The new devices use an electric field to scare away sharks from fishing hooks

A new gadget takes advantage of sharks’ sixth sense to send fish away from deadly hooks.

Sharks, rays and their relatives can detect small electric fields, thanks to bulbous organs concentrated near their heads called ampullae of Lorenzini. So the researchers developed SharkGuard, a cylindrical device attached to fishing lines just above the hook and emitting a short-range, pulsating electric field. The The device succeeded in deterring sharks and rays, possibly by temporarily flooding their sensory system, scientists report Nov. 21. Current Biology.

While many people are afraid of sharks, the fear makes more sense the other way around. Many types of sharks at risk of extinctionlargely due to human activities (SN: 11/10/22).

One of the main problems facing sharks and rays is bycatch, in which the creatures are accidentally snagged by fishermen targeting other fish like tuna, says David Shiffman, a marine biologist and research faculty at Arizona State University in Tempe.

Whether sharks and rays would be repelled or attracted by the electric fields generated by SharkGuard’s devices was an open question. Animals use their extra sense when hunting to detect small electric fields emitted by prey. So marine biologist Rob Enever of Fishtek Marine, a conservation engineering company in Dartington, England, and his colleagues sent out two fishing trawlers in the summer of 2021—both with some regular hooks and some with SharkGuard—and had them catch tuna. .

In short, the sharks wanted nothing to do with SharkGuard’s tools. The video reveals blue sharks approaching a hook using SharkGuard and swerving away with no apparent damage. Upon encountering an unadorned hook, the sharks took the bait, becoming a bycatch.

Sharks and their relatives can detect electric fields using organs in the skin called ampullae of Lorenzini. So the researchers tested whether attaching a SharkGuard device, which emits an electrical pulse every two seconds, to a fishing line just above the hook, could deter the shark. The results, which show a shark taking bait on a regular hook but other sharks veering off the device’s hooks, could hold promise for preventing millions of sharks from becoming bycatch.

Hook with electric repellent reduces blue shark catch rates (Brionas Gluca) decreased by 91 percent compared to standard hooks, dropping the rate from 6.1 blue sharks caught per 1,000 hooks to 0.5 blue sharks caught per 1,000 hooks. and 71% less than surface stingrays (Pteroplatytrygon violacea) using SharkGuard hooks, going from an average of seven rays caught per 1,000 hooks to two rays.

A typical fishing boat like the one used in the study contains approximately 10,000 hooks. So a boat whose full set of hooks are equipped with SharkGuard will go from catching about 61 blue sharks to 5 fish, and 70 surface rays to 20 rays.

When you extend those numbers up to the millions of sharks and rays that are accidentally caught in longline fisheries each year, Enver says, “you get a massive rebound of these pelagic shark populations.”

“It’s definitely a noticeable and important effect,” says Schiffman, who was not involved in the study. “if [the devices] Came into effect via the fishing fleet interacting with blue sharks it is sure to be good news for [them]. “

But that doesn’t mean SharkGuard is up and running. Tuna catch rates were unreasonably low across the board in this study, making it impossible to determine if the device was also bothering tuna. If that was the case, it wouldn’t make sense for hunters to use the device in its current form.

The team is also working to make SharkGuard as smaller, cheaper, and easier to manage as possible, so anglers can “fit it and forget it.” For example, the existing battery, which must be changed every two weeks, will be swapped for one that can be inductively charged while not using fishing line, “like a toothbrush, basically,” says Enever.

Shiffman would like to see SharkGuard tested in different environments and other shark species. “There are a lot of shark species that are caught as bycatch on these long lines,” he says.

And while this invention seems effective so far, no technology will be a silver bullet for shark conservation. “Fixing the bycatch problem is going to require a lot of different solutions working collectively,” Schiffman says.

The need for urgent solutions. “We are now in a situation where many of our marine species are either endangered, endangered or endangered,” Enver says. But the new findings are “a true story of ocean optimism,” he says. They showed that “there are people out there… trying to work these things out. There is hope for the future.”

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