Sharks face a global crisis with over a third of shark species now threatened with extinction (Dulvy et al., 2021)
Sharks form commercial catch globally, but more usually caught unintentionally and then discarded (Clarke, et al., 2007; Patterson, et al., 2014). Pelagic longlining for high-value tuna and bill fish, mainly in sub-tropical and temperate regions, is known to have particularly high bycatch rates – with blue shark (Prionace glauca) being the most commonly encountered species, Hammerheads, Oceanic White Tips, Makos and Threshers are among the pelagic sharks often caught on longlines. Kettemer, et al. (2012) estimates that 20,145,808 pelagic sharks are killed annually through bycatch. Practical and low-cost mitigation solutions that can be implemented on board longline vessels have been lacking, seriously hampering efforts to conserve the world’s sharks (Poisson, et al., 2016).
We have shown that when a longline fishing vessel is fitted out with SharkGuard units the incidence of elasmobranch bycatch is dramatically reduced with minimal impact on the capture of target fish. With funding from the EU (Eurostars) and the British Government (Innovate-UK), SharkGuard has undergone rigorous testing at sea in UK, Australia, and French waters since we developed the first prototype in 2015.
The most recent trials, in July and August 2021, working in a commercial bluefin tuna (Thunnus thynnus) fishery off the Mediterranean coast of France, showed that fitting hooks with SharkGuard reduced average catch rates of blue shark by an incredible 91%, and catch rates of pelagic stingray (Pteroplatytrygon violacea) by 71%. Catch rates of bluefin tuna (target catch) were not significantly influenced by the presence of SharkGuard on the hook.
These exciting results indicate that should SharkGuard’s use be scaled to fishery level and beyond, it could slow and even reverse the decline in shark populations by dramatically and rapidly reducing bycatch in the global pelagic longline fleet.
Shark bycatch mitigation challenge
Until now, an intractable issue has been that many sharks behave in a comparable way to the target tuna and bill fish species: they feed on similar prey and generally occupy the same marine zones. Crucially, however, sharks and other elasmobranchs differ in having acute sensitivity to electrical fields in water, due to their possession of Ampullae of Lorenzini. Sharks use this network of electroreceptors concentrated around the snout to detect very weak voltages produced by prey species (Kalmijn, 1982), but will actively avoid much higher voltages (Marcotte & Lowe, 2008). These insights have been key to developing, prototyping, and successfully testing SharkGuard. SharkGuards are small devices, easily attached close to baited longline fishing hooks, which create powerful, short-range, 3-D electric pulses on contact with seawater. The electric field is enough to deter sharks and other elasmobranchs from approaching or interacting with the hook, while not affecting target species, such as tuna and bill fish, which lack electro detecting Ampullae of Lorenzini.
SharkGuard can be mass-produced, offering an operationally affordable device. As with all our products, SharkGuard has been designed and tested in close partnership with the end users, ensuring low-cost and minimal inconvenience. The device has already been well received by commercial fishers partaking in our sea trials, who could conduct normal operations without being hindered by the presence of SharkGuard units on their standard fishing gear.
We believe SharkGuard is the only viable shark bycatch mitigation method, other than severe restrictions on longline fishing. Based on results from the commercial trials of the SharkGuard in France and average shark bycatch rates per vessel globally, every pelagic longline vessel fitted with the SharkGuard system would reduce shark bycatch by 2,947 individuals.
SharkGuard represents the only effective and practical method of significantly reducing shark bycatch while still allowing the global pelagic longline fleets to operate.
SharkGuard in action...