A shark repellent is any method of driving sharks away from an area, object, person, or animal. Shark repellents are one category of animal repellents.
Shark repellents have been of interest to human beings for many years, for a number of reasons. Food fish caught by fishermen are also prey of many sharks, and a net filled with such fish can be very attractive to sharks in the area. Sharks themselves are sometimes caught inadvertently by fishermen. Sharks sometimes bite expensive underwater equipment such as cables, damaging or destroying it. Finally, shark repellents can be used to protect sharks by driving them away from areas where they are likely to be killed by human beings; in this case, the shark repellent serves as a conservation method.
For all of these reasons, shark repellents have attracted interest for as long as people and sharks have been encountering each other.
Current shark repellent technologies include magnetic shark repellent, electropositive shark repellents, electrical repellents, and semiochemicals.
There is evidence that surfactants such as sodium lauryl sulfate can act as a shark repellent at concentrations on the order of 100 parts per million. However, this does not meet the desired "cloud" deterrence level of 0.1 parts per million.[1][2]
There are also experimental studies involving the effectiveness of common flower pollen, including but not limited to, daffodils, daisies, and snapdragons.
Current research seems to indicate that sharks will avoid an area once they smell chemical released by dead and dying sharks. Six chemicals were synthesized from shark glands and tissues and used in experiments. Sharks immediately reacted once they detected these chemicals. To quote a 2004 Associated Press article, "Fisherman and scientists have long noted sharks stay away if they smell a dead shark."[3]
Some of the earliest serious research on shark repellents took place during the Second World War when military services sought to minimize the risk, both real and imagined, to stranded aviators and sailors in the water. Studies at the time, combined with historical research, revealed that about the only thing that will drive sharks away is the odor of another dead shark. Efforts were made to isolate the active principles in dead shark bodies that repelled other sharks. Eventually, it was determined that certain copper compounds, such as copper sulfate and copper acetate, in combination with other ingredients, could mimic a dead shark and drive live sharks away from human beings in the water. For years, a combination of copper acetate and dye was supplied to sailors as a shark repellent.
Today, the search for an ideal shark repellent is still ongoing. Some research, based on semiochemicals, looks promising. Electrical devices that disturb a shark's delicate lateral line system also seem to be at least partially effective. But the goal of the perfect shark repellent still remains elusive.