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  • Gabe Wilson and Mikey Walsh

Invasive Green Crabs Vs. Soft-Shelled Clams In The Gulf of Maine


“They just boil out of the water”- Maine Clammer Clint Goodenow [1] speaks for many clammers across the Gulf of Maine. The growing population of the Carcinus maenas or green crab along the coast of the Gulf of Maine has created many new issues for native marine species as well as people. C. maenasis an invasive species which found its way into the Gulf of Maine. At first, the crabs were not a problem in the Gulf of Maine. With the long cold winters, green crab populations were in check. However, three major factors have contributed to their population explosion: rising water temperatures, lack of natural predators, and their incredible fecundity.

Green crabs settled into Maine’s waters and found the perfect food source; the softshell clam. The clam industry is important to many people in Maine. It employs over 1,000 harvesters and brings in millions of dollars every year for Maine’s economy. The softshell clam harvest in Maine has recently seen the lowest numbers in decades. One green crab can consume 40 half-inch juvenile clams in just one day. With thousands of crabs on the hunt, the damage happens very fast. “It’s not that there’s not clams, it’s that they don’t survive.” said clammer Chad Coffin

Freeport, Maine [2]. If the clam population continues to decline at this rate, Gulf of Maine clam

harvesters will be negatively affected. The green crab could be the end of a northeast business and a family tradition for many.


There are many factors contributing to a thriving population of green crab in the Gulf of Maine waters. The green crab found their way into the Gulf during the mid-1800s on sailing ships from western Europe, and by the 1870s the green crabs had spread all the way from the Chesapeake Bay to Cape Cod.

The first factor is rising ocean temperatures and milder winters have allowed crabs to survive through traditionally cold winters. Maine’s previous long and cold winters helped prevent the omnivore from rapidly reproducing and gaining in population. The quick rise of ocean temperatures and a string of mild winters over the past several years has caught many off-guard, making it difficult to find solutions for a continually growing green crab population which negatively impact commercially important species such as soft-shell clams.“In 2016, clam landings fell 21 percent, from 9.3 million to 7.3 million pounds, the lowest total reported since 1991, according to the state Department of Marine Resources” [3] with clam landings dropping in millions of pounds each year, the number of clam harvesters is following a similar path. “The clams are still readily available to consumers, but the number of harvesters digging for them has slipped to about 1,600 in Maine. It was more than 2,000 as recently as 2015.” [4] says Patrick Whittle from the Portland Press Herald in summer 2016. The downside is that hundreds of clammers are losing their jobs. On the other hand, this allows remaining clammers to still make a living with the remaining clams. Green Crabs pose a huge threat to the softshell clam business and culture of Maine clammers.

Another factor that plays into the rising populations of green crabs is they are an invasive species. There are no natural predators to prevent them from overpopulating.

The lack of natural predators is further compounded by the fecundity, allowing the green crab invasion to continue to grow at a blistering pace which we have little chance of catching up with. “Invasive green crabs can produce an astounding 200,000 eggs in one reproductive cycle. They have a reproductive season ranging from May to August (July to October in some areas)

and can have more than one reproductive event a year.” [5] says the Maine Clammers Association.

It is no surprise the clam population is decreasing at the rate it is. The green crab orCarcinus maenas is also an adaptable species. For example, the green crab can live in water conditions between 30-88 degrees Fahrenheit, and variable levels of salinity of 3-4. Most of the major oceans fall within these conditions, giving the green crab potential to wreak havoc all over the world.


The recent influx of green crabs in the Gulf of Maine has people trying to figure out what to do about it. Can we eradicate them completely? Or do we have to live with the fact that we can’t get rid of them? These are important questions that clam enthusiasts are evaluating in hopes of regaining a sustainable harvest every year. The Maine Clammers Association (MCA) has playeda prominent role in the war against the green crab. Completely erasing the population of green crabs in Maine, at this point, is nearly impossible, leaving organizations such as the MCA to determine what is the best way to take back control of our waters. As of right now, the MCA has several mitigation strategies that they use on green crabs, the first being the “Five to Stay Alive” trapping program. This program encourages harvesters and fishermen to be responsible for five green crab traps to help reduce the population of green crabs. Another technique that the MCA has used is fencing. Fencing is a technique that uses nets to keep crabs out of productive clam flats, “Fencing is the only known effective tool to limit invasive green crab access to intertidal shellfish resources,” [6] Says the MCA. A partnership with

the town of Freeport and the Maine Clammers Association has been made to do large-scale mitigation projects using fencing. The goal is to put as much fencing as they can to reduce the predation of clams. Along with this fencing, scientific research through trapping will also be done by the MCA, who will then relay the information to their other partners, the Downeast

Institute. Hopefully, this leads to an effective way to trap green crabs and keep them out of productive mud flats.

Also, with a partnership of the town of Freeport, studies led by Dr. Brian Beal at the University of Maine at Machias (UMM) suggest that survival rates of soft-shell clam larvae are less than 0.01% during their first year. During another experiment done by UMM, they found that after allowing the clam larvae to mature in a green crab free zone their chance of survival was significantly increased. This shows that most important factor in soft-shell clam decline is juvenile survival of soft-shell clams rather than a shortage of clam larvae. “Hope is not a

sustainable long-term management plan, I believe the answer lies in aquaculture,” [7] says Dr.

Brian Beals of UMM. The time for standing and neglecting current issues must end if a sustainable solution is possible. The recognition of the issue by the public is the first and biggest step toward a sustainable soft-shell clam business.

So, the question still remains, what can we do with all of these crabs? Jamie Bassett, a crabber from Chatham, Massachusetts proposed his idea at the Green Crab Working Summit in Portland, Maine in June 2018, to harvest the green crabs for culinary use. The crabs are currently almost useless commercially, but Bassett hopes to take steps to change that. By making a business out of the green crabs, their numbers can start to be regulated. The convention which took place showcased the endless options of green crab dishes such as green crab Pokora, and green crab and rhubarb kimchi. Brunswick chef Ali Waks-Adams said, “The idea is it’s not going to go away.

Reach out to other chefs and make it an exportable product. Create the demand for yet

one more product coming out of Maine” [8]. Whether commercializing the green crab is the

solution or not, one thing is for certain, green crab population and damage will continue to grow if something is not done fast.


The growing issue of the soft-shell clam endangerment in the GOM caused by green crabs is an issue which is unknown by most people. The issue, which has only surfaced within the past decade, has gained little media coverage contributing to a lack of awareness. While the potential solutions may be effective temporarily, it is important to have a sustainable solution that will reach the public.One solution is the “Five to Stay Alive” [9] program which proposed that every harvester or fisherman be responsible for 5 green crab traps. The MCA has researched aspects of 5 to Stay Alive such as when and how to trap the green crabs most effectively, which gives confidence that the plan can be successful. This idea which was initiated by the MCA is a good start to the green crab population control, however, the program needs more research to determine the effectiveness of the traps. In order for the program to be sustainable, there has to be proof of its progress to gain public support.

Another solution we discussed was the use of fencing. Fencing is a technique where nets are used to keep the invasive green crabs out of productive clam flats. This has been one of the most effective ways to protect clams from green crabs.

Dr. Brian Beal conducted an experiment where he seeded clams in planter pots and put half of them within fencing and half with no protection. The experiment showed that 60% of the

clams within the fencing survived [10] and not one that was outside survived.

A problem with the use of fencing is that it is easy for netting to get washed away in the tide. It is also evident that some green crabs have been able to get through the netting, even though the technique clearly helps protect a majority of clams. The fencing that the town of Freeport and the Maine Clammers Association recently installed will help provide lots of useful data on fencing techniques and green crabs.

A third solution to the green crab population could be in cuisine. The immense success of other seafood products from the Gulf of Maine gives hope that it may be an option for green crabs as well. By making the green crab another desirable export found in the Gulf of Maine, it can help control the population while also promoting economic prosperity. This solution is still in its early stages, but some Maine chefs are starting to offer green crab dishes such as Brunswick chef Ali Waks-Adams. As of now, marketing green crabs commercially is not a proven solution, but with the right marketing technique, it can most definitely help control the green crab population.

Works Cited:

[1] “War on Invasive Green Crabs.” Maine Clammers Association, Maine Clammers


[2] Whittle, Patrick. Associated Press. “Humans Look to Turn Tables on Green Crabs by Eating them before They Devour Shellfish.” Press Herald, 7 June 2018,

[3] Writer, Penelope Overton Staff. “Invasive Green Crabs Are Putting the Pinch on AnotherClam Harvest.” Press Herald, 22 May

[4] Whittle, Patrick. Associated Press. “Where Have All the Clams Gone? Maine's Harvest Last Year Was Lowest in Decades.” Press Herald, 8 Apr. 2018, t-year-was-lowest-in-decades/.

[5] “War on Invasive Green Crabs.” Maine Clammers Association, Maine Clammers


[6] “War on Invasive Green Crabs.” Maine Clammers Association, Maine Clammers


[7] Overton, Penelope. Staff Writer. “Invasive Green Crabs Are Putting the Pinch on Another Clam Harvest.” Press Herald, 22 May 2017, en-another-harvest/.

[8] Whittle, Patrick. Associated Press. “Humans Look to Turn Tables on Green Crabs by Eating them before They Devour Shellfish.” Press Herald, 7 June 2018,

[9] “War on Invasive Green Crabs.” Maine Clammers Association, Maine Clammers


[10] “War on Invasive Green Crabs.” Maine Clammers Association, Maine ClammersAssociation,

Guisinger, Penny. “Cause of Maine Clam Decline Identified.” Academics, 15 May 2018,

Research. “Freeport: Investigating the Cause of the Clam Decline (2013-2017).” Discovery.

Education. Innovation., Downeast Institute, 5 Sept. 2018, am-decline-2013-2017/.

“Green Crab Overview, December 2013.” About Maine: Facts,



I’m Michael Walsh, but everyone calls me Mikey. I’m a senior at Kennebunk High School right now. Next year I will be attending the University of Maine Orono to studying civil engineering. I love to play soccer, ski, and be on the ocean!

I’m an 18-year-old senior attending Kennebunk High School. I live in Kennebunkport Maine and have my whole life, In my free time, I enjoy skiing, photography, and working on cars. Next year I will be continuing my studies for Mechanical engineering at the University of Maine Orono.

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