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 repellants; modern artificial shark repellants date to at least the 1940s, with the United States Navy using them in the Pacific Ocean theater of World War II.
It has traditionally been believed that sharks are repelled by the smell of a dead shark; however, modern research has had mixed results.
The Pardachirus marmoratus fish (finless sole, Red Sea Moses sole) repels sharks through its secretions. The best-understood factor is pardaxin, acting as an irritant to the sharks' gills, but other chemicals have been identified as contributing to the repellent effect.
Some of the earliest research on shark repellents took place during the Second World War when military services sought to minimize the risk to stranded aviators and sailors in the water. Research has continued to the present, with notable researchers including Americans Eugenie Clark, and later Samuel H. Gruber, who has conducted tests at the Bimini Sharklab in Bimini, and the Japanese scientist Kazuo Tachibana.
Initial work, which was based on historical research and studies at the time, focused on using the odor of another dead shark. Efforts were made to isolate the active components in dead shark bodies that repelled other sharks. Eventually, it was determined that certain copper compounds like copper acetate, in combination with other ingredients, could mimic a dead shark and drive live sharks away from human beings in the water. Building on this work, Stewart Springer and others patented a "shark repellent" consisting of a combination of copper acetate and a dark-colored dye to obscure the user. This shark repellent, known as "Shark Chaser," was long supplied to sailors and aviators of the United States Navy, initially packaged in cake form using a water-soluble wax binder and rigged to life vests. The Navy employed Shark Chaser extensively between 1943 and 1973. It is believed that the composition does repel sharks in some situations, but not in all, with about a 70% effectiveness rating.
On the other hand, Albert Tester questioned the idea that dead shark bodies or chemicals based on them could work as shark repellent. In 1959, he prepared and tested extracts of decaying shark flesh on tiger sharks in Hawaii and blacktip sharks at Enewetak Atoll. Tester found that not only did the dead shark extracts fail to repel any sharks, but several sharks had a "weak or strong attraction" to them. Tester reported a similar failure to repel sharks by a 1959 test at Enewetak of "an alleged shark repellent, supplied by a fisherman, which contained extract of decayed shark flesh as the principle component." Research has continued into the 2000s on using extracts from dead sharks or synthesizing such chemicals.
Since the 1970s, there have been studies of how the Moses sole repels sharks, with Clark and Gruber both studying it. As of 2004[update] it has not found practical use, however, as the chemicals are perishable, and the repellent had to be injected into the shark's mouth to be effective; in nature the substance is secreted on the skin and is thus ingested by sharks when they bite the sole.
Since the 1980s, 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.
There have been validated field tests and studies to confirm the effectiveness of semiochemicals as a shark repellent. From 2005-2010, an extensive study on the effectiveness of semiochemicals as a shark repellent was conducted by scientists from SharkDefense Technologies and Seton Hall University. The study's results were published in the scientific journal Ocean & Coastal Management in 2013. The study concluded that the existence of a putative chemical shark repellent has been confirmed.
Recently, SharkDefense used the same semiochemicals found in SharkTec's product to reduce shark by-catch by 71% in a government grant initiative. The government agency NOAA released these findings in a report to Congress.
In popular culture
In a 2015 a MythBusters episode, the hosts Adam Savage and Jamie Hyneman used an extract of dead sharks, and were able to drive away 10-20 Caribbean reef sharks and nurse sharks in only a few seconds on two separate occasions. The repellent used consisted of extracts from other species of shark bodies, and sharks did not return for over 5 minutes on both occasions.
- Researchers tout shark repellent, 2004 Associated Press, "Fisherman and scientists have long noted sharks stay away if they smell a dead shark."
- Clark, Eugenie; Gorge, Anita (June 1979). "Toxic soles, Pardachirus marmoratus from the Red Sea and P. pavoninus from Japan, with notes on other species". Environmental Biology of Fishes. 4 (2): 103–123. doi:10.1007/bf00005447. Retrieved 15 Feb 2016.
- Tachibana, Kazuo; Sakaitanai, Masahiro; Nakanishi, Koji (1984). "Pavoninins: Shark-Repelling Ichthyotoxins from the Defense Secretion of the Pacific Sole". Science. 226 (4675): 703–705. doi:10.1126/science.226.4675.703.
- Tachibana, Kazuo; Gruber, Samuel H. (1988). "Shark repellent lipophilic constituents in the defense secretion of the Moses sole (Pardachirus marmoratus).". Toxicon. 26 (9): 839–853. PMID 3201487.
- Thomas B. Allen. Shadows in the Sea: The Sharks, Skates and Rays
- US 2458540, Brinnick, Frederic E.; John M. Fogelberg & Horace Stewart Springer et al., "Shark repellent", issued 1949
- Tester, Albert L. (April 1963). "The role of olfaction in shark predation". Pacific Science. 17 (2): 145–170. ISSN 0030-8870. hdl:10125/4935. Retrieved September 25, 2016.
- Walter Sullivan (January 20, 1981). "Natural Shark Repellent is Alluring to Scientists". The New York Times.
- Zlotkin, Eliahu; Gruber, Samuel H. (1984). "Synthetic surfactants: A new approach to the development of shark repellents". Archives of Toxicology. 56 (1): 55–58. doi:10.1007/BF00316354.
- Smith, Larry J. (1991). "The effectiveness of sodium lauryl sulphate as a shark repellent in a laboratory test situation". Journal of Fish Biology. 38: 105. doi:10.1111/j.1095-8649.1991.tb03096.x.
- Sisneros, Joseph A.; Nelson, Donald R. (2001). "Surfactants as Chemical Shark Repellents: Past, Present, and Future". Environmental Biology of Fishes. 60: 117. doi:10.1023/A:1007612002903.
- "Anti-Shark 100 Product Overview". SharkTec. Retrieved 5 June 2017.
- Stroud, Eric (October 2014). "Performance of a long lasting shark repellent bait for elasmobranch bycatch reduction during commercial pelagic longline fishing" (PDF). National Oceanic and Atmospheric Administration.
- Hyneman, James F.; Savage, Adam W. (August 29, 2015). "Dead Shark Repellent MiniMyth". Discovery.com. Discovery Communications. Retrieved September 25, 2016.