Shark Shield

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Shark Shield (originally known as "Protective Oceanic Device" or simply "POD") is a portable electronic device that emits an electromagnetic field and is used by scuba divers, spearfishing, ocean kayak fishing and surfers to repel sharks. The electrical wave-form used in the Shark Shield is based on a technology originally invented by the KwaZulu-Natal Sharks Board of South Africa in the 1990s.[1] The Shark Shield device was developed by the Australian company SeaChange Technology Pty Ltd, and commercialized by its trading company Shark Shield Pty Ltd established in October 2006.[2]

History[edit]

The original wave-form used in the shark repelling technology was devised by three inventors, Graeme Charter, Sherman Ripley, Norman Starkey, and released in 1995 by POD Holdings Ltd, a joint venture company partly owned by the Natal Sharks Board and the South African Government.[1]

In 2001, the KwaZulu-Natal Sharks Board ceased distribution of the SharkPOD. All rights to the intellectual property were licensed to a South Australian based company, SeaChange Technology Pty Ltd, with the inventor Mike Westcombe-Down developing various application patents which resulted in a commercial product line under the brand name Shark Shield in April 2002.[2]

In 2007, Shark Shield introduced the third generation of products to replace the original FREEDOM4, expanding the range of products offered to include the SCUBA7, which replaced the original FREEDOM4, and introducing two new designs: the FREEDOM7, a versatile option that can be used by a broad range of ocean-users, including divers, bathers, bodyboarders, boaters and kayakers; and the SURF7, designed to be fitted onto a surfboard or stand-up paddleboard to offer surfers protection from sharks.

Developed in Natal

Functionality[edit]

All chondrichthyans have highly sensitive electrical receptors called the “Ampullae of Lorenzini” located in their snouts. These tiny gel filled sacs sense electrical current from prey at very close distances, typically less than one meter. They use these short range sensors when feeding or searching for food. They do not use electrical receptors to track animate objects over long distances; other senses such as audition and olfaction are the primary drivers.[3][4]

Shark Shield devices create an electrical waveform that creates an unpleasant sensation impacting the shark’s ‘Ampullae of Lorenzini’. When the shark comes into proximity of the electrical waveform (a few meters in diameter) it experiences uncontrollable muscular spasms causing it to flee the area.[5][6]

The field is projected from two electrodes, which create an elliptical field that surrounds the user. Both electrodes must be immersed in the water for the field to be created. Research conducted by The South African National Space Agency (SANSA) in 2012 estimated the Shark Shield electrical field to be approximately four to five meters in diameter.[7]

While sharks are attracted to electromagnetic pulses produced by potential prey animals, the electronic field emitted by the Shark Shield does not attract sharks to the device and therefore would not increase the risk of attracting sharks to the vicinity of the user. A shark's sensory organs are acutely sensitive to low-voltage gradients (> 5 nVcm), enabling them to detect very low-frequency electronic fields of between 1–8 Hz at short range, after which the other senses (sight, chemoreception and mechanoreception) aid the shark in capturing its prey.[3][4] The range at which an electronic shark deterrent emits a field that is the equivalent of a prey-like stimulus (approx 1–100 nV/cm) is much further than their short range detection facilitates. Should a shark approach the device, the strength of the electric field will get stronger the closer it gets, and will soon cause the shark extreme discomfort, forcing it to turn away. Scientific studies modelling this effect show that the output produced at a 3 meter distance is far greater than that produced by prey, and would drop off significantly beyond a 6 m radius, where it would be beyond the short range detection ability of a shark.[7]

Scientific Research and Effectiveness[edit]

The original "SharkPOD" was tested for eight years off Dyer Island with mainly great white sharks, and was the first electronic device that was proven successful in deterring sharks when tested by Ron Taylor and Valerie Taylor in 1992 on sharks in Australia and South Africa with positive results—they made a documentary about it called "Shark POD". Extensive field testing was conducted on the Shark Shield off Neptune Island, South Australia, using the FREEDOM4 and subsequently the FREEDOM7 by renowned wildlife documentary videographer, Ian “Shark” Gordon. Gordon personally tested the effectiveness of the device on a variety of particularly aggressive shark species, including black-tipped reef sharks, mako sharks, and great white sharks, by setting a tuna bait to attract the sharks while he was wearing a Shark Shield, and then videoing their hasty retreat as they approached within meters of the activated device.[8]

In 2003 C F Smit, Department of Statistics, University of Pretoria, South Africa and V Peddemors, Department of Zoology, University of Durban-Westville, South Africa (Peddemors was employed by the Natal Sharks Board at the time) researched “Estimating the Probability of a Shark Attack when using an Electric Repellent”. Research Summary: In two series of tests of the SharkPOD, data was collected on the time needed to attack the bait, under power-off and power-on (active) conditions. Conclusions were separately drawn after completion of the first experiment (in which there were 8 successful attacks in 98 five minute active periods), and after completion of the second experiment (in which no successful attacks were recorded in 24 ten minute active periods). In general the researchers concluded that the probability of an attack in at most 5 minutes was reduced from about 0.70 in power-off mode to about 0.08 in power-on mode and in a period of at most 10 minutes from 0.90 to 0.16.[9]

In 2010, SafeWork South Australia, the government agency responsible for administering occupational health, safety and welfare laws in South Australia, commissioned the South Australian Research and Development Institute (SARDI) to conduct an independent study into the effectiveness of the Shark Shield FREEDOM7 product. The research team conducted field experiments testing white shark response to both a static bait (natural prey) and a dynamically towed seal decoy at Neptune Islands, South Australia, and Seal Island, South Africa, respectively, documenting their findings in a research report titled: “Effects of the Shark Shield electric deterrent on the behaviour of white sharks (Carcharodon carcharias)”.[5] Research Summary: A total of 116 trials using a static bait were undertaken at the Neptune Islands, South Australia and 189 tows were conducted using a seal decoy near Seal Island, South Africa. The proportion of baits taken during static bait trials was not affected by the deterrent. The deterrent increased the time it took to take a static bait, and the number of interactions per approach. The effect of the Shark ShieldTM was not uniform across all sharks. The number of interactions within two metres of the deterrent decreased when it was activated. No breaches and only two surface interactions were observed during the dynamic seal decoy tows when the deterrent was activated, compared to 16 breaches and 27 surface interactions when the deterrent was not activated. Although the fine-scale positioning and presence/absence data collected to assess the potential of the device to attract white sharks was limited to one trip, our results did not suggest that sharks were attracted to the deterrent. The results showed that the deterrent had an effect on the behaviour of white sharks, but did not deter or repel them in all situations.[5][6]

More recently Shark Shield was used by in the record-breaking swim by Diana Nyad. She used the electronic shark deterrent in her crossing from Cuba to Florida without a cage, with help from Shark Shield.[10]

See also[edit]

A U.S. patent 4,211,980 "Method of creating an electric field for shark repellent" issued to William Stowell in July, 1980, disclosed the technology required to repel sharks in an energy efficient manner based on sharks' extreme sensitivity to electric fields.

References[edit]

  1. ^ a b Control of Sharks. "Patent US5566643 A". Google Patents. Retrieved 25 September 2013. 
  2. ^ a b Kwa-Zulu Natal Sharks Board. "Electrical Shark Repellent". Retrieved 25 September 2013. 
  3. ^ a b Collin, SP (2010). "Electroreception in Vertebrates and Invertebrates.". Encyclopedia of Animal Behavior 1: 611–620. 
  4. ^ a b Kempster, RM; McCarthy ID & Collin SP. (2012). "Phylogenetic and ecological factors influencing the number and distribution of electroreceptors in elasmobranchs.". Journal of Fish Biology 80: 2055–2088. doi:10.1111/j.1095-8649.2011.03214.x. 
  5. ^ a b c Huveneers, C., Rogers, P.J., Semmens, J., Beckmann, C., Kock, A.A., Page, B. and Goldsworthy, S.D. (2012). Effects of the Shark Shield™ electric deterrent on the behaviour of white sharks (Carcharodon carcharias). Final Report to SafeWork South Australia. Version 2 (PDF 927.6 KB). South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2012/000123-1. SARDI Research Report Series No. 632, page 9 at http://www.sardi.sa.gov.au/__data/assets/pdf_file/0005/173876/Risk_Assessment_of_the_Shark_Shield_Report_-_FINAL_19_06_2012.pdf, retrieved 25/06/2012.
  6. ^ a b Huveneers, C; Rogers PJ; Semmens JM; Beckmann C; Kock AA; et al (2013). "Effects of an Electric Field on White Sharks: In Situ Testing of an Electric Deterrent.". PLoS ONE. e62730 8 (5). doi:10.1371/journal.pone.006273. 
  7. ^ a b South African National Space Agency (SANSA) (2012). Interim report on measurement and analysis of the electric fields produced by the SharkPOD and Shark Shield. Doc No: 6035-0006-722-A1. 
  8. ^ "Shark Shield | Freedom Series Testing". YouTube. Retrieved 26 September 2013. 
  9. ^ Smit, CF; Peddemors VM (2003). "Estimating the probability of a shark attack when using an electric repellent.". South African Journal of Statistics 37: 59–78. 
  10. ^ OpenWaterPedia.com. "Shark Shield". Retrieved 25 September 2013. 

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