Considered one of the 10 “most unwanted,” and ranked among the 100-worst alien invasive species worldwide, green crab (Carcinus maenas, aka shore crab, harbor crab, Japanese crab) were first observed in Atlantic Canadian waters in the early 1950s, migrating from the U.S. eastern seaboard where they’ve been established since the early 19th century.
Native to Europe, green crab is a voracious predator of valuable commercial shellfish, including clams, mussels, oysters, scallops, quahogs and even Dungeness Crabs and small lobsters.
According to the Department of Fisheries and Oceans (DFO), marine scientists have identified two different types of green crab in Atlantic Canadian waters. The first green crab populations invaded the Bay of Fundy and southwest coasts of New Brunswick and Nova Scotia in the 1950s. They’re genetically distinct from the green crab that arrived in the 1980s and 1990s north of Halifax. By 1982 to 1983 these second invaders were present along Nova Scotia’s eastern shore and reached Cape Breton and the Bras d’Or Lakes between 1991 and 1995. They reached the eastern end of the Northumberland Strait in 1994 or 1995.
Green crab are now established in most eastern Prince Edward Island river systems, and are in most shallow bays and riverine estuaries of eastern Nova Scotia. They were first detected in the Magdalen Islands in 2004, in Newfoundland in 2007 and DFO reports they have reached northeastern New Brunswick.
Green crab can live four to seven years and are tolerant of a wide range of water temperatures and salinities. Females can release up to 185,000 eggs once or twice per year.
Invasion by European green crab disrupts the balance among species and impacts coastal ecosystem diversity. DFO says green crab is such an efficient predator it out-competes native crab species for food. It’s also known to damage eelgrass beds, which are productive habitat for many juvenile fish species and provides a nursery environment for some 50 per cent of Atlantic Canada’s commercial marine species.
Green crab can completely wipe out beds of bivalve shellfish. According to the U.S. Department of Fish and Wildlife, one green crab can devour 40 half-inch clams in a single day. It disrupts eel fisheries by damaging eels as they enter traps.
With its large numbers, huge appetite and fierce competition with other species for food and shelter, green crab threatens molluscs, crustaceans and finfish. DFO says unless it can be controlled, this aquatic interloper will have significant negative impact on commercial fishing and aquaculture industries. Once green crab invades an area, it has proved practically impossible to eradicate them, but it’s considered feasible to limit population spread.
Various schemes have been tried. In 2003 Louisbourg Seafoods of Louisbourg, N.S. received federal assistance through the ACOA Business Development Program for a market development plan to identify emerging fisheries and work with export customers to develop markets for underutilized seafood species, including green crab.
In 2008 and 2009, Fisheries and Oceans Canada collaborated with fishers, the Fish, Food and Allied Workers of Newfoundland, Memorial University of Newfoundland and the provincial Department of Fisheries and Aquaculture to experiment with various anti green crab methods, including trapping and removal, finding that in areas where sustained removal of green crab took place, a native species, the Jonah crab, regained territory. In some areas, DFO distributes nuisance permits to fishers authorizing them to destroy any green crab they catch to reduce population size.
It’s hoped a commercial market for green crab products can be established. A project at the P.E.I. Food Technology Centre in Charlottetown, in conjunction with Bush Vacuum Technics Inc. of Boisbriand, Quebec, developed a technology to process green crab meat that involves freezing crabs to be processed later, such as in slack periods when supply for conventional species drops off.
Nutrient composition of green crab meat is comparable to that of other North Atlantic crab species and it can be processed, utilized and promoted in a similar manner. Raw minced green crab white meat is highly nutritious, being about 20 per cent protein, one to two per cent minerals, with little fat and hardly any carbohydrate. It has the flavour and characteristics of raw crab, but unfortunately has the consistency of applesauce.
Reportedly quite tasty, green crab is a popular dish in southern Europe and can be used as a base for crab cakes, crab chowders and green crab bisque, a kind of seafood soup. It may also be possible to mix it with other fish and sell the product as a canned crab cocktail.
University of Maine food science associate professors Beth Calder and Denise Skonberg, and their former graduate student Joseph Galetti, who has an undergraduate degree in culinary nutrition, have come up with a possible palatable solution to the green crab problem. Calder and Skonberg advised Galetti on his master’s thesis project, mechanical processing of the European green crab and potential use of minced green crab meat in a value-added product. In Galetti’s thesis, this value-added product is fried pastries (empanadas) filled with minced green crab meat, onion, corn, red pepper, thyme and cayenne pepper.
In consumer panel taste-testing, the minced green crabmeat pastries received an overall rating averaging between “like slightly” and “like moderately,” with more than 63 per cent of taste testers indicating they would “probably” or “definitely” buy the product if it was available locally.
Those findings are encouraging for ongoing product development and commercial production, the researchers agree, especially considering green crab empanadas are a new food category most of the 87 taste testers hadn’t eaten before.
Calder, Skonberg and Galetti (now stationed in New Hampshire as a senior scientist for Nova Scotia-owned High Liner Foods) also brainstormed other potential minced green crabmeat product development options, such as ravioli, wontons, dips, soups, quiches and stuffing.
Calder, a UMaine Cooperative Extension food science specialist and director of the Process and Product Review Testing Services, says because of green crab’s relatively small size, large scale picking of meat by hand isn’t practical, and processors would need feasibility findings to determine whether a high enough green crab meat yield can be sustained to make it a commercially profitable product.
In their recent paper “Mechanical Separation of green crab (Carcinus maenad) Meat and Consumer Acceptability of a Value-Added Food Product,” published in the Journal of Aquatic Food Product Technology, Galetti, Calder and Skonberg found mechanical separation of green crab resulted in an average mince yield of 49.2 per cent.
Green crab is a popular enough table menu selection in Europe to support commercial food fisheries there, mainly in the U.K. and France, with demand reportedly robust enough to have reduced the species’ abundance in parts of its native range.
What’s needed is entrepreneurial initiative to advance a green crab fishery and value-added product development here at home.