In sum, it was some hum - humming toadfish in Sausalito, California

Discover, June, 1986 by John E. McCosker

For the past several summers, houseboat residents in Sausalito, asmall town at the northern end of San Francisco Bay once largely populated by artists and fishermen but now overrun by yuppies, have complained about a loud, eerie drone that begins each evening after sundown during July and August and ends shortly before dawn. Seeming, at low tide, to emanate from the mud, the sound, which has been likened to the din of a squadron of low- flying B-17s, penetrates boat hulls and keeps many of the hundreds of Sausalitans who reside on the waters of Richardson Bay from getting much sleep.

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The cause? Speculation ranged widely. Aha, it's a secret military experiment! (The Army Corps of Engineers, an obvious candidate to be the villain in any environmental controversy these days, maintains a research lab on the waterfront.) No, it's the sewage treatment plant. (Which, it was claimed, was operating only at night so as not to offend sensitive tourists.) Don't forget extraterrestrials. (Sausalito is a lovely vacation spot: What better place for the discern- ing Martian to land?) After considerable expense, extensive acoustical mapping of the bottom of Richardson Bay by technical consultants, and con- tinual denials of guilt by all federal and municipal parties, the cause of the drone was still unknown. Then one morning last July a biologist from San Francisco State University named Tom Niesen picked up that day's San Francisco Chronicle and read of Sausalito's plight. On a hunch, he called the technical consultants dealing with the hum and suggested that the source might be biological. A fish perhaps.

Fish do make noise. Many centuries before Jacques Cous- teau appeared on your TV screen backed by choruses of gurgles, grunts, and snorts, the subject of sonorous fish was treated by both Aristotle and Pliny. More recently, the study of submarine sounds has been a prime undertaking of the Office of Naval Research. Scientists have discovered that noise in the sea comes from a variety of sources, such as the echolocation of whales and porpoises, the popping and snapping of shrimp, and the groans, croaks, creaks, yelps, sobs, and hoots of various fishes.

Fish produce sound in three ways. One is by sudden underwater movements, like those of a large shark or grouper, which displace water and can result in a loud, low-frequency thump. Another is the stridulatory sound of teeth grinding or biting down on the hard parts of prey--not unlike the screech of chalk on a blackboard. The third is produced by muscles that cause vibrations in a spe- cialized resonating chamber-- variously called the gas blad der, air bladder, or swim blad- der--that's found in many kinds of fish.

Recall the last time you cleaned a fish: you came upon a viscous, shiny sac lying just beneath the backbone among the viscera. This gas bladder acts as a ballast chamber, allowing a fish to equilibrate its density to that of the water and thus effortlessly remain at the depth it chooses. It also acts as a drum, for which the East Coast drumfish is named. Croakers, grunts, and toadfish vibrate the drum as rapidly as 150 times a second, and with it the Atlantic toadfish, for example, can produce a variety of grunts, growls, and hums, known as boat whistle or foghorn calls, when in search of a mate. The Pacific relatives of the Atlantic toadfish--called toadfish, singing fish, sapos, or midshipmen--have a similar repertoire.

Familiarity with fish noises is commonplace among ich- thyologists, but largely unknown outside the discipline. When Tim Underwood, a noise specialist at the health department of Marin County, in which Sausalito is located, was advised to consider fish as the source of the Richardson Bay hum, he was incredulous. But he was also desperate. He called the Steinhart Aquarium in San Francisco, which I direct. I was, until then, blithely unaware of the racket in Sausa lito and its considerable consequences, which may excuse my somewhat arrogant ichthyologist's reply to Underwood's query: ''From what you describe, it's obviously Por ichthys notatus, a toadfish.''

As a graduate student studying fish in Baja California, I'd beenkept awake during tequi- la-glazed nights on the beach by a hum with a frequency between 98 and 108 Hz (which is rather like the mournful resonance of the bassoon of the grandfather's theme in Peter and The Wolf) and with a volume two to three decibels above the ambient sound. Investigation disclosed that ten- inch-long male toadfish were guarding intertidal nest sites and hoping by humming to attract mates.

This abundant, cryptic, bottom-dwelling species spends most of its life offshore, probably buried by day in the sandy bottom and feeding nocturnally upon near-bottom shrimp. During the mating season, it moves into the shallow water of bays and estuaries, rich nursery grounds for its young. The eggs are laid and fertilized, and guarded by the male until they hatch. Then the adult toadfish disappear into the northeastern Pacific, not to be heard from until the following summer.

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In sum, it was some hum - humming toadfish in Sausalito, California

Discover, June, 1986 by John E. McCosker

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