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How to be rejected as a titbit for a shark
SCUBA DIVING
WATER babies on South Africa's east coast can stop living in fear of a grey fin appearing above the surface of the water - the Natal Sharks Board has developed the first . truly effective shark repellent The board recently patented the SharkPOD, which is winning acclaim around the world. The POD, or Protective Oceanic Device, works by emitting electrical impulses that sharks find repulsive, causing them to flee in alarm.
"Where dolphins use sonar to track their prey, sharks rely on exceptionally sensitive electrical stimuli," says Theo Meyer, Marketing Manager for POD Holdings which has a licence to manufacture and distribute the device.
When fish or swimmers are active in water, their muscles emit bio-electrical impulses that are captured via pores on a shark's snout. These electrical impulses are "interpreted" in gel-filled organs, called the ampullae of Lorenzini, which prompt the shark to attack if distress is detected.
The POD's electrical field repels sharks approaching from any direction at a range of four to seven metres. In tests conducted by the board, a great white shark was repelled from its favourite main course, seal meat, 48 consecutive times. The tests were repeated successfully with other aggressive species of shark.
Tests on electrical shark repellents were first conducted in the1950s by the US Navy, but with little success. Meyer says: "The sharks board made its discovery by accident in 1974 when tests were being conducted on the suitability of shark meat for human consumption."
Research was resumed in the late 80s and a painstaking trial and error process produced a working model in 1989. "By a process of elimination, we identified the wave frequency and amplitude of electrical impulses that sharks find intolerable."
Jim Morris, a US marketing agent and professional diver, notes that the POD, which can be strapped to the swimmer, should be turned on at all times. "People who have been attacked by sharks report being unaware of their approach until it is too late. You can't assume that you will see the shark, realise it is attacking and then activate the repellent. The device must be on from the beginning to the end of a dive."
The POD's manufacturers are now working on wide area barriers that will eliminate the need for environmentally insensitive shark nets. This should open up new beaches for safe bathing all along the coast. Future applications could include pocket-sized units for swimmers.
Morris notes that the POD not only makes it safer for those braving the deeps, but also for the sharks themselves. "The Jaws phenomenon has prompted an unnecessary slaughter of sharks. The POD will prevent humans and sharks from harming each other."
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