Dolphins use ‘sponge gloves’ to hunt: The clever trick is passed from mothers to their calves. Scientists share fascinating story of dolphins' hunting technique

What if dolphins could use tools just like humans? In the waters of Shark Bay, Australia, some bottlenose dolphins have developed a remarkably clever way to search for food. They pick up marine sponges and wear them over their beaks while looking for prey hidden beneath sand and rubble. Even more fascinating, the behaviour is not simply instinctive. Young dolphins appear to learn the technique from their mothers, turning it into a skill passed through generations.

Are dolphins using tools to hunt?

An article published in PLOS One, titled Why Do Dolphins Carry Sponges?, examined the unusual behaviour of bottlenose dolphins in Shark Bay, Australia. Researchers found that only a small part of the population uses marine sponges as tools. The study found that around 11% of adult female bottlenose dolphins carry sponges while foraging. These dolphins, known as spongers, behaved differently from females that did not use sponges.

Spongers were more likely to live and forage alone, spent more time in deep-water channels, made longer dives and devoted more time to finding food. Despite these possible costs, their calving success was not significantly different from that of non-spongers. The researchers described sponging as one of the only suspected examples of tool use among wild dolphins or whales.

How do dolphins use sponges?

The technique is surprisingly simple but highly specialised. During foraging, spongers pick up conical marine sponges measuring roughly 10 to 25 centimetres and place them over their rostrum, or beak, so that the sponge covers the jaw. The PLOS One study found that the dolphins typically wore the sponge while searching for prey. They often dropped it when a chase began because the sponge covered the area around the beak and could not be used during the actual capture of prey.

Researchers observed 10 female spongers across 1,295 surfacing periods. The dolphins surfaced with sponges after about 77% of their dives. They were much more likely to keep the sponge during longer periods at the surface than during brief surfacings. This suggests that the sponge acts more like a searching tool than a weapon for catching prey.

Why do dolphins carry a sponge?

According to the UK Whales organisation, spongers use the marine sponge like a “beak-glove” while searching through sand and rubble. The sponge may help protect the dolphins' faces from injuries and stings as they rummage around the seabed for sandperch hiding beneath the surface. Once a dolphin finds a useful sponge, it can carry it from one location to another and use it repeatedly.

The technique may also give spongers access to food that other dolphins cannot easily reach. The PLOS One research suggested that using sponges could help dolphins find and extract prey that is partly buried and otherwise difficult or costly to access. This could explain why spongers are especially common in deep-water channel habitats.

Why do only some dolphins use sponges?

Sponging is not a behaviour that every dolphin automatically develops. Researchers documented repeated sponging in 41 dolphins, including 29 females, six males and six dolphins whose sex was unknown. In cases where the mother was known, the mother was also a sponger. Among offspring born to spongers that were observed closely enough to determine whether they adopted the behaviour, most eventually became spongers. The pattern was particularly strong among daughters.

The PLOS One study found that 91% of known female offspring born to spongers adopted the behaviour, compared with 25% of known male offspring. The difference became even more interesting when researchers observed young dolphins closely. All seven daughters studied carried sponges while still dependent on their mothers, usually beginning around their second or third year. None of the five observed sons did so as dependent calves. Among offspring born to non-spongers, researchers did not observe any developing the behaviour during the focal observations.

Dolphins appear to have their own ‘sponge school’

According to the UK Whales organisation, young dolphins learn sponging through repeated exposure to their mothers. The learning process begins early. Calves of sponging mothers spend years watching and practising the behaviour, with youngsters beginning to carry their own smaller sponges at around two to three years old.

The strong female pattern may be linked to the different social roles of male and female dolphins. UK Whales explains that daughters closely follow their mothers' behaviour and may learn skills that help them become successful mothers themselves. Male dolphins, meanwhile, do not take part in childcare and instead focus more on relationships with other males. The result is a remarkable example of animal behaviour being learned and passed between generations.

Spongers prefer deep-water channels

The PLOS One study found that female spongers used deep-water channels almost exclusively, although researchers also recorded some exceptions. One unusual group consisted of a grandmother, mother, daughter and another offspring that repeatedly used a deep non-channel area. The younger dolphins had accompanied their mothers there as dependent calves and continued using the same area after weaning.

Spongers made up at least half of the adult female dolphins in deep-water channels, making them the most common female foraging type in those habitats. Researchers suggested that the sponge technique may allow these dolphins to exploit a food source that other dolphins cannot easily reach. However, sponging may not work equally well everywhere because the right prey and enough suitable sponges need to be available.

Dolphins are not the only tool users in Shark Bay

Shark Bay has another fascinating group known for using tools. According to UK Whales, the “shellers” use giant sea snail shells to trap fish. These dolphins lift shells from the seabed and tip the fish hiding inside directly into their mouths.