BY Erik Vance July 2016 National Geographic
Why Great White Sharks Are Still a Mystery to Us
The Realm of the Great White
The great white is one of six shark species that are endothermic, which means they can raise internal body temperatures over that of surrounding waters. This allows great whites to inhabit extreme depths as well as cold waters of higher latitudes, while still being able to function efficiently to capture swift and agile prey Some great white sharks migrate seasonally over very long distances.
Great whites do not live in groups, nor are they purely solitary creatures. Sometimes they congregate near food.
White sharks maintain a constant body-core temperature of 79°F regardless of surrounding water temperatures. In most sharks, metabolic heat is released at the gills and through the skin. In great whites, however, a unique arrangement of veins and arteries allows transfer of heat between warm and cool blood, retaining heat in the body core.
Red Muscle The central placement of warm red muscle—aided by heat exchangers—means less heat is lost through the skin.
Body Cavity Heat circulating in the gut area may speed digestion and food absorption.
Brain and Eyes Warm blood near the brain and behind the eyes keeps the shark alert and armed with sharp vision in cooler waters. A vein running from the red muscle delivers warm blood to the brain.
The clear waters off Australia’s Neptune Islands are one of the best places in the world to see great white sharks.
Sharks often attack cautiously, apparently fearing injury from a seal’s claw. Frequently they will bite, then back off and allow the prey to bleed to death.
Thanks to Jaws, they’re the ocean’s most iconic and feared fish. But we know surprisingly little about them. Much of what we think we know about great white sharks simply isn’t true. They aren’t merciless hunters, they aren’t always loners, and they may be smarter than experts have thought.
Perhaps no other animal stirs primal panic like a great white shark. But scientists say people may pose more of a threat to great whites than the sharks pose to people.
Meeting a great white shark in the wild is nothing like you expect it would be. At first glance it’s not the malevolent beast we’ve come to expect from a thousand TV shows. It’s portly, bordering on fat, like an overstuffed sausage. Flabby jowls tremble down its body when it opens its mouth, which otherwise is a chubby, slightly parted smirk. From the side, one of the world’s greatest predators is little more than a slack-jawed buffoon.
It’s only when the underwater clown turns to face you that you understand why it’s the most feared animal on Earth. From the front its head is no longer soft and jowly but tapers to an arrow that draws its black eyes into a sinister-looking V. The bemused smile is gone, and all you see are rows of two-inch teeth capable of crunching down with almost two tons of force. Slowly, confidently, it approaches you. It turns its head, first to one side and then the other, evaluating you, deciding whether you’re worth its time. Then if you’re lucky, it turns away, becoming the buffoon again, and glides lazily into the gloom.
There are more than 500 species of sharks, but in popular imagination there’s really only one. When Pixar needed an underwater villain for its animated film Finding Nemo, it didn’t look to the affable nurse shark or the aggressive bull shark. Not even the tiger shark, which would be more appropriate in Nemo’s coral-reef home. It was the great white shark—with its wide, toothy grin—that was plastered on thousands of movie billboards across the world.
The great white shark is the ocean’s iconic fish, yet we know little about it—and much of what we think we know simply isn’t true. White sharks aren’t merciless hunters (if anything, attacks are cautious), they aren’t always loners, and they may be smarter than experts have thought. Even the 1916 Jersey Shore attacks famously mentioned in Jaws may have been perpetrated by a bull shark, not a great white.
We don’t know for sure how long they live, how many months they gestate, when they reach maturity. No one has seen great whites mate or give birth. We don’t really know how many there are or where, exactly, they spend most of their lives. Imagine that a land animal the size of a pickup truck hunted along the coasts of California, South Africa, and Australia. Scientists would know every detail of its mating habits, migrations, and behaviour after observing it in zoos, research facilities, perhaps even circuses. But the rules are different underwater. Great whites appear and disappear at will, making it nearly impossible to follow them in deep water. They refuse to live behind glass—in captivity some have starved themselves or slammed their heads against walls. (Several aquariums have released them for their own safety or because they were attacking tank-mates.)
Yet scientists today, using state-of-the-art technologies, may be on the verge of answering two of the most vexing mysteries: How many are there, and where do they go? Unraveling these mysteries could be critical to deciding how to protect ourselves from them and them from us. When we finally see the great white clearly from all angles, will the world’s most fearsome killer deserve our fear or our pity?
A 24-foot fishing boat sits just off the southern tip of Cape Cod, Massachusetts, on a perfect summer afternoon. The passengers—three scientists, two paying customers, two journalists, and the boat’s captain—lounge on the seats, looking off toward Nantucket. The voice of a spotter pilot flying 1,000 feet above breaks out over the radio in a sharp New England accent. “We’ve got a wicked nice shark over here to the south!”
Fisheries biologist Greg Skomal perks up. He’s standing five feet off the bow on the pulpit, a fenced-in walkway resembling a pirate’s plank. If this were a Hollywood movie, he’d have a harpoon and a peg leg. Instead he carries a GoPro camera attached to a 10-foot pole. He grins like a little kid as the captain guns the engine.
Cape Cod’s Great Whites
The waters off the Cape Cod, unlike other places inhabited by great whites, are shallow enough to spot sharks from the air.
Cameras in seal decoys, months of patience, and a lightning-quick finger on the camera shutter are used near Cape Cod to produce rare high-quality photograph. Great whites here are difficult to photograph because they aren’t attracted to chum. Great white bite the seal decoy.
Before 2004 hardly anyone in modern times saw great white sharks in the waters off the East Coast. Occasionally one would appear near a beach or in a fishing net, but they were anomalies. Elsewhere, great whites congregate seasonally around five “hubs” or territories, including California’s coast down to Mexico’s Baja California, South Africa’s southern shores, and Australia’s southern coast, where they gather to feed on seals. But there’s been no hub on the East Coast, nor have there been many seals. Sharks here were wanderers without a home. Then, in 2004, a single female found her way into shallow inlets and shoals near Woods Hole, Massachusetts.
For Skomal, who’d been tagging other sharks for 20 years, this was the chance of a lifetime—a great white in his own backyard. “I thought it was a fluke. This will never happen again,” he says with his broad, boyish grin under ruffled salt-and-pepper hair. Over the next two weeks Skomal and his colleagues followed the shark, which they named Gretel after the lost girl in the fairy tale, and affixed an electronic tracker on her. Tracking a white shark across the Atlantic Ocean offered a chance to solve so many riddles. But 45 minutes into the journey, Gretel’s tag malfunctioned and popped off. “I went from this superhigh to this really deep low, because I was convinced that this was the shot in my career to study a white shark,” Skomal says.
It wasn’t. Over the next few years he thought a lot about Gretel and wondered whether she was indeed alone. Then, on Labor Day, 2009, everything changed. A pilot saw five great whites off the cape. Over that weekend Skomal tagged them all. “I absolutely freaked out. My adrenaline was pumping. My heart—I could feel it just pounding in my chest. This was everything I was dreaming of.”
White sharks have returned every summer since, leading some to call Cape Cod the sixth hub. How many great whites are there? For that we turn to the hub running from California to Baja California. The effort to count sharks there was pioneered by Scot Anderson while he was a volunteer seabird scientist in the mid-1980s on an island west of San Francisco’s Golden Gate Bridge. Anderson and others have tracked the sharks—at first by sight, then by acoustic tags, and most recently with satellites. During the past 30 years, teams have assembled thousands of observations of individual sharks recognized by the shape and marks of their dorsal fins, while others have used the distinctive line between their gray bodies and white underbellies. Scientists know where the sharks congregate and how they feed. And each year most sharks they see are the ones they saw in previous years.
This raised an intriguing question: With enough observations, could you use the sharks you see to estimate how many you can’t see? In 2011 a team in California did just that and came up with just 219 adults in California’s most shark-rich region. Even among top predators, generally less abundant than their prey, that’s a tiny number. The study shocked the public and came under immediate attack from other experts.
There’s reason to be hopeful. Few if any fishermen target great whites today, yet a global pact, the Convention on International Trade in Endangered Species, gives white sharks its second strongest conservation rating because fishermen catch them unintentionally. With numbers so low, even accidental catches can play havoc with the species, which, as a top predator, has an ecologically important role in managing the oceans.
Of course, counting great whites is a lot harder than counting land animals or even marine mammals. So scientists make massive assumptions about shark movements and then extrapolate. In California the biggest assumption was that a few feeding grounds were representative of the entire hub. Other teams crunched the same data using different assumptions, and one study estimated about 10 times more sharks. (That count was bolstered by adding juveniles, which the first excluded because so little is known about them.) Pretty soon scientists began quantifying white sharks in the other hubs. A team in South Africa estimated the population there at around 900, while another team put Mexico’s Guadalupe Island population, part of the California hub, at just 120 or so.
Are these large numbers or small? Are great whites thriving or dwindling? The world has about 4,000 tigers and 25,000 African lions. Using the lowest estimates, global great white numbers resemble the estimate for tigers, an endangered species. Using the highest estimate, the population is closer to that of the lions, which are classified as vulnerable. Several experts see them heading toward extinction; others see a positive trend. Some say rising seal populations are a sign that great whites are nearly gone, while others say more seals mean more sharks. Aaron MacNeil, an Australian statistician who crunches shark data, says the appearance of sharks around Cape Cod and the increased activity in the Southern Hemisphere suggest the latter. “I haven’t seen any evidence in the last decade that white sharks are declining,” says MacNeil. “Yes, there is a historical depletion of white sharks. But the story is not that they are going extinct. The story is that they are probably increasing very, very slowly.”
Cape Cod may have the highest density of great white sharks in the world
“It’s incredible how camouflaged they can be. People might be right next to them and don’t even see them,” one expert says.
PHOTOGRAPH BY BRIAN J. SKERRY, NAT GEO IMAGE COLLECTION
But today, that reality is settling in among the popular seashore towns as white sharks return to an area they disappeared from decades ago. And as communities search for solutions to keep beaches safe, one question has dominated: Just how many white sharks are out there?
That number has been hard to come by, as counting the elusive and wide-ranging predators is complicated. But researchers with the Atlantic White Shark Conservancy finally have an answer, based on an innovative combination of acoustic tracking, photographic identification, and statistical modeling.
The bombshell: Some 800 sharks—and possibly up to 900—swam the waters of Cape Cod between 2015 and 2018. In comparison, a similar white shark estimate for California’s central coast is 300, while the population for South Africa’s Dyer Island, known as Shark Alley, is thought to number between 800 and a thousand.
Cape Cod has “potentially the highest density of sharks in the world,” says Megan Winton, a fisheries scientist whose data is still in the pre-publication stage.
“We knew there were a lot more sharks out there, but this is the first time we’ve ever had a number for any portion of the species’ range in the North Atlantic, which is huge,” Winton says.
The findings are striking not only because of the number of sharks, but the fact that they’re concentrated along just 560 miles of protected coastline.
The four years of tracking also revealed the sharks, mostly adults between eight and 12 feet long, spend approximately half their time in 15 feet of water or less.
“People might know that white sharks come here, but they think they’re far offshore,” Winton says.
“We’ve seen sharks as big as 15 feet long in just four to five feet of water. And it’s incredible how camouflaged they can be. People might be right next to them and don’t even see them.”
Knowing the risk
White sharks are rebounding in Cape Cod for one simple reason: Their favorite prey, the gray seal, is back on the menu. Hunted nearly to extinction, the seal population began rebounding with the passage of the U.S. Marine Mammal Protection Act in 1972.
Today, the seal population tops 50,000. It took longer for the white sharks, considered vulnerable by the International Union for Conservation of Nature, to follow, but since receiving national protection in 1997 and Massachusetts state protection in 2005, their numbers have steadily grown off the eastern U.S.
“You really can’t think of any other location where white sharks attempting to feed on seals overlap with human activity,” says Greg Skomal, senior fisheries scientist with the Massachusetts Division of Marine Fisheries and a co-author on the forthcoming paper. (Read how to be safe while swimming in shark habitat.)
The risk of a shark bite is very small, Skomal emphasizes; swimmers are much more likely to drown. That said, five sharks have bitten people in Cape Cod since 2012, including a fatal incident in 2018, when a person was killed while bodyboarding in Wellfleet.
To reduce the likelihood of shark-human encounters, scientists need to know where the sharks go and when.
To find out, the Cape Cod scientists created a catalog, or logbook, of individual sharks identified both through tagging and photo documentation of their coloration patterns and dorsal fin profiles between 2015 and 2018.
The team then conducted a three-year survey that compared the number of newly recorded individuals with those previously documented, reconstructing these encounters through statistical modeling to create a population estimate. Unlike previous surveys in South Africa, California, and elsewhere, Winton’s model considered the movements of individual sharks.
The older models assumed “all individuals act and use these areas in the same way, which can impact how good the resulting estimates are,” Winton says. “We created a new model that allowed sharks to move into and out of the area and accounted for where individual sharks like to ‘hang out’ along the coast.”
The advent of portable, high-quality underwater cameras, which the Cape Cod team used has also made identifying individual sharks easier and more accurate, says Taylor Chapple, an assistant professor at Oregon State University who wasn’t involved in the study.
“This type of study is really game-changing for species like white sharks because we can identify a really huge portion of the population, which gives us really strong confidence that our numbers are right,” says Chapple, who has studied white shark populations in California. White sharks typically live up to 70 years old.
In addition, researchers with the Cape Cod-based Center for Coastal Studies are using sonar surveys to map shark movements, which has revealed Cape Cod sharks have a hunting strategy completely unique to the region. (Learn why great whites are still a mystery to us.)
White sharks are ambush hunters, typically stalking their prey in deep water and lunging into the air to take an unsuspecting animal by surprise.
But along Cape Cod’s sandbar-lined coastline, the sharks are forced to hunt in shallow water. They do this, the scientists found, by patrolling a trough between the sandbars until a hungry seal ventures into the water to eat.
Understanding this unusual behavior will help experts predict the sharks’ movements and identify areas particularly dangerous to swimmers.
Shark-detection systems are also giving scientists and the public a better sense of the predators’ activity, with the goal of improving public safety.
Since 2009, Cape Cod researchers have tagged a total of 303 sharks outfitted with acoustical transmitters. Five acoustical monitors on outer Cape beaches can detect sound pulses when a tagged shark goes by, sending this information in real time to lifeguards, beach managers, scientists, and the public via the Sharktivity app.
In 2022, the conservancy logged 193,475 shark detections. It’s not exact—one shark circling the vicinity of a monitor might set it off over and over—but it does provide a general idea, Winton says. (Read why beach warning signs are often ignored by Cape Cod swimmers.)
“Some of the lifeguards have told us the alert system has really changed how they think about the sharks,” Winton says. “They say they used to think they came by every once in awhile but were mostly offshore. Now they realize that in the summer and fall they’re here pretty much all the time.”
EAST PACIFIC
To understand whether great white sharks need our protection, we must know not only how many there are but also where they go. Their migrations aren’t neat, like a bird’s or a butterfly’s. They’re messy, with one hugging the coast while another zigzags hundreds of miles out to sea. Many, but not all, seem to seasonally move between warm and cold water. And the paths seem different for males, females, and juveniles.
Today, with long-term, long-distance tags that can communicate via satellite, scientists are finally getting some clarity. For years scientists have noticed that adult great whites in California and Mexico quit the coast in late fall. Now we know where they go: deep water in the middle of the Pacific Ocean. Why they visit this great white shark “café” remains unclear. “I call it Burning Man for white sharks,” says Salvador Jorgensen, a biologist who studies factors that drive great white migration and ecology. “They are heading out to what some people call the desert of the ocean, and what the hell are they doing out there?”
One possible answer is mating, which might explain why no one has ever observed it. The area is roughly the size of California and thousands of feet deep, which makes it hard to monitor sharks there. But satellite tags tell us that the females swim predictable straight patterns while the males swim up and down in the water column, possibly searching for mates. Thus a rough sketch of the lives of California white sharks is forming. After spending the summer and fall gorging on seals, they head out to the deep ocean to breed, relying on energy stores to live. The males then swim back to the coast while the females wander to unknown places, where they remain for another year or so, perhaps to birth their young. Newborn sharks then show up at feeding grounds—say, the waters off Southern California—devouring fish until they are big enough to join their elders in the north or south hunting seals.
It’s not a perfect picture. Females and males aren’t in the café together for long, and we don’t know where the babies are born. But it explains a lot. For example, as a population rebounds, its young become plentiful, which is likely why Southern Californians have encountered a lot of sharks lately. Yet it’s tougher to figure out elsewhere. Australian sharks forage along the southern coast but don’t seem to have a pattern or café. And in the Atlantic we know even less. “We’ve got wanderers, and we’ve got coastal sharks. And what dictates which, I have no idea,” Skomal says.
Even though he doesn’t understand their migrations yet, Skomal is sure that white sharks have a long history here. At his office in New Bedford, just west of Cape Cod, he opens a document that compiled studies of seal bones from Native American archaeological sites along the eastern seaboard. The discarded bones suggest that seal populations crashed from overhunting perhaps a century before the Declaration of Independence. In other words, we’ve had very few Atlantic gray seals throughout the United States’ 240-year history. Today, thanks to the Marine Mammal Protection Act, seal colonies now populate New England. And when the seals returned, the sharks came home as well.
One bright August morning I board a two-seater plane with Wayne Davis, a veteran spotter pilot for tuna and swordfish who now helps scientists track down white sharks. Unlike the hubs, the water here is so shallow that sharp eyes can spot them from the air. In just 30 minutes of flying we see seven, all patrolling beaches where gray seals are foraging in open waters. On the way back Davis and I fly past several beaches a mile or so to the north packed with vacationers.
So far locals have embraced their new neighbors. There are stuffed animals, T-shirts, posters, and a community art exhibit called “Sharks in the Park.” Even the new high school’s mascot is a great white. Most of the time the sharks are shown from the side—cheerful, buffoonish. Experts warn, though, that at some point someone here will meet the other version—the one with teeth.
Attacks on people are incredibly rare. In waters off California, the chances of a surfer being bitten by a great white shark are one in 17 million; for swimmers, it’s even rarer—one attack in every 738 million beach visits, according to a recent Stanford University study. On Cape Cod, fatalities may not be a question of if, but when. The last lethal shark attack off New England was in 1936, but there have been several close calls recently. A swimmer there was bitten on both legs in 2012, and two paddlers in Plymouth were knocked from their kayaks in 2014, although they escaped unscathed.
If a more serious attack happens, Massachusetts will join the other hubs in weighing the benefits versus the dangers of sharks in their waters.
It may be that great white sharks are rebounding across the world: following the bigger seal and sea lion populations, re-establishing themselves in their old hunting grounds, reclaiming the coasts they nearly lost.
Then again, it may be that great whites today are hanging over the abyss of extinction, clutching the edge by the skin of their jagged teeth. Will we look past our fear and reach out a hand to this creature? Can we take pity on the pitiless eyes of a monster?
