Dolphins on opposite sides of Australia, thousands of kilometres apart, have independently learned to use a remarkable tool: empty seashells as traps. This fascinating phenomenon, known as 'shelling', showcases the ingenuity of these marine mammals and raises intriguing questions about the nature of innovation and cultural transmission in the animal kingdom.
In Shark Bay, Western Australia, researchers have long observed dolphins using large empty sea-snail shells to catch fish. Now, a new study in Marine Mammal Science reveals that dolphins in Hervey Bay, Queensland, have also mastered this technique. The study, led by Alexis Levengood and colleagues, documents two encounters in Hervey Bay, where dolphins named Stevie Nicks and Maserati were observed carrying and using shells to trap fish.
What makes this discovery even more remarkable is the vast distance between the two locations. With no plausible chain of ordinary dolphin associations connecting the two study sites, the researchers conclude that the dolphins on the opposite coasts of Australia have independently invented the same tactic. This finding challenges our understanding of innovation and suggests that similar ecological ingredients can lead to similar solutions in different parts of the world.
The shelling behaviour 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 specialised form of foraging requires more than just carrying an object; it involves locating a suitable shell, exploiting the fish's tendency to hide inside, and maintaining the shell's orientation during the ascent.
The study's findings are based on detailed observations of dolphins in Hervey Bay, including a mother-calf sequence where the calf, Bentley, picked up the same shell used by its mother, Maserati. This sequence suggests potential evidence of vertical social learning, where information is passed from parent to offspring. However, the researchers caution that this is not conclusive evidence of deliberate teaching, as they did not observe the conditions required for teaching, such as a knowledgeable animal changing its behaviour in the presence of a learner.
The idea of independent invention and cultural transmission is further supported by the fact that some dolphins in Shark Bay carry marine sponges over their rostra while probing rubble for buried fish. This technique is believed to be culturally transmitted, passed down through the mother-calf bond. In contrast, shelling appears more flexible, capable of moving horizontally between peers or obliquely from older non-parents to younger animals.
The study's authors emphasise the need for further observations and data to fully understand the frequency and methods of acquiring shelling. Longer observation periods, individual life histories, and social-network data will be crucial in determining how often this behaviour occurs and how it is learned by calves and peers.
In conclusion, the discovery of independent invention of shelling by dolphins on opposite sides of Australia highlights the remarkable adaptability and ingenuity of these marine mammals. It also raises intriguing questions about the nature of innovation and cultural transmission in the animal kingdom, suggesting that similar solutions can emerge in different parts of the world due to similar ecological ingredients.
