Wild dolphins documented using sea sponges as tools

It’s not mealtime for certain bottlenose dolphins living off Australia’s coast unless 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.

These 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, says a team led by biologist Janet Mann of Georgetown University in Washington, D.C. Foragers then drop their sponges, gobble up available fish and retrieve the implements for another sweep, the scientists report online December 10 in PLoS ONE. Dolphins hold the sponge with the bottom of their beaks and can sweep away much more sand than they could otherwise.

Mann’s team documented this behavior among 41 bottlenose dolphins, most of them female, out of a population of several thousand that inhabits 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.