Dolphins on opposite sides of Australia, thousands of kilometres apart, have independently learned to use a remarkable fishing technique. These intelligent marine mammals have seemingly come up with the same ingenious solution to catch fish: by using large empty sea-snail shells as traps. This fascinating discovery highlights the ingenuity and adaptability of dolphins, as well as the potential for cultural exchange and learning across different populations.
The study, published in Marine Mammal Science, documents the first published records of this behaviour in Queensland's Great Sandy Marine Park. It adds to the growing body of evidence that dolphins in Shark Bay, Western Australia, have also mastered this unique fishing technique. The huge geographic separation between the two populations suggests that the invention of this fishing method occurred independently, but it also raises intriguing questions about the mechanisms of learning and cultural exchange.
The technique, known as 'shelling', involves a small fish disappearing into the opening of a dead gastropod shell. The dolphin then inserts its rostrum into the aperture, raises the heavy shell, and tips it above the water, allowing the trapped prey to be brought to the surface. This behaviour is rare and fast, making it easy to overlook, and requires more than just carrying an object. Dolphins must locate a suitable dead shell, exploit the fish's tendency to hide inside it, keep the aperture oriented during the ascent, and drain it without losing the meal.
The Queensland study, conducted by Alexis Levengood and colleagues, provides clear evidence of this behaviour. They observed two encounters in Hervey Bay, involving Indo-Pacific bottlenose dolphins, locally known as 'buthu' in the Butchulla language. In one encounter, a female dolphin named Stevie Nicks used her rostrum to position a baler shell, Melo amphora, at the surface and lifted it out of the water. In another, a mother dolphin named Maserati was filmed using the same shell to catch a fish, and her calf Bentley was observed attempting the same technique.
The study also includes photographs from an ecotour vessel taken in 2013 and 2019, suggesting that this behaviour has been present in Queensland for years. The authors argue that the geographical separation between the two populations supports the idea of independent innovation, as there is no plausible chain of ordinary dolphin associations connecting the two study sites.
However, the study also acknowledges the possibility of cultural exchange and learning. The authors note that similar ecological ingredients, such as large empty shells on the seabed, small fish that use those cavities as shelter, and dolphins capable of manipulating awkward objects, may have offered similar opportunities for learning. The study did not compare genetic lineages and social networks across the continent, but it suggests that the invention of this fishing method could have spread through social associations.
The study of tool use by aquatic animals highlights the importance of water in changing both the physical demands and opportunities for object manipulation. Shelling is a compact example of this, as buoyancy helps move a large shell, while gravity becomes useful only when the dolphin lifts it clear of the surface. The study also notes that invention can happen independently and still become cultural once it appears, as evidenced by the spreading of the shelling technique among associates in Shark Bay.
The Hervey Bay mother-calf sequence adds a possible transmission route, as Bentley picked up the same shell three minutes after watching Maserati use it. However, the study does not provide conclusive evidence of deliberate teaching, as it is not clear if Bentley learned by observation or already had experience with shells. The authors caution that more observations are needed to understand the mechanisms of learning and cultural exchange.
In conclusion, the discovery of dolphins using the same fishing technique on opposite sides of Australia highlights the ingenuity and adaptability of these marine mammals. It also raises intriguing questions about the mechanisms of learning and cultural exchange, suggesting that a useful behaviour may originate more than once and travel through different social routes. Further research is needed to understand the frequency and mechanisms of this behaviour, but for now, it presents a compelling natural parallel, showcasing the power of innovation and cultural exchange in the animal kingdom.
