MARINE RESEARCH
In a small control room on the Bahamian island of North Bimini, Marine Biologist Arthur Myrberg pushed a button, then stared intently at a television monitor. Within half a minute, the TV screen came alive with thrashing sharks, groupers, snappers and other large inhabitants of the deep. Myrberg's surprising underwater show had once again started on cue—as it does whenever he signals his aquatic actors.
By pressing the button, the University of Miami scientist had set off a low-frequency sound projector submerged in 60 ft. of water on the ocean floor. To any carnivorous fish within earshot, the signals probably seemed similar to the noises made by other fish when they are feeding, being attacked or under other conditions of stress. Excited by the apparent proximity of prey, the sharks and other predators greedily converged on the sound projector.
Sound Assumption. Myrberg's shark-calling technique is an outgrowth of his studies of fish behavior financed by the Office of Naval Research and the National Science Foundation. After starting his research on North Bimini in 1965, he proceeded on the assumption that fish communicate better acoustically than by sight or smell. Sound, after all, is carried farther in water than in the air, and three or four times as fast.
For his initial study, Myrberg chose the bicolored damselfish, which is abundant and active in the clear waters off North Bimini and emits a large variety of sounds. By recording underwater noises and observing the behavior that accompanied each sound, he quickly learned parts of the damselfish language and began using it to control his subjects. By playing a recorded chirping sound, for example, he caused the damselfish to twist 45 degrees and then make a U-shaped dip, a pattern it often follows during spawning. Another recorded call actually caused color changes on the body of the fish.
"One day," says Myrberg, "I was sitting there hitting the 'chirp' button, but visibility was so bad that I couldn't follow the little damselfish." Frustrated, he told his sound man to try a different set of signals. No sooner did the sound projector begin broadcasting a low-frequency tone than "bang, the whole area was filled with sharks." A chance turn of the dials had paid off with completely unexpected information,
Finny Barrier. Scientists now foresee exciting possibilities in the control of fish by sonic commands. They might, for example, be used to lure dangerous fish away from swimming areas or from divers in the sea. There are even potential military applications. By broadcasting intermittently at a popular shark frequency, a sound projector could provide a moored ship with an effective finny barrier against enemy frogmen.
More impoitant, Myrberg's studies of the linguistics of fish may help to fill the world's food needs. Once sharks and other predators that normally swim singly or in small groups can be concentrated into selected areas, it may become profitable for commercial fishermen to "harvest" them, thereby tapping a rich new source of protein. Similar tactics might be used to satisfy less adventuresome tastes in seafood. "If we can make this little damselfish twist and turn around in the open sea," says Myrberg, "maybe some day we can make a snapper jump into a net."