An Electric Pulse Could Scare Sharks Away From Fishing Hooks

Electric pulse-emitting devices attached to baited hooks may scare sharks and rays away from fishing lines, new research suggests. This could dramatically decrease the number of sharks accidentally caught and killed by fishers who are targeting other species such as tuna.

“Many shark and ray populations are declining due to overfishing—particularly oceanic species such as blue sharks and pelagic stingrays that are commonly caught on longlines globally,” Phil Doherty, a marine conservation scientist at the University of Exeter in the United Kingdom, says in a statement. “There is an urgent need to reduce bycatch, which not only kills millions of sharks and rays each year but also costs fishers time and money.”

An estimated 100 million sharks and rays are caught by fishers every year, resulting in more than a quarter of these species being threatened, per the World Wildlife Fund.

The device—called SharkGuard—takes advantage of sharks’ “sixth sense,” or their ability to detect electromagnetic fields using specialized organs around their nose and mouth called ampullae of Lorenzini. The technology was designed by engineering company Fishtek Marine. 

To test SharkGuard, Fishtek Marine partnered with researchers from the University of Exeter to send out two fishing vessels on 11 combined trips in July and August 2021. Each vessel was outfitted with standard fishing gear and deployed a total of 18,866 hooks baited with sardines. The team fitted half of the fishing hooks with SharkGuard, and the other half went without, serving as controls. 

Using the device decreased bycatch of blue sharks from around 6.1 sharks caught per 1,000 hooks to 0.5 caught, a 91 percent reduction. Pelagic stingray catches dropped from about 7 rays per 1,000 hooks to just 2, representing a 71 percent reduction. The team published their results in November in the journal Current Biology.

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“It’s definitely a notable and significant effect,” David Shiffman, a marine biologist and researcher at Arizona State University who was not involved in the study, tells Science News’ Darren Incorvaia. “If [the devices] went into effect across the fishing fleet that interacts with blue sharks, it would certainly be good news.” 

But while SharkGuard devices seemed to reduce bycatch of unwanted species, researchers aren’t sure yet if they also deter the target species, bluefin tuna. The devices appeared to reduce tuna catch by about 42 percent—but this number was not statistically significant, which “is encouraging,” the team writes in the paper. “Factors such as soak time or local tuna abundance are likely having a greater impact.” Tuna catch for both types of hooks was unusually low.

Future studies might provide insight into why the SharkGuard hooks caught fewer tuna. “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,” co-author Pete Kibel, co-founder and director of Fishtek Marine, tells the Guardian’s Anna Turns. The team is now working on a lighter version of their device, and Kibel hopes SharkGuard will be commercially available by 2024, per the publication. 

While the need for solutions to bycatch is urgent, the study is “a real story of ocean optimism,” Rob Enever of Fishtek Marine tells Science News. “There’s people out there… trying to resolve these things. There’s hope for the future.”

Margaret Osborne | | READ MORE

Margaret Osborne is a freelance journalist based in the southwestern U.S. Her work has appeared in the Sag Harbor Express and has aired on WSHU Public Radio.