100 million sharks, skates and rays are accidentally caught every year by the world’s commercial fisheries, threatening several pelagic species with extinction.
Currently, one quarter of Chondrichthyans (shark, ray and chimaeras species) are classified as threatened by the Red List criteria of the International Union for the Conservation of Nature.
The main threat they face is overexploitation through capture fisheries (Worm, et al., 2013, Dulvy, et al., 2014). In some cases they are target species, but more often they are a by-product (incidentally caught but retained) or bycatch (incidentally caught but unwanted and discarded) (Clarke, et al., 2007, Patterson, et al., 2014). It has been estimated that approximately 50% of the global elasmobranch catches consists of individuals incidentally captured, mostly in pelagic longline fisheries (Oliver, et al., 2015). Blue shark (Prionace glauca) is the most encountered bycatch species in pelagic longline fisheries mainly around sub-tropical and temperate regions (Bonanomi, et al., 2017).
Significant gains have been made globally in recent years with the designation of protected marine areas, including 29% of the total area of protected oceans having been designated for shark conservation. However, it is becoming apparent that these protections are neither appropriately enforced, nor appropriately located to prevent elasmobranch extinctions (Dulvy, et al., 2017, Bradley, et al., 2018), and with limited spatial refuge from industrial longline fishing effort that is currently centred on ecologically important oceanic shark hotspots (Queiroz, et al., 2019). To date, a lack of such solutions has hampered efforts to improve the conservation status of the world’s elasmobranchs (Poisson, et al., 2016). Technical solutions that can be implemented onboard longline vessels within and out-with protected areas are urgently required.
SharkGuard the story so far...
SharkGuard MKII in action...
Shark bycatch mitigation challenge
The Ampullae of Lorenzini in sharks has long been known to be able to detect weak voltage currents in the range typically produced by prey species (Kalmij, 1982). A voltage as low as 5 nV/ cm, or 5/1,000,000,000 of a volt measured in a centimetre-long ampullae can be detected by sharks (Smith, 1991) and it has been demonstrated that sharks will respond to an electric field intensity of 1 V/m and will swim rapidly away from a field strength of 10 V/m (Marcotte and Lowe, 2008). While electropositive metals and magnets have been demonstrated in controlled studies to stimulate a response in some shark species, there are a range of inter-specific differences and con-specific challenges which limit the effectiveness of these as deterrents (e.g. Robbins, et al., 2011, O’Connell, et al., 2011). These inconclusive findings are likely to be due to the fact that the voltages generated by magnets and electropositive metals are many thousands of times weaker than the minimum voltage strength required to elicit a strong response. In 2015, Fishtek Marine developed an early prototype device that emits an electrical pulse around longline hooks that is powerful enough to be effective at deterring sharks from taking baited hooks.
SharkGuard Prototype I
Following successful tank trials in 2015 to test the response of Ground shark (Scyliorhinus canicula) to a prototype SharkGuard we undertook six trips on-board commercially operated sports fishing vessels in three locations in the UK and Australia.
A total of 16 elasmobranchs were caught during the trials, 15 on control lines (inc. 13 Blue shark Prionace glauca) and one on the shark guard treatment (Sevengill shark, (Notorynchus cepedianus). These promising results provided the basis for further development.
SharkGuard Prototype II
Following successful trials of prototype I, Fishtek Marine worked with French industry partners to secure funding from the EU (Eurostars) to develop and test a more advanced prototype device in an Atlantic bluefin tuna (Thunnus thynnus) fishery in the Mediterranean. Prototype II was driven by 2 x AA alkaline batteries and emitted an electrical pulse with programmable characteristics enabling the pulse train, duty cycle and electric field strength to be varied. A paired vessel trial was undertaken to compare elasmobranch bycatch rates on a SharkGuard treatment versus a control treatment (standard gear) in the Autumn of 2019.
The number of pelagic stingrays (Pteroplatytrygon violacea) caught per 1000 hooks was reduced by 66% between control and active SharkGuard hooks. Although the catch rate of sharks was low throughout the trials, no blue shark was caught on a SharkGuard hook through the trials. The catch rate of bluefin tuna for SharkGuard hooks was also reduced, however this is likely due to the weight of the SharkGuard units altering the fishing depth of the baited hooks. Originally the SharkGuard was designed to reduce the globally unsustainable catch rates of blue sharks (and other high risk species e.g. Silky shark (Carcharhinus falciformis) and Shortfin mako shark (Isurus oxyrinchus).