Mary Roach - Grunt

In 1958, the head of the Biology Branch of the Office of Naval Research, Sidney R. Galler, set out in pursuit of answers. He funded a shark research panel (the Shark Research Panel) and helped establish the Shark Attack File, a database of global incidents that continues today as the International Shark Attack File. David Baldridge’s statistical analysis of nine years of Shark Attack File data gave the world—I’m quoting a 2013 National Marine Fisheries Service paper here—“most of what we know today about shark attacks.” Much of the rest comes from studies the Office of Naval Research funded in the 1950s on shark predation, olfaction, and feeding behavior. “If you had a good idea for research on sharks,” Baldridge told the author of a historical account of shark research, published in Marine Fisheries Review, “you went to Sid.”

ALBERT L. Tester went to Sid. He had a good idea, he had three species of shark in the ocean outside his door, and he had a pair of fifty-foot-long seawater tanks for experimenting. Tester worked at the Eniwetok Marine Biological Laboratory in the Marshall Islands. (Eniwetok was one of the atolls, along with Bikini, [52] The creator of the two-piece swimsuit, Louis Réard, named it “bikini” because of the explosive reaction he hoped it would generate. The false prefix “bi” has duped many over the years—including the inventors of the monokini, the tankini, the trikini—into wrongly assuming that bikini means “two pieces” in Marshallese. In fact, it means “coconut place”—making the term deliciously if inadvertently appropriate. upon which the US had tested nuclear bombs; the lab provided data on the effects of radioactive fallout on sea life—and, if anyone tracked the obituary pages over the ensuing decades, Eniwetok staff.) Tester set out to determine what, specifically, draws a shark to its prey. Do sharks hunt mainly by sight or smell? If it’s smell, which smells? Whose smells? If repelling sharks wasn’t a reasonable option, a sailor or aviator’s best bet was not attracting them in the first place.

Let’s start with the good news. Human urine does not attract sharks. When presented with anywhere from a half teaspoon to a third of a cup, blacktip sharks in Tester’s tanks took no interest. Neither excited nor repelled, the sharks simply noted the substance, as evinced by a quick turn, or “swirl,” which is, I guess, how one acknowledges pee in the pool when one has no eyebrows to raise or shoulders to shrug.

Human perspiration is likewise uninteresting to the shark. It was sufficiently hot and humid in the shark house that Tester and his grad students were able to collect what they needed by sponging each other’s bodies and wringing the sponge into a bucket of seawater that was then quietly siphoned into the shark tank. In general, the sharks, and who can blame them, were mildly put off. The perspiration of Albert L. Tester was particularly repulsive to them. At concentrations as low as one part per million, Tester’s sweat caused a captive blacktip shark to shake its head and make “a rapid exit from the area.”

All-over body sweat—the cooling waters of the eccrine glands—is different from flop sweat. Had Tester done what my friends at the Monell Chemical Senses Center did to me—gathered the pungent armpit exudations of a human under stress—his results might have been different. The sharks might have detected the scent of distress, of easy pickings, and gone into attack mode.

That is precisely what happens when a shark’s preferred prey falls under stress. The shark senses a no-hassle meal and closes in to attack. Tester harassed a bucket of groupers by “threatening them with a moving stick” (elsewhere referenced as “poking”). Pumping water from the bucket—scientific nomenclature: “distressed grouper water”—into the shark tank provoked a “violent hunting response.” Since the prey were outside the tank, we know it wasn’t the sight or sound of grouper pandemonium that set off the sharks’ predatory moves. It had to be some chemical exuded through the groupers’ skin or gills. And not just any grouper scent would do the trick. When “quiescent grouper water” was introduced into the tank, the sharks paid little heed.

Fish blood and fish guts—two blaring sensory trumpeters of piscine distress—also trigger vigorous hunting moves. So powerful is the chemical signal, Baldridge found, that sharks could be roused to devour a rat—not normally an item of gustatory interest—if its fur were coated with “mullet blend” (whole mullets blenderized with a little water). In a different study, sharks were inspired to attack a kitchen sponge that had been dipped in a bowl of fish body fluids. “Sharks,” wrote Baldridge, “will strike essentially anything that has been treated with fish ‘juice.’”

That includes spearfishers. In particular peril are those who swim around with the day’s catch hanging from their belts or trailing from lines. At the time Baldridge ran his analysis, the Shark Attack File had logged 225 incidents that mentioned the presence of wounded fish and/or fish blood or guts. “Sharks,” marveled Tester, “are able to track down and converge on a distressed fish (such as a live fish suspended from a hook through the jawbone but otherwise uninjured) with uncanny speed and accuracy.”

Spearfishing probably serves to explain why 17 percent of the Shark Attack File victims were wearing wetsuits. The original theory put forth was that the sharks mistook people in black wetsuits for seals. Perhaps that happens too, but where spearfishing was involved, it’s more likely that the wetsuit’s accessories—the spear and the belt of oozing fish—drew the shark.

Dead fish also ring the dinner bell. Tester exposed blacktip and gray sharks to a sushi bar of fish flesh: tuna, eel, grouper, snapper, parrot fish, giant clam, octopus, squid, and lobster. All of them he classed as attractants. Sharks prefer to take no risks. They prefer to go after a meal that’s not going to put up a fight. Injured is good. Dead is better.

Which makes you wonder about the alleged shark-repellent qualities of decomposed shark flesh. Tester wondered, too. He secured some “alleged shark repellent” from a fisherman, another sample from a fisheries lab, and a sample his team prepared on their own by leaving hammerhead and tiger shark flesh outside in the tropical heat for a week. No repellent effects were observed. On the contrary, it sometimes functioned as an attractant. “Our results… seem to be at variance with those of Springer…. No convincing explanation can be made.” Tester perhaps unaware of the powerful attractant effect of kickbacks from shark-processing plants.

As with fish, so with humans. Over and over, in the shark attack reports of World War II, corpses took the hit. A floating sailor could dispatch a curious shark by hitting it or churning the water with his legs. (Baldridge observed that even a kick to a shark’s nose from the rear leg of a swimming rat was enough to cause a “startled response and rapid departure from the vicinity.”) “The sharks were going after dead men,” said a survivor quoted in a popular book about the 1945 sinking of the USS Indianapolis , an event that often comes up in discussions of military shark attacks. “Honestly, in the entire 110 hours I was in the water,” recalls Navy Captain Lewis L. Haynes, in an oral history conducted by the US Navy Bureau of Medicine and Surgery, “I did not see a man attacked by a shark….” They seemed to have been, he said, “satisfied with the dead.” Haynes says fifty-six mutilated bodies were recovered, but there’s nothing to suggest that any more than a few of them were bitten into while alive.

Why, then, do sharks hang around life rafts? For what’s underneath. Schools of fish loiter there, either for the shade or to feed on smaller marine life that gathers to take the shade on the raft’s underside. Recalled one World War II sailor: “Larger fish came to feed on those minnows, then larger ones to get them; finally the boys with the peculiar dorsal fins arrived to see what the fuss was about.” Here’s one more, just because I like it: “The shark submerged and swam directly under the raft…. We all sat very quiet,… and the radar man abandoned the idea of defecating over the side for fear of capsizing. The shark repeated this behavior several times but at no time seemed concerned with us.”