Marine scientists have designed a piece of technology that could drastically reduce shark bycatch by emitting short electrical pulses as a deterrent.
The small battery-powered device, known as SharkGuard, reduced the numbers of blue sharks accidentally caught by commercial fishing gear in a French longline tuna fishery in the Mediterranean by 91% and stingrays by 71%, according to a study in the peer-reviewed journal Current Biology.
Clipped on to the line next to a baited hook, SharkGuard emits a short pulse every two seconds. When that pulse temporarily overstimulates the electrical sensors around a shark’s nose and mouth – called the ampullae of Lorenzini – the shark swims away.
Dr Phil Doherty, lecturer in marine conservation science at the University of Exeter and lead author of the study, said that although SharkGuard is doing what it has been designed to do, further sea trials are required to assess its effectiveness in other fisheries.
“It’s reducing blue shark and pelagic [oceanic, not bottom dwelling] stingray catch on these hooks, so we can be quite confident for these species in this fishery,” he said. “But [SharkGuard] needs to be designed on a case-by-case basis to ensure it’s fit for purpose.”
Every year an estimated 100 million sharks, skates and rays are killed by fishing and bycatch. Since 1970, the global abundance of oceanic sharks and rays has declined by 71% due to fishing practices.
Longline fishing rigs can be more than 30 miles long, with hundreds of branch lines hanging down from one main floating surface line. The SharkGuard clips on to the branch lines next to each baited hook. Further research will establish the thresholds required to deter different sharks.
Pete Kibel, co-founder and director of FishTek, the marine engineering company that designed SharkGuard, hopes the device will be commercially available by 2024. “The clever bit is miniaturising the whole thing to create something that is operationally viable for fishermen,” he said. “I’m confident that we will get between 70% and 95% [reduction] across the critically endangered pelagic shark species that we’re trying to conserve.”
Kibel said the latest trial showed a nominal reduction in tuna catch, the target species. “We believe this is likely due to the weight of the SharkGuard units altering the fishing depth of the baited hooks, rather than the electrical pulse emitted,” he said. The company said it is designing a lighter, induction-charged version without batteries.
Bycatch mitigation tools are just one part of the solution for protecting sharks from fishing, according to Ali Hood, director of conservation at UK charity Shark Trust.
“Limiting or even prohibiting the catch of sharks and rays based on scientific advice is only the first step in seeing populations rebuild,” she said.