Grunt: The Curious Science of Humans at War

by Mary Roach

  The Navy was losing patience. A hundred thousand dollars—$1.5 million in today’s currency—had been spent, and they were no closer to having a practical, effective shark repellent than they’d been a year ago. The OSS was edged out, and the project taken over by the Office of Naval Research and the Naval Research Laboratory (NRL). The first thing the Navy did was to make the field tests more realistic. Springer and Burden had been baiting lone meandering specimens—“casual sharks”—using hunks of mullet as their man-in-life-belt stand-ins. The NRL wanted a better approximation of the thrashing aftermath of a downed ship or plane and the “large schools of frenzied sharks” that that scenario was thought to attract and inspire. The so-called feeding frenzy was a state of mind in which, it was speculated, olfaction took a back seat to the “mob impulse.” In August 1943, copper acetate was brought on board a shrimp trawler off Biloxi, Mississippi, and tested for its ability to protect “trash fish”—flailing, panicked specimens tossed off the back because they weren’t shrimp. Guess what? Even five to six pounds of copper acetate per bushel of trash fish “did not by any means” interrupt the het-up mob trailing the boat. “The sharks hardly paused.”

  The final slap in the face of Project 374 would come in the form of a paper by Navy Captain H. David Baldridge Jr.: “Analytic Indication of the Impracticability of Incapacitating an Attacking Shark by Exposure to Waterborne Drugs.” By plotting the speed of a closing shark against the speed of dilution and the concentration needed to put the creature out of commission, Baldridge showed that such a large quantity of drug would be needed that it “does not appear to be at all reasonable as an approach to the control of predaceous shark behavior.” As one of Burden’s colleagues put it: “You can’t do much with a pint of liquid in an ocean.”

  Taking a cue from the octopus, Navy researchers next looked into using clouds of inky dye as a way to hide crewmen from potential predators. Under those same “mob psychology” conditions, all feeding activity was stopped until the dye had diluted to the point at which it no longer obscured the prey. Production began at once. Shark Chaser’s active ingredients: 80 percent black dye and 20 percent pink pill—a little copper acetate having been added to the pot† for some false peace of mind. From 1945 all the way through to the Vietnam War, packets were available for the emergency survival supplies of lifeboats, life rafts, and life jackets on military vessels and planes. Even the post-splashdown survival kits of the Mercury astronauts were stocked with Shark Chaser.

  Through all of it, there’d been skeptics among the Navy brass. Rear Admiral Ross T. McIntire, Chief of the Navy’s Bureau of Medicine and Surgery, made the eminently reasonable point that a package labeled SHARK CHASER in bold capital letters might in fact lower, not raise, morale, planting, as it would, the seed of terror in minds that had been, until that moment, occupied by the real threats of ocean survival: dehydration, starvation, drowning, heat, cold. Especially given the “negligible danger,” to use McIntire’s words, that sharks posed to Navy personnel.

  How negligible? Opinions varied, but at one point in the proceedings, the Commander of the South Pacific Fleet issued a memo to all naval bases and hospital ships soliciting “authentic cases of injury to personnel from attack by sharks.” With all hands reporting, the final count was two cases. (One additional attack was later determined to have been a “vicious eel.”) The OSS responded in time-honored intelligence-agency style: They disappeared the report. “The report on shark attacks has been destroyed, as you requested,” reads an interoffice memo to Harold Coolidge from a staffer in December 1943.

  It was another stink bomb for the OSS. They’d set out to develop a shark repellent based on one man’s experience and another’s political connections, with no solid data to support a need. If you look back at the Ecuador incident—the original impetus for all this—it really wasn’t a testament to the danger or ferocity of sharks. If anything, it was a testament to the disinterest and/or shyness of sharks. The flight officer was adrift in a life jacket for thirty-one hours, yet he emerged from the ocean unmauled by the retinue of sharks that followed him most of the way to shore.

  If you wanted to preserve morale, the better approach would have been to share these reassuring facts and statistics. “Correct information,” wrote McIntire, “would be more universally operative in alleviating those fears than any repellent that could be devised.” Beginning in 1944, that is what the Navy did. Their Aviation Training Division distributed copies of a pamphlet called Shark Sense to all future fliers: 22 pages of comforting facts, illustrated with comic drawings of cringing, perspiring, fleeing (“HALP!”) sharks.

  And it proved true. In a review of 2,500 aviators’ accounts of survival at sea during World War II, there were just 38 shark sightings, only 12 of which resulted in injuries or death.

  As reassuring as it was, Shark Sense failed to address the most urgent questions on the minds of men afloat in the bedlam of a disaster at sea. Is it true that a shark can smell a drop of human blood in an ocean of seawater? Does noise arouse a shark’s curiosity, or scare it away? What about movement? Some accounts—including that of the swimming Ecuadorian—indicated that thrashing scared a shark away; others suggested it sparked their interest. No one really knew.

  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,‡ 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.”

  And so it continues to be. I know of only one recorded instance in recent history of a shark’s biting Navy personnel. In 2009, a bull shark took off the hand and foot—in one bite—of an Australian clearance diver during a counter-terrorism exercise in Sydney Harbor. I asked Naval Special Warfare Command communications specialist Joe Kane about sharks attacking Navy SEALs. “You’re coming at this the wrong way,” he said. “The question is not, Do Navy SEALs need shark repellent? The question is, Do sharks need Navy SEAL repellent?”

  The modern US Navy has no formal shark-attack curriculum. One diver recalls being told to descend slowly and take cover on the bottom should he sense a threat. A 1964 Air Force training film called Shark Defense advises downed aviators to blow a stream of bubbles or yell into the water. I asked veteran shark videographer Robert Cantrell what he thought of this advice. Cantrell has swum among sharks, cageless, for three decades. This is a man who will apply the adjective “nippy” to a group of excited blue sharks. His answer, an answer Baldridge and Tester often came up with, is that it depends on the kind of shark. Screaming into the water may briefly deflect a bull shark, Cantrell notes, but not a tiger shark. Bubbles scare blue sharks, but other species ignore them.

  The last Air Force suggestion was a puzzler: “Tearing up paper into small pieces and scattering them all around.” I suppose it was meant as a means of distracting the shark—or maybe just the sailor, now absorbed in the challenge of locating sheets of paper while afloat at sea. On one of Cantrell’s expeditions, he threw some stale bagels overboard. Tiger sharks swam over immediately; bull sharks ignored them. Cantrell’s main advice to the diver who encounters a shark? “Enjoy the experience.”

  Let us turn now to the question on many a sailor’s mind: Is it true that human blood draws sharks? The results of Baldridge’s and Tester’s experiments are inconsistent. Sometimes the sharks behaved as though attracted to the blood; other times they avoided the test area. Tester wondered whether the freshness of the blood was a factor. In his own experiments, blacktip sharks and greys were strongly attracted to blood less than one or two days old—at concentrations as weak as .01 parts per million of seawater. But Baldridge’s analysis of the Shark Attack File data belie this finding. In only 19 of 1,115 cases was the victim bleeding at the time of the attack. “It is difficult,” he concluded, “to accept the concept that human blood is highly attractive and exciting to sharks in general when so many shark attack victims have been struck a single blow and then left without further assault even though they were then bleeding profusely from massive wounds.”

  In Baldridge’s own tests, he presented four species of shark with the novel menu option of a swimming, bleeding lab rat. As fellow mammals, rats should possess blood that’s about as enticing (or unenticing) to a shark as our own. As he expected, the sharks showed no interest.

  The bottom line is that the preponderance of shark attacks, like most animal attacks, are prey-specific. If you don’t look or smell like dinner, you are unlikely to be so treated. Predators are attuned to the scents of creatures they most want to eat. Sharks don’t relish human meat. Even though a shark can detect human blood, it has—unless starving—no motive for tracking it to its source.

  That fact should be reassuring to women who enjoy swimming in th
e ocean but worry about doing so during their periods. But menstrual blood is different, in a uniquely shark-worrisome way. If you’ll permit it, a brief shore leave; the US Navy of the 1960s was not interested in menstruating women. The National Park Service, however, was. In 1967, two women, at least one of them menstruating, were killed by grizzly bears in Glacier National Park. Conjecture arose that it had been the blood that inspired the attack. Wildlife biologists didn’t buy it, and one of them, Bruce Cushing (delightfully mis-cited in subsequent bear attack/menstruation research as Bruce Gushing), set out to collect some data. Cushing opted to study polar bears, because they feed almost exclusively on seals, yielding a clean baseline with which to compare the animals’ zeal for menstruating women.

  If you put seal blubber in a fan box and aim the aroma at the cage of a wild polar bear, that bear will exhibit what Cushing called “maximal behavioral response.” It will lift its head and sniff the air. It will begin salivating heavily. It will get up and pace. It will chuff. It will groan. Only one other item that Cushing placed in the fan box could make a polar bear groan: a used tampon. Chicken didn’t do the trick, nor horse manure, musk, or an unused tampon. Coming in a close second: menstruating women. The women weren’t in the fan box, but in a chair facing the polar bear cage, where they “sat passively,” perhaps marveling at the strangeness of life on Earth. Cushing also tested ordinary blood, drawn from people’s veins; this elicited no response whatsoever from any of the four participating bears.