Meet the dolphins who wear tools to find their dinner

Fishing rods? So last season. Some dolphins in Western Australia have developed their own rather more unusual piece of hunting equipment: a sea sponge worn on the end of their beak.

In the clear waters of Shark Bay, Indo-Pacific bottlenose dolphins have been observed breaking basket-shaped sponges from the seabed and carrying them over their rostrums or beaks, as they hunt for fish hiding on the ocean floor. The behaviour is known as “sponging”, and it is one of the best-documented examples of tool-use by any whale or dolphin in the wild.

It might look like an accidental encounter with some bathroom accessories, but the dolphins know exactly what they are doing.

The sponge acts rather like a protective glove, allowing a dolphin to probe among rough sand, rubble and other hazards without damaging its sensitive beak. In doing so, it can disturb fish hiding beneath the seabed that would otherwise be difficult to find.

And these aren't just any fish. Research suggests sponging gives dolphins access to prey which can be particularly difficult to detect using echolocation - including fish like barred sandperch without the gas-filled swim bladders that usually provide dolphins with a useful acoustic target.

But there is a catch.

Putting a sponge over your face isn't necessarily helpful when you navigate partly by sound. Research published in Royal Society Open Science found that sponge tissue can actually distort the dolphins' echolocation signals. Different sponges can alter sound in slightly different ways, meaning a dolphin has to learn how to compensate while hunting.

In other words, sponging isn't a shortcut. It's a skill that has to be almost continually adapted. 

And that may help explain the most fascinating part of the story: dolphin mums appear to be passing that skill down through generations.

Research stretching back decades in Shark Bay has shown that calves learn by spending years alongside their mothers - with the tradition particularly likely to pass from mothers to daughters. One study found that while sons and daughters had similar opportunities to watch their mothers sponge, 91% of daughters took up the technique compared with only 25% of sons surviving to weaning.

That makes sponging more than simply clever behaviour. Scientists regard it as a form of knowledge acquired socially and handed from one generation to another, with one variety of sponge even being more highly favoured above the others. Long-term research in Shark Bay continues, with scientists studying how the availability of different sponges may help maintain this extraordinary tradition.