come up empty. “They are alive and [can be] highly productive.”

Chad Coffin, a clam harvester from Freeport and co-author of the study, said Wednesday that the problem’s extent has been obscured by the fact that the number of clam harvesters in the state has declined sharply since the early 1970s, from around 6,000 to roughly 1,500 now. Many still are getting decent catches, he said. And many believe that the fishery can continue to be managed effectively by seeding mud flats with “spat,” or tiny clams, limiting the number of harvester licenses, and hoping for more frequent cold winters instead of by finding ways to control predation.

The number of tiny clams that settle on the mud flats “isn’t the issue,” said Coffin, who also is head of the Maine Clammers Association. “Everything is getting eaten.”

Credit: Sara Randall/Downeast Institute

Coffin echoed Beal in saying that adopting more of an aquaculture approach that seeks to limit predation seems to be the best way to preserve the fishery. But more also needs to be done to preserve access to the intertidal zone, where marine harvesters increasingly run into legal challenges from waterfront property owners.

“I don’t know if [the Casco Bay clam fishery] can survive long term,” Coffin said. “We’re basically squandering it. Burying your head in the sand isn’t the answer.”

There has been some effort over the past several years to put a dent in Maine’s growing population of green crabs, an invasive species that has been in Maine since the 1800s but whose numbers have soared this decade. Fishermen and seafood entrepreneurs have dabbled, without much success, in developing green crab products and markets. Next month, a conference for people with an interest in the topic is scheduled to be held at O’Maine Studios in Portland.

Softshell clams have long been one of the more lucrative fisheries in Maine, though it and others lag far behind Maine’s iconic $433 million lobster fishery in terms of economic impact. Since 2001, more than $10 million worth of clams have been harvested in Maine each year, with a record value of $22.8 million harvested in 2015.

The annual harvest value dropped by $10 million, however, from 2015 to 2017, when the volume dropped to 1.4 million pounds, the lowest amount harvested in Maine since 1930.

Beal said reasonable changes can be made to decrease predation and to encourage fishermen to adopt more of an aquaculture approach. Fishermen could collect their own clam spat in wooden boxes like those used in the study, he said.

Credit: AP Photo/Patrick Whittle, File

Allowing clam harvesters to lease portions of some mud flats — state law allows coastal towns to lease out up to 25 percent of any mud flats that lie within their borders — would allow them both to collect the spat and to have exclusive rights to those clams as they grow them to harvest size, Beal said. Reducing the minimum size from 2 inches to 1½ inches would have no impact on the population but would make the grow-out process shorter, he said.

Short of trying to cultivate clams at protected lease sites, more could be done to promote natural reproduction by clams, Beal added. The state could adopt a maximum size limit, which would help protect the high-volume spawners that produce most of the brood stock, and it could enact rolling harvest closures along the coast from late spring to early summer, which would help clams replenish their numbers from one year to the next by allowing them to spawn before being harvested.

The rise in predation brought on by climate change is “shaking the foundation of traditional clam management,” Beal said, and new approaches need to be adopted in order for the fishery to survive.

“It is not rocket science,” he said of growing clams in wooden boxes. “Anyone can do this stuff.”

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Bill Trotter

A news reporter in coastal Maine for more than 20 years, Bill Trotter writes about how the Atlantic Ocean and the state's iconic coastline help to shape the lives of coastal Maine residents and visitors....