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Magnetic shark repellents utilize permanent magnets, which exploit the sensitivity of the Ampullae of Lorenzini in sharks and rays (electrosense). This organ is not found on bony fish (teleosts), therefore, this type of shark repellent is selective to sharks and rays. Permanent magnets do not require power input, making them ideal for use in fisheries and as bycatch reduction devices. Sharkbanz, released in 2014, is a wearable commercially available device intended for recreational users. However independent tests of Sharkbanz products in 2018 highlighted that they did not work.[1]
During November 2004, Sharkdefense researcher Eric Stroud accidentally dropped a magnet onto a rubber mat near a captive tank at the Oak Ridge Shark Laboratory. He noticed that juvenile nurse sharks (G. cirratum) near the tank wall swam away. While the initial event may have been due to vibrations, it led him to test the effects of the magnet on the captive sharks. Placing the magnet within the tank, Eric observed that nurse sharks avoided the region around the magnet. Follow-on tests in 2005 with Michael Herrmann at the laboratory used an acrylic Y-Maze and showed preference towards non-magnetic exits and strong conditioning. During February 2005, Patrick Rice and Eric Stroud conducted tonic immobility trials at the Bimini Biological Field Station, Bahamas, which confirmed that juvenile lemon sharks (N. brevirostris) and juvenile nurse sharks (G. cirratum) roused when permanent magnets were presented within 50cm of the sharks nares. Mobility was not terminated when strong electromagnets were placed near the sharks.
On January 1, 2009, a peer-reviewed publication described experiments in Australia showing the efficacy of using magnets to deter sharks.[2]
On January 12, 2010, Craig O'Connell from SharkDefense also published a peer-reviewed paper on the efficacy of magnetic shark repellents.[3]
In 2014, Sharkbanz released its first commercially available product. The device is a bracelet or anklet which contains a rare-earth magnet.[4]
Biology
Several species of sharks have demonstrated the ability to sense magnetic fields (Kalmijn, 1978; Ryan, 1980; Klimley, 1993; 2002). The Ampullae of Lorenzini organ within sharks is used to detect weak electrical fields at short ranges. The detection range of this organ is effective only within inches, as sharks sense bioelectrical fields in the final stages of prey capture. The flux per unit area of certain permanent magnets, particularly Neodymium-Iron-Boride and Barium-Ferrite magnets, corresponds closely with the detection range of the Ampullae of Lorenzini. The fields generated by these permanent magnets (ferrite and rare-earth types) decrease at the inverse cube of the distance from the magnet to sharks and rays. Therefore, at distances of a few meters from the magnet, the field exerted is less than the Earth's magnetic field. Animals which lack that Ampullae of Lorenzini organ do not display aversive behavior in close proximity to the magnetic field, making this technology selective.
When a shark swims through the Earth's magnetic field, electromagnetic induction – a phenomenon which generates voltage in an electrical conductor moving through a magnetic field – creates an electric field around the shark. Minute differences in the Earth's magnetic field at different locations result in minute differences in the induced electric field which may be detected by the shark's sensitive electroreceptors, especially as the head region moves back and forth during swimming (Lohmann and Johnsen 2000).
In 2011, the first test of a permanent magnet repellent on a Great White shark was successfully conducted in South Africa with Chris Fallows and Craig O'Connell (SharkDefense). The test was successful, with the shark flinching despite feeding stimulus present, and was featured on Great White Invasion on Discovery Channel's Shark Week.[5]
Craig O’Connell, previously a partner with Sharkdefense, completed his Master's Thesis at Coastal Carolina University with regards to magnetic shark repellents as selective shark bycatch reduction devices. His studies involved Southern Stingrays (D. americana), adults nurse sharks (G. cirratum), blacktip sharks (C. limbatus), adult lemon sharks (N. brevirostris), and Atlantic Sharpnose sharks (R. terranovae) and showed a reduction of shark catch on demersal longlines and rod-and-reel studies. Craig is currently a PhD student at U Mass Dartmouth, continuing shark magnetoreception studies.
In 2008, the Department of Primary Industries and Fisheries (DPI&F) and James Cook University, Australia, reported success with permanent magnets in captive studies with grey reef sharks, hammerheads, sharp-nosed sharks, blacktip sharks, sawfish and the critically endangered spear tooth shark.[citation needed]
In 1995 researchers found that sharks have a heightened sensitivity to low frequency electrical fields, at a close range. This helped with the development of technologies like SharkShield, which is a product that is used for various water-sport activities (such as surfing) that emits a 3-D electronic field that surrounds person who is using it. The closer a shark is to the SharkShield, the more likely the shark is to turn away in discomfort.[6]
In 2018 independent tests were carried out on five Shark Repellent technologies using Great white sharks. Only Shark Shield’s Ocean Guardian Freedom+ Surf showed measureable results, with encounters reduced from 96% to 40%. SharkBanz bracelet & SharkBanz surf leash, which utilises magnetic shark repellent technology, showed no measureable effect on reducing shark attacks.[1]
O’Connell, C.P., D.C. Abel, and E.M. Stroud. 2011. Analysis of permanent magnets as elasmobranch bycatch reduction devices in hook-and-line and longline trials. Fish. Bull. 109(4): 394–401.
O’Connell, C.P., S.H. Gruber, D.C. Abel, E.M. Stroud. and P.H. Rice. 2011. The responses of juvenile lemon sharks, Negaprion brevirostris, to a magnetic barrier. Ocean Coast. Manag. 54(3): 225–230.
O’Connell, C.P., Abel, D.C., Rice, P.H., Stroud, E.M. and Simuro, N.C. 2010. Responses of the Southern Stingray (Dasyatis americana) and the Nurse Shark (Ginglymostoma cirratum) to Permanent Magnets. Mar. Freshw. Behav. Phy. 43: 63–73.
O'Connell, C.P. 2008. Investigation of Grade C8 Barium Ferrite (BaFe2O4) Permanent Magnets as a Possible Elasmobranch Bycatch Reduction System. In: Swimmer, Y., J.H. Wang, and L. McNaughton. 2008. Shark deterrent and incidental capture workshop, April 10–11, 2008. U.S. Dep. Commer., NOAA Tech Memo., NOAA-TM-NMFS-PIFSC-16. 72p.
PUBLICATIONS IN PREPARATION
O’Connell, C.P., P. He, T.J. O’Connell, M.K. Maxwell, R.C. Reed, C.A. Smith, E.M. Stroud and P.H. Rice. (In Preparation). The Use of Permanent Magnets to Reduce Elasmobranch Encounter with a Simulated Beach Net. 2. The Great Hammerhead Shark (Sphyrna mokarran).
O’Connell, C.P., P.He, J. Joyce, E.M. Stroud, and P.H. Rice. (In Preparation). Effects of the SMART Hook™ (Selective Magnetic and Repellent-Treated Hook) on Spiny Dogfish Catch in the Gulf of Maine.
O'Connell, C.P., E.M. Stroud, P. He, T.J. O'Connell, P.H. Rice, G. Johnson, and K. Grudecki. (Submitted). The Use of Permanent Magnets to Reduce Elasmobranch Encounter with a Simulated Beach Net. 1. The Bull Shark (Carcharhinus leucas). Ocean Coast. Manag.
OTHER REFERENCES
Kalmijn A.J., 1971 The Electric Sense of Sharks and Rays. Journal of Experimental Biology 55, 371–383
Kalmijn A.J., 1982 Electric and magnetic field detection in elasmobranch fishes. Science, Vol. 218, Issue 4575, 916–918
Klimley, A. P. 1993. Highly directional swimming by scalloped hammerhead sharks, Sphyrna lewini, and subsurface irradiance, temperature, bathymetry, and geomagnetic field. Marine Biology. 117, 1–22.
Klimley, A. P., S. C. Beavers, T. H. Curtis, and S. J. Jorgensen. 2002. Movements and swimming behavior of three species of sharks in La Jolla Canyon, California. Environmental Biology of Fishes. 63, 117–135.
Related Research Articles
The hammerhead sharks are a group of sharks that form the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a cephalofoil. Most hammerhead species are placed in the genus Sphyrna, while the winghead shark is placed in its own genus, Eusphyra. Many, but not necessarily mutually exclusive, functions have been postulated for the cephalofoil, including sensory reception, manoeuvering, and prey manipulation. Hammerheads are found worldwide in warmer waters along coastlines and continental shelves. Unlike most sharks, some hammerhead species usually swim in schools during the day, becoming solitary hunters at night. Some of these schools can be found near Malpelo Island in Colombia, the Galápagos Islands in Ecuador, Cocos Island off Costa Rica, near Molokai in Hawaii, and off southern and eastern Africa.
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.
A neodymium magnet (also known as NdFeB, NIB or Neo magnet) is the most widely used type of rare-earth magnet. It is a permanent magnet made from an alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed independently in 1984 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet available commercially. Because of different manufacturing processes, they are divided into two subcategories, namely sintered NdFeB magnets and bonded NdFeB magnets. They have replaced other types of magnets in many applications in modern products that require strong permanent magnets, such as electric motors in cordless tools, hard disk drives and magnetic fasteners.
The lemon shark is a species of shark from the family Carcharhinidae. Lemon sharks can grow to 3.4 metres (11 ft) in length. They are often found in shallow subtropical waters and are known to inhabit and return to specific nursery sites for breeding. Often feeding at night, these sharks use electroreceptors to find their main source of prey: fish. Lemon sharks enjoy the many benefits of group living such as enhanced communication, courtship, predatory behavior, and protection. This species of shark gives birth to live young, and the females are polyandrous and have a biennial reproductive cycle. Lemon sharks are not thought to be a large threat to humans. The lemon shark's life span is unknown, but the average shark is 25 to 30 years.
Electroreception or electroception is the biological ability to perceive natural electrical stimuli. It has been observed almost exclusively in aquatic or amphibious animals, because water is a much better conductor than air. The known exceptions are the monotremes (echidnas and platypuses), cockroaches, and bees. Electroreception is used in electrolocation and for electrocommunication.
The winghead shark is a species of hammerhead shark, and part of the family Sphyrnidae. Reaching a length of 1.9 m (6.2 ft), this small brown to gray shark has a slender body with a tall, sickle-shaped first dorsal fin. Its name comes from its exceptionally large "hammer", or cephalofoil, which can be as wide as half of the shark's total length. The function of this structure is unclear, but may relate to the shark's senses. The wide spacing of its eyes grants superb binocular vision, while the extremely long nostrils on the leading margin of the cephalofoil may allow for better detection and tracking of odor trails in the water. The cephalofoil also provides a large surface area for its ampullae of Lorenzini and lateral line, with potential benefits for electroreception and mechanoreception, respectively.
A shark repellent is any method of driving sharks away from an area. Shark repellents are a category of animal repellents. Shark repellent technologies include magnetic shark repellent, electropositive shark repellents, electrical repellents, and semiochemicals. Shark repellents can be used to protect people from sharks by driving the sharks away from areas where they are likely to kill human beings. In other applications, they can be used to keep sharks away from areas they may be a danger to themselves due to human activity. In this case, the shark repellent serves as a shark conservation method. There are some naturally-occurring shark repellents; modern artificial shark repellents date to at least the 1940s, with the United States Navy using them in the Pacific Ocean theater of World War II.
A ferrite is a ceramic material made by mixing and firing large proportions of iron(III) oxide (Fe2O3, rust) blended with small proportions of one or more additional metallic elements, such as barium, manganese, nickel, and zinc. They are electrically nonconductive, meaning that they are insulators, and ferrimagnetic, meaning they can easily be magnetized or attracted to a magnet. Ferrites can be divided into two families based on their resistance to being demagnetized (magnetic coercivity).
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fish ; however, they are also reported to be found in Chondrostei such as reedfish and sturgeon. Lungfish have also been reported to have them. Teleosts have re-evolved a different type of electroreceptors. They were first described by Stefano Lorenzini in 1678.
Barium ferrite, abbreviated BaFe, BaM, is the chemical compound with the formula BaFe12O19. This and related ferrite materials are components in magnetic stripe cards and loudspeaker magnets. BaFe is described as Ba2+(Fe3+)12(O2−)19. The Fe3+ centers are ferromagnetically coupled. This area of technology is usually considered to be an application of the related fields of materials science and solid state chemistry.
Ocean Guardian is the manufacturer of devices that use Shark Shield Technology. The electrical wave-form used in the Shark Shield Technology is based on a technology originally invented by the KwaZulu-Natal Sharks Board of South Africa in the 1990s.
The nurse shark is an elasmobranch fish within the family Ginglymostomatidae. The conservation status of the nurse shark is globally assessed as being data deficient in- the IUCN List of Threatened Species owing to the lack of information across its range in the eastern Pacific Ocean and eastern Atlantic Ocean. They are considered to be a species of least concern in the United States and in The Bahamas, but considered to be near threatened in the western Atlantic Ocean because of their vulnerable status in South America and reported threats throughout many areas of Central America and the Caribbean. They are directly targeted in some fisheries and considered as bycatch in others.
Orectolobus hutchinsi, the western wobbegong, is a species of carpet shark in the family Orectolobidae. The western wobbegong shark is a moderate sized marine shark found off the coast of Western Australia. Its scientific name is Orectolobus hutchinsi, and it was first identified in 1983 by Dr. Barry Hutchins, but was only recently classified, described, and published in 2006. O. hutchinsi is found on the shallow continental shelf in Western Australia from Coral Bay to Groper Bluff. This species is distinct from other wobbegong sharks because the western wobbegong shark has a yellowish brown upper body and darker brown saddles on their backs. Unlike other wobbegong sharks from the same area, the western wobbegong shark doesn’t have white rings or blotches on their backs.
The scalloped hammerhead is a species of hammerhead shark, and part of the family Sphyrnidae. Originally known as Zygaena lewini, its genus name was later changed to its current name. The Greek word sphyrna translates into "hammer" in English, referring to the shape of this shark's head. The most distinguishing characteristic of this shark, as in all hammerheads, is the 'hammer' on its head. The shark's eyes and nostrils are at the tips of the extensions. It is a fairly large hammerhead, but is still smaller than both the great and smooth hammerheads.
Electropositive metals (EPMs) are a new class of shark repellent materials that produce a measurable voltage when immersed in an electrolyte such as seawater. The voltages produced are as high as 1.75 VDC in seawater. It is hypothesized that this voltage overwhelms the ampullary organ in sharks, producing a repellent action. Since bony fish lack the ampullary organ, the repellent is selective to sharks and rays. The process is electrochemical, so no external power input is required. As chemical work is done, the metal is lost in the form of corrosion. Depending on the alloy or metal utilized and its thickness, the electropositive repellent effect lasts up to 48 hours. The reaction of the electropositive metal in seawater produces hydrogen gas bubbles and an insoluble nontoxic hydroxide as a precipitate which settles downward in the water column.
SharkDefense is a research organization and think tank focused on shark bycatch reduction. Its core research involves chemical and electrochemical shark repellent technologies. SharkDefense's repellent experiments have been featured extensively in the US and European media.
The following outline is provided as an overview of and topical guide to sharks:
Passive electrolocation is a process where certain species of fish or aquatic amphibians can detect electric fields using specialized electroreceptors to detect and to locate the source of an external electric field in its environment creating the electric field. These external electric fields can be produced by any bioelectrical process in an organism, especially by actions of the nerves or muscles of fish, or indeed by the specially developed electric organs of fish. Other fields are induced by movement of a conducting organism through the earth's magnetic field, or from atmospheric electricity.
Most fish possess highly developed sense organs. Nearly all daylight fish have color vision that is at least as good as a human's. Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form the lateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey. Sharks can sense frequencies in the range of 25 to 50 Hz through their lateral line.
Polyandry in fish is a mating system where females mate with multiple males within one mating season. This type of mating exists in a variety of animal species. Polyandry has been found in both oviparous and viviparous bony fish and sharks. General examples of polyandry occur in fish species, such as green swordtails and Trinidadian guppies. Specific types of polyandry have also been classified, such as classical polyandry in pipefish cooperative polyandry in cichlids and convenience polyandry in sharks.
↑ Rigg, D.P., Peverell, S.C., Hearndon, M., Seymour, J.E. 2009. Do elasmobranch reactions to magnetic fields in water show promise for bycatch mitigation? Marine & Freshwater Research, 60, 942-948.
↑ O’Connell, C.P., Rice, P.H., Stroud, E.M., Abel, D.C., Simuro, N.C. 2010. The Effects of Permanent Magnets on the Southern Stingray (Dasyatis americana) and the Nurse Shark (Ginglymostoma cirratum). Marine and Freshwater Behavior and Physiology. A second, confirming paper is currently in peer review.
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