The green crab, this unwanted invader hunted in Quebec

It is already almost everywhere in the Atlantic. Present since the early 2000s on the Magdalen Islands, it has not yet touched the coasts of Gaspésie and the North Shore. Monitoring the green crab, an invasive species, has become a priority in Quebec.

In the marine environment, it is the invasive species that undoubtedly has the most negative repercussions on the ecosystem and, in turn, on fisheries.

To feed, the green crab digs and destroys the seagrass beds where the small fish feed. The very voracious beast is also fond of molluscs such as clams or mussels. It is also aggressive and forces the displacement of other species such as the rock crab.

Climate change may affect the risk that species will be able to establish themselvesdeclares biologist Andréanne Demers, directly referring to the green crab.

The senior biologist at Fisheries and Oceans Canada (DFO) for aquatic invasive species also wishes to raise awareness among mollusc harvesters and amateur fishermen of the importance of identifying this small crustacean, which reaches a size of 10 to 12 cm at adulthood. Detecting it as early as possible would limit the damage.

An expanding distribution area

The footprint of the green crab has been well documented in Nova Scotia since the late 19^e century.

Despite its proven presence for years, there are currently few ways to eliminate green crabs. As long as there is a supply of larvae, as long as there is reproduction… It’s the ocean, so it can happen through ocean currents, it’s very difficult to stop it. It has no major predator, the lobster seems to feed on it, but not enough to affect the population, reduce its numbersobserves Andréanne Demers.

The threat of the green crab is therefore far from being new, but it has taken on a new dimension in recent years.

This green crab, native to the Mediterranean, has never appreciated cold waters. Its presence therefore remained limited for years to Nova Scotia. A variety less sensitive to cold, which lives in the waters of the North Sea, was however spotted in Canadian waters at the end of the 20^e century.

This type of green crab is now present throughout the Gulf as far as Newfoundland. It also crossed with the first species. This new subspecies, according to the researchers, is more tolerant of changes in water temperature and also more combative.

The return of the green crab to the archipelago

In Quebec, green crabs were spotted in the Madelinot archipelago in the early 2000s. For a long time, the control measures worked well. And oops: in 2022, Madelinot eel fishermen report a greater number of individuals.

Particular attention was paid in 2023 and around 300 individuals were caught in Bassin Bay in the fall.

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In collaboration with the committee ZIP of the archipelago, more sustained efforts to limit the spread were made this year. Andréanne Demers specifies that the primary goal is to try to capture as many as possible during periods when females are activethat is to say around spring or late in the fall.

The goal is to catch as many as possible in Bassin Bay to prevent the crustaceans from going elsewhere to the Magdalen Islands. More than a thousand specimens will have been extricated from the waters in 2024.

Many questions arise about the impact of the green crab on the Islands. The interactions between this species and the lobster are not very well known, particularly in the context of climate change.

Increased surveillance

The Gaspé coast seems spared until now. The green crab, which likes salt marshes, sandy beaches and eelgrass, could nevertheless colonize the Gaspé barachois.

We are probably at the limit of its range.suppose Mme Demers. Will climate change cause it to travel further, to be more aggressive in Quebec? That remains to be seen.

The biologist adds that its distribution area will depend on the food available and physicochemical parameters such as temperature, salinity or pH.

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Two individuals were discovered in Belledune, New Brunswick, opposite Baie-des-Chaleurs in 2023. Since then, tests ofADN environmental studies which were carried out in Chandler in 2024 did not detect anything.

The North Shore is also under surveillance due to its proximity to the coast of Newfoundland. The green crab has in fact invaded several bays, particularly in the southeast.

Green crab fishing

Fishing can be seen as a solution to control the green crab population. Biologists are, however, cautious about this solution, due to the risks associated with contamination which could increase its dissemination.

In Nova Scotia, however, green crab is the subject of a commercial fishery in the southwest and east of the province. Lobster fishermen may also keep it as bycatch.

The first green crab fishing began in 2010 as part of a pilot project. Its objective at the time was to provide alternative fishing for large eel fishermen and to address concerns about the effects of green crabs as an aquatic invasive species.

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The program became permanent in 2014 and was expanded in 2017, notably with the granting of permits to First Nations. All crabs caught can be sold, including as bait for lobster fishing, except crabs caught for the purposes of controlling aquatic invasive species.

Nova Scotia has 113 commercial green crab fishing licenses, 75 of which are in operation. According to data provided by Fisheries and Oceans, fishermen have brought back to the dock an average of 72 tonnes of green crabs since 2019. Average annual revenues remain marginal, i.e. $152,000 for all landings.