Fish Croaks Like a Frog, But Why?

November 7, 2005

With its staccato, drumlike call, the Atlantic croaker (Micropogonias undulatus) sounds more like a frog than a fish.

Abundant from Cape Cod to Mexico, the species belongs to a family of fish known as drums. The fish makes its namesake call by vibrating special muscles against its swim bladder.

Why croakers croak when and where they do remains unclear. Damon Gannon, a staff scientist at the Mote Marine Laboratory in Sarasota, Florida, hopes to uncover some answers.

Such findings would further our knowledge of the species, which is a key food source for bottlenose dolphins, and the potential effects of human noise pollution on other fish.

In recent years studies have suggested that noise from ships, seismic oil exploration (the use of sound to find deposits), military sonar, and other sources adversely impacts whales and dolphins. But whether those same effects extend to fish is little studied, Gannon said.

Arthur Popper, an expert on noise pollution and fish at the University of Maryland in College Park, said, "There is concern, a valid concern, that the oceans are getting noisy."

The biologist said there is not much research on the issue, noting that peer-reviewed scientific literature on the subject is limited to fewer than ten papers on several fish species. Most of those papers have involved research conducted by Popper and his colleagues.

"The caveat is that there are 25,000 to 30,000 species of fish," he said. "And we know a little about effects of sound on only very few."

Not Like the Others

Gannon, of the Mote Marine Laboratory, first learned about Atlantic croakers' incessant croaking as a graduate student at the Duke University Marine Laboratory in Beaufort, North Carolina. At the time, Gannon was studying the feeding habits of bottlenose dolphins.

He found that dolphins eat mostly noise-making fish, such as spots, seatrouts, and croakers.

Gannon began to study how bottlenose dolphin diets differ in different habitats and found that the marine mammals gorge on croakers inside estuaries.

Continued on Next Page >>


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