Originally published in Island Ad-Vantages, April 10, 2014
Invasive green crabs inundate area waters, decimate clam flats
Abby Barrows, Monitoring and Outreach Coordinator at Marine Environmental Research Institute in Blue Hill, Maine discusses the green crab problem at Penobscot East Resource Center in Stonington.
by Ruby Nash
On Thursday, March 20, Abby Barrows of the Blue Hill-based Marine Environmental Research Institute presented sobering news to a small, but concerned group of clammers, lobstermen, and fishermen in Stonington.
The topic of the presentation: the explosion of the green crab population, which has been of increasing concern over the past 18 months.
It shows no sign of abatement.
In August 2013, the Maine Department of Marine Resources conducted a one-day green crab trapping survey along the entire Maine coast. Twenty-eight towns participated, resulting in 193 traps collected coast-wide. A variety of traps were used, but the results were the same: green crabs have inundated the Maine coastline. Stockton Springs reported an average of 191 crabs per trap, with many other towns reporting similar or higher numbers.
The peninsula area was under-represented in the study, so Barrows and Carla Guenther, the Fisheries, Science and Leadership Advisor at Penobscot East Resource Center in Stonington, organized their own version of the survey in November 2013. The Penobscot Bay area reported much lower numbers—only 133 crabs in seven traps total—but this has since been attributed to the crabs’ seasonal migration to deeper waters as cold weather approaches.
Bailey Bowden of the Penobscot Shellfish Conservation Committee was at the presentation on Thursday night, and he provided his own numbers on green crabs in Northern Penobscot Bay. In the summer of 2012, Bailey and others set traps for crabs. When they returned 12 hours later, every trap was full. That catch was 10 bushels of crabs, at 350 crabs per bushel. They reset the traps, and returned after four hours to find another 10 bushels of crabs. After resetting again, they returned in two hours to find the same result: 350 green crabs in their traps.
“Our summer’s trapping effort didn’t even keep up with reproduction,” said Bowden. The explosion of crabs is due to a shift in temperature throughout the coast of Maine. Last year was one of the warmest winters on record for regional waters. Green crab females carry at least 165,000 eggs per mating cycle. With the influx of warm waters, more and more of the larvae are reaching maturity.
The green crabs, which Barrows described as akin to a cockroach, are hardy and omnivorous. They like a variety of environments (marshes, eelgrass beds, inter-tidal, and rocky areas), can survive in low salinity (they have been seen in the same environment as frogs) and will eat just about anything (juvenile lobster, scallops, clams, quahogs, and algae to name a few).
This does not bode well for species in the area. Early research at the nearby Mount Desert Island Biological Laboratory shows that the green crab appears to be decimating eelgrass beds. Eelgrass is a natural habitat for many important native species such as cod, hake, lobster, clams, and mussels. The crabs rip up or cut out the grass in their relentless search for food.
During her presentation, Barrows provided an example of their appetite: an adult crab can eat three dozen mussels in one day. Bowden confirmed that the Northern Penobscot Bay clam population has been decimated by the infestation.
“In 2012 we were making $150,000 to $200,000 in clams out of the flats in Penobscot, and in six months the green crab ate every clam,” Bowden said. “We now have an average of one half of a clam per square foot, and it should be 20 clams per square foot.”
There are a variety of efforts to curb the tide of green crabs, but so far the major hurdle is incentive. “There really is no green crab market in Maine,” Barrows said.
There was talk of using them as lobster bait, people eating them in Europe, chefs in the U.S. specializing in invasive species, making them into compost, or possible uses as vitamin supplements in cat food or aquaculture. The Department of Marine Resources plans to list potential buyers and markets on its webpage.
As the DMR has recognized the problem, some hurdles to fishing the crab have been overcome. Initially lobstermen could trap for the crabs for personal use (such as baiting), but they could not sell them. Now, with an additional $10 license, lobstermen can trap and sell them. Still, there is little incentive to do so without a market.
“If those little crabs were $20 a piece, we would fish them to extinction,” Bowden said. “It’s an incentive issue.”
As the problem progresses and the impacts of green crabs on generations of lobster, fish, and shellfish begin to take shape, the pressure for a solution will increase.
“[The problem is] not just affecting some clammers in Maine,” said Barrows. “It’s everywhere and it’s very real. It’s going to have a large impact on our fisheries and inter-tidal environments.”
The entire region faces the problem, and solutions are being tested everywhere, including netting in the Freeport area, and trapping efforts to the north. For example, Newfoundland held mitigation workshops during which 25,000 pounds of green crabs were caught in 22 days of intense trapping.
“It’s going to take consistent pressure in order to control the resource at this point,” said Guenther, “unless we have a bunch of really cold winters that wipe them out.”