Dolphins Invent Shelling Foraging Tactic Independently in Australia

Bottlenose dolphins residing on opposite sides of Australia, separated by nearly 4,000 kilometers, have independently developed a sophisticated foraging technique known as "shelling." This behavior involves using empty seashells to trap fish, a remarkable instance of convergent evolution in tool use among marine mammals. Researchers have documented this unique tactic in Western Australia's Shark Bay for years, and a new study published in Marine Mammal Science presents the first confirmed records from Queensland's Great Sandy Marine Park on the east coast.

The geographical expanse between these two dolphin populations, Shark Bay and Hervey Bay, makes it highly improbable that the behavior spread directly between them. This suggests that dolphins in both regions, thousands of kilometers apart, arrived at the same solution for catching prey independently. While researchers observed the matching behavior, they did not witness the initial moment of invention in either location.

The "shelling" method turns a common fish refuge into a specialized trap. Small fish attempting to hide from predators can seek shelter inside large, empty gastropod shells. For most predators, this would signal the end of the hunt. However, a dolphin employing this tactic inserts its rostrum into the shell's opening, lifts the heavy shell to the surface, and then tilts it to drain the water and any trapped prey directly into its mouth. This requires significant dexterity, as the dolphin must locate a suitable shell, exploit the fish's instinct to hide, maintain the shell's orientation during its ascent, and effectively drain the contents without losing the meal.

Dolphin Tool Use Evolves Across Continents

The initial detailed scientific descriptions of dolphins using shells for foraging emerged from Shark Bay. Subsequent observations confirmed that this tactic is rare, swift, and easily missed by researchers. It is considered a specialized form of foraging that demonstrates a clear understanding of object manipulation and prey behavior. The shell acts as a tool, enhancing the dolphin's ability to capture fish that would otherwise be inaccessible.

In Queensland's Great Sandy Marine Park, researchers Alexis Levengood and colleagues documented intriguing encounters in Hervey Bay during 2025. Their study highlights two instances involving Indo-Pacific bottlenose dolphins. On July 6, an adult female dolphin, nicknamed Stevie Nicks, was observed positioning a baler shell (Melo amphora) and lifting it out of the water across three surfacings. Despite the detailed observation, the researchers could not confirm if a fish was successfully caught.

A subsequent observation on October 1 involved a mother dolphin named Maserati and her calf, Bentley. Drone footage captured Maserati repeatedly surfacing with a baler shell. Although a fish was seen escaping the shell, it was unclear if Maserati caught it. Minutes later, Bentley was filmed using the same shell, placing his rostrum into the opening and attempting similar movements. Photographic evidence suggests a fish may have been visible, but again, a successful catch could not be confirmed.

These recent observations, along with older photographic records from 2013 and 2019 in the same region, suggest that the practice of shelling in Queensland predates the 2025 research. The consistency of the behavior and its presence across vast distances on opposite coasts provides compelling evidence for independent innovation.

The parallel development of shelling by dolphins on Australia's west and east coasts is significant. It suggests that similar environmental conditions—such as the availability of large empty shells, small fish seeking refuge in them, and dolphins possessing the cognitive ability to manipulate objects—can lead to similar behavioral adaptations. This phenomenon is a powerful illustration of how different populations can independently discover and refine tool-use strategies to enhance their survival.

Research into animal behavior, particularly tool use in aquatic environments, highlights the unique challenges and opportunities presented by water. The buoyancy of shells aids in their transport, while gravity becomes a crucial factor only when the dolphin lifts the shell clear of the water's surface. This complex interaction of physical forces underscores the sophisticated understanding dolphins must possess to effectively employ this foraging strategy.

In Shark Bay, the "shelling" behavior has been observed to spread through social networks. A 2020 study analyzed numerous dolphin encounters and found strong evidence that the technique is transmitted between individuals through social associations. This finding was significant as it provided the first quantitative evidence of a toothed-whale foraging tactic spreading beyond the mother-calf bond. It suggests that dolphins can learn this complex skill from peers or other associates, not just their mothers, highlighting the social complexity of dolphin communities.

While the Shark Bay research indicates a strong social component to the spread of shelling, the independent invention observed in Queensland suggests that such innovations can arise spontaneously in different populations. The Hervey Bay mother-calf observation offers a potential route for social learning, where Bentley may have learned by observing his mother, Maserati. This could represent a form of vertical social learning, passing information from parent to offspring, though definitive proof of deliberate teaching remains elusive.

The researchers emphasize the need for caution when interpreting such behaviors in intelligent animals. While social learning is plausible due to dolphins' sophisticated communication and long maternal care periods, specific cognitive processes cannot be definitively inferred from single events. The independent invention and subsequent potential spread of "shelling" by dolphins across Australia offer a fascinating glimpse into the adaptive capabilities and cognitive flexibility of these remarkable creatures.