Despite it being incredibly unlikely that a person will be injured by a shark, there is still an enormous fear of shark attacks and pervading concern that ocean users are at risk from sharks when in the water. Therefore, there is advancing sector of the technology industry devoted to developing devices which can repel sharks away from people in the water. But how do these "electric shark deterrents" work? And are they effective?
Sharks Can Sense Electricity
Whilst possessing all of the 5 senses that human beings enjoy, sharks are also capable of detecting electrical currents and magnetism through sensory organs called the Ampullae of Lorenzini. Some sharks are capable of detecting as little as a flashlight battery from thousands of kilometers away!
This sense is so acute that it can be overloaded when in contact with relatively large charges. This is how it is possible for people to put sharks into a hypnotic state known as "tonic immobility" - physical contact with the shark on the snout, where the sensory organs are densely packed, overwhelms the system and puts the shark in a state of shock. To learn more, check out Fin & Tonic.
Electrical Devices Can Repel Sharks
Electric shark deterrents are electronic devices which can be worn as anklets or attached to surf boards. They produce a voltage gradient at a specific pulse frequency, which over-stimulates a shark's electrosensory system. This causes the shark to bolt away from the source and not return (Huveneers et al, 2013).
For example, when a device called No Shark (formerly Electronic Shark Defense System (ESDS)) (patented by Wilson Vinano) is active, it has been shown that the frequency of bites upon a bait is significantly reduced (Egebert et al, 2019).
Another device, called the Shark ShieldTM (from Ocean Guardian), has been shown to be effective in deterring great white sharks (Carcharodon carcharias) from close approaches. The device produces a steep voltage gradient (9.7–15.7 V/m) at a constant electric pulse rate of 1.67Hz (Smit & Peddemors, 2003; Huveneers et al, 2013; Kempster et al, 2016).
During testing, white sharks were attracted in close using food baits. When the Shark Shield device was active, the sharks did not approach closer than 82 cm of the food in 82.7% of interactions (Huveneers et al, 2013; Kempster et al, 2016). In another trial, the Shark ShieldTM was shown to reduce the risk of attack on a bait to only 0.8% (Smit & Peddemors, 2003).
Not All Devices are as Effective as Others
There are many different products currently on the market, but as they are still under development, some are more effective than others. Many researchers have concerns that the efficacy of these devices needs to be more thoroughly tested (Egebert et al, 2019)..
Scientists are now rising to the challenge... Under rigorous testing, researchers concluded that the No Shark device was less effective when compared to Shark ShieldTM, in repelling white sharks to a safe distance from a swimmer (Egebert et al, 2019).
Hopefully as the technology advances and testing continues, we will begin to see more reliable devices become available on the public market.
Electronic Repellants Could Protect Whole Beaches
The question then becomes, if we are able to make reliable, personal shark repellants, could the technology be scaled up to protect multiple ocean users at once? That is exactly the goal of the team developing the SharkSafe Barrier - a magnetic barrier, which repels sharks from bathing beaches (O’Connell et al, 2012; O’Connell et al, 2014a; O’Connell et al, 2014b; O’Connell et al, 2017).
The SharkSafe Barrier mimics the shape of kelp forests; physically blocking entry to sharks, as many potentially dangerous species do not enter any gap that is narrower than the space between the tips of their pectoral fins. Additionally, the device contains magnets which creates a persistent electromagnetic field greater than that of the Earth’s natural geomagnetism. The idea is that the visual and magnetic repellants work together to repel sharks (O’Connell et al, 2012; O’Connell et al, 2014a; O’Connell et al, 2014b; O’Connell et al, 2017).
Under scientific testing, the SharkSafe Barrier has been shown to be effective at excluding potentially dangerous sharks like the great white, great hammerheads (Sphyrna makkaron) and bull sharks (Carcharhinus leucas) (O’Connell et al, 2012; O’Connell et al, 2014a; O’Connell et al, 2014b; O’Connell et al, 2017).
Electromagnetic Barriers could replace Harmful Beach Nets
There is a very real need for new technology to protect ocean users from sharks because current measures are incredibly damaging. In order to try to stop shark attacks upon humans, many countries have fitted shark nets around bathing beaches. Sadly, what many people do not realise, is that these nets not only block sharks from entering the waters used by people, but they are actually designed to kill any sharks that become tangled in them. Not only is this a terrible threat to endangered species of sharks, but also for many other animals... the nets do not discriminate and kill many other non-target species, like turtles, rays and dolphins. These devastating impacts are simply not acceptable.
These technologies are still under development, but if SharkSafe Barriers and personal devices could reliable enough to replace shark nets globally, there is the potential for thousands of sharks and other animals to be saved every year, whilst still ensuring ocean users feel secure (O’Connell et al, 2017).
If you feel that shark nets are unethical, you can join Sea Shepherd and the Shark Angels in their campaigns to replace the nets with more sustainable options.
References
Egeberg, C.A., Kempster, R.M., Hart, N.S., Ryan, L., Chapuis, L., Kerr, C.C., Schmidt, C., Gennari, E., Yopak, K.E. & Collin, S.P. (2019). Not all electric shark deterrents are made equal: Effects of commercial electric anklet deterred on white shark behaviour. PLoS One, 14(3): e0212851. Access online.
Huveneers, C., Rogers, P.J., Semmens, J.M., Beckmann, C., Lock, A.A. & Goldsworthy, S.D. (2013). Effects of electric field on white sharks: In situ testing of an electric deterrent. PLoS One, 8:5, e62730. Access online.
Kempster RM, Egeberg CA, Hart NS, Ryan L, Chapuis L, Kerr CC, Schmidt C, Huveneers C, Gennari E, Yopak KE, Meeuwig JJ & Collin SP (2016). How close is too close? The effect of a non-lethal eectric shark deterrent on white shark behaviour. PLoS One, 11:7, e0157717. Access online.
O’Connell CP, Andreotti S, Rutzen M, Meÿer M & He P (2012). The use of permanent magnets to reduce elasmobranch encounter with a simulated beach net. 2. The great white shark (Carcharodon carcharias). Ocean & Coastal Management, 97. Access Online.
O’Connell CO, Andreotti S, Rutzen M, Meyer M, Matthee CA & He P (2014a). Effects of Sharksafe barrier on white shark (Carcharodon carcharias) behavior and its implications for future conservation technologies. Journal of Experimental Marine Biology and Ecology, 460, 37-46. Access online.
O’Connell CP, Hyun S-Y, Rillahan CB & He P (2014b). Bull shark (Carcharhinus leucas) exclusion properties of the SharkSafe BarrierTM and behavioral validation using the ARIS technology. Global Ecology and Conservation, 2. Access online.
O’Connell C.P., Andreotti S, Rutzen M, Meӱer M & Matthee CA (2017). Testing the exclusion capabilities and durability of the Sharksafe Barrier to determine its viability as an eco-friendly alternative to current shark culling methodologies. Aquatic Conservation: Marine and Freshwater Ecosystems. Access online.
Smit CE & Peddemors V (2003). Estimating the probability of a shark attack when using an electric repellent : applications. South African Statistical Journal, 37:1. Access online.
By Sophie A. Maycock for SharkSpeak
