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Sci & Tech

Electrical pulses drastically reduce variety of sharks caught by chance

The primary trial of the ‘SharkGuard’ know-how decreased 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 concentrating on


21 November 2022

Gray reef sharks (Carcharhinus amblyrhynchos) in Bora BoraAn electrical pulse-emitting, pinkie-finger-sized machine connected to fishing hooks seems to dramatically scale back the unintended catch of sharks and rays in preliminary discipline assessments. The know-how, known as “SharkGuard”, might allow fishers to reap goal species like tuna whereas limiting unintentional bycatch deaths of sharks world wide.

Since 1970, the worldwide abundance of sharks and rays has declined by 71 per cent. A significant reason for this has been unintended snags on longline fishing hooks, which include a horizontal major line with lots of or 1000’s of hooks trailing under.

The SharkGuard machine hitches a experience on this identical fishing gear and is affixed a number of centimetres above a hook. The machine – concerning the dimension and form of a AA battery – works by emitting a pulsing electrical cost that creates an electromagnetic discipline 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 intention of the pulsing machine is to “overwhelm the senses” says Phil Doherty on the College of Exeter within the UK. Like a human standing too near a speaker blasting music, “it’s overstimulating”, he says.

A cylindrical device roughly the size of a pinky against a white background. The device has two bronze-colored caps on the end, and through the transparent housing, internal electronics are visible.

The SharkGuard machine is small, however it’s a huge deterrent towards sharks and rays that danger turning into bycatch

Rob Enever

To check the know-how, Doherty and his colleagues deployed SharkGuard on two fishing vessels off the shoreline of southern France over 11 totally different journeys in the summertime of 2021. Every vessel was outfitted with 22 longlines with greater than 9000 hooks. On each ships, half of the hooks have been secured with a SharkGuard machine in an alternating sample to see if there was a distinction in shark bycatch between pulsing and non-pulsing hooks. SharkGuard decreased 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 machine carried out within the discipline.

“I used to be fairly shocked, particularly on the blue shark… I imply, that’s enormous.”

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

“It might be actually fascinating 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 units have a battery lifetime of 65 hours, one thing developer Fishtek Marine is at the moment working to increase. Nonetheless, the upfront value and energy could possibly be offset by permitting fishers to haul in additional of the goal species.

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

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