DOLPHINS have developed tools to help them hunt for food, according to new research, which suggests the mammals could be even smarter than previously thought.

Bottlenose dolphins from an extended family in Australia’s Shark Bay have taken to protecting their noses with pieces of sponge when foraging for fish on the abrasive sea bed.

Scientists at Georgetown University in Washington DC believe a single dolphin discovered the foraging technique by chance and then passed it on to her offspring. Its use has had a marked impact on the dolphins’ hunting and social behaviour as the animals deploying the sponge tool spend more time alone, rummaging through sand.

While several animals use tools by instinct – such as birds that cover themselves with leaves for camouflage — the US scientists say discovering a new tool is a direct sign of intelligence.

“There’s a strong link between animals with larger brains and tool users,” said Janet Mann, a marine biologist who led the research. “Bottlenose dolphins have a brain second in size only to humans.

“Dolphins are already good at catching fish so they don’t need tools, but they’ve discovered this sponge makes their job easier. Working out how to use tools in a creative way like that is a hallmark of intelligence.” The foraging technique came to light a few decades ago – very recently in evolutionary terms – when a local fisherman spotted what looked like a strange tumour on a dolphin’s nose.

Researchers eventually worked out that the “tumour” was a conically shaped sponge and it became apparent that the dolphins would spend considerable time searching for one the right shape to fit their nose.

The sponge is used to scatter the sand gently on the sea floor and disturb buried fish. When a fish is spotted, the dolphin drops the sponge and gives chase.

Scientists discovered that although dolphins tried to teach the hunting technique to all their young, it was mainly female offspring that grasped the concept. Those males that use sponges for hunting do so discreetly and avoid other male dolphins.

Mann admits we still do not understand dolphins well. “It’s hard to get inside their heads because their brains are constructed differently and it’s very hard to analyse their language, but they do seem very intelligent,” she said.

“Dolphins are able to recognise themselves in mirrors and have complex societies and personalities,” she added. “Most people agree that processing social information places a high demand on the brain. However, manipulating a sponge requires a lot less brainpower than manipulating a person.”

Sea sense

¤ Dolphins display self-awareness and are able to recognise themselves in mirrors
¤ They can interpret television images and copy human actions
¤ Their echo-location system is better than the most advanced military sonar systems

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