These devices use an electric field to scare sharks from fishing hooks

These devices use an electric field to scare sharks from fishing hooks

These devices use an electric field to scare sharks from fishing hooks

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ISRDO Team 22 Nov, 2022 - in Fisheries
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  • fisheries
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The sharks' heightened sense of smell is used by a new device designed to scare them away from hooks.

Ampullae of Lorenzini are rounded organs located close to the skull that allow sharks, rays, and their relatives to sense very weak electric fields. Because of this, scientists created SharkGuard, a cylinder-shaped gadget that connects to fishing lines immediately above the hook and creates a pulsating, short-range electric field. Researchers present their findings in Current Biology on November 21. They found that the gadget effectively deters sharks and rays, likely by momentarily overloading their sensory system.

Many individuals are terrified of sharks, which is understandable given the plight of many shark species, which is threatened by human activity (SN: 11/10/22).

According to David Shiffman, a marine biologist and faculty research associate at Arizona State University in Tempe, bycatch, in which sharks and rays are mistakenly grabbed by fisherman seeking other species like tuna, is a big threat to sharks and rays.

It was unclear if the electric fields produced by SharkGuard devices would repel or attract sharks and rays. To locate their prey, the creatures rely on their enhanced awareness of electrical fields. Rob Enever, a marine scientist at Fishtek Marine, a conservation engineering firm in Dartington, England, and his colleagues loaded two fishing boats with both standard hooks and SharkGuard hooks in the summer of 2021 and sent them out to catch tuna.

Simply put, sharks avoided areas where SharkGuard devices were present. Blue sharks in the video approach a hook protected by SharkGuard and then turn away from it. Sharks were accidentally caught as bycatch when they fell for a simple hook.

When compared to conventional hooks, electric repellant hooks lowered blue shark (Prionace glauca) capture rates by 91%, from an average of 6.1 blue sharks caught per 1,000 hooks to 0.5 sharks. Pelagic stingrays (Pteroplatytrygon violacea) were 71% less likely to be caught when employing SharkGuard hooks, with an average of just 2 stingrays caught per 1,000 hooks.

About 10,000 hooks are carried on a fishing vessel like the ones used in the research. If all of a boat's hooks were equipped with SharkGuard, the number of blue sharks caught would drop from 61 to 5, and the number of pelagic rays caught would drop from 70 to 20.

Enever predicts "huge recovery of these pelagic shark populations" when these estimates are extrapolated to account for the millions of sharks and rays that are taken unintentionally each year in longline fisheries.

Shiffman, who was not involved in the research, said, "It's obviously a remarkable and substantial impact." Incorporating these gadgets into the whole of the fishing fleet that encounters blue sharks would be fantastic news for the sharks.

While this may be true, it does not indicate that SharkGuard is complete and ready for release. We cannot yet say if tuna are similarly disturbed by the device or not since capture rates were abnormally low across the board in this investigation. If they are, then it is pointless for fisherman to utilise the gadget as it is designed.

So that fisherman can simply "fit and forget" SharkGuard, the development team is also aiming to make it more compact, affordable, and simple to administer. For instance, Enever plans to replace the fishing line's weekly-replacing battery with one that can be induction charged "like a toothbrush, essentially" while the line is not in use.

Shiffman wants to see SharkGuard tried out on various species of sharks and in diverse habitats. Quite a few shark species are taken inadvertently by these longlines, he adds.

No technology, no matter how promising it may appear at the moment, will be a panacea for shark preservation. Shiffman argues that "a number of diverse remedies functioning in concert" are necessary to address the issue of bycatch.

This problem requires immediate attention. Many of our pelagic species are now considered "critically endangered," "endangered," or "vulnerable," as stated by Enever. This new information, though, is "a true narrative of ocean optimism," as he puts it. In doing so, they demonstrate that "there are individuals out there... working to address these difficulties. The future isn't completely bleak.

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