The behavior, called sponging, involves a dolphin affixing a marine sponge over its snout to protect itself while it pokes and prods for fish on the sea floor. Researchers believe the use of this sponge tool is a fishing technique that mother dolphins teach to their children.

The study is published in this week's Proceedings of the National Academy of Sciences.

"We believe that the marine sponge (which the dolphin breaks off and wears) acts as a kind of glove to protective their sensitive rostra," said marine biologist Michael Krützen of the University of Zurich, who worked at the University of New South Wales in Australia during the study, which he led.

"That probing (of the sea floor) might disturb fish that hide in the sand, which would then be easy targets for the dolphins."

Material culture involves tool-based traits acquired through social learning from select members of the same species. It only has been identified a handful of times in the nonhuman animal kingdom. Chimpanzees appear to have material culture, based on observations of them using tools, such as makeshift stone hammers and anvils to crack nuts, as do orangutans.

To determine if dolphins also possess behavioral traits that can vary culturally, Krützen and his team analyzed DNA taken from known dolphin spongers located at Shark Bay, Western Australia. They focused on DNA to see if there was a genetic explanation for the fact that only 13 dolphins within this particular population appear to use sponges as foraging tools.

The scientists studied the 10 possible modes of inheritance, such as through mitochondrial DNA that comes from mothers, and determined whether these methods could apply to the sponging dolphins. The researchers were able to rule out genetic inheritance because the documented spongers consist of 12 females and one male.

Mitochondrial DNA, for example, would pass down to both sons and daughters, but females mostly engage in sponging. The single male sponger, however, suggested that a female-only chromosome, even a recessive one, is not at work. Krützen believes mothers teaching their offspring is the only other possible explanation for the sponge glove usage.

Most male dolphins simply may not have a lot of time for sponging.

"If they are sexually mature, they spend a significant amount of time chasing females, in particular in breeding season," Krützen told Animal Planet News.

Krützen said the one known male sponger could be an older male that lost his other male alliance partners and now has more time for fishing.

The researchers believe the glove technique might have originated from a female that they think lived not too long ago and just came up with the technique on her own.

Dolphins use other clever fishing techniques, such as "kerplunking," or slapping the water's surface to create a vortex that seems to stun fish. Sponging, however, is the only known example of tool use.

Hal Whitehead, one of the world's leading cetacean biologists, told Animal Planet News that he is convinced by the new research. He said material culture probably is rare in marine mammals, although he has seen animals "apparently playing with logs or seaweed," which perhaps might serve as tools.

Carel van Schaik, an anthropologist at the University of Zurich who has studied culture among orangutans, also agrees with the dolphin findings.

"The sponges are obviously some kind of tool, and the distribution strongly suggests social transmission of what is not a common skill," van Schaik told Animal Planet News.

"I was not surprised because dolphins have been convincingly shown to be good imitators, and it would be unlikely that such a specialized, derived ability would simply go completely unused in the wild," van Schaik said.