Electric pulses drastically cut number of sharks caught by accident

The first trial of the ‘SharkGuard’ know-how diminished the bycatch of blue sharks and pelagic rays by as a lot as 91 per cent, however did not affect the tuna that fishers have been focusing on

By Corryn Wetzel

Grey reef sharks (Carcharhinus amblyrhynchos) in Bora BoraAn electrical pulse-emitting, pinkie-finger-sized system connected to fishing hooks seems to dramatically cut back the unintentional catch of sharks and rays in preliminary area exams. The know-how, known as “SharkGuard”, might allow fishers to reap goal species like tuna whereas limiting unintentional bycatch deaths of sharks around the globe.

Since 1970, the worldwide abundance of sharks and rays has declined by 71 per cent. A significant explanation for this has been unintentional snags on longline fishing hooks, which encompass a horizontal important line with lots of or hundreds of hooks trailing beneath.

The SharkGuard system hitches a experience on this similar fishing gear and is affixed a number of centimetres above a hook. The system – concerning the dimension and form of a AA battery – works by emitting a pulsing electrical cost that creates an electromagnetic area across the SharkGuard’s place.

Sharks and rays have electrosensory organs of their pores and skin that detect refined adjustments in underwater electrical fields. So, the goal of the pulsing system is to “overwhelm the senses” says Phil Doherty on the University of Exeter within the UK. Like a human standing too near a speaker blasting music, “it’s overstimulating”, he says.

To check the know-how, Doherty and his colleagues deployed SharkGuard on two fishing vessels off the shoreline of southern France over 11 completely different journeys in the summertime of 2021. Each vessel was outfitted with 22 longlines with greater than 9000 hooks. On each ships, half of the hooks have been secured with a SharkGuard system in an alternating sample to see if there was a distinction in shark bycatch between pulsing and non-pulsing hooks. SharkGuard diminished the bycatch of blue sharks (Prionace glauca) and pelagic stingrays (Pteroplatytrygon violacea) by 91 and 71 per cent, respectively. Bluefin tuna (Thunnus thynnus), which lack electrosensory organs, appeared unbothered.

Doherty was impressed by how nicely the system carried out within the area.

“I was quite shocked, especially at the blue shark… I mean, that’s huge.”

Though SharkGuard reveals preliminary promise, the outcomes ought to be taken with warning, says Nicholas Dulvy at Simon Fraser University in Canada who was not concerned within the work. The system might have various effectiveness between completely different shark or ray species, as every has a singular configuration of electrosensory organs.

“It would be really interesting to see how this works in, say, hammerhead and silky sharks,” says Dulvy.

Outfitting a longline fishing vessel with SharkGuard prices about $20,000 and the gadgets have a battery lifetime of 65 hours, one thing developer Fishtek Marine is presently working to increase. Still, the upfront price and energy may very well be offset by permitting fishers to haul in additional of the goal species.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2022.09.003