(Bloomberg) -- Tuna sashimi may be tasty but every bite comes with a high body count: the millions of sharks killed each year when they’re inadvertently caught by industrial fishing vessels. Now a new technology has shown promising results in sharply reducing the slaughter of a top predator key to keeping ocean ecosystems healthy.

Called a SharkGuard, the cylindrical device is attached to a baited fishing hook and emits a three-dimensional electric field that can be sensed by sharks and rays. The electrical pulse overstimulates the animal’s electroreceptors that it uses to locate prey, and like fingernails on a chalkboard, repels the shark away from the hook.

In July and August 2021, two longline vessels fishing for bluefin tuna off the south coast of France tested SharkGuard on hundreds of baited hooks. During the trials, “bycatch” of blue sharks per 1,000 hooks fell 91.3% while the snaring of stingrays fell 71.3%, according to a peer-reviewed paper. The study was published last week in the journal Current Biology by scientists from the University of Exeter in the United Kingdom and Fishtek Marine, the UK company that developed SharkGuard.

An estimated 100 million sharks are killed annually by commercial fisheries, and shark populations have fallen 71% since 1970, according to scientists.

“I see this as being potentially a game-changer,” said Rachel Graham, a marine scientist and a member of the International Union for Conservation of Nature’s Shark Specialist Group, which determines the conservation status of shark species. “The use of these instruments will be very helpful for companies to be able to label their tuna or their other target species as being ‘shark safe,’ like they do with dolphin-safe tuna.”

Graham, the founder and executive director of ocean-focused nonprofit MarAlliance, was speaking from Panama, where she was attending a meeting of the Convention on International Trade in Endangered Species of Wild Fauna and Flora. The international treaty organization voted on Friday to regulate the global trade in 60 species of sharks, including blue sharks. That requires CITES’ 183 member nations and the European Union to not issue permits for export of protected sharks unless such trade is sustainable and does not threaten the species’ survival.  The move comes amid a growing demand for shark meat.Robert Enever, head of science at Fishtek and a co-author of the paper, said retail companies that have environmental, social and corporate governance reporting requirements might declare, “‘We're going to require that when we buy tuna, you don’t kill sharks,’” Enever said. “You have this technology that can reduce the millions of sharks destroyed every year.”

Sara Mirabilio, a fisheries specialist at North Carolina Sea Grant, tested a prototype of a similar device developed by Australian company Ocean Guardian during a 15-day trial in 2021. Catch of nine shark species fell more than 50%, she said.

“I absolutely believe we can harness this electro-sensory capability of sharks and use it as a deterrent,” said Mirabilio, who will be conducting further trials of the device over the next two years. “Somebody is going to come up with a retail-ready device soon. It’ll just be a matter of fishermen’s willingness to use it.”

The SharkGuard capsule contains a battery-powered capacitor that generates an electric field. The current iteration of the device has its limitations and it is not yet commercially available. The battery must be changed after 65 hours, which would not be feasible for vessels that deploy thousands of hooks on fishing lines that can stretch for miles.

A solution, though, is under development. Fishtek has obtained funding from Schmidt Marine Technology Partners to create an induction charging system that would be built into the bins that store longline hooks. When the hooks are reeled in, said Enever, they would dock in a charging cup and be fully powered for the next deployment.

“Technologies like SharkGuard can be transformational,” said Jake Hanft, program manager for Schmidt Marine Technology Partners, a San Francisco-based organization that issues grants for the development of ocean technologies and is part of the Schmidt Family Foundation established by Wendy and Eric Schmidt, the former Google chief executive officer.

“It's an elegant and productive way to keep sharks and rays off longlines without disrupting the fishing of target catch, reducing bycatch by incredibly impressive rates,” he said.

SharkGuard is one of several technologies under development to reduce incidental killing of sharks. In January, scientists published a study that found that attaching LED lights to huge fishing nets off the coast of Mexico slashed by bycatch of sharks and rays 95%.

Fishtek estimates a SharkGuard induction charging system for 2,000 hooks would cost about $20,000 and last three to five years. To persuade commercial fleets to adopt SharkGuard, though, Fishtek will have to demonstrate the technology doesn’t reduce catch of tuna and other seafood.

Catch of bluefin tuna during the trials in France was unseasonably low but it could not be determined if SharkGuard was a factor, according to the paper. Enever noted that a Fishtek device of a similar size has been deployed by longline fisheries on hundreds of thousands of hooks to deter killing of seabirds without an impact on catch.

Graham said devices like SharkGuard are mostly likely to be deployed on longline vessels regulated by regional fisheries management organizations. “If they want to be sustainable, absolutely SharkGuard can help them,” she said.

“But we are seeing a really big surge in demand for shark meat across multiple countries around the globe,” she added. “So if people are just increasing fishing effort across the board, they may not want to reduce their catch of sharks. And I think that's going to be one of the key challenges to adopting this type of technology.”

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