The Adriatic Sea, depleted by overfishing, is no longer able to feed the dolphins, who follow trawlers en masse in search of food.

Dolphins begin to follow fishing boats to feed fish trapped in nets, or taking advantage of the large amount of waste thrown into the sea. It might seem like a brilliant adaptation strategy, but it isn't. Rather, the fact that bottlenose dolphins have begun feeding en masse following fishing boats is a clear indicator of a dramatic situation. Adriatic sea, impoverished by decades of industrial fishing, is no longer able to feed the last cetaceans that still populate its waters.

The Adriatic Sea, one of the most impoverished and overexploited regions in the world

According to FAO data from 2024, the Mediterranean Sea has one of the highest rates of exploitation of fish stocks in the world: Overfishing affects 63% of fish populations in this region, and fishing pressure is double the level considered “sustainable”. Adriatic sea, in this context, is traditionally one of the most heavily overexploited areas: the intensity of trawling here is among the highest in the world, and the conditions of the seabed are among the worst anywhere.

La bottom trawling, which can count on the support of state subsidies, does not limit itself to catching fish: the heavy nets dragged along the seabed destroy habitats, flatten the underwater hills that provide shelter to dozens of species and release organic carbon released by the disturbed sediments. The result is that in the Adriatic, between 1948 and 2005, for example, the elasmobranchs have declined by more than 94%, and the common dolphin (Delphinus delphis), once abundant, has practically disappeared.

The only cetacean species that survives in the central-northern Adriatic is the bottlenose dolphin (Tursiops truncatus). These dolphins, however, have adopted a very worrying behavior, which reflects the serious impoverishment of the Mediterranean waters and which could have unexpected effects on cetacean populations: this is what emerges from a new study published in the journal Frontiers, which analyzed eight years of survey data (2018-2025) covering 17.755 kilometers of navigation effort off the Italian regions of Veneto and Marche.

Dolphins follow fishing boats: a clear indicator of ecological collapse

Observing 859 trawlers During 148 days of trawling, the research team led by Dolphin Biology and Conservation discovered that Adriatic dolphins began following fishing vessels en masse to feed on what was caught in the nets or discarded back into the sea. The results, the scientists explain, are surprising: on average, researchers observed dolphins following nearly one in four fishing vessels (24,7%). For otter trawlers, one of the most destructive fishing methods, the percentage rises to over 40%. In the Marche region, the situation is even more dire: Three out of four otter trawlers (75,9%) had dolphins in tow.

That the Tursiops truncatus It was known that it fed following trawlers, but the extent of the phenomenon is astonishing: based on photo-identification data, it has in fact emerged that 86% of adult dolphins tagged in Veneto and 90% of those tagged in Marche They have been photographed at least once while searching for food behind boats.
How do you explain Giovanni Bearzi, among the authors of the study,

These dolphins don't follow trawlers by choice. They do so because the Adriatic has been so severely depleted by decades of overfishing that natural prey is no longer reliably available. This is a clear indicator of ecological collapse, not an example of successful dolphin adaptation.

In essence, dolphins have learned to interact more and more often with boats and fishing gear, to extract fish trapped in nets, to wait for by-catches to be thrown back into the sea, not because it is convenient, but because it is the only way to survive in a sea that is no longer able to nourish them naturally.

Risks for dolphins and the cultural transmission of behavior

The relationship between dolphins and trawlers, the researchers explain, is not without its risks for dolphins themselves. Following trawlers exposes them to entanglement and collisions with fishing vessels and encourages them to consume low-quality food. The long-term effects on dolphin health, reproduction, and population dynamics remain unknown and are the subject of further research.

More generally, the study warns that promoting the continued use of trawlers in the Adriatic is inadvisable not only for dolphins, but for marine biodiversity as a whole: the nets that today feed dolphins, after all, are the same ones that have destroyed the ecosystem on which those dolphins depend.

As he explained Randall R. Reeves, senior author of the study and chair of the scientific advisory board of the U.S. Marine Mammal Commission,

"When a large percentage of marine predators switch to opportunistic feeding around fishing gear, it's fairly certain that human influence has reached a tipping point. Trawlers may increase an individual dolphin's food intake in the short term, but any benefits from this opportunistic feeding are at least partially offset by the ecosystem devastation and prey depletion caused by fishing gear."

By the way, this behavior from scavenger It involves adult individuals, young individuals and even pups (present in 7% of the observed groups): even if the younger specimens seem to remain at a certain distance from the boats, they dive and resurface above the towed nets together with the adults. This is a sign of the cultural transmission of the new behavior – an acquisition that, according to scientists, could strengthen the segregation of “scavenger” dolphins from those that do not interact with fishing vessels.

Here are three insights that might interest you:

Trawling costs Europe 90 times its profit
European Swordfish Market Fuels Illegal Fishing
Pelagos, the cetacean sanctuary in the heart of the Mediterranean