Sharks Repelled by Metal That Creates Electric Field

Helen Scales
for National Geographic News
May 1, 2008

A metal mix that reacts with seawater to produce an electric field could help curb the global death toll of sharks caught inadvertently on longline fishing gear.

An alloy of the rare earth metals palladium and neodymium caused captive sandbar sharks to avoid hooked bait, according to a recent study released by the National Oceanic and Atmospheric Administration (NOAA).

"We could see them shudder and then dash away," said study co-author Rich Brill, a NOAA fisheries biologist.

The team hopes that suspending ingots of the metal on fishing gear will help deter wild sharks from longlines meant to catch commercial species such as tuna and swordfish.

The lines snag an estimated 11 to 13 million unwanted sharks each year, contributing to worldwide shark declines. (Related news: "8 Million Sharks Killed Accidentally off Africa Yearly" [April 17, 2007].)

"Being slow growing and slow to reproduce, sharks usually cannot take a lot of fishing pressure," Brill said.

It's also possible that the metal could deter sharks from attacking human swimmers, but the researchers are cautious about this application, as the alloy only works at a distance of about 20 to 24 inches (50 to 60 centimeters).

"If you had a very large bull shark coming toward you, the metal may work," said study co-author Eric Stroud, a chemist from the research company Shark Defense.

"But would you really want to be that close to the shark?"

Mixed Metal

Sandbar sharks are among the largest coastal sharks in the world, reaching up to 8 feet (2.4 meters) long and weighing up to 200 pounds (90.7 kilograms).

Like other sharks, sandbars hunt by sensing the tiny electrical fields given off by their prey. (See photos of sharks on the prowl.)

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