How Wild Dolphins Use Sea Sponges as Hunting Tools

Wild dolphins have been filmed placing sea sponges over their snouts and using them as tools while foraging on the seabed.

This unusual ability is passed from parent to offspring, and is far more complex than almost any other form of animal behaviour seen in the wild.

Yet the sponge markedly alters the acoustic signals dolphins send and receive, hampering their ability to locate prey with sonar. That raises an obvious question: why use one at all?

Dolphins hunting with sponges

In Shark Bay, Western Australia, some Indo-Pacific bottlenose dolphins, Tursiops aduncus, have been recorded picking up marine sponges and placing them over their beaks.

The research was headed by Ellen Rose Jacobs, Ph.D., of Aarhus University, whose work focuses on dolphin behaviour and sound.

Jacobs collaborated with Georgetown University’s Shark Bay Dolphin Research Project, which has monitored these dolphins since 1984.

By tracking the journey of sponges from the seabed to the snout, the researchers sought to establish both the advantages of these sponge tools for dolphins and the drawbacks of this unusual behaviour.

Protection from rocks and stings

While dolphins hunt this way, the sponge protects the sensitive skin of their snouts from sharp rocks and stinging creatures commonly concealed in sand.

However, it also deflects the “click” sounds used for echolocation - the process of locating prey by listening for echoes - meaning the returning signal is distorted.

In a detailed report, Jacobs explained that the sponge changes the sound information available as a dolphin looks for fish.

“Everything looks a little bit weird, but you can still learn how to compensate,” said the team lead during fieldwork in Shark Bay.

Clicks, echoes, and jawbones

The clicks dolphins use to communicate travel through the melon, a fatty organ that directs sound forwards, before radiating through the water.

Returning echoes enter through the lower jaw, whose fat-filled tissues transmit vibrations towards the middle and inner ear.

With a sponge covering the snout, part of the outgoing sound beam and the returning echo have to travel through sponge tissue twice.

This additional layer may scatter sound energy and blur its timing, making the brain work harder before a pursuit can begin.

Analysing dolphin sponge behaviour

To determine whether the dolphins continued clicking while wearing a sponge, Jacobs listened underwater as they searched channel bottoms.

Her recordings confirmed that they produced active clicks, while the Aarhus University team used a physics-based computer analysis to map the resulting sound changes.

After scanning real sponges and creating digital models, the researchers traced a click from its initial release through to the echo returning to the dolphin.

Their findings indicated continual variation: every sponge has a distinct shape, leaving learners to deal with fresh challenges from hour to hour.

Shape matters more than size

Sponges with different forms generated different acoustic effects, even where dolphins made similar foraging movements in the same habitat.

Cone-shaped sponges, including Echinodictyum mesenterinum, channelled the outgoing click into a straighter path. By contrast, basket-shaped Ircinia sponges generally dispersed the click’s acoustic signature across a broader area.

In the simulations, this broader beam also reached the dolphin’s jaw with reduced strength, producing an echo that was weaker and more prolonged.

As dolphins regularly select new sponges, slight differences in form may determine whether a particular tool feels suitable for the task.

Learning takes years, not days

Although many nearby dolphins watched the practice, only around 5% of animals observed in this population continued to use sponges.

Young dolphins remained alongside their mothers for roughly three to four years, and this extended teaching period developed strong muscle memory.

By observing the same method thousands of times, calves learned largely within family relationships rather than across broader social groups.

Restricted opportunities to practise meant that most dolphins never trained for long enough to overcome the sensory disruption created by wearing sponges over their noses.

Why the benefit stays high

After mastering the technique, a dolphin could use the sponge to explore sandy channels and drive out fish sheltering beneath rubble.

The dolphins pressed their protected beaks across the seabed, disturbing barred sandperch, before releasing the sponge to pursue the prey. Wild sponges ranged in size from a softball to a cantaloupe, so the tool also needed to suit the hunt.

Because the reward was food overlooked by other dolphins, a small number of specialists still chose to spend time mastering this more demanding method.

Culture with hard limits

Tool use may spread rapidly among animals when it offers benefits without interfering with other abilities, but sponging comes with a cost for dolphins that adopt it.

Although tools frequently help animals obtain food or prevent injury, scientists have devoted much less attention to the concealed challenges that may stop such tools spreading throughout a population.

The team connected the cost of using sponge tools with a gradual learning process, even though the foraging rewards remained substantial.

This trade-off helped account for why other dolphin families living alongside the sponging group did not imitate them, despite regular contact.

Dolphins, sponges, and cultural transmission

Dolphins forage in cloudy water by producing rapid clicks and listening to the echoes that return. It is a remarkable system, yet so-called sponging behaviour demonstrates how readily it can be disrupted.

When boat engines roar nearby and human activity increases, background noise can overwhelm the faint returning signals on which dolphins depend.

Put a sponge over the snout and the signal becomes even less clear. Additional environmental noise can turn an already challenging hunt into one that no longer works at all.

This is why quiet feeding areas are so important. For dolphins that effectively navigate and feed through sound, what they are able to hear determines what they can eat.

The sponge also reveals a wider story. A single tool, collected by one dolphin and transmitted to others, can ultimately shape the life of an entire family group. It influences what they learn, where they forage and how they interpret their surroundings.

Many questions remain unanswered. Why do certain dolphins favour particular sponges? As the ocean becomes noisier each year, which foragers will continue to thrive and which will be left behind?

These are the questions researchers will investigate next.