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ANIMALS

The Shocking Truth : Scientists Thought They Knew the Ways of the Electric Ray

March 22, 1987|WILLIAM JORDAN | William Jordan is a Long Beach-based science writer.

About 15 years ago Dick Bray, a young graduate student in marine biology, was diving off the Santa Barbara coast with some friends. He was just swimming along slowly, minding his own business, examining the reef below, when something soft and gentle settled on his head like a floating rag. Before he could react, a tremendous, walloping zap! stunned him. Then a second, slightly weaker zap. And a third, yet weaker one.

"I don't know if it ran out of gas or just lost interest in me," says Bray, now a professor of marine biology at Cal State Long Beach. "And I'm not in the habit of sticking my finger in electric sockets, but from what I remember as a kid, that's what it felt like--three gigantic shocks."

Bray's reference to an electric socket is quite apt. The ray was a very small individual, about five or so pounds, and an electric ray of that size can generate about 60 volts and 10 amps, about half of the standard household current. A larger individual (the species in question, Torpedo californica , can grow to more than four feet and 90 pounds) could probably generate energy in proportion to its size; hundreds of volts are quite possible. As Bray now admits, "It's accurate to say that that increased my interest in them."

He began to make mental notes and to learn more about this resident of the California coast, and a remarkable fish it seemed to be. Everything from the ray's appearance to its internal wiring was unique. An average adult is several feet long, weighs about 20 or 30 pounds, has the tail and skin of a shark (which is a close relative), but in front of the tail the body expands and flattens into a wide, circular disk, almost like batter poured on a griddle. The eyes are set on the top of this disk; the mouth is inserted on the white underside. What was even more impressive to Bray is that the electric organs make up about 15% of body weight.

As for the ray's habits, not much was known at the time. On the basis of casual observations during the day, the scientific community assumed that rays were sedentary and sluggish. They were thought to spend their time lying on the bottom covered in sand and to use their zappers only to discourage aggression.

Several years later, Bray, assisted by fellow student Mark Hixon, began a nocturnal study of Naples Reef, off Santa Barbara; he had noticed that rays seemed to be creatures of the night. He saw an average of two per dive, whereas during the day he had seen an average of one per 15 dives. Not only were the rays more abundant, but they were actively swimming--none of this sedentary lying in the sand--and Bray got the definite impression that they were foraging for food. The impression was borne out by one of those fortuitous, once-in-a-lifetime events.

One night, Bray and Hixon were swimming along when they spotted a 30-inch ray coming directly toward them. "As you might expect, we started backing up," Bray says. The ray kept slowly advancing. At the same time, it tilted its body up at about a 45-degree angle, exposing its underside, which became a dazzling white sheet in the glare of the diving lights. As this little drama played on--the ray swimming menacingly closer and closer, Bray and Hixon backpedaling vigorously to avoid an out-of-body stimulation--a third actor arrived on the scene. Apparently attracted by the spectacular white disk glowing in the dark, an eight-inch jack mackerel came swimming up from behind them and proceeded erratically, this way and that, toward the ray. Bray and Hixon watched with relief as some other poor thing came between them and an invigorating jolt; but they were completely unprepared for what happened next. Just as the mackerel and the ray were about to collide, the ray lunged forward with a powerful stroke of its tail, ducked its head into a forward roll and, in the same motion, curled its body around the mackerel, like a huge fingerless hand in a cuplike, enveloping embrace. Continuing its forward roll, the ray reached the bottom of its orbit, belly facing the night sky, and it was then that Bray glimpsed the mackerel, gripped in the palm of doom. Its body quivered. Its jaws protruded in a frozen, silent cry. Its fins stood stiff and erect. Deja vu was definitely in the water, and Bray had no doubts as to why.

The ray completed its roll, and as it did, its body began to undulate at the margins, wave upon wave sweeping from back to front, carrying the mackerel into position under the ray's mouth. Several quick gulps, and the fish disappeared. The entire process from attack to disappearance took fewer than 10 seconds.

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