A new gadget captures the fish’s sixth sense to send fish running away from deadly hooks.
Sharks, rays and their relatives can detect small electric fields through bulbous organs called ampullae of Lorenzini. So the researchers developed the SharkGuard, a cylindrical device that attaches to fishing lines just above the hook and emits a short, pulsed electric field. Thought to be successful in warding off the sun and rays, probably overwhelming his sensitive period, scientists report on November 21st. Current Biology.
While many are afraid of sharks, the opposite is the fear of the sea; Many shark species are in danger of extinction, mainly due to human activities (SN: 11/10/22).
One major problem with sharks and rays is bycatch, where the creatures are caught by fishermen other than by accident, such as tuna, says David Shiffman, a marine biologist and faculty research associate at Arizona State University in Tempe.
Whether sharks and rays were repelled or attracted by the electric fields generated by the SharkGuard devices was an open question. Animals use their extra senses when hunting to detect prey gifted with small electrical fields. So marine biologist Rob Enever of Fishtek Marine, a conservation engineering company in Dartington, England, and colleagues launched two fishing vessels in the summer of 2021 — both equipped with normal hooks and some hooks with SharkGuard — and had them fish for fish. .
In short, SharkGuard wanted nothing to do with shark gadgets. The video opens with a blue shark hooking up with SharkGuard and the reverse with no visible damage. With an unset hook, the shark took the bait, becoming a bycatch.
Hooks with electric bait reduced catch rates of blue sharks (Prionace glauca) from 91 percent with standard hooks, from an average of 6.1 blue sharks dropped per 1,000 hooks to 0.5 sharks. And 71 percent fewer pelagic stingrays (Pteroplatytrygon violaceum) using SharkGuard hooks, out of seven rays caught per 1000 hooks averaged two rays.
A typical fishing boat like this used in the study has about 10,000 hooks. So the boat, whose entire line of hooks was equipped with SharkGuard, went on to catch about 61 blue scales at 5, and 70 pelagic rays at 20.
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When you get those numbers up to the millions of sharks and rays that are accidentally caught in long-haul fisheries every year, he says, “you’re going to have a great recovery of these pelagic shark populations.”
“It’s definitely a significant and significant effect,” says Shiffman, who was not involved in the study. “Yes [the devices] he has implemented a fishing fleet that interacts with blue sharks, which is certainly good news [them].
But that doesn’t mean that SharkGuard is ready to be rolled out. Tuna catch rates were inappropriately low across the board in this study, making it impossible to determine yet whether tuna were also affected by the artifact. If they are, it is not appropriate for fishermen to use the current form of the technique.
The team is also working to make SharkGuard smaller, cheaper and as easy to administer as possible, so fishermen can “fit it and forget it”. For example, the current battery, which needs to be changed every two weeks, will be wrapped for something that can be done while the fishing line is not in use, “like a toothbrush, basically,” En Ever says.
Shiffman would like to see SharkGuard tested in different environments and on other types of sharks. “There are many species of sharks that are caught in these remote areas,” he said.
And while this discovery appears to be effective so far, no technical technique will be a silver bullet for stream conservation. “Fixing this Bycatch problem will require a lot of different solutions working in concert,” Shiffman says.
Urgent need for solutions. “We’re in a situation right now where many of our pelagic species are either critically endangered, endangered or vulnerable,” En ever says. But the new discoveries are “the true story of the best pelagics,” he says. They show that there are people out there… trying to sort these things out. There is hope for the future.”
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