FREEPORT, Maine (NEWS CENTER) -- One of Maine's oldest commercial fisheries is in trouble, and the reason appears to be a very aggressive and very hungry predator.

The people who harvest clams say their livelihoods are being threatened by the green crab. Shellfish harvesters say the green crabs are devouring the beds where small clams grow, and have drastically reduced clam production in some of the state's best digging areas. They warn the commercial clam industry itself is threatened if the crabs continue to spread.

Clams and other shellfish are the third largest of Maine's commercial fisheries, after elvers and lobsters. According to statistics from the Maine Department of Marine Resources, diggers harvested more than 11,000,000 pounds of soft-shell clams in 2012, with a value over $15,000,000.

But members of the Maine Clammers Association say they believe that harvest will be dropping because of the presence of the crab.

"Everything's disappearing," says Abden Simmons of Waldoboro, who is a member of the state Shellfish Advisory Board. "The only thing living there is the green crab. So what's living is being eaten up. Clams, mussels, oysters, everything."

Green crabs are not new to Maine. Dr. Brian Beal of the University of Maine at Machias says the crabs have been in Maine waters for more than 100 years. However, their population has increased dramatically, to the point that Beal, too, believes the green crabs are a serious threat to clam populations, and the people who make their living from them.

The cause of the crab explosion isn't clear, although Beal believes it's a result of warmer ocean water. He says there was a big jump in green crab population in the mid-1950's, another warm water period. In fact, warm water at that time is blamed for a dramatic drop in shrimp populations. The current warm-water cycle has again decimated Maine shrimp, to the point that this winter's fishing season had to be cancelled.

Scientists say green crabs aren't the only threat to Maine shellfish. They also point to a change in the ocean water itself, called ocean acidification. State Rep. Mick Devin, a researcher at the University of Maine Darling Marine Center, says increasing amounts of carbon are going into the ocean as a result of climate change. He says that carbon turns into carbolic acid in the salt water, which then lowers the pH and makes the water more acidic.

Devin says scientists have found higher acid levels will hurt the ability of crabs and other shellfish to form shells, which will threaten their growth. He says that lobsters may also be affected. Devin is leading an effort in the Legislature to form a special task force in Maine to study the potential impacts of ocean acidification, which he says pose a greater long term threat to clams than the green crab.

Clammers, however, say they need to deal with the crab first. "There's no baby clams coming around now for the acidification to ruin anyway," says Freeport digger Clint Goodenow. To fight back, he and other midcoast harvesters are focused on trapping the crabs before they reach the clams.

Abden Simmons has designed a special crab trap that reportedly worked well during the summer of 2013, and Brunswick and Freeport are now ready to deploy hundreds of the traps to catch the crabs.

The other answer, according to scientist Brian Beal, is to create a profitable market for the crabs. "We need to start eating green crabs," says Beal. " They're good to eat." Several fishing groups and businesses are exploring ways to harvest and sell the meat.

A Canadian businessman was in Brunswick recently to build interest in processing green crabs, and said he plans to open a processing facility in Maine. Other ideas being explored include making compost and fertilizer.

Harvesters say trapping and marketing the crabs can't happen soon enough. They say the crabs have moved to deeper water during the winter, but expect they will be back in large numbers again this year, eating as much or more than ever.

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