These tools drive sharks away from fishing hooks by creating an electric field.
A novel device uses the sixth sense of sharks to direct fish away from lethal hooks.
Thanks to bulbous organs called ampullae of Lorenzini that are clustered close to their heads, sharks, rays, and their cousins are able to detect very small electric fields. In order to combat this, scientists created SharkGuard, a cylindrical device that attaches to fishing lines just above the hook and creates a pulsing, short-range electric field. The scientists disclose their findings in Current Biology on November 21. They speculate that the device successfully deters sharks and rays by momentarily overwhelming their sensory system.
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According to David Shiffman, a marine biologist and faculty research associate at Arizona State University in Tempe, bycatch is a significant issue for sharks and rays, as the animals are unintentionally caught by fishermen who are pursuing other fish, such as tuna.
It was unclear whether the electric fields produced by SharkGuard devices would repel or attract sharks and rays. When hunting, the animals use their extra sense to find the tiny electrical fields that their prey emit. So, in the summer of 2021, two fishing vessels were sent out and instructed to fish for tuna by marine biologist Rob Enever of Fishtek Marine, a conservation engineering firm in Dartington, England, and his colleagues. Both fishing vessels were equipped with some standard hooks and some hooks that had SharkGuard.
In other words, the SharkGuard devices were completely ignored by the sharks. Blue sharks can be seen on video approaching a hook protected by SharkGuard and swerving away seemingly unharmed. Sharks took the bait when they came across an unadorned hook, becoming bycatch.
When compared to conventional hooks, hooks containing the electric repellant significantly lowered the catch rates of blue sharks (Prionace glauca), which fell from an average of 6.1 blue sharks per 1,000 hooks to 0.5 sharks. Additionally, only two pelagic stingrays (Pteroplatytrygon violacea) were taken per 1,000 SharkGuard hooks, down from an average of seven per 1,000 hooks previously.
About 10,000 hooks are on a typical fishing boat like the ones used in the study. So a boat with SharkGuard on every hook would reduce its catch of pelagic rays from 70 to 20, and the number of blue sharks would drop from 61 to 5.
You will see a “huge comeback” of these pelagic shark populations when you scale those figures up to the millions of sharks and rays that are unintentionally taken in longline fisheries each year, according to Enever.
According to Shiffman, who was not engaged in the study, “it’s obviously a notable and significant effect.” “It would undoubtedly be excellent news for [them] if [the gadgets] were implemented across the fishing fleet that interacts with blue sharks.”
However, this does not imply that SharkGuard is prepared to be released. Overall tuna catch rates in this investigation were unusually low, making it impossible to say yet whether tuna are similarly troubled by the device. If they are, using the tool in its present configuration wouldn’t make sense for fishers.
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The team is also striving to reduce the size, cost, and complexity of SharkGuard so that fisherman may “fit and forget” it. For instance, the existing battery, which must be replaced every few weeks, will be changed for one that can be induction charged while the fishing line is not in use, “essentially like a toothbrush,” according to Enever.
SharkGuard should be evaluated in various settings and with various shark species, according to Shiffman. According to him, numerous shark species are trapped accidentally on these longlines.
Even if this idea appears to be working so far, there is no technology that can completely solve the problem of shark conservation. According to Shiffman, “fixing this bycatch problem will involve a number of diverse solutions operating in concert.”
There is a pressing demand for remedies. Many of our pelagic species are currently either severely endangered, endangered, or fragile, according to Enever. However, he claims that the recent discoveries represent “a real story of ocean hope.” They demonstrate that “there are people out there… striving to fix these problems. Future prospects are positive.