Dolphins on opposite sides of Australia, thousands of kilometres apart, have independently learned to use empty seashells as traps to catch fish. This remarkable invention, known as 'shelling', has been observed in both Shark Bay on the west coast and Hervey Bay on the east coast. The study, published in Marine Mammal Science, presents the first published records of this behavior from Queensland's Great Sandy Marine Park, adding to the growing body of evidence that dolphins have the capacity for independent innovation.
The behavior involves a small fish disappearing into the opening of a dead gastropod shell, which is then carried to the surface by the dolphin. The dolphin inserts its rostrum into the aperture, raises the heavy shell, and tips it above the water, allowing the trapped prey to be brought within reach. This specialized form of foraging requires more than just carrying an object; it involves locating a suitable dead shell, exploiting the fish's tendency to hide inside it, and maintaining the aperture's orientation during the ascent.
The study's authors, Alexis Levengood and colleagues, 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 surfaced repeatedly with a baler shell while a drone filmed from above, capturing a fish escaping and Maserati chasing it. The calf Bentley then surfaced with the same shell, attempting to use it in a similar manner.
The study's findings suggest that the dolphins on the two sides of Australia have independently invented the same tactic, but it is important to note that the study did not run a test that could reconstruct the exact first moment of invention on either coast. The authors argue that the observations contribute evidence of independent innovation across Australia's west and east coasts, but they cannot rule out unrecorded occurrences elsewhere.
The study also highlights the role of social learning in the spread of this behavior. The authors suggest that Bentley may have learned by watching Maserati use the shell, providing evidence of vertical social learning, meaning information passed from parent to offspring. However, the study acknowledges that this is not conclusive evidence of deliberate teaching and that the calf may have learned by observation or already had experience with shells.
The most interesting interpretation, according to the authors, is that a useful behavior may originate more than once and then travel locally through different social routes. The study emphasizes the importance of longer observation, individual life histories, and social-network data to understand how often shelling occurs and how calves or peers acquire it.
In conclusion, the study presents a compelling natural parallel, suggesting that similar prey, similar shells, and similarly flexible minds have produced one remarkably similar invention. Once discovered, the trick may cease to belong to one clever dolphin and begin moving through a population as culture.
