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Airdate: Nov 07, 2005
Scientist: Damon Gannon


Atlantic Croakers use sound to stay in contact with each other.

ambience: croaker distress call
That's not a frog or an insect. So what's croaking? Well, stay tuned. I'm Jim Metzner and this is Pulse of the Planet. Meet the Atlantic Croaker, a saltwater fish that lives off the Eastern coast of the United States. Damon Gannon is with the Mote Marine Laboratory in Sarasota, Florida.

"Croakers belong to the family of fishes known as the drums. The family is called the drums because of their sounds that they make by muscles that surround their swim bladder that strum the swim bladder like the head of a drum. And when you catch them and hold them in your hand, they will croak, and that's some sort of distress call."

ambience: more croaker distress call

Until recently, scientists thought that Croakers made sounds only when in distress and during spawning season, like other fish in the "drum" family. But Gannon says that they now think Croakers might be using their call to communicate year-round.

ambience: juvenile croakers

"What you're hearing right now is what I believe is a contact call of croaker. These are juvenile croaker that we caught in the estuaries. We put them in a pond that was filled with water straight from the estuary, and lo and behold these croaker make sound pretty much all the time. But they make sound more often at night than they do during the day, and I believe that this I'm hypothesizing at this point that this is a contact callThe waters that they live in in the estuaries are very murky, very turbid, and it's difficult, perhaps, for these aggregations of fish to stay together if they were only using visual cues. But with sound they might be able to maintain their group cohesion Living in a group is important for the survival of these animals, either to avoid predators or to find food or something of that nature."

There's evidence that the Atlantic croakers calls may actually attract predators, so why they continue to croak is a bit of a mystery. We'll hear more in future programs. Pulse of the Planet is presented by the National Science Foundation. I'm Jim Metzner.