Shark repellents are essentially any method of driving away sharks from an area or a person. Interest in shark repellents go back a long time where scientist and inventors constantly trying to create different kinds of repellents ever since the growing fear of shark attacks spread more through cinema and media coverage of isolated incidents than by actual threats. It was reported that in the year 2000 a total of 79 incidents of shark attacks were recorded worldwide, out of which only 11 were fatal, and in 2006 a total of 61 attacks worldwide were recorded.
Still the interest in shark repellents is ever growing, with various forms being marketed to local governments to install in beaches, or to fish farmers to protect their fish, and to researchers, surfers and scuba divers.
The main forms of shark repellent technologies used today are in the form of Magnetic Repellents, Electropositive shark repellents and Semiochemical.
Electropositive Shark Repellents
These use an electropositive metal which when immersed in an electrolyte generates a voltage which overwhelms with ampullary or electro-sensory organ in sharks, producing a repellent action. This ampullary organ isn’t found in other bony fish other than sharks and rays making its effectiveness shark-specific. The whole process is electrochemical where the chemical electrolyte reacts with the metal alloy, and does not require an external power supply. However is said that electropositive shark repellents are not 100% effective, and are only useful when a shark is using its electro sensory organs, and will not help when a shark is in a feeding frenzy. Hence the usage of these repellents is limited to fisheries or fish farms where they can keep predators away from stocks. Also electrochemical metals have a very limited lifespan and need to be changed constantly requiring constant maintenance and upkeep costs.
Magnetic Shark Repellants
Magnetic repellents as the name suggests use permanent magnets to exploit the shark’s electroreceptor’s located in its nose known as Ampullae of Lorenzini, which similar to the electropositive method, impacts only sharks and rays which possess this organ. Several species of sharks have demonstrated the ability to sense magnetic fields and magnets are said to over-stimulate the electro-sensory receptors thereby effectively repelling them. However once again if the sharks sense of smell is overpowering the electro-sensors, or if the magnet is not in sufficient range to impact the sharks sensors, the shark may still attack. Research is still being conducted on the effectiveness of this method. The advantage of using magnets is that they need not be large and bulky, so not need to be renewed and can be worn by surfers and divers as necklaces/anklets or bracelets. Magnets are also being purported to be the answer to shark conservation by having long line fisherman attach a magnet to each long line just above the hook to prevent sharks being caught in them.
Semiochemical Shark Repellents
Semiochemical repellents consist of a chemical mixture that sends out a signal to the shark which is derived from one of its natural responses. Semiochemicals encompass pheromones, allomones, kairomones, attractants and repellents. Certain extractions have the ability to trigger a flight reaction in sharks making them the most effective form of repellent. However identifying and isolating the correct cue mixture is no easy task, but some researchers have claimed to find the right formula. Semiochemical repellents are currently sold in the form of surface aerosol cans and liquid canisters for fisherman and researchers and most liquid/aerosol shark repellents sold in the market today are semiochemical repellents.
All repellents to date are only partially effective and no form of shark repellent is a 100% effective against sharks. The effectiveness of each of the above techniques varies from one shark species to the next. Using a shark repellent is not a license to go swim with sharks, nor is it a substitute for common sense which is your best defense against a shark attack.
