While the menacing fin of a shark has figured in many human nightmares, people may be the stuff of shark nightmares. In addition to intentionally hunting sharks for food, fishermen often catch them inadvertently. A new plan hopes to reduce this bycatch by repelling sharks with electric fields.
Sharks have an innate ability to detect electric fields, useful for sensing the bioelectric activity of their prey. Researchers discovered that strong electric fields could repel these predators, most likely by overwhelming their electricity sensors.
"It's a sense we don’t have," said Richard Brill, a biologist at the National Oceanographic and Atmospheric Association (NOAA)'s Northeast Fisheries Science Center and head of the Cooperative Marine Education and Research Program at the Virginia Institute of Marine Science. "The closest [analogy] I can come up with is if you get exposed to a bright light, you squint and look away."
A recent test showed that small disks of a rare metal alloy called palladium neodymium interact with the salt in seawater to produce electric fields strong enough to ward off sharks. These disks could be attached to fishing lines to deter sharks from fishers aiming for other animals, thereby reducing bycatch of endangered shark species.
"We were just slack-jawed when we saw how well it worked," Brill told LiveScience. "I was stunned, I thought this was the stupidest idea I'd ever heard. I saw the evidence and thought, 'This can't be right.'"
To test the idea, the scientists placed the small metal disks in a tank with captive juvenile sandbar sharks. They were surprised to find that the metal had such a strong effect: The sharks generally wouldn't swim within 24 inches (61 centimeters) of the disks, or bite at bait hung within 12 inches of the disks.
Brill and his colleagues presented the results of the study earlier this month at a NOAA-sponsored shark deterrent workshop in Boston.
Most fish cannot detect electric fields, so the metal disks could be perfect for deterring sharks without affecting the animals fishers hope to catch.
"That's the beauty of this method — it's sort of a secure communications channel," Brill said.
Before now, divers have used electric field-emitting devices to ward off sharks while they swim, but that posed problems.
"The idea of using it to deter sharks from fishing gear was never practical because they were so big," Brill said. The new metal disks are small enough, and hopefully can be produced cheaply enough, to be feasible as a fishing aid. Not only would this help unsuspecting sharks from being accidentally caught, but it would save fishers the trouble of having sharks damage fishing gear and eat bait that was meant for fish such as tuna or swordfish.
"It would be better for everybody concerned if we just didn't interact with them," Brill said.
About 11 million to 13 million sharks worldwide are caught as bycatch every year, sometimes more than the targeted fish species, according to NOAA. In addition, sharks are hunted for food, especially for their fins, considered a delicacy in some Asian diets. Hunters sometimes simply cut off a shark's fin and leave the animal to die in the ocean (a finless shark can no longer swim or feed).
The researchers plan to test the new devices in the open ocean this summer. The study was funded by the Pacific Islands Fisheries Science Center of NOAA’s National Marine Fisheries Service in Honolulu.
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