Bottlenose dolphins follow a trawler off the coast of Veneto, Italy. Dolphin Biology and Conservation
Off the eastern coast of Italy, large numbers of bottlenose dolphins are looking to fishing trawlers as a source of food, a sign that dolphins may be struggling to feed themselves in waters depleted by overfishing.
Dolphins in the Adriatic Sea are most drawn to otter trawlers, which drag a large conical net near the ocean floor, according to the study, published in Frontiers in Mammal Science. Dolphins trailed 26 percent of otter trawlers near Veneto and 76 percent near Marche, eating discarded fish or darting into moving nets to gather food.
“We estimated that the bottlenose dolphin populations of Veneto and Marche, combined, exceed 1,000 individuals,” said coauthor Silvia Bonizzoni, head of the group Dolphin Biology and Conservation. “Between 86 and 90 percent of the dolphins, depending on region, were photographed one or more times while they were following trawlers.”
On average, dolphins followed 41 percent of otter trawlers and 35 percent of midwater trawlers, which also drag conical nets but operate closer to the surface. That compares to previous research from the Adriatic, carried out in the 1990s, which found that dolphins were trailing just 10 percent of trawlers. Dolphins have, it seems, grown more reliant on trawlers for food despite the many hazards involved.
“It is known that bottlenose dolphins are occasionally injured or killed by trawl gear,” said coauthor Randall Reeves, of the U.S. Marine Mammal Commission. “Dolphins may also suffer hearing damage that results from chronic exposure to the noise of trawlers. 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.”
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