Shark Bay dolphins use sponges to hunt for hidden fish

Some Shark Bay dolphins in Western Australia have developed a hunting method that could have come from a workshop: they fit marine sponges over their rostra and probe the seabed for concealed fish. Known as sponging, this behaviour is unusual even among this population, and is particularly notable because the knowledge is passed chiefly from mothers to daughters.

Why do these dolphins wear a sponge on their snout?

The sponge serves as a foraging tool. Once fitted over the rostrum, it allows the dolphin to disturb sediment, gravel and sections of the seabed where small fish may be hiding. Its soft structure also protects a sensitive part of the animal’s body as it repeatedly makes contact with the substrate.

This approach gives dolphins access to prey that cannot be located as easily through echolocation alone. Some fish in these habitats live close to the bottom and lack a swim bladder, the air-filled organ that would usually create a more noticeable echo for dolphins. Physically stirring the substrate can force them out of their hiding places.

How does sponge hunting work on the seabed?

The method requires far more than merely finding a sponge. The dolphin must select a suitable one, place it on its rostrum, dive, and use it during its search for food. Researchers have identified distinct stages during a foraging sequence:

• the dolphin picks up a marine sponge from the seabed;
• it positions the organism over the end of its rostrum;
• it pushes and moves the sponge across the substrate;
• it attempts to flush fish from among sediment and stones;
• it drops the tool after locating prey and needing to catch it.

The technique also brings an unexpected cost. Acoustic modelling suggests that the sponge alters the signals involved in echolocation, distorting some of the clicks and echoes received by the animal. Dolphins must therefore forage while adjusting to a change in their own sensory system.

Why is the technique passed mainly from mothers to daughters?

Long-term studies at Shark Bay point to vertical social transmission: calves learn by watching their mothers throughout the years they remain close to them. An analysis published in 2019 found strong evidence that sponge use spreads within maternal lineages, rather than simply occurring because dolphins inhabit the same environment.

Daughters are more likely to take up the strategy. Research into males that also use sponges found that about 91% of daughters born to practising mothers adopted the behaviour, compared with roughly 50% of sons. This indicates that the tradition is not exclusively female, although it shows a marked difference related to the offspring’s sex.

What makes Shark Bay dolphin sponging an animal culture?

Researchers do not call the practice culture merely because it is rare. The key factor is that it is socially learned and continues across generations. Genetic, ecological and behavioural research has helped rule out a simple explanation based only on genetic inheritance or sponge availability. Features supporting this interpretation include:

• calves follow mothers that already use the tool;
• not every dolphin living in the same area adopts the method;
• the behaviour remains concentrated in particular lineages;
• learning it requires years of observation and practice;
• females are more likely to sustain the tradition.

For these reasons, sponging has become one of the most closely studied examples of tool use in cetaceans. This population remains socially connected to other dolphins that never use sponges, showing that sharing the same habitat is not enough for the technique to spread to every individual.

An underwater tradition maintained across generations

Shark Bay dolphins demonstrate that a feeding strategy can follow a very different path within one population. While some chase fish without using any object, others carry sponges, stir up the seabed, and rely on an ability learned over years spent with their mothers. The tool even changes how the animals receive the echoes they use to sense their surroundings.

Its predominance among females adds an unusual dimension to this tradition. Because daughters are more likely to repeat their mothers’ behaviour and later pass it on to their own offspring, certain lineages retain a foraging technique that other Shark Bay families do not use. In this case, kinship, social learning, sex and feeding combine to preserve one of the most distinctive traditions ever recorded among marine mammals.