Bottlenose dolphins in the Adriatic Sea are increasingly following trawlers to scavenge for food, a shift driven by chronic overfishing. A study published in the journal Frontiers reports that in one area, 76% of trawlers were followed by dolphins, a significant increase from the 10% recorded in the 1990s. Researchers Giovanni Bearzi, Silvia Bonizzoni, Nathan B. Furey, and Randall R. Reeves found that this reliance on human-provided food is being passed down to calves, creating a cultural transmission of foraging habits.
Why are dolphins increasingly following fishing vessels?
Dolphins are forced to scavenge because their natural prey has become difficult to find due to intense fishing pressure. According to Giovanni Bearzi, president of Dolphin Biology and Conservation in Italy, the Mediterranean Sea experiences fishing rates twice the level considered sustainable by the UN Food and Agriculture Organization (FAO). As natural ecosystems become impoverished, trawlers provide a source of food. Bearzi notes that the current ease of locating these dolphins is tied to the presence of trawlers.
The study draws parallels to other species, such as polar bears that have begun scavenging in rubbish dumps as their traditional food sources dwindle.
What are the long-term risks to dolphin populations?
Dr. Randall Reeves, chair of the Committee of Scientific Advisors at the US Marine Mammal Commission, explains that foraging behind trawlers exposes dolphins to physical injury from gear and potential hearing damage caused by chronic exposure to the noise of trawlers. Furthermore, this behavior alters the animals’ diet, social organization, and communication patterns. The reliance on human activity is described by researchers as a “warning sign.”
How is this behavior passed between generations?
The transition to scavenging is a learned cultural behavior. According to the research team, baby dolphins observe their mothers foraging in the wake of trawlers and learn that kind of behaviour. Giovanni Bearzi emphasizes that the decline of other species, such as the common dolphin—which has virtually vanished from the Adriatic—serves as a warning sign.
Comparison: Trawler Interaction Rates
| Time Period | Percentage of Trawlers Followed |
|---|---|
| 1990s Research | 10% |
| Recent Study | 76% (in one area) |
How can the marine ecosystem recover?
The researchers advise against continued use of trawlers, to protect dolphins and conserve marine biodiversity. The recommendation is to fish less and fish in less destructive ways. Bearzi suggests that if destructive fishing practices were halted, marine resources could “bloom very quickly,” allowing dolphin populations to return to hunting their natural prey, as they did for centuries. The study, Bottlenose Dolphin Reliance on Trawlers in Prey-depleted Adriatic Sea Regions, highlights that for these animals, taking the risks is better than going hungry.
Frequently Asked Questions
- Are dolphins physically harmed by following trawlers?
Yes, according to Dr. Randall Reeves, dolphins are occasionally injured or killed by trawl gear and may suffer from hearing damage due to chronic exposure to the noise of trawlers. - Is this behavior new for dolphins?
Dolphins have always followed fishing boats, but the researchers said the behaviour seemed to have increased in intensity. - Why are common dolphins disappearing from the Adriatic?
Researchers note that the common dolphins are not common any more and have virtually vanished.
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