Scientists Finally Discovered What Is Killing Great White Sharks — The Findings Are Disturbing

[00:00:00]Is it possible that there is something out here that we literally haven't seen before?

[00:00:05]>> Off the coast of South Africa, marine biologists watched in stunned silence as the ocean's most feared predator fled in terror. Not from humans, not from boats, not from nets. [music] The great white shark, the creature that has haunted human nightmares for 50 years, was running from something else entirely.

[00:00:22]And what scientists [music] discovered when they finally pieced together the full picture was not just shocking, it was a warning. A warning that the most dangerous predator on Earth is being erased. And what is doing the erasing should terrify all of us far more than any shark ever did. Hi, my name is Matthew and this is Reef Discovery. The king of the ocean is disappearing. To understand why the death of the great white shark matters, you first need to understand what the great white shark actually [music] is. Not the movie version, not the one from 1975 with the mechanical jaw and the dramatic music.

[00:00:57]The real animal.

[00:00:58]>> [music] >> Carcharodon carcharias has been swimming in Earth's oceans for roughly 11 million years. Let that number sit for a moment.

[00:01:05]11 million years. The ancestors of modern great whites were hunting in these waters before our [music] earliest human ancestors stood upright on the African savanna. They survived the extinction event that killed the dinosaurs. They survived ice ages. They survived the geological reshaping of entire ocean basins. They are, in every meaningful sense of the word, survivors.

[00:01:28]Adult great whites can reach lengths of 20 ft and weigh over 5,000 lbs. Their teeth, the ones that inspired a thousand nightmares, are not their most impressive feature. Their most impressive feature is their sensory system. Great whites can detect a single drop of blood diluted across 100 L of water. They can sense the electromagnetic fields produced by the muscle contractions of prey animals buried in sand. They can feel pressure changes from a struggling fish from over 800 feet away.

[00:01:59]They are not just apex predators. They are the most sophisticated hunting machines evolution has ever produced for the ocean environment. And they play a role in ocean ecosystems that goes far beyond eating things. Great whites are what ecologists call keystone predators.

[00:02:15]Their presence shapes the behavior of every species below them in the food chain. When great whites patrol a coastline, seal populations stay concentrated in specific areas rather than spreading out and overgrazing coastal fish nurseries.

[00:02:30]Mid-level predators like smaller sharks and rays regulate their feeding patterns around [music] great white territories.

[00:02:36]The entire ecosystem calibrates itself around the presence of the apex predator at the top. Remove the great [music] white and the whole system starts to wobble. Researchers have estimated the global great white population at somewhere between 3,000 and 5,000 individuals.

[00:02:54]That number sounds manageable until you realize it represents the entire global population of one of the oceans most critical species. For comparison, there are more giant pandas in captivity right now [music] than there are great white sharks in the entire Pacific Ocean. We have spent 50 years being afraid of great white sharks. We made blockbuster films about them. We put their silhouette on warning signs [music] and merchandise and Halloween costumes. We obsessed over them as predators and somehow, [music] while we were busy being terrified of great white sharks, something started killing them.

[00:03:28]Systematically.

[00:03:29]Globally.

[00:03:31]And almost without anyone noticing.

[00:03:33]The mysterious die-offs begin.

[00:03:37]The first sign that something was seriously wrong came from South Africa.

[00:03:41]Gansbaai, a small coastal town on the Western Cape, had been known for decades as the great white shark capital of the world. The waters around Dyer Island were so reliably populated with great whites that a thriving cage diving tourism industry had built up around them. Operators could virtually guarantee sightings. Scientists based their long-term [music] population studies there because the sharks showed up year after year with the kind of consistency that made baseline research possible. Then, in 2017, the sharks vanished. Not reduced, not declined, vanished. Marine biologist Alison Towner, who had been studying the Gansbaai population for years, described going out on survey trips and finding nothing. Waters that had reliably held dozens of great whites were empty. The seals at Dyer Island, normally kept in check by predator pressure, began behaving differently almost immediately.

[00:04:36]They spread into areas they had avoided for years. Their population started expanding in ways that disrupted local fish populations. The cage diving operations collapsed overnight. The tourism economy of an entire coastal community evaporated. And scientists were left staring at an empty ocean trying to figure out what had happened.

[00:04:56]At first, the disappearance was localized to Gansbaai. Researchers hoped the sharks had simply moved, shifted their range in response to some temporary change in prey distribution or water temperature. Sharks do that.

[00:05:10]They are highly mobile animals capable of crossing entire ocean basins. But then similar reports started coming in from other locations.

[00:05:18]Off the coast of California, long-term population monitoring showed declining encounter rates in areas where great whites had been reliably sighted for decades. In Australia, strandings of great white sharks began increasing with necropsy reports describing animals in unusually poor [music] physical condition. In the Mediterranean, a population already considered critically small was showing further contraction.

[00:05:43]The disappearances were not happening in one place. They were happening everywhere at roughly the same time for reasons that were not immediately obvious. Scientists did what scientists do. They formed competing hypotheses.

[00:05:55]They argued [music] at conferences. They published preliminary findings that contradicted each other, and for [music] several years the real picture remained frustratingly unclear. But one piece of evidence kept coming back into every conversation. Two orcas off [music] the South African coast. And what those two animals were doing was unlike anything recorded in the history of marine biology. The orca [music] theory. Killer whales as apex predators. Their names were Port and Starboard, [music] named for the directions their distinctive dorsal fins flopped, which, yes, sounds like the setup to a marine biology joke. But this is entirely real and considerably less funny than it sounds. Port [music] and Starboard are a male orca pair, first documented hunting in South African waters around 2015.

[00:06:42]Orcas are known to prey on sharks in various locations around the world. This was not new information. What Port and Starboard were doing, however, was something researchers had never witnessed at this scale or with this level of apparent precision. The pair developed a hunting technique specifically designed for great white sharks, and the details of that technique, when researchers pieced them together from carcasses washing ashore and underwater footage, were genuinely disturbing. Port and Starboard were not killing great whites opportunistically.

[00:07:12]They were targeting them surgically. The carcasses that washed up on South African beaches showed a pattern so consistent it was almost methodical. The sharks had been opened precisely at the liver, and only the liver had been consumed. The great white shark liver is enormous. It can account for up to 25% of the shark's total body weight. It is extraordinarily rich in lipids and squalene, a compound with extremely high caloric density. Port and Starboard had essentially discovered that great white sharks are walking nutrient packages, and they had learned exactly where the package was and how to open it. What happened next was the part that truly stunned [music] researchers. Word spread, not among humans, among great whites. Within a remarkably short period [music] after Port and Starboard began their hunting campaign around Gansbaai, the great white population abandoned the area entirely. These are animals that have no natural predators. Animals [music] that have been the apex predator in their environment for millions of years, and they left immediately, completely, as if a biological alarm had triggered a massive evacuation. Towner and her colleagues attached satellite tags to great whites in the region and tracked their movements. The data showed sharks that had maintained stable home ranges for years suddenly making long-distance movements away from the area, often within hours of an orca attack in the vicinity. Some left and never came back. This was a discovery with enormous implications for how we understand predator-prey dynamics. The great white sharks were not just responding to direct predation pressure.

[00:08:50]They were responding to the presence of a more effective predator with what looked remarkably like coordinated avoidance behavior. Port and Starboard did not just kill great white sharks in Gansbaai. They restructured the local ecosystem by driving the apex predator out, creating what researchers described as a predator vacuum that immediately began to be filled by other species with consequences rippling through the entire food web. The orca story made international headlines. It was dramatic. It was visual. It had two identifiable villains with memorable names, and it fit neatly into a narrative that humans find compelling, nature red in tooth and fin, one apex predator displacing another, the circle of life doing its brutal thing. But the researchers who were looking most closely at the global picture knew that Port and Starboard, extraordinary as they were, could not explain [music] what was happening everywhere else. But, orcas aren't the whole story. Two orcas, however skilled and however disruptive to one regional population, cannot account for declining great white numbers off the coast of California.

[00:09:58]They cannot explain strandings in Australia. They cannot be responsible for the contraction of Mediterranean populations that had been shrinking since the 1980s. Port and Starboard were a spectacular, visible, documentable cause of one regional [music] collapse.

[00:10:14]They were not the explanation for a global pattern. And when researchers started digging into the global pattern, what they found underneath it was considerably darker than two unusually clever killer whales. The first clue came from the strandings. When great white sharks wash up dead on beaches, marine biologists conduct necropsies, the animal equivalent of an autopsy.

[00:10:36]For decades, these examinations focused on obvious causes of death, propeller strikes, entanglement in fishing gear, evidence of predation, blunt trauma, the kinds of things you can see with the naked eye. But, in the early 2000s, a small number of researchers started looking at stranded great whites differently. Instead of just documenting the obvious, they began collecting tissue samples, blood, muscle, liver, blubber, and sending those samples to toxicology labs. What came back from those labs opened a door that nobody in mainstream marine biology was particularly eager to walk through.

[00:11:13]Because on the other side of that door was a finding that implicated not two orcas, not overfishing, not climate change alone, but something that connected every stranded shark, every declining population, and every empty ocean to a single source.

[00:11:29]Us.

[00:11:30]And I know that [music] sounds like I am building to a dramatic conclusion, and I am. But I want to be clear that I am not editorializing [music] here. I am describing what the tissue samples actually showed, and what they showed was, frankly, one of the most disturbing things I have read while researching this channel. What the tissue samples revealed. The results from the toxicology analyses of great white shark tissue began accumulating across multiple independent research [music] programs throughout the 2000s and into the 2010s.

[00:12:00]Researchers at the University of California, Davis analyzed blubber samples from great whites tagged off the California coast. Scientists in South Africa collected tissue from stranded animals and from biopsies of living sharks. Australian marine toxicologists examined samples from their regional populations.

[00:12:19]And when these independent research teams started comparing notes [music] at scientific conferences, a picture emerged that was consistent across every ocean basin where great whites live. The sharks were carrying extraordinarily high concentrations of persistent organic pollutants. Polychlorinated biphenyls, known as PCBs, are industrial chemicals that were manufactured and used extensively throughout the 20th century in electrical equipment, hydraulic fluids, and industrial applications. They were banned in the United States in 1979 and progressively restricted worldwide after that because researchers established clearly that they cause cancer, disrupt hormone systems, impair immune function, and accumulate in biological tissue with devastating efficiency. Here is the thing about PCBs that makes them particularly nightmarish. They do not break down.

[00:13:15]Not quickly, anyway. They persist in the environment for decades. They dissolve in fat, not water, so they concentrate in the fatty tissues of animals.

[00:13:24]And every time a predator eats contaminated prey, the predator accumulates the contaminants from everything that prey animal ever ate.

[00:13:32]This process, called biomagnification, means that the higher you sit in a food chain, the more concentrated your toxic load becomes. Great white sharks sit at the very top of the marine food chain.

[00:13:44]They are the apex of the apex, which means every PCB molecule that entered the ocean food web over the past century has been working its way upward, concentrating at every trophic level until it ends up at maximum concentration in the tissues of the animal at the top.

[00:14:01]Researchers found PCB concentrations in great white shark tissue that exceeded safe thresholds by factors of 10, 20, sometimes 50 times higher than levels associated with serious biological damage in other marine mammals. But, PCBs were only the beginning.

[00:14:18]Perfluoroalkyl substances, the chemicals known as PFAS and sometimes called forever chemicals because they do not degrade in the environment, were found in great white tissue samples at concentrations that alarmed toxicologists.

[00:14:34]PFAS compounds are associated with immune suppression, thyroid disruption, and reproductive failure. They were not even being manufactured at significant scale until the 1950s, which means the contamination [music] timeline tracks almost perfectly with the period when great white populations began showing signs of stress. Heavy metals told the same story. Mercury, lead, and cadmium concentrations in great white liver tissue, the same organ that Port and Starboard [music] found so appealing, were at levels that researchers described in one paper as incompatible with normal physiological function. Now, here is where it gets personal for the sharks and deeply uncomfortable for us.

[00:15:16]The immune system impacts of this toxic load were measurable and severe. Great whites with the highest contaminant concentrations showed evidence of compromised immune response, meaning they were less capable of fighting infections, healing wounds, and recovering from physical stress. Animals that would normally shrug off injuries from prey encounters were dying from infections that a healthy shark would have cleared without difficulty. The reproductive data was, if possible, even worse. Female great whites with elevated PCB and PFAS loads were showing reproductive failure rates significantly higher than less contaminated individuals. Pups from contaminated mothers were being born with elevated toxic loads of their own, inherited through [music] maternal transfer, meaning the contamination was not just affecting living animals. It was being passed [music] to the next generation before those animals were even born. The sharks were not being killed by a single dramatic event. They were being slowly poisoned over decades chemical legacy that predated most of the researchers who were now documenting its effects.

[00:16:22]The ocean itself is changing.

[00:16:25]If the contamination findings were not enough, and they should have been more than enough, the researchers looking at the full picture identified a second major threat operating simultaneously and independently of the toxic load. The ocean that great white sharks evolved to hunt in no longer exists. Great whites are dietary [music] specialists in ways that people rarely appreciate. Adult great whites primarily hunt marine mammals, seals, sea lions, elephant seals, and dolphins. These prey [music] species are energy dense, rich in the lipids that great whites need to fuel their enormous metabolic demands. A single large elephant seal can provide enough caloric energy to sustain a great white for weeks.

[00:17:07]Marine mammal populations along major great white hunting grounds [music] have been under pressure from multiple directions simultaneously.

[00:17:15]Commercial fishing has depleted the fish stocks that seals and sea lions depend on, creating food stress in [music] prey populations that ripples upward. Prey behavior has shifted as climate change alters coastal oceanographic conditions, [music] and in some regions, seal populations have recovered so strongly under protection programs that they have overshot the capacity of local ecosystems, creating boom and bust cycles that make prey availability unpredictable for the sharks that depend on them.

[00:17:44]But, the more fundamental problem is water temperature.

[00:17:48]Great white sharks are not cold-blooded in the way most people assume. They are partially endothermic, capable of maintaining their core body temperature above the surrounding water temperature through a specialized heat exchange system in their circulatory system. This gives them a metabolic advantage in cool water. It allows them to hunt effectively in temperature ranges that would leave other predators sluggish. As ocean surface temperatures rise, the thermal environments that great whites are optimized for are shifting poleward.

[00:18:18]Prey species are following cooler water northward and southward toward the poles. Great whites are following their prey, and the migration corridors and seasonal aggregation sites that have defined great white behavior for thousands of years are becoming unreliable. The finding that disturbed scientists. In 2022, a research synthesis was published that brought together data from long-term population studies, toxicological analyses, satellite tracking programs, and climate modeling into the most comprehensive assessment of great white shark survival threats ever attempted. What that synthesis revealed was something that researchers had suspected but not yet demonstrated with this level of evidence. The threats were not additive.

[00:19:03]They were multiplicative. Here is what that means in practice. If contamination alone reduced a great [music] white's reproductive success by 30%, and prey depletion alone reduced it by another 30%.

[00:19:16]A naive calculation would suggest a combined impact of 60%. Bad, but potentially [music] survivable for a population with enough individuals. But that is not how compounding biological stressors work. The contamination impairs the immune system, which reduces the shark's ability to cope with the metabolic stress of longer migrations for food, which increases physiological stress hormone levels, which further suppresses immune function, which reduces reproductive success, which is already compromised by maternal transfer of toxins to pups, which means surviving pups start life with elevated toxic loads and compromised immune systems of their own. The stressors were feeding each other, creating a cascade that was moving faster than any single threat would suggest. One of the researchers involved in the synthesis, when asked to describe the finding in plain language at a conference presentation, said something that reportedly silenced the room.

[00:20:14]She said they were not looking at a species under pressure. They were looking at a species in the early stages of a collapse that the data suggested was already past the point where removing any single threat would be sufficient to reverse the trajectory.

[00:20:28]Past the point. That phrase appeared in several subsequent papers and commentaries. It is the kind of phrase that scientists use carefully because it carries implications that go beyond scientific description into territory that is deeply uncomfortable. Past the point means that even if we stopped all chemical pollution tomorrow, the contamination already in the food web >> [music] >> and in the tissues of living sharks would continue to cause harm for decades. The great white alive today that was born to a contaminated mother has already inherited a toxic burden it will carry for its entire life. Past the point [music] means that even if climate change was somehow arrested immediately, the ocean reorganization already in progress would continue disrupting prey distributions and migration patterns for years. Past the point means that the window for preventing significant population decline may have already closed, [music] and what researchers are now managing is the rate of that decline, not whether it occurs. The finding that disturbed scientists most was not any single piece of evidence. It was the realization that they were looking at a convergence, multiple independently serious threats arriving simultaneously on a species with a life history that makes recovery extraordinarily slow. Great white sharks do not reproduce quickly. Females do not reach sexual maturity until they are approximately 15 years old. Gestation lasts between 12 and 18 months. Litter sizes are small, typically two to 10 pups. And those pups, as we have established, are now being born pre-contaminated.

[00:21:59]A species that takes 15 years to produce its first offspring and is simultaneously facing immune suppression, reproductive failure, prey depletion, and habitat disruption does not bounce back quickly. It does not bounce back at all if the conditions causing the decline remain in place long enough. What happens if they disappear?

[00:22:20]I want to pause here and address something that I suspect some people watching this are thinking. Sharks are scary. The movies told us so. The news stories about rare attacks reinforce it every summer. There is a part of the human brain that hears about declining shark populations and produces [music] something embarrassingly close to relief.

[00:22:39]I understand that reaction. I am not judging it. But, I want to walk you through what the ocean actually looks like without great white sharks, because the answer to that question should produce something considerably less comfortable than relief. The ocean is not a collection of individual animals.

[00:22:55]It is a system.

[00:22:56]And apex predators are not just the top of that system. They are the regulators of it. When great white sharks disappeared from the waters around Gansbaai, researchers documented what happened next in real time. The seal population, freed from predation pressure and behavioral suppression, expanded rapidly. Expanding seal populations competed more aggressively for fish. The fish species that seal populations preyed upon declined.

[00:23:23]Species that depended on those fish declined in turn. The ecosystem reorganized itself around the absence of the predator that had been structuring it. This is not speculation. This is documented observation. It happened over a period of months, fast enough that researchers could watch it in real time.

[00:23:40]Scale that up to a global decline of great white sharks, and you are looking at a cascade that touches every level of marine ecosystems across multiple ocean basins simultaneously.

[00:23:51]There is a concept in ecology called a trophic cascade. The ripple effects that flow through an ecosystem when a predator is removed from the top of the food web. The most famous documented trophic cascade is what happened in Yellowstone National Park when wolves were reintroduced in 1995 after decades of absence. The reintroduction of the apex predator changed not just the prey populations, but the behavior of those populations, the vegetation of the park, the courses of rivers, and the distribution of dozens of species that had never directly interacted [music] with a wolf. The ocean equivalent of removing great white sharks globally would be a trophic cascade of a scale that marine ecologists describe with language [music] usually reserved for geological events. Fisheries that billions of people depend on for protein would be affected. Coastal ecosystems that provide storm protection and support tourism [music] economies would reorganize in unpredictable ways. The carbon storage capacity of ocean ecosystems, already under pressure from acidification and warming, would be further compromised as food web disruptions alter the distribution of organic matter through the water column.

[00:25:02]The disappearance of great white sharks would not be a shark problem. It would be an ocean problem, and an ocean problem at that scale is a human problem. The uncomfortable truth, Jeremy Wade, the biologist and television presenter, who spent nine seasons documenting freshwater monsters before walking away from his show because he could not continue presenting a fantasy while watching ecosystems [music] collapse, described his experience as finding a monster that could not be caught with a fishing rod. The monster was us.

[00:25:34]I keep coming back to that framing because it applies here with uncomfortable precision. Great white sharks are not disappearing because of two unusually clever orcas, though Port and Starboard are genuinely remarkable animals, and their story deserves to be told. They are not disappearing primarily because of shark finning, though that industry has caused devastating damage to shark populations globally. They are not disappearing because of climate change alone, or prey depletion alone, or chemical contamination alone. They are disappearing because of the accumulated weight of what industrial human civilization has done to the ocean over the past 100 years.

[00:26:12]The PCBs in great white shark tissue were manufactured by companies that no longer exist under regulations that no longer apply in an era when the connection between industrial chemistry and ocean apex predators was not something anyone was thinking about. The PFAS compounds were developed because they were useful, extraordinarily useful, and the people who developed them were not thinking about great white shark reproductive rates. The fishing industry that depleted the prey species great whites depend on was feeding people. The industrial processes that warmed the ocean were powering economies. The runoff that carries heavy metals and persistent chemicals into coastal waters comes from infrastructure that supports modern life. None of it was designed to kill great white sharks.

[00:26:57]All of it is killing great white sharks.

[00:27:00]And here is what makes this genuinely different from a story about two orcas hunting with unusual sophistication. Two orcas can be studied, documented, and their impact can be monitored and assessed. The hunting behavior of Port and Starboard, however [music] extraordinary, is a natural process that ecosystems have mechanisms to respond to over time. Chemical contamination that persists for decades in fatty tissue accumulates across entire ocean food webs and transfers from mothers to offspring does not give ecosystems time to respond. Warming oceans driven by atmospheric carbon that will remain elevated for centuries do not offer the option of waiting for conditions to normalize. A global food web disruption affecting prey availability across multiple ocean basins simultaneously does not have a local solution. The researchers who published the 2022 synthesis were not alarmists. They were people who had spent careers carefully, methodically documenting what was happening to one of the ocean's most important species. When they used phrases like past [music] the point and convergence of threats, they were not reaching for dramatic effect. They were describing [music] what the data showed.

[00:28:12]And the data showed something that should be front-page news, but is not because we have a collective very human tendency [music] to look away from information that implicates us in something we cannot easily fix. The great white shark has survived 11 million years of planetary upheaval. It survived the asteroid impact that ended the age of dinosaurs. It survived ice ages that transformed entire ocean basins. It swam through geological epochs that reshaped the continents [music] themselves. It may not survive us. And not because we hunted it deliberately. Not because we made a decision as a civilization to eliminate the great white shark, but because we made 10,000 smaller decisions over 100 years that accumulated into something that functions exactly like that decision without anyone ever consciously making it. That is what disturbs the scientists most, not the scale of the impact, though the scale is staggering.

[00:29:05]The thing that keeps researchers awake is the mechanism. The way that the accumulation of individually defensible choices, [music] manufacturing useful chemicals, catching fish to feed people, burning fuels to power economies, can converge on an outcome that nobody chose and nobody wanted, and that may now be very difficult to reverse. The window is not [music] closed. I want to be clear about that, because the researchers I have read and the data I have examined [music] do not support a conclusion of inevitability.

[00:29:36]Great white populations, small as they are, still exist. The contamination levels, high as they are, are not uniformly distributed. Climate shifts, serious as they are, [music] are not yet irreversible. There are still things that can be done. Expanded marine protected areas that reduce fishing pressure and allow prey populations to recover. Continued restrictions and cleanup efforts targeting persistent chemical pollutants.

[00:30:02]Shark finning bans with genuine enforcement. Long-term monitoring programs that track population trends and contaminant loads and give us the data we need to understand whether conditions are improving or deteriorating. These are not small undertakings. They are not cheap. They require political will that is often absent and public attention that tends to be captured by more immediate concerns. But the alternative is watching the ocean's apex predator cross a threshold from which population recovery becomes biologically impossible. And then spending the next several centuries managing the cascade of consequences that follows. The great white shark spent 11 million years at the top of the ocean food chain. We have had meaningful industrial impact on its survival for roughly 100 years. 100 years against 11 million. The monster is not in the water. The monster is the system we built on land, and the fact that we built it without understanding what it would do to the water. Now you know what is killing great white sharks.

[00:31:02]The question is whether knowing is enough to make us care. I think it has to be. This is Matthew. This is Reef Discovery. And if this story disturbed you, good. It should.