Sightings of dolphins carrying sponges on their snouts to protect their sensitive noses while dislodging fish and crustaceans from the rocky ocean floor has been recorded since the 1980s.

But researchers at the University of New South Wales added a new dimension to their research by using computer modeling of behavior and genetics to estimate how long the technique, which they call "sponging", has gone on.

"What's unique about the sponging behavior is that only about five percent of dolphins use the sponges as a tool, and it's only one maternal line," said Anna Kopps at the University of New South Wales Evolution Ecologist Research Centre.

"What's new about this study now is we've got the time perspective," she told Reuters.

Scientists believe one single female started sponging in Shark Bay, Western Australia, and all her descendants in that area learned the behavior from their mothers.

Knowing this, and that the sponging was done 30 years ago, computer modeling allowed them to study the spread of the behavior over the past three decades -- and then reverse the process using genetics and behavior to figure out when it might have begun.

Ultimately, they estimated that sponging has been going on for some 180 years, or roughly eight generations of dolphins.

"It's interesting that the behavior doesn't spread to the entire population and it doesn't go extinct either," said Kopps.

Dolphin offspring are dependent on their mothers for about four years, giving them ample time to observe and learn survival techniques. The maximum lifespan of a dolphin is about 40 years.

"We don't know if it's teaching or other forms of learning," Kopps said.

While male dolphins also learn sponging from their mothers, the study found they don't pass the technique on.

"Some males use it but not many and it will be a dead end because they don't learn from the dads," Kopps said.

(Reporting by Pauline Askin; Editing by Elaine Lies and Paul Tait)

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