Mussel weakness: Massive decline in Casco Bay poses questions about once-thriving population

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BRUNSWICK — It used to be common to lift up thick mats of seaweed on the shores of Casco Bay and uncover thousands of dark blue mussels nestled among the rocks.

But over the last few years, people who harvest and work to conserve the mollusk say areas that used to be full of thriving mussel beds have been bare.

The common mussel had disappeared. 

Volunteers have scoured southern areas of the bay, finding dwindling groups of 30 or fewer mussels, or none at all. Researchers have looked further afield, confirming that the pattern in Casco Bay is being repeated up and down the Maine coast.

“Everything I have seen suggests something is changing,” said Cascade Sorte, a scientist at the University of California at Irvine, who is finishing up a two-year survey of blue mussels in the Gulf of Maine.

“I know that the mussel population is changing, but I don’t know why,” Sorte said.

She isn’t alone. Experts confirm that something has happened to Casco Bay’s wild mussels, but no one can point, with any confidence, to a single reason.

Theories span topical concerns, including warming sea water, invasive predators, ocean acidification, disease and over-harvesting. Most think it is a combination of factors.

Meanwhile, mussel growers are having success, raising even more questions about the disappearance. 

But with an absence of in-depth research – Sorte’s study and a survey by the Friends of Casco Bay are the only two projects focused on Maine’s blue mussels – answers are elusive.

Friends of Casco Bay, a Portland-based environmental group , started looking into the rumors in 2013. The group dispatched volunteers in kayaks and small craft to survey  productive mussel beds mapped out by the Department of Marine Resources in 2009. 

The results were disturbing.

At 13 of the 21 sites visited, surveyors found no mussels, while in three other areas coverage was down to 5 percent, according to FCB data.

“All the reports from people that first summer were ‘yeah, I see the place identified on your map, but I’m not seeing any mussels there,'” said Peter Milholland, volunteer coordinator for FCB.

So far, volunteers have combed shoreline from South Portland to Yarmouth. This summer Milholland hopes to expand efforts to Brunswick, West Bath and Harpswell. 

Phil Gray, a longtime mussel harvester from Harpswell, already knows there’s nothing to find.

Gray picked wild mussels in Casco Bay for 15 years, temporarily giving up in 1991 when the market collapsed. 

When he started harvesting again in 2007, he was shocked to find nothing left of previously dense colonies along the Freeport shoreline. 

“I couldn’t believe it. That area, that used to be one of the largest producers of wild mussels on the Maine coast, had next to nothing,” Gray said. “It was unbelievable, they were just gone.”

In the past three years, Gray has seen whatever small beds were left on the New Meadows River vanish. He also found fewer young mussels mixed in with the adults.

When he did find the young bivalves, he left the bed untouched, only to return the next year and find nothing but shells, Gray said. 

He’s gone from harvesting 1,000 pounds a week to making a 115-mile round trip to the Rockland area to bring back a tenth of that. The decline has forced him to abandon the space he has usually rents to sell his catch at summer and winter farmers’ markets in Brunswick.

“I’ve gotten to the point where there are no more quality wild mussels to be had,” Gray said.

Research suggests that the issue extends further than Casco Bay.

Sorte, the UC Irvine researcher, said her results show that mussel beds mapped in the 1970s in the Pemaquid region have seen an approximately 50 percent decline, a pattern repeated from Cape Cod to Quoddy Head.

“The directional trends we are seeing are all down,” Sorte said. “There are no suggestions that they are going up.”

Her research builds on studies that show changes on a national and international scale.

A 2010 study from a University of North Carolina researcher found that because of warming oceans, mussels – once found as far south as North Carolina – now extend only to Delaware.

A study by the University of Glasgow in Scotland in December showed that ocean acidification made mussel shells more brittle and vulnerable to predators and other threats.

But even as once gigantic colonies of mussels dwindle to nothing, the alarm is muted, especially when compared to the flurry of studies, legislation and press that followed the invasion of green crabs into the soft-shell clam industry.

“Mussels are an important food source, important ecologically, but no one seems to be keeping tabs on it,” Sotre said.

Harvesters of wild mussel, at least in Casco Bay, don’t carry the same weight as other fisheries, according to Denis Nault, who heads up the DMR’s shellfish program.

Investigating the issue “hasn’t been a high priority,” because the wild harvesting industry in Casco Bay is so small, Nault said.

In 2013, Maine’s mussel catch, both wild and farm-raised, was 13.3 million pounds, worth approximately $2.3 million, a sliver of the $16.9 million soft-shell clam catch. There were only 52 mussel licenses in the state that year, down from 58 in 2010, according to DMR figures.

While DMR is aware of the sudden and rapid decline of mussels in Casco Bay, its experts are at a loss to explain it.

“It’s hard to say exactly what the factors are,” Nault said.

“The variability of settlement for any bivalve shellfish are huge,” he added. “If I could say; ‘oh, it’s that factor there, or it’s this,’ I wouldn’t be running a state program, I’d be making my millions elsewhere.”

Carter Newell, who raises mussels in the Damariscotta area, said competition for space from other species, like sea squirts, and threats from predators could explain some of the decline.

Overfishing by commercial draggers could also have reduced the number of spawning mussels each year and damaged the bed surface that mussels use to attach, Newell noted. 

But he also can’t put his finger on a cause.

“Because there are so many interrelated factors, it is difficult to pinpoint which are the most important,” Newell said in an email.

Gray, Harpswell mussel harvester, believes he knows exactly what is to blame: the green crab plague.

Mussel larvae float around in the water until they find a suitable landing spot, usually a nearby colony, he said. In their first year, they are vulnerable to predation.

The tremendous number of green crabs in the past few years are “just cleaning out the crop of new mussels,” Gray said.

But in a controlled growing environment, mussels are thriving.

Matt Moretti, who runs Portland’s Bangs Island Mussels, has expanded the operation since he bought it four years ago, adding three rafts located near Bangs and Clapboard islands in Casco Bay. His company brought in 200,000 pounds of mussels last year.

At Bangs Island, wild mussel seed is collected and grown on ropes descending from the rafts.

“One of the advantages of the way we farm mussels is that we have no contact with the bottom,” Moretti said. “So the green crab issue is harder for us to see.”

While his company’s adult mussels provide plenty of larvae for the next harvest, new mussels also have to be coming from somewhere else, Moretti said. The Bangs Island site was recently completely stripped, but regrown with wild spawn, he noted.

“It’s strange, because we’re getting good seed sets, but from everything I’ve heard, the wild beds just aren’t around anymore,” Moretti said.

There are some positive signs. Milholland, of Friends of Casco Bay, said volunteers noticed more mussels grouped on mooring ropes, underneath floats and on wharf pilings, away from the shoreline.

Gray reported he’s noticed small colonies growing in parts of Harpswell. Given how prolific mussels are, the population could recover from its near-demise.

Still, only time will tell if Casco Bay’s mussels will rebound.

“It’s up to Mother Nature now,” Gray said.

Peter L. McGuire can be reached at 781-3661 ext. 100 or pmcguire@theforecaster.net. Follow him on Twitter @PeteL_McGuire.

Sidebar Elements


Sunbleached blue mussel shells litter a Portland cove on Casco Bay. All evidence suggests that wild blue mussels have largely disappeared from the area in recent years.

A small clutch of mussels clings to the surface of a rock on a Portland beach. Evidence suggests that previously thousands-strong colonies of mussels on the shores of Casco Bay have been reduced to almost nothing in recent years.

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