Maine Department of Marine Resources

Survey confirms green crab threat to fishery

Tue, 12/31/2013 - 6:30pm

Maine Department of Marine Resources Director of Public Health Kohl Kanwit recently presented to more than 600 researchers, entrepreneurs and Maine shellfish harvesters scientific verification that green crabs are threatening Maine’s third most lucrative fishery — soft shell clams.

The cross-section of stakeholders attended or logged in to a webcast of the December 16 Green Crab Summit, co-hosted by Maine Sea Grant and the DMR. The event was held to examine the challenges and opportunities of non-native green crabs, whose population has exploded in recent years and which feed on bivalves like soft shell clams. Last year, soft shell clams generated approximately $15 million in landed value and approximately $45 million in overall economic benefit to Maine’s economy.

Kanwit discussed results of a green crab trapping survey, conducted over two days in nearly 30 coast-wide locations. “We had conversations with industry last spring about the extent of the green crab problem and the consensus was that green crabs are a serious problem,” Kanwit said. “But we were uncertain about the extent and degree of the problem so we designed a survey to verify industry observations.”

DMR staff worked with University of Maine, Machias Professor of Marine Ecology Dr. Brian Beal to develop a plan the survey. “We worked with volunteers from nearly 30 municipalities to conduct the survey,” Kanwit said.

“Our primary goal was to provide a snap shot of the locations and relative abundance of the green crab populations along the coast, and to raise the level of awareness of municipalities about green crabs and their impact on shellfish resources which are so important to our coastal economy,” Kanwit said. “As scientists, we also wanted to confirm the observations reported to us by industry.”

Volunteers were asked to set up to 10 traps on soft bottom favored by soft shell clams. Traps used included lobster traps as well as specialized traps designed for specifically for harvesting crabs.

Of the 208 traps set, 193 had crabs in them. The communities with the most crabs per trap were Stockton Springs with 191, Freeport with 181 and Scarborough with 151.

While Kanwit acknowledges that the variables in trap type and bait used make the data imperfect for scientific research, the project did accomplish its most important goal. “We were able to verify reports from harvesters that green crabs are present in most of the towns in numbers that are detrimental to bivalve shellfish resources,” Kanwit said.

The event included presentations by entrepreneurs who are hoping to capitalize on the green crab population by processing them for aquaculture fish meal and other products. However Department of Marine Resources Commissioner Patrick Keliher reiterated the Department’s position that green crabs are an invasive species to be controlled if not eradicated.

The commissioner, who decided last summer to get a first-hand look at the problem, visited areas of the coast with known concentration of green crabs. “I couldn’t believe what I was seeing,” Keliher said. “I was astounded by the prevalence of green crabs.” He was not only surprised by the number of crabs, but by their destruction of eel grass beds, important as habitat and an indicator of near shore health. “The absolute destruction was nothing short of amazing.”

The site visits helped confirm the commissioner’s resolve to work toward eradicating green crabs versus managing them as a sustainable resource, which is the goal of commercial fisheries management. “Do we want to manage an invasive species for sustainability? My answer is no,” Keliher said. “I’m pleased to see all the different stakeholders attending today and taking part in this discussion and I’ll continue to listen to ideas that advance economic opportunity. But at the end of the day, we need to find a way to eradicate them.”

Summit webcast recordings can be found at More information on green crabs can be found at The DMR will be hosting another information session at the Fisherman’s Forum in March and will also be holding a workshop for municipalities in early 2014 on how to implement a green crab control plan. Information on those events will be available on the DMR website at