Observations reveal why the cetaceans cover their beaks when hunting
In 1984, researchers spotted dolphins doing something unusual in Shark Bay, Western Australia. When the animals got hungry, they ripped a marine basket sponge from the sea floor and fitted it over their beaks like a person would fit a glove over a hand. The scientists suspected that as the dolphins foraged for fish, the sponges protected their beaks, or rostra, from the rocks and broken chunks of coral that litter the sea floor, making this behavior the first example of tool use in this species.

But why do dolphins go to all of this trouble when they could simply snag a fish from the open sea?

The answer, researchers hypothesize and report online today in PLoS ONE, is that the bottom-dwelling fish are a lot more nutritious. Some species also don't have swim bladders, gas chambers that help other fish control their buoyancy as they travel up and down the water column. In the Bahamas, where dolphins are also known to forage for bottom-dwelling fish, dolphins hunt partly by echolocating these bladders, which give off a strong acoustic signal. That helps the cetaceans find prey even when it's buried in sea sand.