Bottlenose dolphins have been admired as some of the ocean’s most skilled predators. However, in parts of the Adriatic Sea, many of these animals are doing something very unusual. Rather than relying entirely on natural hunting, the dolphins are increasingly trailing commercial fishing boats in search of an easy meal. 

Two bottlenose dolphins chase a midwater trawler in the waters off Veneto, Italy. Provided by Dolphin Biology and Conservation

This may seem like a clever shortcut, but according to a new study, it’s a sign that something has gone badly wrong beneath the surface.

According to the study authors, bottlenose dolphins in the northern Adriatic are relying on fishing trawlers at unprecedented levels. This trend points to a growing shortage of natural prey in one of the world’s most heavily exploited marine ecosystems. It suggests that dolphins are adapting to environmental decline rather than thriving within it.

A sea where food is becoming harder to find

The Adriatic Sea has been shaped by decades of intensive trawl fishing. Trawlers drag large nets through the water or across the seafloor to catch fish, but the practice can also damage marine habitats and disrupt food webs. 

According to the researchers, the Mediterranean experiences fishing pressure roughly twice the level considered sustainable, while the Adriatic has become one of the most heavily trawled seas in the world. 

Years of such intensive trawling have not only reshaped the seafloor but also depleted many of the fish species bottlenose dolphins normally hunt. For instance, a long-term analysis estimated that the Adriatic Sea now contains about 41 percent less forage fish and nearly 49 percent less bottom-dwelling fish than it did decades ago.

The ecological consequences have been severe. Many marine predators that once lived in the region have declined dramatically or disappeared altogether. Common dolphins, once widespread in the Adriatic, now survive only in a handful of hotspots. 

“The common dolphins are not common anymore. Except for a very few hotspots in the Adriatic, they have virtually vanished. One species has gone, and that is not a good sign. It’s a warning sign,” Giovanni Bearzi, one of the study authors and founder of the organization Dolphin Biology and Conservation, told The Guardian. 

With other large predators largely gone, bottlenose dolphins have become the Adriatic’s dominant predator even as their own natural food supply has diminished. The growing scarcity of prey may be one reason these animals are spending more time around commercial fishing vessels.

Previous studies documented the animals feeding on fish discarded by trawlers or catching prey disturbed by the nets. Scientists have therefore long known that these animals sometimes take advantage of fishing operations.

However, what remained unclear was whether dolphins were simply exploiting an opportunity or becoming genuinely dependent on fishing vessels because natural prey had become too difficult to find. The new study suggests the latter may be happening. 

This situation is similar to polar bears scavenging at garbage dumps when their traditional food sources become scarce. In both cases, animals are adjusting to human-altered environments because their natural ecosystems can no longer reliably support them.

Tracking thousands of encounters between dolphins and trawlers

To understand how widespread this behavior has become, the researchers monitored fishing vessels operating off the Italian regions of Veneto and Marche. Between 2018 and 2025, they spent 148 survey days at sea, covering more than 17,700 kilometers and conducting 859 inspections of trawlers. 

They also photographed individual dolphins, allowing them to identify animals that repeatedly visited fishing vessels. The results revealed a striking level of interaction. 

Dolphins were observed following 76 percent of trawlers in the Marche study area and 26 percent of those operating in Veneto. More specifically, they followed 41 percent of bottom otter trawlers and 35 percent of midwater pair trawlers, but only 1.5 percent of beam trawlers. 

Beam trawlers attract little interest because they are harder for dolphins to approach and generally target prey that is less appealing to them.

According to photo-identification data, between 86 and 90 percent of the local bottlenose dolphin population—more than 1,000 animals across the study regions—now uses trawlers as feeding sites. 

This represents a major shift from the early 1990s, when studies in the Adriatic found dolphins following only about 10 percent of the inspected trawlers. 

A behavior that has become part of daily life

Now the dolphins are not merely waiting for fishermen to throw unwanted catch overboard. The dolphins catch fish escaping from nets, feeding on injured or disoriented prey stirred up by trawling activities, removing prey trapped on the outside of nets, and scavenging discarded organisms left in the vessels’ wake. 

“On days when fishing vessels are not operating, dolphins must find food on their own, but on days when they are, dolphins forage near the trawl nets,” Bearzi said.

The researchers argue that this pattern reflects more than opportunistic feeding.

“Long-term, consistent, and deliberate association with a given food source might be interpreted to mean there is a high degree of ‘reliance’ on that source. In the case of bottlenose dolphins, trawlers appear to be dependable, undemanding foraging targets,” the study authors added.

Moreover, the behavior is being passed from one generation to the next. Young dolphins often accompany their mothers to trawlers, where they observe adults feeding around the nets and gradually learn the same techniques. 

The researchers believe this cultural transmission is causing the strategy to spread throughout the population.

A new survival strategy that comes with risks

While trawlers may provide a dependable source of food, they also expose dolphins to dangers. Animals can become entangled in fishing gear, sometimes suffering serious injuries or death. 

“Dolphins may also suffer hearing damage that results from chronic exposure to the noise of trawlers,” Randall Reeves, senior study author and Chairman of the Committee of Scientific Advisors at the US Marine Mammal Commission, said.

Moreover, researchers note that feeding around trawlers can alter dolphins’ diet, movement patterns, and social behavior. 

“It is risky behavior. However, finding sufficient prey away from trawlers in an overfished sea may be too difficult. It appears that for these animals, taking the risks is better than going hungry,” Reeves added

It is still unclear how long-term dependence on trawlers affects dolphin health, reproduction, or population growth. Future studies could investigate these issues.

For now, the study’s message is straightforward. Bottlenose dolphins have shown remarkable flexibility in adapting to a changing sea, but their growing reliance on trawlers may be less a success story than a warning. 

However, despite the troubling trend, the researchers do not view the situation as hopeless. They describe bottlenose dolphins as highly resilient animals capable of adapting to changing conditions. 

They suggest that if trawl fishing is reduced and marine ecosystems are given time to recover, dolphins could once again rely primarily on natural prey rather than fishing vessels. Plus, this could help support the return of other species that have declined or disappeared from parts of the Adriatic over the past several decades.

The study is published in the journal Frontiers in Mammal Science.