Electronic Device Designed to Work as Underwater Shark Repellent

Seven miles from shore and 30 feet down, a six-foot blue shark circled the diver warily. Then, in a quick, graceful turn, it made for the bag of bait the diver held in his hand.

When the shark was only a few feet from the bag, the diver pressed a button and in the same second the shark veered sharply away. A second shark approached and the scene was repeated.

The apparent cause of the sharks’ flight was a device which, by exploiting their unique sensitivity to electrical fields, could make the ocean safer for California’s divers, surfers and others who frequent the deep.

The Shark POD, developed by South Africa’s Natal Sharks Board, is already on the market in South Africa and Australia and Japan, and several units are being evaluated by the Australian military. It is expected to be available on the West Coast sometime this spring.

The Sharks Board, a government agency created to protect swimmers and divers while preserving shark populations, also is developing a model that can be enclosed in surfboards, life jackets and kayaks.

Other versions under consideration would be deployed just offshore in lieu of shark nets to protect beach-goers.

“It will basically alleviate that fear that people have, especially that fear that set in with the ‘Jaws’ phenomenon,” said Jim Morris, a Los Angeles diver who conducted a recent demonstration off Santa Catalina Island.

Morris, under contract to market the POD in the United States, believes it also will make the waters safer for sharks by reducing the terror that has prompted their widespread slaughter.

The Shark POD was designed to stimulate gel-filled organs--known as ampullae of Lorenzini--that detect electrical fields, and other sensors that detect vibration.

The ampullae help the shark find prey at close range by homing in on electrical impulses generated by muscle movement.

The POD consists of the battery pack and two probes that emit the field. The battery and one probe are strapped to the diver’s air tank. A second probe is placed on a fin.

Powered by a rechargeable battery, the POD envelops the diver in a 12-volt protective field for up to 90 minutes, Morris said.

Marine biologist Adrianus Kalmijn, of the Scripps Institute of Oceanography in San Diego, said the ampullae can sense the most minute electrical fields.

“If they base what they do on that, then the basis is solid. It’s no surprise whatsoever that sharks would react,” said Kalmijn, who pioneered research on the shark’s use of electrical fields to detect prey.

The U.S. Navy experimented with electrical repellents in the 1950s, but found them only partially effective, Kalmijn said. Eventually, hungry, determined sharks penetrated the fields to reach bait.

But Kalmijn, who has not seen the POD, said he would not rule out the possibility that improvements in technology have made the POD more effective.

Morris contends the POD is better, partially because of refinements in the pulse of its electrical field. In one test off the South African coast, the device repelled a great white away from the species’ favorite food, seal meat, 48 consecutive times, he said.

“We’re not recommending jumping in the middle of a feeding frenzy with this device,” he said. “It’s designed to be turned on and run continuously from the beginning of the dive.”

Morris, however, said he was planning his own tests in California in which he hoped to lure great whites and tigers into determined, full-speed attacks into the POD’s electrical field.

It was in such a mode that a great white attacked Marko Flagg during a dive off Point Lobos, near Carmel, on June 30, 1995.

“I looked down and to the left, and I just saw this huge circle of teeth coming at me from out of the murk,” he said.

Flagg was lucky. The worst of the shark’s bite was blocked by an underwater navigational computer strapped to his chest and the air tank on his back.

In December, he went back into the water off Santa Catalina Island to try out the POD on the less-aggressive blue shark. In nine of 10 approaches, sharks clearly were turned away.