Aggressive fish, symptoms of the upheaval of the marine environment

In recent years on the Tunisian coasts, in Sousse, at Cap Bon, in Bizerte and on other beaches, if you stand still for a few minutes in a calm sea, there is a good chance that you will feel rather painful biting in your feet and legs: these are small fish that come to feed on human skin and about which the testimonies, sometimes amused, sometimes flabbergasted, are more and more numerous.

But beyond the bather’s comfort, this phenomenon is part of a major ecological upheaval, one of the symptoms of which is the appearance in the Mediterranean Sea of ​​species that are increasingly aggressive for humans, but above all for the environment. ‘ecosystem.

Among the fish that bite bathers there is the sar, we are told Sami Mhenni, chief engineer in marine sciences and founding president of Houtiyat, an association for the study and research of fish. For him, it is a Mediterranean fish which, in the past, did not attack people in such large numbers and with such viciousness.

This new behavior in this species normally fond of crustaceans and molluscs could be explained by several factors: the rise in water temperature due to global warming, the overexploitation of maritime resources, the upheaval of the marine ecosystem, transport commercial, tourist navigation and offshore drilling between Tunisia and Italy. So many reasons for the disruption of these schools of fish.

“Scientists suggest that the sar, threatened in its natural habitat, expresses its stress by developing aggressive behavior. Any disturbance of the environment where a fish lives can cause reactions in its behavior. He can even change physically. And when the environment on the Tunisian coasts becomes hot, dirty, impoverished and noisy, it is normal that certain species react badly”, assures the engineer.

Explosion in the number of alien species

So will fish aggressiveness get worse in proportion to environmental degradation? What is certain is that the scientific indicators are not very optimistic. The phenomenon is not limited to Tunisia.

In the 2.5 million square meters of the Mediterranean basin, threats are likely to increase with the intrusion of new species, which reproduce while upsetting the balance. In June 2021, an alarming report from WWF, an environmental protection organization, assured that “The Mediterranean is the most invaded sea in the world. In recent decades there has been an explosion in the number of alien species establishing themselves in the basin, with catastrophic consequences for local biodiversity”. And for good reason [résume le communiqué de presse qui accompagnait le rapport] :

“With temperatures rising 20% ​​faster than the global average and sea level rise expected to exceed one meter by 2100, the Mediterranean is becoming the fastest warming sea in the world. the planet.”

This warming beyond all predictions, combined with overfishing, pollution, coastal development and maritime transport, implies the progressive tropicalization of the sea and therefore a change in marine fauna.

Species that arrive from the Indian Ocean, the Caribbean and the Red Sea through the Suez Canal or in the ballast tanks of large ships take some time to acclimatise. The number of new species would rise today to a thousand, in a sea where the temperature has increased by 1.5% compared to normal. Some disappear, others manage to reproduce spectacularly. It is this last case which becomes the most frequent.

Venomous Thorns and the Portuguese Galley

Among these species is the lionfish, armed with poisonous spines and native to the Indian Ocean. The first appearance observed by scientists in the Mediterranean of this fish dates back to the early 1990s. Today, in countries such as Turkey, it is one of the dominant species and poses a dangerous threat to the ecosystem.

“In addition to being venomous for humans, it is a voracious fish that shaves everything in its path and does not let other species feed”, says Sami Mhenni, who confirms the presence of this fish in Tunisia, but in lesser proportions than in countries in the eastern Mediterranean basin, where the water is warmer. For now.

Another dangerous fish: the rabbitfish, which comes from the Red Sea, is particularly devastating and toxic. In 2019, it was found on the stalls of a market in the Sfax region, while its consumption could cause fatal inflammation in humans. And like the sar, this fish is aggressive towards swimmers. According to Sami Mhenni, in Libya, where he is now colonizing the waters, a video testimony shows that he started biting bathers at the edge of a beach.

But here too, the most important thing is that the marine ecosystem suffers. Algae forests, which were the natural habitats of several species, have been completely razed by the rabbitfish. An ecological disaster whose consequences are already palpable: maddening scarcity of fish in certain regions and loss of their bearings.

There is also the jellyfish. This animal manages to reproduce effectively in a high temperature sea. According to the WWF:

“On the high seas, high temperatures make the Mediterranean more hospitable to invasive jellyfish from tropical waters. In the Gulf of Gabes, fishermen claim to often have more jellyfish in their nets than fish.”

Latest visitor: the Portuguese galley or Physalia physalis. Native to the Indian and Atlantic Oceans, this poisonous organism made disturbing appearances on the coasts of the Cap Bon peninsula in 2021.

Lack of follow-up on the ground

For Sami Mhenni, the Tunisian state is not inactive in the face of these major upheavals: “The Ministry of Agriculture, Water Resources and Maritime Fisheries has worked on many of these cases. He distributed posters to warn fishermen about dangerous species. He contacted them to raise awareness. He warned consumers when the rabbitfish was found in a market in Sfax. He studied science. But the follow-up on the ground is lacking.”

In fact, the work of the State is no longer enough in a configuration as global and complex as global warming. The question that arises at this stage is, in fact, whether a maximum of citizens will quickly become aware of the danger, in order to actively participate in changing things on a large scale:

“State communication with citizens, especially on social networks, is very important. It should be more intense. And then you have to know how to popularize the data. Tunisian scientists should come out of their ivory tower to raise awareness of the major challenges ahead.”

A way of saying that swimmers should consider the aggressiveness of fish such as sar, lionfish or rabbitfish less as a simple inconvenience for their bathing than as one of the signs of the ecological disaster underway in the big blue.

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