How the Mediterranean became the most infested sea in the world

How the Mediterranean became the most infested sea in the world

In October 2014, Lotfi Radaoui traveled the shallow sandy waters near Ghannouch, a small coastal town in the Gulf of Gabes in Tunisia, with a group of local fishermen. The fishermen traversed beds of seaweed and algae and made an unusual catch.

Entangled in their web was a species of crab, Portunus pelagicus, or blue crab, not native to the region. Even more remarkable, the fishermen didn’t just find one blue crab — their nets had caught 24 of them.

Radaoui, then a researcher at the Faculty of Sciences of Tunis at the University of Tunis El Manar, noted the discovery with interest. Little did he know, however, that a year later this non-native or alien species would become a national bane.

Soon after, the blue crab population exploded. Hakim Gribaa, a fisherman on the island of Djerba, remembers it like it was yesterday. “There were panic stations,” says Gribaa. “The crab made up almost 70% of my catch and I didn’t know what to do with it.”

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The blue crabs were fertile, reproducing up to four times a year with 100,000 litters per female. This crustacean is “very aggressive,” Gribaa says – destroying nets and biting fishermen and other fish. The terror the crabs caused was so great that they became known locally as “Daesh,” the Arabic acronym for the group that calls itself Islamic State.

First, the livelihoods of the fishermen were overturned. “We had no idea,” says Fethi Naloufi, a fisheries engineer and head of the Interprofessional Group of Fishery Products in Zarzis, a public organization responsible for promoting fisheries and aquaculture in Tunisia. Disposing of the crab by-catch also became a challenge. “They stayed piled up in the harbor or were thrown back into the sea,” says Naloufi.

The blue crab has turned the Tunisian fishing industry upside down in more ways than one. But after the initial shock, it has now grown into one of the most sought-after seafood in the region.