SalemNews.com, Salem, MA

December 14, 2013

Invasive crabs threatening region's clams

by JAMES NIEDZINSKI
Staff Writer

---- — ESSEX — The soft-shelled backbone of this town’s economy is under attack from an old enemy, with invasive species of crabs gobbling up clams throughout Essex Bay, experts say.

There may be two invasive species threatening the deep-fried favorite of Essex, the European green crabs and the Asian shore crabs. But Essex Shellfish Constable Billie Knovack says there is especially an uptick in European green crabs in Essex, and that means fewer for clammers to reel in.

“We have a green crab invasion,” he said earlier this month.

Usually, Knovack explained, the winter kills off the crab population. But warmer waters and warmer weather — which he attributed to climate change — means more time for the crabs to hunt Essex’s soft-shelled clams.

“It’s a much more opportune environment,” he said. “If you’re a crab, this is beautiful weather,” he said in 40-degree temperatures at the town landing earlier this month.

Knovack said there are no hard numbers as to the amount of European green crabs in the Essex River or Essex Bay, but the clams are disappearing. About two to three years ago, commercial clammers were meeting their annual 250-pound clam quota; now, clammers are catching about 150 pounds each annually, he said.

In addition, erosion is causing Crane Beach and Plum Island to draw more sand into Essex Bay, which may give more ground to clam flats. But the predatory crabs are still there, as well.

This threat is nothing new. The clam-hunting crab arrived on American shores in the 1880s said Alan Young, who holds a doctorate in biology and teaches at Salem State University.

While the green crab is the classic predator of shellfish and invertebrates, the Asian shore crab may also pose a threat to the seafood industry in Essex and beyond.

Young notes that the first appearance of the relatively new invasive species was in 1988, but it is now found up and down the East Coast.

“The larvae spend about a month drifting in the water so (they) can be transported considerable distances along the coast pretty quickly,” he wrote in an email. The crabs were found locally in Salem and Marblehead in 2000.

Unlike the invasive European green crab, the Asian shore crab prefers rocky cobble beaches but can be found in soft sands, as well.

“It is very successful as an invasive species, at least partly because its reproductive rate is very high,” Young said. “A single female can produce 50,000 eggs three to four times during the summer, whereas native crabs reproduce only twice each season.”

Asian shore crabs also feed on juvenile clams and other invertebrates, but pose less of a threat than the European green crab because the shore crab generally hunts in places where clams are absent anyway, Young wrote.