Where When How — Nov/Dec 2011
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Dive Training Shark Repellent
Alex Brylske


DARN SHARK... The Story of Shark Repellents

Our attitude tOward sharks is very interesting. It can be summed up in two words: fear and fascination. For divers, especially, sharks inspire awe to the point where shark diving is now one of the most popular underwater activities on the planet. Surveys indicate that, each year, tens of thousands of divers enter the water with the sole intent of viewing - and sometimes directly interacting with - these incredible animals. Shark diving has not only helped dispel the myth of “Jaws,” but has turned many into vehement advocates for shark protection.

Still, while the reputation of the ruthless man-eater is waning, in part due to the nowcommon practice of shark diving, one can’t escape the reality that sharks do retain the nasty habit of biting, and sometimes killing, humans. So, to most people who haven’t had the privilege of seeing them underwater, they’re still near the top of the list of critters to be feared. To some, the fear of sharks is even more visceral than that of other predators like big cats or grizzly bears. And the reason is probably understandable. In the case of land predators, one can always carry a gun big enough to thwart an attack. Not so with sharks. Regardless of how remote the statistics tell us an attack may be, the fact is that anyone who enters the ocean could become the victim of a predator against which there is no effective weapon. Instead, in the absence of a weapon, protection has typically come in some form of repellent.

Some History

Fear of sharks in North America, surprisingly, is a recent phenomenon. In his book, “Twelve Days of Terror,” author Richard Fernicola meticulously recounts the events of the 1916 shark attacks in New Jersey that inspired Peter Benchley’s most famous book, “Jaws.” In it, Fernicola explains that before the faithful events of July 1916, American scientists, including some of our most renowned ichthyologists, doubted that sharks would attack a person in the temperate waters. Some believed that even big sharks lacked the jaw strength to inflict serious injury, let alone sever a limb. In fact, at least one man was so sure that shark attacks were nothing to be feared that he put his money where his mouth was. In 1891, banker and adventurer Hermann Oelrichs offered a $500 reward in the New York Sun “for an authenticated case of a man having been attacked by a shark in temperate waters” north of Cape Hatteras, North Carolina. Oelrichs wanted proof that “in temperate waters even one man, woman, or child, while alive, was ever attacked by a shark.” The reward was never claimed and scientists remained convinced that America’s East Coast was inhabited by harmless sharks. As Fernicola documents so well in his book, that all came to a terrible end when, over the span of just 12 days, four people were killed and one seriously injured by what was believed to be a great white (though evidence now points to a bull shark).

One of the earliest ways to repel sharks was suggested as early as 1895, and involved the benign sea hare (Aplysia). It was discovered to be unpalatable to sharks, and thought to excrete along with its characteristic purple dye - some repulsive substance. But very little formal work on repellents was done until several decades later.

The first serious research on shark repellents took place during World War II. Alerted by reports from fishermen that dead shark carcasses often deterred sharks from feeding, the U.S. Navy took up the task of finding an effective repellent to protect aviators and sailors who found themselves in “shark-infested waters.” The Navy’s research kicked into high gear after the sinking of the USS Indianapolis (an event dramatized by the character Captain Quint from the film “Jaws”). Of the approximately thousand men who survived the initial torpedo attack, only 316 were alive after floating for four days in the Pacific, many victims of a shark attack.

The Navy’s cocktail of compounds resulted in a small package of chemicals called “Shark Chaser.” It was issued to thousands of military personnel, but turned out to be little more than a psychological buttress, with no real effect. Even its own research showed Shark Chaser to be ineffective. After the war, scientists at the Office of Naval Research continued the quest for an effective repellent, testing more than 100 chemicals, also to no effect. By the mid- 1960s all funding for chemical repellents was eliminated.

In the 1970s renowned shark expert Dr. Eugenie Clark found that excretions from a fish called the Moses sole, Pardachirus marmoratus, repelled whitetip reef sharks. The active ingredient was identified as a substance called Pardaxin.
Unfortunately, the research didn’t go anywhere. As it could not be synthesized, the natural supply of Pardaxin was insufficient.
Plus, it had a very short shelf life.

Throughout the 1980s and 1990s research continued on other Pardaxinlike substances. Dr. Samuel “Sonny” Gruber at the Bimini Biological Field Station found yet another promising compound, sodium dodecyl sulfate (SDS). The compound worked better and was cheaper than Pardaxin but, like Pardaxin, SDS was effective only when injected directly into the shark’s mouth. (Another difference between Pardaxin and SDS is that the latter is lethal.) However, a device using SDS, called the “Shark Skunker,” did reach the market. It operated like a fire extinguisher, requiring large amounts of SDS to be effective.

While some researchers worked on chemical compounds, others looked to mechanical devices. Perhaps the most well known, and effective, was the shark cage.

(Famed great white attack survivor Rodney Fox is credited with its invention.) Another device, now used extensively all over the world to protect divers from sharks, is the stainless steel chainmail suit first popularized by filmmakers Ron and Valerie Taylor.

In the realm of armament, “bang sticks” - devices that held a shotgun shell round of rifle ammunition were also popular in the 1960s and 1970s. Personally, I remember as a much younger diver owning still another shark weapon called a “Shark Dart.” As the name implied, it was thrust into the body cavity of a shark, activating a carbon dioxide cartridge. The expanding gas would - in theory force the shark’s internal organs out of its mouth. Fortunately, I never had an occasion to use it.

Other antishark strategies included deploying tubes along the seabed to create a bubble curtain. The mass of bubbles was thought to deter sharks from crossing the boundary. Another device developed by the U.S. Navy resembled a black garbage bag with a buoyant ring around the top. Dubbed the “Shark Shield,” the would-be victim climbed inside, and out of sight and smell of the predator. Sound has been used as a shark deterrent, too. Based on research from the 1970s, a patent for an acoustic shark repellent device called the “Shark Stopper” was issued in 2002.

Even other animals were used as shark repellents. In the 1970s the U.S. Navy and Mote Marine Laboratory experimented with training bottlenose dolphins (Tursiops truncatus) to attack and kill sharks as a way to protect Navy divers.

New Insights Into Old Ideas

Although the Navy’s Shark Chaser was considered a failure, it turns out that they were on to something. As mentioned, the Navy based its approach on accounts of fishermen, later confirmed by research at Woods Hole Oceanographic Institution, who told of using rotting shark carcasses to deter live sharks from eating their catch. However, to understand why dead sharks may repel live sharks, you first must know something about how sharks maintain the salt balance between their tissues and the seawater in which they live. This is a considerable challenge for marine creatures, and is referred to as osmoregulation. Unlike their bony fish cousins, sharks and rays don’t maintain salt in their tissues at a lower level than that of the surrounding water. Instead, they balance their internal levels with that of the seawater by using high concentrations of urea and a chemical known as trimethylamine N-oxide or TMAO. Maintaining this balance is one reason why, with the singular exception of the bull shark, elasmobranchs cannot survive in fresh water. Of course, when a shark or any organism dies, it begins to decay; and when that occurs the urea is converted to ammonia by enzymes. That, the Navy assumed, was what sent shark scurrying. They also added acetic acid (vinegar) and a copper compound to the final Shark Chaser mix.

Dr. Patrick Rice, senior marine biologist and one of the principals in a company called Shark Defense Technologies LLC, says the Navy was close, but wrong. “The key wasn’t the ammonia but the TMAO,” Rice says. But, he says, “You can’t really fault them because in the 1940s scientists lacked the sophisticated analytical tools that exist today. Vinegar and copper have no effect on sharks, and ammonia is actually a shark attractor. It’s some compound or compounds that occur when the TMAO breaks down that repels them.”
Other members of the Shark Defense team, Eric Stroud and Craig O’Connell, have so far found more than 500 compounds that make up the slurry from rotten shark carcasses, all bacterial metabolites of the shark tissue. Of the 500, about 120 have shown potential as repellent compounds. And of that number four are very effective and have been isolated and systematically tested on more than 13 different sharks species.

The substances under study by Shark Defense belong to a group of compounds termed semiochemicals, and function as messengers that sharks use for orientation, survival and reproduction. The repellent semiochemicals are thought to trigger a flight response. The idea of using these compounds for shark repellent was proposed 20 years ago, but only recently have Stroud and his team brought the technology to the point where it shows true potential. So far, the most promising semiochemical candidates have been scaled up, and with the help of Dr. Samuel Gruber and Grant Johnson and the Bimini Biological Field Station, the team has documented several successful field tests on wild feeding sharks. (Some of their research was featured on an episode of the Discovery Channel’s “Dirty Jobs” with Mike Rowe.) Interestingly, the semiochemical extracts repel only elasmobranchs - sharks and rays - not bony fish. Field tests have shown that these chemicals actually attract bony fish species. In fact, the extract has been used by some of the Shark Defense team in two fishing tournaments, both of which they won. While the original semiochemical extracts were made from rotting shark carcasses, Shark Defense is now working on synthesizing the product. This will preclude the need to, ironically, use dead sharks to repel live ones.

Beyond Chemistry

While chemical compounds show great promise, this is not the only approach that has been used in developing shark repellents. As most divers who have any interest in sharks know, a specialized organ - the ampullae of Lorenzini - gives sharks and rays the unique ability to detect minute electrical signals (such as the impulse generated by the beating heart of potential prey). High-powered electrical impulses can actually overwhelm this sensory system, sending sharks running. This is the idea behind two other antishark devices now on the market, the Shark-Shield® and SharkPOD®.

More recently researchers have determined that this sensory mechanism is so acute that some sharks may actually detect the weak electrical signal of Ear th’s magnetic field. During a laboratory experiment with captive sharks in a tank in 2003, Stroud accidentally found that sharks are also sensitive to magnetic fields produced by magnets. In par ticular, Stroud has shown that the signals emitted by Neodymium-Iron-Boride and Barium- Ferrite magnets correspond closely with the detection range of the sharks’ ampullae of Lorenzini.

One proposed use of magnets is in modifying the design of yet another shark protection technology: shark nets. Since the 1960s underwater nets have been used to fence off portions of popular beaches in South Africa and Australia. Attack data indicates that they do have a protective effect, but they come with a considerable cost. Each year thousands of sharks are entangled and killed in these nets. Adding magnets to the nets has been suggested as one way to reduce the mortality, and this is where Craig O’Connell, a Shark Defense principal, is focusing his research.

Another application of magnets involves one of the most endangered marine mammals on earth, the Hawaiian monk seal. (Its Caribbean cousin has been extinct since the 1950s.) In the Northwest, Hawaiian Islands seal populations are preyed upon by sharks, which prowl the nesting areas looking for adults and pups as they enter the water. A magnetic fence has been proposed as a conservation measure, though it’s still in the idea phase. Because sharks are sensitive to magnetic fields, emerging shark protection technology may employ the use of magnets.

The Real Reason to Repel Sharks

While saving human lives is what comes to mind when most folks think of shark repellents, that’s not the only reason. It’s not even the primary objective for the scientists at Shark Defense. As their company mission states, “To reduce unwanted shark bycatch and increase selectivity during commercialized fishing practices, as well as protect humans from shark attack.”

Because many countries don’t keep records of the number of sharks taken by fishers, estimates of shark mor tality are notoriously soft. But several sources, including the UN Food and Agriculture Organization, estimate that each year between 70 million and 100 million sharks are killed. To put that into perspective, that’s 273,000 per day or 11,000 per hour. Most are finned, and go to fill the demand for shark fin soup in Asia. However, a large por tion are caught unintentionally bycatch - on the hooks of longline fishers targeting species such as tuna and swordfish. But because hooks are made of metal, the shark’s unique electrosensitivity could be their saving grace.

Field experiments conducted by Shark Defense researchers have confirmed that the electrical fields caused by alloys of highly electropositive metals deter some shark species. The advantage of this approach to shark deterrence is that there’s no power input required to create the electrical field. Shark Defense scientists are now focusing on quantifying behavioral responses to various pure metals and alloys, understanding the electrochemical and corrosion processes involved, and improving gear design in incorporating these metals into fishing gear. Field trials are still ongoing, but based on the success so far, the company’s new Selectively Magnetized And Repellent Treated (SMART™) hook is now available to fishers. (See www.repelsharks.com for details.) Studies on the effectiveness of the SMART hook, as well as other research by the Shark Defense team, has been published in a number of peer-reviewed sources and presented at several scientific meetings and symposia.

Like all apex predators, sharks are vital in keeping marine ecosystems in balance. In doing so, they also play a vital role in the evolution of their prey species. They cull weak and wounded animals and help populations of prey species remain healthy. As has been witnessed in other instances where apex predators are eliminated, removing sharks could have a catastrophic effect on the entire marine ecosystem.

We could be living the reality of a world without sharks already. Research is conclusive that we have reduced many species of sharks to less than 90 percent of the pre-exploitation population. Some species may already be ecologically extinct, meaning that they no longer fulfill their function in the ecosystem. What is most ironic is that, in the end, the true role of shark repellents may very well be to save sharks, not humans.