One of this past summers suspense films, Open Waterin which two stranded divers in the Caribbean wait to be rescued in shark-infested watersis predicated on a common fear among beachgoers. Now, an Oak Ridge, N.J.-based company called Shark Defense has found a chemical shark repellent that may protect real-life divers.
Shark attacks worldwide are rare, with only about 55 attacksincluding four deathsoccurring in 2003. But media hype surrounding a few beach incidents in 2001, deemed the year of the shark, pushed the issue into the public spotlight and attracted the attention of Eric M. Stroud, a chemical engineer and cofounder of Shark Defense. He wondered whether chemists were working on a solution to the problem. Where are the chemical repellents? he asked himself.
Caribbean Reef Shark
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The quest began from reported incidents. I found much anecdotal evidence, often quoted from fishermen, claiming that shark carcasses seemed to repel other sharks. Stroud says. I then began to study the decay processes of shark tissue to find out what was going on. A literature search revealed a paucity of scientific research and propelled Stroud to look for a chemical repellent based on compounds extracted from shark tissue.
Stroud, research assistant and cameraman Michael M. Herrmann, and other team members collected dead sharks from fish markets and fishing piers in New Jersey. They also sought the expertise of Samuel H. Gruber, a shark biologist at the Bimini Biological Field Station in the Bahamas.
In April 2003, the team went to its first field test in South Bimini with various fractions of extracts from the shark carcasses. Most of these didnt work at all, but two fractions caused some noticeable behavioral effects. The team members were excited by what they saw and came back in July 2003 with a refined, purified version of one of the substancesnow called A-2that worked very well.
Because the fractions were collected from shark tissue, the research teams theory is that A-2 is a semiochemical, a naturally occurring signaling molecule of which pheromones are a subclass. Sharks use these compounds to orient themselves and reproduce. Interestingly, some semiochemicals have the ability to trigger a flight response. Unfortunately, these trace chemicals are difficult to isolate and detect. The semiochemical works as a chemical messenger and is detected by the olfactory system. As Stroud explains: Upon detection, the sharks turn tail rapidly. We test under competitive feeding conditions and are able to stop the sharks from feeding.
The team hasnt yet tested the repellent on all shark species. Four species have undergone repeated testing: the Caribbean reef, blacknose, lemon, and nurse sharks. Successful preliminary tests were conducted on bull sharks and blue sharks. And testing is scheduled on the great white sharkthe species responsible for the most human deathsas well as the tiger shark and the great hammerhead.
A-2 appears to be a shark-specific repellent. The team has seen reef fish that continue feeding in the A-2 dispersal cloud while sharks are in flight. In addition to repelling sharks, another criterion of a successful repellent is its ability to awaken sharks from tonic immobilitya natural state of paralysis that occurs when a shark is turned upside-down.
Although the original discovery was made using extracts, Stroud and coworkers later figured out how to make A-2 synthetically. At first, the team guessed at the structures. They knew the molecular weights from mass spectrometry and the identity of some functional groups from Fourier-transform infrared spectroscopy. Some qualitative tests confirmed the presence of functional groups such as primary and secondary amines. They had an outside lab work with them to figure out how many compounds are present in natural A-2; more than 60 constituents have been identified. But as Stroud explains, When you separate out A-2, no single component works really well in field tests. There is a synergistic effect, we guess, when you use the soup instead of the [individual] ingredients. We made a number of best-guess assignments, synthesized them, and tried them one by one and in certain combinations. We optimized the synthetic formula through some good trial-and-error work.
Stroud is not revealing the composition of synthetic A-2, but he says the eight compounds in it are water soluble, are organic, and have pheromone-like structures with molecular weights ranging between 70 and 110. The composition differs from that of an older repellent that contained copper acetate, incorporated nigrosine dye, and was pressed into cakes. Research conducted during World War II included the search for a shark repellent to protect sailors against the shark menace in the event that they were cast into the sea from a sinking ship. The research resulted in the Navy's use of copper acetate, dubbed shark chaser, which turned out to be ineffective.
The stability of A-2 looks great so far. It is stored at room temperature and has been out in the ocean, shipped all along the coast, been in the hot Bimini sun, and the cold New Jersey winters, Stroud says. He cant peg an exact cost yet, but it does not cost a fortune to make, luckily. The team members are currently synthesizing the repellent on a few-kilogram scale. But they dont plan to scale up production until they find a commercial partner.
As for A-2s commercial potential, Stroud is hopeful yet realistic. We will not certify it for human use until years of testing indicate it is safe to do so. The first target applications will be reducing unintentional shark catching in the fishing industry, protecting underwater equipment prone to shark bites, preventing endangered sharks from becoming ensnared in fishing nets, and using A-2 in rescue operations. Ideas for using A-2 in suntan lotion, on hollow surfboards, and as a spray-on product are great, Stroud says, but it will take much more time to confirm the data before we make a claim like that.
Who knows? If the divers depicted in the movie Open Water had been equipped with A-2, the repellent might have taken a bite out of the drama. But the characters no doubt would have enjoyed safer swimming through chemistry.