• The blue crab has invaded Mediterranean lagoons in recent years.

  • This particularly aggressive species poses major problems for the ecosystem.

  • Projects are being carried out to try to control this species.

This blue crab is far from a dream. This particularly aggressive species has invaded the lagoons of the Mediterranean arc at great speed. Originally from the American Atlantic coasts, this crab, imported, according to the most probable hypothesis, by the ballast water of ships, flows gently into the ponds of the western Gulf of Lion. Particularly the lagoon of Canet-en-Roussillon, in the Pyrénées-Orientales, which the species, capable of swimming 15 km per day, colonized on its way up from Spain. This is where it is most present, on the French side.

But she also has a crush on the ponds of Leucate and La Palme, in Aude, and Thau, in Hérault.

And attacks Corsica.

In 2019 and 2020, several tons of this species, with exceptional fertility, were collected in Canet-en-Roussillon.

In 2021, catches exceeded 10 t, according to Pascal Romans, head of the aquarium service at the Oceanological Observatory of Banyuls-sur-Mer.

He unbalanced "the whole food chain", in Canet-en-Roussillon

The problem is that this crab, which can reach up to 23 cm in width, causes significant damage in these already particularly fragile ecosystems. First, it devours (almost) everything it finds in its path. “The blue crab has an extremely diverse diet, and has unbalanced the entire food chain,” explains Pascal Romans. Green crabs, small fish, eels… He makes his lunch of them. “And we see that some birds are starting to leave, because, probably, their food is no longer available,” continues the researcher.

This voracious crab, with bluish claws, is also a nightmare for fishermen.

“It has extremely sharp claws, notes Pascal Romans.

The classic nets, he makes crumbs.

And the nets a little more adapted, it still manages to damage them.

And the fish, the little that remains, escapes.

Jean-Claude Pons, one of the last eel fishermen on the pond of Canet, went up, with his nets, blue crabs by kilos, at the end of last year.

"In December, the last net I lifted, there were maybe 30 kg," says the fisherman.

We don't know what to do anymore.


A problem, too, for swimmers?

The fear is that this super-villain will also destabilize the economy of shellfish farming, if it develops on the ponds of Leucate or Thau. Because oysters and mussels, blue crabs love it, too. “The mussels, they break them and eat them without any problem, continues Pascal Romans. As for oysters, we know that up to half adult size, they manage to open them. A study has been launched, carried out by the State and the Occitanie region, to try to limit their proliferation and support fishermen.

But beyond that, the blue crab could also be a problem for swimmers.

Because its claws can cause serious injuries.

“If you attack him, he won't run away.

He is extremely lively, points out Pascal Romans.

And above all, its claws are so long that if you take it from behind, it will manage to catch you.

He can break a finger.

People are always told to be very careful, because it's straight to the hospital.

And if he does not love the sea as much as he loves lagoons, he sometimes ventures there.

Patrick Valdivia, instructor and fishing guide in Canet-en-Roussillon, fears that this poses "some concerns for swimmers", he notes.

“Maybe even this summer.



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