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Airdate: Nov 09, 2005
Scientist: Damon Gannon


With Atlantic Croaker as its prey, the bottlenose dolphin just has to LISTEN for its dinner.

ambience: croaker calls

If you were a hungry dolphin, this would sound like dinner. I'm Jim Metzner and this is Pulse of the Planet. We're listening to the calls of the Atlantic Croaker, a saltwater fish that bottlenose dolphins consider a tasty treat. Damon Gannon is a scientist at the Mote Marine Laboratory in Sarasota, Florida. He says that dolphins carefully monitor the soundscape, listening for signals like this.

"If a dolphin is... listening for the sounds that its prey make, it can probably identify the species. It can get information on the location of where that sound producer is, where that fish is in the environment. It can probably tell something about the size of the fish that's making that sound because the fish are making these sounds with their swim bladders, and as the fish grows in length, that swim bladder gets longer. And the frequency of sound that it produces drops, so lower frequencies are made by larger fish. So the dolphin can get a lot of information from these sounds produced by fish.”

Damon Gannon and his colleagues have done a series of experiments playing recordings of the sounds of different undersea creatures to see if they would attract the dolphins.

"And it turned out that the dolphins swim toward and approach the sound source when you play fish sounds and investigate the sound source."

ambience: sounds of snapping shrimp

"We used the sounds of snapping shrimp as the control because they are very common in the dolphins' habitat but they're not a prey item of the dolphins. When we played these snapping shrimp control sounds, the dolphins did not respond at all, either they did not move toward the sound source and they did not increase their echo location."

So the question is, if they're going to attract dolphins who want to eat them, why do croaker fish croak? We'll hear more in future programs. Pulse of the Planet is made possible by the National Science Foundation. I'm Jim Metzner.