Singin' in the Sea

POSTED 11 NOV 2004


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Some salt-water fish have to sing for their mates.

small satellite image of hurricane Charley
(164KB) When Hurricane Charley passed over Charlotte Harbor, Fla. in August 2004, winds reached 140 mph. Quite a racket, eh? Sound file: Mann Laboratory


The classic musical "Singin' in the Rain," showed the value of a fine voice, romance-wise. But silver-screen song-and-dancester Gene Kelly probably had no clue that the same story may hold in the silvery sea.

Fish in the ocean -- some of them at least -- have to sing to attract mates.

map of florida with charlotte harbor circledAnd while we're not sure how these fish would react to a romantic Parisian rain shower, we now know they sing their gills out in a hurricane. During mating season, drum fish in the Gulf of Mexico are literally as loud as a hurricane underwater -- whether or not a hurricane is stirring the sea.

That's what Jim Locascio, a grad student who studies fish sounds and behavior with David Mann at the University of South Florida, found during Hurricane Charley.

Actually, these fish make their pounding noise by flexing a muscle on their "drum," an air-filled bladder that controls buoyancy. Gills have nothing to do with it.

A whale of a surprise?
Everybody knows groups of whales stay in touch with sound, and that frogs and birds sing to attract mates. But few know about drum fish, a group that includes redfish, spotted sea trout, sand sea trout and silver perch. Drums are among 800-plus species of fish that make some kind of sound, says Locascio.

fish: Silver perch (Bairdiella chrysoura) Courtesy Jim LocascioA few, including the goliath grouper, make sub-woofer warning sounds, at about 40 hertz (cycles per second).

The drums, however, "sing" at a higher pitch: 150 to 1,600 hertz. Far from warning intruders, they are wooing mates.

Drums, like most other fish, don't do sex like mammals: Females drop eggs, and males drop sperm, directly into the water. At that point, it's the same ol' sperm-chase-egg routine.

But if you are a drum guy, how do you gather the girls for some reproduction, especially in the cloudy near-shore waters where many fish spawn?

Drums use sound, which is not surprising once you think about it, says Locascio. "It's amazing that more fish don't do this. It's a very effective channel of communication, especially in turbid, coastal and estuarine waters, where visibility is often less than a meter." While light is easily blocked, sound can travel a thousand meters or more, Locascio says. "It travels very far, especially the low frequency sounds produced by fishes, is directional, and is not weakened, so it's a great way to get these large gatherings of fish. They are tantamount to a big fish orgy."

Frogs do it. Birds do it. And some fish do it: Attract mates with song.

The technique may be logical, and we landlubbers are certainly used to hearing a gang of frogs sing for their mates, but, "When fish do that, most people are surprised," says Locascio.

hear me sing (60 KB): sand seatroutSand seatrout just after the hurricane. Hear the individual fish purring?
Sound file: Mann Laboratory

The orgy starts around dusk, when a few drums flex their sonic muscles (want to hear the (60KB) song?) After an hour or two, says Locascio, you could be hearing an uncountable number of fish.

While Locascio can distinguish the unique sounds of different species, females may be getting even more information from the songs. (Yes: It's a guy thing. Only males sing.)

sound trout say: Hear us all sing (44KB)Chorus of sand seatrout less than two hours after the hurricane passed. This cacophony is a typical a nightly fish chorus.Sound file: Mann Laboratory

And the big bass sings bass
Whenever we talk about mate selection, we are talking about evolution. To Locascio, the evolutionary significance of fish-songs is "the big question." Do female drums emulate female birds, which select mates based on the quality of their songs? Are the drum dames selecting the guy with the golden gills, er, drums? "It's at least possible that a female can select her mate, or give an advantage to a mate, because she likes the way his voice sounds," Locascio says.

A bigger, older fish would produce a lower frequency, and might be a better mate, genetically speaking.

In practical terms, Locascio hopes to prove that louder mating is more effective mating. One of the key challenges of fisheries management, he says, is knowing when and where adults spawn and linking newly recruited juvenile populations to a particular spawning population. If it's possible to predict how many young will be produced simply by eavesdropping, fisheries scientists could anticipate future fish production -- at least for species that sing for their suitors, he explains. "The Holy Grail of fisheries research, is where are these fish being spawned, and what specific ecosystem factors influence the success of their development?"

If sound intensity correlates with spawning productivity, Locascio continues, "and I don't have any question that it does, it would be a tremendously powerful application" for understanding fish reproduction. (None of which addresses the perilous political problem of managing fish to satisfy competing economic and environmental interests.)

One thing's clear. You can't fault the drum for losing interest in mating, just because a hurricane like Charley was lambasting Charlotte Harbor.

The fish were, as usual, as loud as a hurricane.

So now we all know it. Gene Kelly wasn't bothered by a bit of rain in Paris. And when it's mating time, not even a hurricane can interfere with drum reproduction.

-- David Tenenbaumlittle fish swims away from author


Bibliography
Sound Production and Communication in the Spotted Seatrout, Gilmore, R. G., Jr. 2003, pp. 177-195. in S. Bortone, editor. Biology of the Spotted Seatrout, CRC Press Boca Raton, Florida.

Delimiting Spawning Areas of Weakfish … Using Passive Hydroacoustic Surveys, Luczkovich, J. J., et al. 1999, Bioacoustics 10:143-160.


 

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