Dolphins wield tools of the sea: sponges utensils of choice for 'workaholics' of ocean realm.

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You know it's mealtime for certain bottlenose dolphins off Australia's coast when they sport cone-shaped sea sponges on their beaks. These mammals are not following a strange, marine-based dress code. Their behavior has been identified as the first clear case of tool use by wild dolphins or whales, a new study concludes.

The dolphins dive to the bottom of deep channels and poke their sponge-covered beaks into the sandy ocean floor to flush out small fish that dwell there, a team led by biologist Janet Mann of Georgetown University in Washington, D.C., reports online December 10 in PLoS ONE. Foragers then drop their sponges, gobble up available fish and retrieve the implements for another sweep. Dolphins hold the sponge with the bottom of their beaks and can sweep away much more sand than they could without the tool.

Mann's team documented this behavior among 41 bottlenose dolphins, most of them female, out of a population of several thousand that inhabit Australia's Shark Bay. The researchers estimate that sponge-carrying dolphins, or spongers for short, devote at least 17 percent of their time to ferreting out bottom-dwelling fish using these beak-borne prods.

"It turns out the brainiacs of the marine world can also be tool-using workaholics, spending more time hunting with tools than any nonhuman animal," Mann says. Chimpanzees and other nonhuman primates spend a small amount of time using tools. One population of woodpecker finches spends an estimated 10 percent of its time using twigs and cactus spines to pry insects and spiders out of tree holes.

Indirect evidence of tool use during foraging does exist for killer whales and sea otters, remarks biologist Hal Whitehead of Dalhousie University in Halifax, Canada. "In the marine environment, individuals may heavily concentrate on particular cultural practices, especially when foraging," he says.

Not everyone regards such food-gathering tactics as purely the products of social learning or culture. Genetic traits and habitat characteristics may influence how animals forage as much as or more than any cultural traditions, argued Kevin Laland and Vincent Janik, both biologists at the University of St. Andrews in Scotland, in a 2006 paper.

Further research needs to tease out the effects of genes, environment and culture on this sponge-assisted foraging, says Michael Krtitzen of the University of Zurich, who studies social behavior of bottlenose dolphins and orangutans.