Professor Listens to Fishy Sounds from the Deep

Newswise — When University of South Florida College of Marine Science biological oceanographer David Mann listened to recorded sounds from extreme deep water sent to him by Susan Jarvis of the Naval Undersea Warfare Center, he immediately thought the croaking sounds belonged to some type of deep sea fish. Jarvis recorded the sounds with four underwater microphones she was using to eavesdrop on whales in the Bahamas. Mann, who specializes in marine bioacoustics, thinks the newly recorded sounds may be a "love call" emitted by a variety of deepwater fish whose identity is still unknown. He has a list of suspects, however. Among them are deep sea cods, grenadiers, cusk eels and roughies.

"The discovery of a new sound from the deep sea can be used as a starting point for identifying the species making the sound," explains Mann. "Sound is an ideal way for animals to communicate in the ocean and, since many predators hone in on fish sounds, issuing a mating call would be one of the few times a fish might reveal its location to predators."

Mann and Jarvis published their findings in the May issue of the Journal of Acoustical Society of America ("Potential sound production by a deep sea fish," 115, pgs 2331-2333).

The sound Jarvis recorded is something like rapid snoring or, as Mann describes it, similar to a stick dragging along iron railings (http://www.marine.usf.edu/bio/fishlab/).

Many fish produce sound during courtship, and he speculates some deep sea fish could produce such a sound by using muscles located along their swim bladder.

"There is very little data on reproduction in deep sea fishes, and we don't know a lot about where they spawn," says Mann, who studies hearing and sound production in fish to better understand the timing and place of courtship and spawning of sound-producing fish. "We don't know if they spawn continuously, or only at certain times of the year."

Now that a sound from the deepest blue has been documented and there are possible candidates, Mann expects he can listen with more specialized equipment and identify the crooner. Identifying the fish that goes with the sound may help scientists to learn more about their reproduction patterns.

"Many deep sea fish are slow to reproduce and can be easily wiped out," says Mann, who is thinking of using an underwater vehicle to further record and even photograph the fish. "It is important to understand reproductive behaviors in the deep sea to be able to predict the impact of fisheries in the deep sea ecosystem."