Mary Roach - Grunt

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 the 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.

In other words, it isn’t the blood that makes a tampon attractive to polar bears. It’s something uniquely… vaginal. Some kind of secretions that, please forgive me, smell like seals. This makes sense, does it not? When a feminine hygiene company hires a lab to test the efficacy of a scented menstrual product, the standardized odor employed for this purpose is known as a “fishy amine.”

So alluring is the intensely vaginal/sealy scent of a tampon that a polar bear seems not to notice that it does not also taste like seal. In 42 of 52 instances, a wild polar bear who encountered a used tampon affixed to the top of a stake (scientific nomenclature: “used tampon stake”) ate or “vigorously chewed” it. Only seal meat was more consistently pulled from the stake and consumed. Paper towels soaked with regular blood—here again, nailed to a stake like a skull warning foolhardy jungle explorers—were eaten just three times.

What does this tell us about sharks? Should women be worried? Hard to say. How crazy are sharks for seal meat? Do dead groupers smell like used tampons? Unknown. I’d stay in my deck chair, if I were menstruating you.

Cushing concluded his paper by suggesting that since polar bears enjoy used tampons, there was a strong possibility other ursids would, too. But bears, like sharks, vary by species. Forest bears aren’t connoisseurs of stinky marine life as polar bears are. Grizzlies like salmon, but they take them fresh. Black bears forage for garbage, so who knows what they’ve come to develop a taste for over the years.

To settle the matter, here comes the US Forest Service. Had you been off-loading garbage at a certain Minnesota dump on August 11, 1988, you would have been witness to an arresting sight. “We tied… [used] tampons to a monofilament line and spin-cast them to foraging bears,” wrote Lynn Rogers and two colleagues at the North Central Forest Experiment Station. Despite some fine fly-casting chops on show—the bait being “cast past the bears and dragged back under their noses”—20 out of 22 tampons were ignored. Such was also the fate of used tampons proffered “by hand” to black bears that frequented—though perhaps not anymore—an experimental feeding station. Also ignored: five used tampons tied together and thrown at a group of black bears, as well as all but one of a tasting flight of sodden tampons placed in the middle of a bear trail—four soaked with menstrual blood, one with nonmenstrual blood, and one with rendered beef fat. Ten out of eleven bears “swept their noses closely over the group, ate the tampon containing beef fat, and walked on.”

All in all, a resounding testament to the safety of national forests, and the patience of black bears.