Stealth Bombers of the Deep Carry Shocking Arsenal
They glide through the night-dark water, silent and nearly invisible, wings primed with deadly lightning bolts. Woe to the fish or human that finds itself the target of an electric ray.
“They’re the stealth bombers of the deep,” says biologist Richard N. Bray of Cal State Long Beach, holding up photographs of a ray and the radar-evading warplane. “They even look alike.”
Long the object of wonder and speculation, these mysterious nocturnal creatures only recently have begun to be studied in their natural habitat, the open ocean. Scientists such as Bray, using sophisticated electronic equipment and videotape, are continually surprised by what they are seeing.
“We’re learning about their attack patterns,” says Bray. “We used to think their movements were pretty limited. Now, by tracking with telemetry, we find that they range over large distances.”
This information could be of special interest to divers. The largest electric rays can deliver shocks equivalent to household current. They are known to zap people as well as fish. Although no fatalities are documented, rays are suspected in some cases in which divers have died unaccountably in areas where the animals are found.
“They aren’t normally aggressive toward humans,” says neurochemist Stanley Parsons of UC Santa Barbara. “But they are naturally curious. They’ve been known to follow divers just out of sight, above and behind. When the diver starts to rise to the surface, he may rise right into the ray’s stomach.”
Which could be like sticking one’s head into a large light-bulb socket.
Ancient Greeks used electric rays as torture devices. In the early 19th Century, physicians experimented with them as a form of shock therapy.
Today they are proving to be a valuable tool for biomedical research. Because of the peculiar structure and properties of their electricity-generating organs, they are yielding vital information about such maladies as Parkinson’s disease, muscular dystrophy and Alzheimer’s disease.
Electric rays are one of several kinds of fish that make their own electricity. Another well-known shocker is the electric eel.
They are found in every ocean. One species, the Atlantic’s gigantic Torpedo nobiliana , grows as long as six feet and weighs up to 200 pounds.
Ever since Charles Darwin published his theories of natural selection in the mid-1800s, scientists have puzzled over how and why certain fish evolved electricity-producing organs. The prevailing theory is that they first were used for navigation.
Some species of fish still use relatively weak electrical discharges for that purpose. At some point, electric rays and eels made the jump to using the discharges as weapons, both for hunting and as a defense.
“To our knowledge electric rays have no predators, including sharks, which are extremely sensitive to electrical fields,” says Bray, whose work is supported partly by the National Geographic Society. “The only kind of fish that will attack an electric ray is a dumb fish.”
Smart fish, Bray believes, learn by experience to leave electric rays alone.
“One time I was diving in an area off Santa Barbara,” he says. “I saw an electric ray swimming along. At the same time a harbor seal swooped down playfully to see what I was doing. The seal saw the ray and did a double take. It took one look at it and then disappeared.”
The physiology of electric rays and their electricity-producing organs have been studied extensively in laboratories. Organs--actually, modified muscles--are located on either side of the ray’s disk-shaped body.
Each electrical discharge lasts only five-thousands of a second. But during a predatory attack lasting four or five seconds, an animal may discharge as many as 150 times a second at 40 volts each before tapering off.
Bray recalls accidentally swimming up into a ray. It rewarded him with three quick shocks to the top of the head.
“It really hurt,” he says. “But what really discouraged me is that it was one of the smallest electric rays I’d ever seen at that reef, maybe only 18 inches across.”
