MY QUEST TO DIVE WITH A TIGER SHARK TOOK ME TO the Hawaiian Islands, where tigers are abundant. Scientists like Carl Meyer, PhD, of the University of Hawaii have been studying tigers for the past twenty years, uncovering exciting new information about one of the few shark species big and strong enough to play a major role in protecting the marine ecosystems around the world.
I traveled to Honolulu on the island of Oahu in Hawaii. The most southern part of the United States, Hawaii has one of the longest coastlines in the country; only Alaska, Florida, and California enjoy longer coastlines. Everywhere I looked, luxurious green mountains soared over a blue sea. The tallest mountain, Mauna Kea—on the Big Island—stands 13,800 feet above sea level. However, if you measure the base from the seafloor, it rises 33,500 feet, which makes it taller than Mount Everest.
Meyer asked me where I wanted to meet, and I suggested the North Shore solely because that’s where world-class surfing takes place. Storms in the Pacific Ocean create winds that whip up the waves. As the waves barrel over thousands of miles, they begin to merge and grow in strength. With no impediment to their movement, they can reach heights of 40 to 50 feet in winter, equal to the length of a semitrailer truck. So I headed to the North Shore and found seven miles of pristine coastline. The waves were calm.
I was immediately struck by the remarkable way Meyer articulates the issues facing sharks today. “The broad goal of our research,” he explained, “is to learn more about the natural ecology of tiger sharks, and other species of sharks, that are found in Hawaii. It’s important to understand the ecology of these animals in order to develop effective conservation strategies for these important top predators. We use electronic devices to determine where these animals travel in the ocean, and the types of habitat that they use. We’re also interested in learning things like how fast they grow, how often they eat, and where they reproduce.”
Tiger sharks prefer to live in tropical and moderate coastal regions, thriving in murky waters and estuaries. The tiger shark’s name does not come from the aggressiveness of the shark but from the pattern of dark stripes along the sides of its body. The tigerlike stripes are most prominent during the shark’s youth, when it is vulnerable. Because tiger sharks stay close to the coast, the camouflage turns them into meandering shadows directly below the water’s surface. When the sharks reach adulthood, the stripes slowly disappear. The tiger is one of a kind. Its broad head, which is almost square when seen from above, gives the shark the chiseled-jaw look of a movie star. Its nostrils, called “nares,” are quite pronounced,1 splayed in front of the snout. Tucked inside the tiger’s eye is the nictitating membrane, which covers the eye for protection when the shark is feeding. This same membrane is found in many shark species, but there is an important difference between the eyes of tigers and those of other sharks. The tiger’s sclera, or white of the eye, encloses its black center. While the mako’s eye is completely black, which gives the shark a serious, “I mean business” look, the more soulful tiger’s eye is closer in its color composition to a human eye (a white circle with a black center), which gives the shark a more thoughtful, sometimes mischievous, demeanor. This is appropriate because the tiger is an ambusher and a thinker, absorbing its surroundings. Tiger sharks have made many appearances in YouTube videos in which scuba divers are petting their noses and the sharks are seemingly enjoying it. The eyes in these video clips have an impish look with a hint of playfulness. Natives of the Hawaiian Islands call the tiger shark “niuhi” and hold the shark’s eyes in reverence. Legend has it that many Hawaiian kings ate niuhi eyes to help them predict the future. The mother of King Kamehameha, the most famous Hawaiian king, requested niuhi eyes during her pregnancy because she believed they would help the future king become a better leader.
Despite the tiger shark’s folkloric ability to foretell the future, when it comes to hunting, the tiger shark remains the emperor of the ambush. The Big Four sharks—the great white, tiger, mako, and hammerhead—all take a different approach to hunting. The attack sharks, the great white and the mako, capitalize on their blazing speed to catch underwater prey and use their powerful jaws to settle the matter with a clear-cut finality. The tiger is different. Its Latin name, Galeocerdo cuvier, hints at the shark’s true nature: cunning. (Galeocerdo translates roughly as “fox shark,” and cuvier refers to the surname of eighteenth-century French naturalist Jean Léopold Nicolas Frédéric, Baron Cuvier, also known as Georges Cuvier, who came up with the idea of classifying animals into different phyla, or kingdoms.) Capable of swift and deadly attacks, tiger sharks possess the speed to catch a wily dolphin. For the most part they swim slowly and methodically, waiting and sensing for the right opportunity to strike since they are at their core an ambush predator.
Innately curious, the tiger is known to come right up to a diver’s cage, even to the divers themselves, because underwater cameras generate an easily detectable electrical signal, which draws in the nosy shark. Tiger sharks gather information with their mouth, which is why divers regularly misinterpret a bite to their camera as an act of aggression, rather than the harmless, exploratory gesture it is. Tiger sharks like to sneak up on divers, disappearing and reappearing like a magician’s trick, which unnerves many.
Another way to differentiate tigers from other shark species is their teeth. Like most sharks, a tiger replaces its rows of new teeth repeatedly throughout its life. But that is where the similarities in dentition end. While other shark teeth grab and hold prey, like kitchen forks, the tiger’s teeth act more like diamond cutters and are composed of two parts. The forward part of the tooth is shaped like an A, and its razor-sharp tip is serrated for cutting into its prey. The back part of the tooth is flat, with a slight downward curve. These serrated teeth can crush bone, saw muscle, and rip fins. The tiger’s teeth are a weapon of mass fish destruction. According to numerous tests, the tiger’s jaw can generate a force of 3 tons per square centimeter, which is equal to the weight of two cars. For almost all creatures, a turtle shell is practically impossible to penetrate. But a tiger shark can smash the tough carapace, turning the turtle into a heap of blood and sinew. The shark’s bristling arsenal of twenty-four identical teeth in its upper and lower jaws is an evolutionary triumph. And tigers need those teeth because they have the broadest diet of any shark species.
“They eat all kinds of reef fishes. They eat many types of invertebrates—things like lobsters and big marine snails,” Meyer told me. “They eat a lot of octopus, they eat birds, they eat marine mammals, they eat other sharks, they eat turtles, they eat sea snakes. They eat all kinds of stuff that washes out into the ocean—dead cats, dead cows, bags of skinless, boneless chicken. So, that really sets them apart from a lot of other sharks, which have much narrower diets.”
Sometimes, however, what tigers eat is rather shocking.
In 1935, in New South Wales, Australia, commercial fishermen accidentally caught a 1,600-pound tiger shark. Because they weren’t hunting the shark, they set it free in a tank, while they arranged delivery to the Sydney Aquarium, which requested the shark for an exhibit. Sharks do not do well in captivity, and this tiger shark refused to eat for a week. Eventually, he vomited up several objects, one of which was a human arm. The appendage featured a tattoo of two boxers on the shoulder. The police conducted an investigation and, based on the tattoo, identified the victim. Someone had killed the man, chopped him up with a knife, and thrown the severed body parts into Sydney Harbour, where the tiger shark had found them. The police investigation ended there because, according to Australian law, a single arm did not constitute a murder. The shark didn’t get off as easily, however, because the aquarium decided he was too difficult to keep. The director ordered his staff to butcher the shark, a second innocent victim in this bizarre tale of murder.
Since this curious case, researchers and fishermen have continued to find a number of other strange items in tiger stomachs: boat cushions, tin cans, license plates, tires, and the head of a crocodile. The shark is a high-tech machine assigned the modest job of ocean cleanup. The ocean owes a debt of gratitude to the tiger shark for maintaining it. When tigers remove garbage—weak and sick fish—they remove from the ocean bacteria and viruses that can harm reefs and seagrass. However, the tiger’s work extends beyond mere custodial work: as apex predators, tiger sharks play an important role in maintaining the balance of fish species across the ecosystem. Moreover, the research shows that areas with more apex predators have greater biodiversity and higher densities of individuals than do areas with fewer apex predators.2
Tiger sharks are fast growers. On average, tigers reach 12 feet by age seven. The fastest-growing tigers are this long by age four. In human terms, this is like a toddler being the size of a sumo wrestler. Other species of sharks grow only a few inches per year. In addition, tigers are among the largest of the various shark species. The larger tigers usually grow to a length of 18 feet, about the height of a giraffe, but some may reach more than 22 feet.
TIGERS AND HUMANS OCCASIONALLY INTERACT, MOST COMMONLY when skin divers harpoon fish. The fish’s telltale electrical distress signal attracts tigers. The sharks are more interested in getting a free lunch than they are in the divers, and shark attacks on humans are rare.
They still do occur, however. According to Hawaii’s Department of Land and Natural Resources (DLNR), there were nineteen confirmed shark incidents reported around the islands of Oahu and Hawaii, between 1995 and 2015, which is less than one per year. Around Maui, there were thirty-eight confirmed incidents, or less than two per year. Though Oahu and Hawaii are six times more populous than Maui, the less densely populated island experienced twice as many shark attacks. In 2012 and 2013, twenty-three bite incidents occurred, a threefold increase above the average rate of attacks. Again, most of these attacks occurred in the waters around Maui.
The DLNR’s Division of Aquatic Resources recruited Carl Meyer to help them figure out why more attacks were occurring in Maui and what, if anything, Hawaiian state authorities could do to protect beachgoers and vacationers there. Highly regarded in Hawaii and on the mainland for his innovative research on the ecology and management of sharks and reef fish, Meyer studies movement patterns, habitat use, and trophic ecology of sharks and fish, as well as the navigational abilities of sharks. To more closely monitor the sharks around all three islands, he captured and fitted twenty-four tigers with pop-up archival transmitting tags (PATs), which can record data for many weeks or months without transmitting. At a preprogrammed time, the tag pops off, floats to the surface, and starts an immediate data dump, transmitting summary information to satellites. While the summary data is still valuable, it is incomplete. Unless scientists physically retrieve the tag, they can’t access the full data set each PAT contains. And if the battery dies before the tag is retrieved, data will be lost.
Meyer waited for the tags to pop up. When one PAT rose to the surface, its signal went out to a lab at the University of Hawaii. Right away, lab technicians notified Meyer, who had already arranged for a boat team to go out and retrieve the tag. There was a problem, however: severe weather was preventing the team’s small 15-foot boat from venturing out to sea. The landlocked scientists circulated the tag’s geolocation to fishermen in the area. None of them spotted the tag, and the clock was ticking. Fortunately, the weather improved enough to risk letting the Hawaiian team motor out 43 nautical miles east in the middle of the rough seas. They used a special directional scanner to locate the signal, but the 4- to 6-foot waves made it difficult to spot the small tag. With only two minutes remaining before the captain’s predetermined turnaround time, the team spotted the tag off the coast of Maui and brought it aboard. The mission was accomplished, and none too soon—the satellite tag battery had only twelve hours of power left. If they had waited one more day, the tag’s data would have been lost forever.
The information from that tag, combined with other material the team collected, allowed Meyer to piece together an extraordinary picture of the tiger shark’s travels and revealed, per the DLNR’s mandate, the reason why shark attacks occurred more frequently in Maui. Tiger sharks prefer certain areas over others—one of which is the coastal shelf, the relatively shallow water surrounding the Hawaiian Islands where the water is less than 600 feet deep. This area is more conducive for feeding and reproducing, according to Meyer. And because there is considerably more of this coastal shelf habitat around Maui than any other Hawaiian island, more tiger sharks gathered there. Meyer noted that the tigers he tagged in the waters off Oahu traveled to the coastal shelf off Maui, while the Maui tigers he tagged stayed put. A significant gathering of tigers formed there, which is why Maui experienced more attacks.
Increase the number of sharks in a specific area and the likelihood of an attack increases. That’s just math. Still, the actual rate of tiger shark bites is incredibly low when considering that tigers regularly approach the beach, often in only a couple of feet of water. “It just so happens that the areas that are the most attractive to tiger sharks are also the places where humans like to play in the ocean,” said Meyer, who described the spike in attacks between 2012 and 2013 as a statistical anomaly, a one-year aberration. “From a strictly statistical perspective,” he said, “twenty-three incidents in two years can just be chalked up to ‘the elements of chance’—especially considering how many people in Hawaii partake in ocean activities—as opposed to some environmental trigger or some other trigger.”
Rather than closing the beaches of Maui—or, worse, launching an ill-advised shark-culling campaign—he instead recommended that Hawaiian state officials keep the beaches open. Sure enough, the number of attacks returned to the mean. In 2018, there were only three confirmed shark bite incidents in the state.
“In spite of the shark’s size, humans do not need to fear them,” he said. “Shark bite incidents are very, very rare, and are actually very unusual behavior. If tiger sharks really wanted humans as prey, it just wouldn’t be safe to go swimming.”
Since the state ended its study of shark attacks in 2016, Meyer has continued to learn a tremendous amount about the travels of the tiger sharks from the tagging studies. “Tiger sharks, in particular, are very cosmopolitan in their movements,” he said. “They range everywhere from the shallow waters right next to beaches, to far out into open ocean—sometimes, more than 1,000 miles out into the open Pacific Ocean. And they also range between the surface and depths of around 1,000 meters—that’s around 3,000 feet. And because they’re ranging between the surface and these depths of 3,000 feet, they’re encountering temperatures that range from tropical warm oceans down to very cold temperatures that are similar to the Arctic Circle.”
Meyer uses the same kinds of cutting-edge technologies to study other coastal sharks in Hawaii, including the sandbar shark, a common species in the region. These sharks are relatively small; a large adult is only about 6 feet long. Meyer captured a sandbar shark and ingeniously fitted it with a video camera to find out what it was up to. When Meyer recovered the camera, he saw that the shark swam out a couple of miles offshore and, after a couple of days, went down to a depth of about 300 feet and joined a huge aggregation of sharks. “This aggregation consisted of a variety of species, including other sandbar sharks, blacktip sharks, but also large numbers of scalloped hammerhead sharks,” Meyer said. The group of sharks gradually moved from 300 feet in depth up toward the surface; at dusk, the aggregation dispersed, and the sharks went their separate ways. “The most likely theory is that this sort of phenomenon is actually an antipredation mechanism. So although we’re talking about sharks, who are relatively large—anywhere from 4 or 5 feet up to, maybe, 10 feet in length—they are still subject to predation by larger sharks, like tiger sharks. About 40 percent of the diet of the largest tiger sharks is made up of other sharks. So, we think that these mixed-species aggregations form for the purpose of protecting the sharks within the aggregation from predation from large species.”
Meyer is convinced that fear is the driving force in these aggregations. If this was a mating aggregation, which is another reason why sharks aggregate, then the scientists would expect to see only one species of shark in the pods because one species, like sandbar sharks, cannot mate with another, like scalloped hammerheads. I used to think that sharks were the one animal above having to fear living in the ocean, but fear is ubiquitous in the underwater world. The sharks revealed an ability to come up with a strategy for survival with their compatriots. Their behavior shows a consciousness of themselves and others and an ability to collectively figure out a way to survive in a harsh environment.
When it comes to sex and reproduction, scientists are still learning about the breeding habits of tiger sharks. One thing they do know is that tiger sharks have a large number of pups, more than most other shark species. Tiger sharks are ovoviviparous, which means they have eggs that hatch inside the womb so they give birth to live young, usually about thirty or forty pups at a time, though tigers sometimes birth as many as eighty pups. But with a gestation period of fifteen to eighteen months,3 tigers take a long time to reproduce. While they are protected from overfishing in Hawaii, the sharks are in peril in many other parts of the world.
Because I wanted to get close to a tiger shark, I signed up for a cage-diving trip in Maui and soon was on the deck of a 45-foot powerboat. I was not alone in my fascination with sharks. A dozen other people joined me for the dive. We were all ready to dangle in a cage floating just below the surface to get a glimpse of sharks. Each person that I talked to had their own reason for participating in the adventure. Some were daredevils, while others were more like me: they wanted to see the beauty of sharks up close. The day was sparklingly clear, and as we headed out to sea, the green mountains of Maui faded. I am used to the harsher look of the Atlantic Ocean. Its green waters are always seemingly dressed with white caps. In contrast, the Pacific that day was unusually calm, its blue color vibrant and warm. When one is on the Pacific, the ocean whispers to the soul.
I talked with one of the guides about her experience diving with tigers. Now in her mid-thirties, she had worked on this operation for three years and enjoyed being outdoors. “Tigers can be mysterious,” she said, as the wind blew through her long blond hair. “They can see you, but you can’t see them. They like to sneak up on you, too. It is as if they’re playing a game with you to see if you can tell where they’ll come from.”
We motored up to an orange buoy. Raising the aluminum shark cage on the stern with a winch, the crew swung it over the side. The 6-feet-by-12-feet steel cage splashed in the water. As a practice, the crew doesn’t drop chum in the water because the sharks have learned to congregate near the sound of the engines. They know that the fishing boats will carve up and throw their bycatch overboard. The engines signal that an easy meal is to be had. For apex predators to survive at the top of the food pyramid, they need such logical reasoning. We just had to wait for the sharks to come to us.
I dropped inside the cage, eager to finally encounter a tiger shark. As I descended underwater, my entire world turned a beautiful monochrome, a beautiful azure vista, dazzling in its simplicity. The islands of Hawaii are a time capsule of the time before overfishing and overdevelopment took their toll on the sea. From inside my cage, a gray mirage appeared. It slinked closer and, as it neared, I could discern its tall dorsal fin. Patrolling the underwater arena with purpose, the shark circled my cage with a graceful push of its tail. Other sharks began to appear and join in: Galápagos sharks. These large sharks are found around the world and are usually 7 to 9 feet long. Dark gray above with a light underbelly, the Galápagos shark has no distinctive markings. I admired the sharks’ strength and torpedo shape. They examined me with quick eye movements, curious but without emotion. Not recognizing a source of food, they swam away.
Where was my tiger, though? Ten minutes underwater and nothing. I received the signal to return to the boat. My trip to see the tiger failed, and my quest would have to continue. With patience, I may possibly get to see a tiger eventually. But for now, they are not ready to reveal themselves to me.
The mysterious ambusher, hiding in the blue miasma, probably saw us. It may have wondered what these trespassers were doing but decided we were not worth its time. I can imagine it turning its massive head from us and slowly swimming away to play its role in the ocean. On the boat trip back to shore, I thought about all the ways that tiger sharks make the Hawaiian Islands what they are. Divers that come from all over the world to see the beautiful reefs of the Hawaiian Islands may not realize that the abundant and diverse sea life is the handiwork of the sharks—or that the seagrass is so luxuriant due to the tiger’s protection.
Native Hawaiians recognize how the tigers molded their world, and they came to know them even before the age of telemetry tags. In Hawaiian mythology, the oral myths warned of shark bites in the months of October and November. Meyer was able to show that they were right.4 Most bites take place in the fall months during the pupping season. Sharks need a tremendous amount of energy to nourish each litter of shark pups during pregnancy. Previous scientific studies have shown that pregnant females of other species of shark are in poor condition in the run-up to giving birth and during the postpartum period. After the females significantly deplete the energy from their livers during pregnancy, they are in greater need for food during these fall months.
Another belief about sharks in Hawaiian mythology is that they are gods. The early Hawaiians understood that tiger sharks are crucial to the health of the planet’s oceans, which cover 70 percent of the world’s surface. Yet humans have hunted and butchered them and viewed them as creatures only to be feared.
AFTER MY DIVE, I ASKED MEYER ABOUT COMMERCIAL FISHING for sharks beyond the Hawaiian Islands in the Pacific Ocean. He broke down the shark fisheries into two groups. The first group impacting shark populations worldwide consists of the fisheries that are intentionally targeting and capturing sharks. The second group comprises those that are fishing for other fish species, particularly tuna, and catch sharks by accident. “Between these two, undoubtedly, the biggest impact is from the former group, the industrial shark fishing; they are targeting sharks for their fins. And this is a fishery that then takes those fins and sells them to Asian markets, where they’re made into shark-fin soup.” I asked Meyer how many sharks are being killed for this market. He said, “It’s resulting in millions of sharks being removed from the oceans every year, just to supply that demand.”
Shark-fin soup is a dish that is associated with affluence in Asia. Historically, the imperial family and court members dined on shark-fin soup during the Song dynasty around 1000 CE. Between the end of the last Qing dynasty and now, shark-fin soup has remained in high demand. Chinese Communist officials have only recently banned shark-fin soup at official functions, more in an effort to end extravagant state spending than as a conservation effort. The long-held and deeply rooted perception that shark-fin soup suggests wealth and status continues. Compounding the issue is the belief in Chinese culture that shark fins contain medicinal properties that can boost sexual potency, clear up bad skin, and prevent heart disease. However, no scientific evidence exists to support this belief. In fact, studies have shown that shark fins contain neurotoxins, and eating shark-fin soup may raise the risk of dementia.5 Similarly, mercury accumulates in the tissues of top apex predators, and eating shark-fin soup exposes the consumer to mercury poisoning.
The shark fins that end up in soup go through a tortuous path. Countries like Indonesia, Costa Rica, Peru, Ecuador, Spain, and South Africa bring their fins to collection points around the world, and the biggest hub is Hong Kong, which processes 40 percent of all shark fins. The value of each fin depends on three criteria: species, the quality of the fin, and the type of fin. Thick fins—preferably from silky sharks and blue sharks—with discernible veining are considered the highest quality, while the most valuable fin is the lower section of the shark’s caudal, or tail, fin, which often goes for between $150 and $300 per pound. Because of a lengthy processing treatment that requires two separate stages of dehydration and skinning, individual fins lose most of their mass. A single kilogram of fin, for instance, yields only 0.1 kilogram of dried shark fin. This is why sharks are finned in such high numbers.
Of the total number of shark fins that enter Hong Kong, 40 percent of the fins processed there are then reexported to other countries, most notably China. The remaining 60 percent of the fins are sold and shipped to dried seafood markets or to tony hotels and restaurants throughout Hong Kong, where the fins are prepared for soup. In addition to silky sharks and blue sharks, vulnerable species like hammerheads and oceanic whitetips routinely end up in this controversial dish.
“Now the problem is that people in Asia as a whole,” Meyer explained, “want to serve shark-fin soup, which means the demand for shark-fin soup is continuous.” The conservation issue becomes tougher to solve because it’s not just about coming up with technical measures that can help reduce the catch of sharks; it’s about persuading people not to eat shark-fin soup. Reducing the demand for shark-fin soup is the only way to mitigate the tremendous impact of this industry on shark populations worldwide. Some countries look at the ocean as an inexhaustible supply of whatever fish they want to eat. With millions of sharks dying for soup, it seems that humankind is playing a dangerous game with the planet’s top ocean predator.
Many people do not like sharks, and the basis for that view is that sharks are creatures to be feared. But is this fear of being attacked justified? I went in search of the answer to the question: How dangerous are sharks?