December 10, 2008

Australian Dolphins Use Tools To Find Food

Marine biologists say that many female bottlenose dolphins in Western Australia's Shark Bay area spend a disproportionately large amount of time using sponges to root for prey on the ocean floor.

They say this causes some dolphins to work longer hours than others for their food.

Scientists say the female bottlenose dolphins living in 30- to 50-foot-deep channels off Australia's western coast that bury their noses in sponges and use them as tools to root through the sandy ocean floor for bottom-dwelling prey are the only known instance of dolphins or whales using tools.

Marine biologist Janet Mann of Georgetown University and colleagues have done the first in-depth analysis of this curious behavior.

They say the sponges protect the dolphins' noses from abrasion. "They can also cover more area than they can with their beak, which is pretty narrow," she said.

The scientists said around 11% of female dolphins in Western Australia's Shark Bay area use the technique, passing it down to their daughters.

However, only a very small proportion of their male offspring learn the technique. Once they are weaned, they tend to go off and socialize with other males, searching for schools of fish in packs.

Mann said it is unknown whether the males' failure to use the technique means they get less food.

The research team found that although the sponge-bearing females spend a disproportionately large amount of their time searching for food, and thus lead a more solitary life than females in areas with a higher abundance of prey, it does not reduce their ability to conceive and raise offspring.

Marine biologists say several other marine species have also been observed using tools.

Some crabs cut up sponges and wear them as camouflage. And sea otters use shells, rocks -- even bottles -- to open abalone and other shellfish.

But the dolphins spend a much higher proportion of their time using tools than any species, marine or land-based, other than humans, Mann said.


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