A nightmarish event — first for humans, and then later for sharks — happened on July 30, 1945. Just four days earlier, the USS Indianapolis transported the world's first combat-ready atomic bomb to the American air base at the Pacific island of Tinian. The United States was still reeling from Japan's attack on Pearl Harbor, and the tensions of World War II gripped many.
On that fateful late July day, two torpedoes fired by a Japanese submarine struck the Indianapolis. The ship literally split up to the keel. Its crew, most without life rafts, jumped, or were tossed, into the Pacific. Nine hundred men wearing life jackets bobbed up and down with the waves.
Sunrise the next day, sharks began to arrive at the site. First a few, and then more and more, were attracted to the area. The sharks bit and killed several of the men, all of whom were already suffering from exposure and lack of food and drinkable water. Four long days passed before a rescue vessel came. The horror of what rescuers found still shocks today: 579 men dead, some chewed to pieces. Of the entire crew, 321 came out of the water alive, but only 317 ultimately lived.
Although real, this level of disaster was extremely rare in recorded history. Most shark species avoid contact with humans. But the combination of starving sharks and bleeding, available, flailing flesh can, and did, lead to the inevitable conclusion. Horrified, the U.S. military quickly pumped funding into shark repellent research.
The first major find was that sharks hate the smell of dead sharks. Attaching a dead shark to one's life preserver hardly seemed a practical solution, so the scientists further analyzed what chemicals could be at work. Copper compounds, such as copper sulfate and copper acetate, seemed to drive off sharks, but a man-made substance based on these compounds proved mostly impractical and ineffective.
Fast forward to 1974, when ichthyologist Eugenie Clark discovered that the Moses sole, Pardachirus marmoratus, secretes an astringent, frothy, soap-like poison called pardaxin that repels sharks. The toxin proved difficult to package and store, so researchers went back to the drawing board. Soon Israeli zoologist Eliahu Zlotkin had a light bulb moment: If the sole toxin was similar to soap, could plain old soap do the trick?
Sure enough, studies suggest sharks despise a face, or mouthful, of soap. Components like sodium and lithium lauryl sulfate irritate a shark's delicate gill filaments. Sodium ions rush in from the water and basically freak out sharks. Liquid ivory soap seems to work particularly well. The problem is that users have to squirt the stuff right in the shark's face. Also, all of that soap can pollute the environment.
More recently, investigators have turned to electricity to drive off the toothsome fish. Shark expert George Burgess, who is coordinator of museum operations at the Florida Museum of Natural History, put it bluntly: "Electrical currents and sharks don't agree with each other." Sharks possess electro-receptors in their snouts that are designed to pick up even the faintest electrical impulses. The kind of amplified electricity that humans artificially generate can lead to muscle spasms and excruciating pain in sharks.
According to Burgess, though, application of this technique has led to either ineffective, or deadly, glitches. Electrical wires buried near South African shark hot spots washed up and were tossed ashore. A "personal electrical field" for divers failed when a man wearing it was attacked. Workers — shocked repeatedly themselves — could not save him.
Research on shark repellents continues, but now conservationists put the emphasis on keeping sharks away and safe from humans. Since the Indianapolis disaster and the popular thriller movie Jaws, millions upon millions of sharks have been needlessly slaughtered. The fact is that only four to five people each year lose their lives due to shark attacks. More people, 150, die each year from being knocked in the head by a falling coconut. Does that mean we should chop down all the coconut trees?
Burgess instead advises to stay in groups while engaging in open-water activities. "There is safety in numbers," he explains. Do not wander far from shore, and avoid going in the ocean in darkness and twilight hours. Surfers seem to suffer a disproportionate number of shark hits, but Burgess said that is likely due to them splashing their hands and feet near the water's surface. It is mostly a myth that sharks go after surfboards. Only great whites, from below, seem to confuse board shapes with those of more desired prey.
Repellents can only go so far. As Burgess puts it, "The best repellent is humans using their head."