• SharkieSophie

Shock Therapy

Updated: Apr 26

Despite it being incredibly unlikely that any single person will be attacked by a shark, there is still prevalent fear of sharks 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?



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! These senses are so sensitive that they 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.


Ampullae of Lorenzini (black dots) on the snout of a sandtiger shark (Carcharius taurus)

Electric shark deterrents are electronic devices which can be worn as anklets or attached to surf boards. They are designed to produce a voltage gradient at a specific pulse frequency, which over-stimulates this electrosensory system; causing the shark to bolt away from the source.

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. During testing, white sharks were drawn in used food baits, but 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).


There are many different products currently on the market, but as they are still under development, some are more effective than others. Under rigorous testing, scientists concluded that the No Shark device was less effective when compared to Shark Shield® in repelling white sharks to a safe distance from a swimmer. Many researchers have concerns that the efficacy of these devices needs to be more thoroughly tested. Hopefully as the technology advances, we will begin to see more reliable devices become available (Egebert et al, 2019).



But can the same idea be scaled up to protect multiple ocean users at once?


Well that is exactly the goal of scientists developing the SharkSafe Barrier. Scientists and engineers are currently developing a magnetic barrier, which repels sharks from bathing beaches. Many large, potentially dangerous sharks do not enter into kelp forests, as they will not slip through any gap that is narrower than the space between the tips of their pectoral fins. The SharkSafe Barrier mimics the shape of kelp forests and physically blocks the entry of sharks. Additionally, the device contains magnets which creates a persistent magnetic 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).


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).


Shark killed in a beach net (Image source: www.dailytelegraph.com.au)

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.


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, 20–28.


O’Connell, C.O., Andreotti, S., Rutzen, M., Meyer, M., Matthee, C.A. & 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, 300–314.


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, 17.


By Sophie A. Maycock for SharkSpeak.

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