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Mitigating the effects of green crabs (Carcinus maenus) through incentives in the lobster aquaculture industry

Emily Walker, Meredith Braun and Jeffrey Meltzer Submitted in partial fulfillment of the requirements for ES242, Colby College, Spring 2015

1.0 Introduction 1.1 Context of Study The Gulf of Maine is home to one of the most productive fisheries in the world and is a valuable asset to the state’s tourism industry, which employs a high percentage of the population (NECWA 2007). However, the health of the Gulf of Maine is currently facing serious threats. According to one recent report, the Gulf is warming faster than 99% of the world’s oceans (GMRI 2014). This warmer water increases native species’ vulnerability to diseases and invasive species. Green crabs are one such invasive species and are currently internationally recognized as one of the top 100 worst invaders in the world; however, at present, they have little to no commercial value (Johnson et al. 2014). Green crabs are native to Atlantic Europe, the western Baltic, and west Africa to Mauritania, though they have been widely introduced to North America and Australia (Invasive Species Compendium 2011). Ballast water from European ships first introduced green crabs on the East Coast of North America; their first reported sighting was in 1817 (Kanary et al. 2014). Recently, East Coast locals have observed significant increases in green crab populations that have consequently increased ecosystem destruction as well as predation on the economically important softshell clam (McClenachan et al. 2014). Studies have also linked increased green crab populations to the collapse of the blue mussel fishery (Johnson et al. 2014). 1.2 Green Crab Ecology

As generalists, green crabs can survive in a wide range of conditions (Invasive Species Compendium 2011). Green crabs are excellent osmoregulators, tolerating a wide range of salinities and temperatures, which allows them to inhabit both estuaries and the ocean (Invasive Compendium 2011). They are abundant in the intertidal and subtidal zones (Johnson et al. 2014) and can be found in all lagoon habitats, including intertidal sand flats, subtidal sand and mud flats, and seagrass beds (Wong and Dowd 2013). Additionally, they can endure relatively low levels of dissolved oxygen, which enables them to survive hypoxic conditions (Invasive Species Compendium 2011). Studies have shown that these hearty crabs can survive starvation for up to three months and out of water at room temperature for over one week (Johnson et al. 2014). Green crabs are omnivores and have been documented to prey on species from at least 104 families and 158 genera (Invasive Species Compendium 2011; Johnson et al. 2014). Though they prefer bivalves, they are chemosensory foragers, permitting them to consume this wide array of prey items (Johnson et al. 2014). Green crabs are also considered ecosystem engineers as they modify their environment through degradation of foundation species for digging (Kanary et al. 2014).

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1.3 Green Crab Life History

Green crabs can often have multiple mating events per year and produce about 165,000 offspring per event (Johnson et al. 2014). Surface currents transport free swimming planktonically dispersed green crab larva from their natal site (Invasive Species Compendium 2011; Kanary et al. 2014). On the East Coast of North America, green crabs have been found to survive up to six years and range in size from a carapace width of 1-2 cm to 9-10 cm (Invasive Species Compendium 2011). 1.4 Green Crab Status

Figure 1. Areas of widespread and localized green crab presence in North America (Invasive Species Compendium 2011).

Through anthropogenic vectors and oceanographic dispersal of planktonic larvae, the range of green crabs has expanded predominantly northward and even to the west coast of North America (Figure 1; Kanary et al. 2014). Since the 1960s, green crabs have been found as far north as Nova Scotia (Wong and Dowd 2013). At present, further expansion north along the western coast of North America towards suitable habitat in Alaska is predicted (Invasive Species Compendium 2011). As the most widely distributed intertidal crab, the International Union for

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the Conservation of Nature (IUCN) has classified the green crabs as one of the world’s 100 worst invaders (Invasive Species Compendium 2011; Johnson et al. 2014; Kanary et al. 2014). 1.5 Objective of Study This paper examines the potential usage of green crabs as bait for lobster aquaculture in an effort to mitigate its significant impacts on Gulf of Maine ecosystems. This plan would simultaneously promote mitigation of this destructive invasive species, reduce pressure on local bait fisheries, and provide a cheaper source of bait for Maine lobstermen. In Nova Scotia, scientists have successfully experimented with the usage of green crabs as bait, demonstrating that specially designed traps can catch approximately 1,187 green crabs per trap per night to be sold as bait for profit (McCarthy 2013). Herring currently serve as the primary source of bait for lobster fisheries, but their population faces severe decline due to overfishing (Brogan 2014). Green crabs have emerged as a potentially more sustainable and economical alternative to herring (McCarthy 2013). This study investigates the possible policy implications of transitioning from herring to green crabs as lobster bait, technical requirements for this change, and necessary gear adaptations. 2.0 Implementation of the Plan 2.1 Short Term Goals The short-term goals of this plan include creating a market for green crabs by using them as bait for lobster aquaculture. Green crabs would be selectively harvested using traps, as this is the easiest initial control method due to its few environmental constraints and little initial research required (Green Crab Control Committee 2002). In Martha’s Vineyard, MA, targeted efforts of removing green crabs have reduced predation on commercial bivalves in small ponds and embayments (Green Crab Control Committee 2002). In addition, evidence suggests that green crab populations in Portugal have declined due to harvest in a commercial fishery (Green Crab Control Committee 2002). Kanary et al. (2014) found that the steady state population density of green crabs does decrease as harvesting levels increase and that their populations are particularly susceptible to harvesting of juveniles. Therefore, in order to control green crabs, it is crucial that a high percentage of the juveniles be harvested (Kanary et al. 2014).

Though control measures can be challenging and expensive, they can be achieved on small-scales, such as within an aquaculture site or an isolated bay or estuary (Invasive Species Compendium 2011). As the shellfish aquaculture industry holds great economic importance, it has been the leader in experimenting with usage of green crabs as bait (Invasive Species Compendium 2011). In particular, the American lobster (Homarus americanus) industry has held interest in harvesting green crab for the use of bait (Kanary et al. 2014). In Nova Scotia, a commercial green crab bait fishery for the American lobster currently operates and is likely to be developed in other areas of Atlantic Canada soon (Kanary et al. 2014). Successful mitigation of green crabs could be achieved by developing such a commercial green crab bait fishery in Maine. Control methods could be accelerated by creating further incentives for targeting efforts

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of green crab juveniles. As mature green crabs pose a threat towards juvenile lobsters, this control may be accomplished by educating lobster fishermen on the potentially negative impacts green crabs have on lobster populations. This education may incentivize them to utilize green crabs as bait and potentially even pay greater amounts of money for juvenile green crabs. 2.2 Long Term Goals

Kanary et al. (2014) found that although green crab populations can be controlled through harvesting, they cannot be completely eliminated, as the reproductive success of the crab is too high. This study found that in areas where the northern green crab, a stronger competitor and predator, and the southern green crab coexisted, the overall impact of green crabs could be mitigated through harvesting of the crabs and then introduction of more southern green crabs to the area (Kanary et al. 2014). It is possible that native crab competitors occupying similar niches to the southern green crab may be able to fill a similar role (Kanary et al. 2014). Therefore, restocking harvested areas with native crab competitors in order to further promote control may complement green crab harvesting efforts (Kanary et al. 2014).

As the usage of green crabs as bait for lobsters has the potential to lead to overexploitation of lobster populations, it is critical to include in this plan a way to prevent this from occurring. At the New England Aquarium there is an American lobster research program in place that focuses on investigating methods for raising lobsters in captive environments (New England Aquarium 2015). By using green crabs to feed lobsters in these captive environments, this plan could simultaneously increase lobster populations and decrease green crab populations. 2.3 Techniques

In order to successfully render the green crab a viable bait alternative for the Maine lobster industry, this study primarily focuses on determining a method in which bait fisheries can catch sufficient numbers of green crabs. Past studies have shown that varying styles of traps can be effective in catching green crabs in significant numbers. In August of 2013, the Maine Department of Marine Resources performed a one-day green crab trapping survey in which 28 towns collectively set 208 traps along the Maine coastline (Webber 2013). Fourteen of the set traps were lobster traps that the participants already owned, with the other 14 being crab, bait, eel, or other traps (although specific designs were not mentioned). The lobster traps, although mildly successful, caught the second-lowest number of crabs per trap, with a median number of 66 crabs per trap. The crab traps, however, caught a median number of 203 crabs per trap (Webber 2013). Multiple traps were placed at each site, and when crab and lobster traps were placed next to each other, the traps designed to catch crabs still caught the most (and largest) crabs (Webber 2013).

Incorporating these findings, this green crab mitigation study aims to design and create a plan for a successful green crab bait fishery with a high catch per unit effort (CPUE) utilizing crab traps for the current local bait fisheries along the coast.

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2.4 Products Needed The primary products needed for this plan are the traps required to catch the crab. As

Webber’s study for the Maine Department of Marine Resources (2013) demonstrated, although lobster traps are intended for a larger catch they can also be used as a moderately successful green crab trap if modified by closing the vents. However, even with this modification, crab traps consistently out-fish lobster traps (Webber 2013). Therefore, while lobster traps are likely to be more readily available to fishermen along the coast (thereby eliminating additional costs), the lessened catch efficacy may result in reduced profits.

Chris McCarthy, a Parks Canada Ecologist at the Kejimkujik National Park, presented his research at the Green Crab Summit at the University of Maine, Orono in December 2013, indicating considerable success in ameliorating green crab populations in Nova Scotia using “Russell” traps (McCarthy 2013). Colloquially called “The Terminator” by local fishermen, these traps remove large numbers of green crabs in short periods of time (McCarthy 2013). These Russell traps (which are actually modified shrimp traps) allowed McCarthy and his team to catch up to 1,187 green crabs in a single trap in one night, resulting in over a million total crabs being removed throughout the three-year study (McCarthy 2013). It is anticipated that with the usage of these Russell traps, the Maine bait fishery for green crabs can eventually reach a similar level of success. 2.5 Market for Green Crabs

The continued use of finfish as bait for the lobster industry presents a considerable problem, as supplies of traditional bait fisheries continue to fall victim to overfishing and subsequent population declines (Ryan et al. 2014). As these stocks decline, particularly those of Atlantic herring, bait prices increase steadily because bait is sourced from greater distances (Ryan et al. 2014). The herring fishery in Maine has already been closed for the 2015 season, with all herring fishing prohibited between January 1 and May 31 of 2015 due to overfishing (Brogan 2014). Ninety-two percent of the total allowable catch (TAC) had already been harvested by October 2014 (Maine Department of Marine Resources 2014). With this closure, vessels with federal permits for Atlantic herring are not allowed to retain or land over 2,000 pounds of herring per day within the closed coastal area (Maine Department of Marine Resources 2014). Similar fishing prohibitions occurred in 2014. This trend of exceeding the TAC does not bode well for the health of the herring fishery, and it is the goal of this study to supplement the herring bait fishery with green crabs, thereby reducing pressure on the herring and eventually aiding populations in rebounding.

In addition to presenting as an ecologically superior alternative to traditional finfish baits, green crabs have the potential to be a much more economical bait choice for local lobster fishermen. Wyeth and Williams (2013) found that the substantial cost of other, more traditional baits (up to $10,000/year) made the cheaper green crab an attractive option to fishermen. The most recent data available indicates a market price of herring bait hovering around $1.30/pound (Deese & Arnold 2014). With green crabs purchasable at approximately $0.83/pound (or $100

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per crate), they offer an attractive option at only 64% of the price of herring (Deese & Arnold 2014). 2.6 Business Plan

Maine’s $15 million clam industry (and the 1,700 people it employs) along with its $350 million lobster industry face considerable threats from invasive green crabs (Beem 2014). Although mitigating the impacts of green crabs in Maine presents considerable expenses, action is critical. The plan of this study to harvest green crabs and to sell them as bait for the lobster industry focuses on the harvesting of green crabs by Maine herring fishermen. However, due to the formidable number of green crabs, a variety of fishermen, volunteers and students are needed to help harvest the green crab in order to make a difference.

This study plans a partnership with several organizations that currently work on green crab mitigation in Maine, including the Gulf of Maine Research Institute, Downeast Institute for Applied Marine Research, the National Marine Fisheries Service, the Maine Department of Marine Resources (DMR), the University of Maine, and several municipalities. In order to succeed, this proposal primarily requires partnership with the Maine herring fishermen, who would transition to harvesting green crabs, and with Maine lobstermen, who would use the green crabs as bait. It also requires a strong partnership with the Maine Clammers Association, who share a strong interest in green crabs as they threaten the soft shell clam industry (Johnson et al. 2014). Finally, due to the extreme density of green crabs, volunteers, such as from school groups, summer camps and local businesses, are also needed for harvesting efforts.

The primary expenses for this plan include an initial salary “insurance” pool for a select number of fishermen and funding for modified shrimp or “Russell” traps. Herring fishing already involves boats and lines, so a transition to crab harvesting would only require new traps. McCarthy (2013) found that Russell traps were the most effective in catching green crabs. Since the shrimp fishery is currently closed due to warming water temperatures, obtaining shrimp traps for this plan should not be very difficult or costly (Trotter 2014). The salary insurance would ensure that the herring fishermen earn a living wage until the green crab bait industry becomes viable. It will also likely ameliorate any reluctance herring fishermen may have to switching their fishing practices towards green crab harvesting. Current issues with the herring industry, including its costliness ($10,000 per year to lobstermen) and its competing demand as food for human consumption, will aid in creating a viable market for green crabs as lobster bait (Wyeth and Williams 2013).

This study will look for support for funding from the DMR as the green crab poses a significant threat to Maine’s marine resources. In 2012, a $25,000 fund in the DMR annual budget for crab fencing was defunded (Beem 2014). This study aims to restore and redirect this funding towards incentivizing herring fishermen to transition to green crab harvesting. In 2001, a law requiring a $25 license to harvest green crabs was enacted (Beem 2014). However, in August of 2014 the DMR repealed licensing requirements (Van Allen 2014). Fishermen no longer need this special license to catch and sell green crabs, and lobstermen are allowed to take them as bycatch; additionally, green crab harvests are no longer required to be reported to the

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state (Van Allen 2014). This removal of licensing requirements has opened up the green crab fishery to allow for more freedom in green crab catch numbers as well as for an additional source of income, adding incentives to commercial fishermen and lobstermen.

Municipalities could also aid in further funding for this plan. Several towns have already dedicated funding for green crab removal. For example, Freeport spends about $70,000 per year to combat the green crab in an attempt to rescue their clamming industry (Beem 2014). Considering the dire potential effects of the green crab on ecosystem functionality, fishery health, and tourism, it is likely that other city and town councils can be encouraged to follow suit.

Funding from other sources, ranging from nonprofits to private businesses, is also warranted due to the potential financial distress associated with green crab invasion. A study in Puget Sound, Washington found that the annual losses from the shellfish industry from invasive green crabs range from $1.03 - 23.8 million and that decreases in shellfish processing and distribution would cost 442 jobs, creating an addition $17.6 million in losses (Mach and Chan 2013). Another study found that green crab destruction would cost $22.6 million in annual damage to the East Coast shellfish industry alone (Invasive Species Compendium 2011).

In Nova Scotia, there are 53 licensed green crab fishermen and, as mentioned previously, they earn about $100 per 120 pound tote of green crabs, or about $0.83/pound to be used as lobster bait (Beem 2014). Since herring bait currently costs $1.30/pound, there is a financial incentive to transition to green crabs as bait (Deese & Arnold 2014). The National Marine Fisheries Service’s recent closing of Maine’s herring industry for the 2015 season creates an optimal incentive to make this transition (Brogan 2014). 2.7 Government Role

For this plan to be successful, active cooperation from local, state, and national governments is essential. As suggested by McClenachan et al. (2014), co-management, or “regulatory decision-making through collaboration among user-groups, government, officials, and scientists,” is an effective mechanism to manage ocean problems exacerbated by climate change because they invite the most user buy-in. This plan aims to form a green crab committee composed of members from all three levels of government, along with representatives from the herring and lobster fishing industries and citizen volunteers. This diverse array of people will offer a wealth of perspectives and ideas and ensure that all stakeholders are invested in the outcome. Once the green crab bait industry is established, it is envisioned that government’s role will diminish as ascendency of the private market allows for its continued success. 3.0 Implications of Green Crab Removal 3.1 Ecological and Environmental Implications

Green crabs are severely impacting the New England coastal ecosystems. In recent years, eelgrass beds have experienced significant declines due to the foraging behavior of the crabs (Invasive Species Compendium 2011; Johnson et al. 2014). Eelgrass is critical to maintaining the

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health of coastal ecosystems by enhancing nutrient cycling, water quality and sediment dynamics, and by providing food and habitat for an array of organisms (Johnson et al. 2014). In 2001, Maquoit Bay in Brunswick, Maine contained 567 hectares of eelgrass but due to green crab activity, resampling of this bay in 2013 revealed that eelgrass had been reduced to only 96 hectares (Johnson et al. 2014). Though this area was once a rich fishing ground, filled with rare animals, fish, invertebrates and waterfowl wading birds, today it is rare to even see a lobster due to the high presence of green crabs (Johnson et al. 2014). Green crabs have also reduced the abundance of shellfish in New England (Invasive Species Compendium 2011). As green crabs are capable of consuming over 15 clams per day and exceeding densities of 24,700 per hectare, they can have devastating effects on clam populations (Johnson et al. 2014). In Massachusetts, commercial clam landings fell from 8.6 million pounds in 1940 to 0.63 million pounds in 1948 due to the presence of the crab (Johnson et al. 2014). However, in the past, severe winters have been correlated with declines in green crab populations and increases in clams and eelgrass beds, which suggests that these native species are able to rebound in the absence of green crabs (Johnson et al. 2014). In Essex, MA in the early 1920s and 1930s, clams and eelgrass beds had almost disappeared until a severe winter in 1934, when they were able to increase in population (Johnson et al. 2014). By implementing this proposal, clam populations and eelgrass beds will hopefully increase to similar levels.

Though it is believed that the control of green crabs along Maine’s coast would benefit the ecosystem overall, it may negatively impact some organisms that have become accustomed to a food web including green crabs (Wong and Dowd 2013). Wong et al. (2013) found that when green crabs were removed, predator-prey interactions that were strongly affected were those that depended on green crabs for diet, such as gulls and Bamboo worms. However, if green crabs were replaced with native crabs, the native crabs may fill that prey role for native birds and fishes. 3.2 Economic Implications The estimated economic cost of green crabs’ detrimental presence on the East Coast was last estimated to be $44 million annually in 2014, with $22.6 million due to decimation of the shellfish fishery alone (Mach & Chan 2013). Other studies have estimated total losses from the shellfish industry (since the green crabs’ introduction) as ranging between $719 and $806 million, with losses increasing yearly by $82,000 (Environmental Protection Agency 2008). Although costs already accrued through shellfish fishery loss may not be recoverable, green crab population decreases would reduce pressure on shellfish. This decline in pressure should create shellfish stock increases and boosts to the struggling fishery, supporting mitigation efforts. The presence of the green crabs also impacts eelgrass beds, which offer invaluable shelter and foraging grounds for numerous species. When invading green crab populations decimate eelgrass beds, restoration efforts are enforced in certain areas. The average restoration area on the East Coast is seven acres per bed, with restoration of each acre costing $49,000 (Environmental Protection Agency 2008). If green crabs continue to proliferate at their current rate and populate these beds, the United States Environmental Protection Agency (EPA) (2008)

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estimates a decline of 17.5 - 22.5% of ongoing eelgrass restoration projects, resulting in additional costs of $60,000 - $77,000 per bed. Scientists from the Nature Conservancy recently found that a single acre of healthy eelgrass bed in “certain bays” has the economic potential to produce as much as $8,000 in “commercially important fish” in a year (Nature Conservancy 2014). If Maine’s beds rebound from reduced green crab foraging and slashing, the entirety of the coast has the opportunity to earn thousands of dollars’ return in commercially and economically viable fish catches. Between the years of 2007 and 2010, the EPA calculated total costs for green crab management and control efforts to amount to $285,000 annually (Environmental Protection Agency 2008). Within this sum, the Green Crab Control Committee (2002) estimated field mitigation efforts alone to account for $75,000. This number may be an under-representation of the actual costs associated with removal and amelioration reachable only by “‘in-kind’ support … through research organizations, management agencies, and volunteer efforts” (Green Crab Control Committee 2002). 4.0 Conclusion

It is critical that action is taken to mitigate the impacts of the destructive green crab on Maine’s coastal ecosystems. Inaction portends the decline of scallops, mussels, clams, sea grass, seabirds, fish and other crucial native species to this ecosystem. If green crabs continue to proliferate, they “will reduce the enjoyment, job security and revenue that recreational and commercial crab and shellfish harvesting provides” (Invasive Species Compendium 2011). The goal of this proposal is to mitigate the green crab population in the long term, which will allow the softshell clam fishery and eelgrass habitats to rebound. By creating an economic incentive to harvest the green crab, this plan aims to mitigate the impacts of this invasive species, bringing economic and environmental relief to the region.

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5.0 Works Cited Beem, E. A. 2014. The Green Crab Invasion. DownEast. Brogan, B. 2014. Invasive green crabs creep back into Casco Bay. Bangor Daily News.

http://bangordailynews.com/2014/07/28/news/portland/invasive-green-crabs-creep-back-into-casco-bay/ Deese, H., and S. Arnold. 2014. Green crabs as lobster bait working in Nova Scotia. The Working Waterfront. Environmental Protection Agency. 2008. Ecological and Economic Impacts and Invasion Management Strategies

for the European Green Crab. GMRI. 2014. As Climate Changes, Spring’s Early Arrival Alters Gulf of Maine Ecosystem. Gulf of Maine Research

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Green Crab Control Committee. 2002. Management Plan for the European Green Crab. Invasive Species Compendium. 2011. Carcinus maenas (European shore crab). CABI. Johnson, M., C. O’Neil, K. Rizk, and K. Walsh. 2014. The State of Coastal and Island Wildlife in Maine. The State

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control of competing green crab genotypes. Theoretically Ecology 7. Mach, M. E., and K. M. A. Chan. 2013. Trading green backs for green crabs: evaluating the commercial shellfish

harvest at risk to European green crab invasion. F1000Research 2:66. Maine Department of Marine Resources. 2014. Notice to Atlantic Herring Fishery: Closure of Area 1A Directed

Fishery in State and Federal Waters, Effective October 26, 2014. http://www.maine.gov/dmr/rm/herring/area1a10-26-14.htm

McCarthy, C. 2013. Estuary Therapy: Advances in Coastal Restoration at Kejimkujik National Park Seaside. Parks Canada

McClenachan, L., G. O’Connor, and T. Reynolds. 2015. Adaptive capacity of co-management systems in the face of environmental change: The soft-shell clam fishery and invasive green crabs in Maine. Marine Policy 52:26-32.

Nature Conservancy. 2014. Restoration Works: Saving the Prairies of the Sea. The Nature Conservancy. http://www.nature.org/ourinitiatives/habitats/oceanscoasts/howwework/restoration-works-sea-grass-beds.xml

NECWA. 2007. The Gulf of Maine. New England Coastal Wildlife Alliance. http://www.necwa.org/gulf-maine.html,

New England Aquarium. 2015. American Lobster Research Program. http://www.neaq.org/conservation_and_research/projects/fisheries_bycatch_aquaculture/aquaculture_research/american_lobster_aquaculture_research/

Ryan, S. M., S. T. Livingstone, J. P. Barry, P. J. Williams, and R. C. Wyeth. 2014. Laboratory comparison of American lobster, Homarus americanus, foraging responses to invasive green crab, Carcinus maenas, and two traditional finfish baits. Marine and Freshwater Behaviour and Physiology 47:291-297.

Trotter, B. 2014. Officials cancel 2015 Gulf of Maine shrimp season, citing weak shrimp stock. Bangor Daily News. http://bangordailynews.com/2014/11/06/business/officials-cancel-2015-gulf-of-maine-shrimp-season-citing-weak-shrimp-stock/.

Van Allen, J. 2014. Rule changes put green crabs on Maine’s front burner. http://www.pressherald.com/2014/08/14/green-crab-on-maines-front-burner/, Portland Press Herald.

Webber, M. M . 2013. Results of the One-Day Green Crab Trapping Survey Conducted Along the Maine Coast. Maine Department of Marine Resources.

Wong, M. C., and M. Dowd. 2013. Role of Invasive Green Crabs in the Food Web of an Intertidal Sand Flat Determined from Field Observations and a Dynamic Simulation Model. Estuaries and Coasts 37:1004-1016.

Wyeth, R., and J. Williams. 2013. Green Crab as Lobster Bait. St. Francis Xavier University.