For sharks that live in the open ocean, longline fishing is the number one threat, with an estimated 20 million pelagic sharks taken annually by fishermen in search of tuna and other desirable species. Now, a new study reports in Current Biology November 21 shows that new technology, known as “SharkGuard,” can allow longline fishing to continue while reversing the dramatic decline in endangered sharks worldwide.
“The underlying implication is that commercial longline fishing may continue, but it will not always necessarily result in mass bycatch of sharks and rays,” said Robert Enver of Fishtech Marine, Dartington, Devon, UK. “This is important in balancing the needs of fishers with those of the environment and contributes to national and international biodiversity commitments for long-term sustainability.”
Enever and his colleagues saw the huge need to slow or even reverse the decline in global shark populations based on evidence that more than 100 million sharks, skates and rays are caught each year by the world’s commercial fisheries. A quarter of all sharks and rays are also classified as threatened. They believed that shark deterrents that showed promise for protecting divers and surfers from sharks would also be used in tuna fisheries to protect sharks from bycatch.
How it works? SharkGuard emits a small, localized, pulsating electric field. When attached to a fishing line, it creates an electric field around a baited hook. The aim is to discourage sharks and rays, which detect electrical signals via their electroreceptors, from biting without hindering the hunting of other fish.
To see how well it works, the researchers conducted sea trials in July and August 2021 in the south of France. Two trawlers fished 22 longlines on 11 separate voyages, posting a total of more than 18,000 hooks. Their results showed that SharkGuard hooks significantly reduced the number of blue sharks and stingrays caught compared to standard control hooks. The catch rate for these species per unit effort decreased by 91% and 71% for sharks and rays, respectively. Bluefin tuna catch rates were not significantly affected by the presence of SharkGuard on the hook.
“Sharks don’t take the bait and they don’t get stuck on the hooks,” Enever said.
Researchers note that compared to catching and releasing species that are caught and released, including sharks, SharkGuard offers a more comprehensive solution. If its use was scaled up to the level of the entire fishery, it would mean a significant reduction in the interaction between sharks and fishing gear.
For now, however, the device has limitations, including the need for frequent battery changes. They are now working to overcome this barrier, so that fishermen can “fit it in and forget it,” while still protecting sharks and other bycatch species. A full set of inductively charged SharkGuard rigs for 2,000 hooks are expected to cost around $20,000 and last 3-5 years (about $4-7k per year), which they note is a modest annual cost for most commercial tuna fishing operations.
They are now encouraging fishermen experiencing high bycatch rates of sharks and rays, as well as retail businesses intending to improve the sustainability of their supply chain, to seek contact with Fishtek Marine early on as marine trials and engineering developments are planned for marketing.
“there is hope!” Enver said. “With the ongoing backdrop of stories of dramatic declines occurring across all species, it’s important to remember that there are people out there working hard to find solutions. SharkGuard is an example of where, given the right support, a solution can be rolled out on a scale sufficient to reverse the current decline in numbers World Sharks.
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