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How to manage invasive species in the Mediterranean?

The Ebro Delta is the largest wetland in Catalonia, a fishing ground where hundreds of aquatic species live together. For centuries, the local association – the “Brotherhood of San Pere” – has been fishing in the largest lagoon, the Encanyissada.

But a few years ago, their usual catches suddenly vanished. Instead, they found a surprising newcomer in their nets: the blue crab – a North American crustacean that has invaded the area, decimating local species.

Raul Paulino, fisherman, says: “What happens is that he eats all the young fish, he also eats all the eggs and destroys our nets! He eats everything! He ate all the fish in the area.”

The other species having largely disappeared, local fishermen have turned to catching blue crab for the market: “In the first years, there were a lot of them, but their price was quite low, continues Raul. Now it’s the opposite. , there are less but it’s more expensive. That’s how it is, it’s the life of the fisherman”.

Authorize the fishing of invasive species

Local researchers say allowing professional fishing of these new crabs is the best hope of stopping the explosion in their populations. Catalonia has created a special co-management committee whose aim is to provide better scientific advice, improve harvesting methods and rationalize the blue crab trade through fishing markets.

This part of Spain is closely watched by other regions, increasingly affected by blue crab invasions. The General Fisheries Commission for the Mediterranean has launched a regional research program on the spread of blue crab throughout the Mediterranean.

“We have to solve the problems with knowledge. And this knowledge comes from all the parties involved in the problem – that is to say the fishermen, the fisheries administration, the scientists, but also the NGOs”, explains Pere Abelló, senior researcher in crustacean biology at ICM-CSIC

Innovative gear and large-scale fishing infrastructure developed in Catalonia appear to be effective: populations of blue crabs have reportedly stopped growing, although further studies are needed to confirm this. Even so, the blue crab, which was likely brought from America by commercial ships, is set to stay.

“For now, it must be said that the eradication of this species is practically impossible due to its characteristics, believes Verónica López, fisheries biologist at IEPAAC. But our goal is to be able to control the population at minimum levels. , to allow other species to recover and fishermen to benefit again from all the resources they previously had”.

The blue crab is also invading restaurants

What helps against blue crab invasion is that it tastes great. This makes its intensive fishing a winning solution for the environment, the fishing industry and consumers.

Restaurateurs like Albert Guzmán have happily adopted this North American invader as their new local delicacy. Atlantic blue crab may look unfamiliar in Mediterranean cuisine, but the chef says it fits perfectly with other seafood, whether served as a main course, but also in broths, snacks, appetizers -mouths, sauces or even in a paella.

“We used to use different, much more expensive species, like lobsters or spider crabs, which had to be delivered from Galicia, says Albert. Now we have blue crab, which has a flavor and a similar tastes, so we have a premium product at a price point that is affordable for restaurants, which is also a good thing.”

Pearl oysters in Greece

Invasive species have not only landed in Catalonia. In the Greek part of the Mediterranean, in the Gulf of Elefsina west of Athens, the fisherman Giórgos Grívas collects large oysters. Originally from the Indo-Pacific region, they have spread to Hellenic waters since the opening of the Suez Canal, one of the main routes of invasion of the Mediterranean by foreign marine species.

“Here is the so-called pearl oyster, pinktada imbricata radiata, presents Giórgos. In addition to being able to be eaten, it can also sometimes offer us its pearls. It can be cooked raw, baked, steamed or fried, in pasta or the risotto.”

The fishermen supply the local fishmongers who retail the pearl oysters at 5€/kilo – but this trade is limited by a lack of regulation. Unlike mussels and other popular local molluscs, Greek legislation does not cover the exploitation of the pearl oyster for human consumption.

Adapt regulations

Professor at the University of Patras, John Theodorou strives to move the lines. His research suggests legalizing the exploitation of pearl oysters in Greece, so they can be fished sustainably and sold with greater added value.

“This is very important, he says, because it can offer fishermen an alternative way to improve their income, as pressure on natural stocks of other shellfish increases due to overfishing and climate change.”

Legalization could also benefit aquaculture. In Sagiada, near the Albanian border in western Greece, Spyros Stasinos and his father raise tons of seashells on submerged ropes. The only invasive species that cause them problems are sea squirts, which must constantly be detached from the ropes.

But they don’t really care about the pearl oysters, which are sometimes found in their harvest. It could even be another product for sale, if the regulatory framework allows it.

“We can’t grow them legally, nor sell them, explains Spyros. So we collect them mainly for our own consumption, when we organize parties or when we receive guests.”

In this Greek region where the aquaculture sector is booming, shellfish farms are excellent neighbors to fish farms: mussels and oysters help preserve the water from excess nutrients, while providing healthy local seafood. The culture of pearl oysters could be perfectly integrated into it.

The invasion of hundreds of alien species over the past decades is a challenge for the Mediterranean Sea – and an opportunity for industries to adapt to this new reality and make the most of it.


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