[0:00]An ancient arena for ocean giants.
[0:08]In one corner, enormous yellowfin tuna, nearly twice the length of a man, weighing over 800 pounds, one of the fastest fish in the ocean. In the other corner, sharks. Thousands of them. Crushing teeth, lightning fast speed, and street gang numbers. But the tuna remain one step ahead. This is Shark versus Tuna.
[0:55]Some call it the rock. A Jurassic Park lost in the South Atlantic Ocean.
[1:08]Over a thousand miles from land in any direction, this is Ascension Island. Darwin's best kept secret.
[1:24]Everything that lives here or stops here is either hunter or hunted. Ascension plays host to one of nature's greatest showdowns. Thousands of the ocean's most deadly predators arrive from far and wide to fight it out in a high stakes Battle Royale.
[1:58]Schools of Jacks dominate the drop-offs. Thousands of green turtles come here annually to nest on the sandy beaches, and swarms of huge predatory fish. Like barracuda, marlin, and wahoo lurk in the open water. But no one is safe, except maybe this enormous yellowfin tuna. This superfish normally lives life in the desert of the open ocean where food is scarce. But every Easter, Ascension Island becomes an oasis for giant tuna migrating across the Atlantic. It's one of the largest concentrations of yellowfin in the world.
[3:02]To get in and out of the rock alive, you must be big, smart, and fast.
[3:12]Despite being near the top of the food chain, tuna are a favorite meal for sharks. If they can catch them. So not only must the yellowfin be an exceptional predator, it must be a wily escape artist too. The average yellowfin is by no means small, but Ascension is home to giants.
[3:38]Nearly twice the length of a man, and as heavy as a horse, this is one of the fastest fish in the ocean. Even the US Navy studied it as a model for submersible drones. Built for speed, the tuna's gills are over 30 times larger than other fish its size to draw in more oxygen, and its heart is 10 times bigger with a faster heartbeat. Like the great white shark, the yellowfin is warm-blooded, which allows it to swim faster for longer and exploit the colder deeper waters where other predators can't hunt. Little can keep up with or escape this turbo-charged fish.
[4:30]And their next feeding stop is Ascension Island.
[4:39]The tuna's arrival acts like a dinner bell for some of the ocean's fiercest marine predators.
[4:50]At this time of year, the tuna are set to run a gauntlet of sharks. And they aren't the only ones that want a piece of the tuna.
[5:09]Tales of Ascension's big game fish attract sports fishermen and trophy hunters from all over the world.
[5:20]Of all the fish they target here, the giant yellowfin is highly prized. Some carry a $20,000 paycheck.
[5:36]The wily tuna doesn't take the bait this time. An eight-foot wahoo does.
[5:58]Below the surface, the fish's struggles are a call to arms.
[6:08]At Ascension, everyone's hungry.
[7:04]They try to eat everything, even the bony head.
[7:30]With the sharks distracted in frenzy, the tuna escape. But the battle lines are drawn.
[7:39]These sharks mean business, and there are thousands of them.
[7:56]Like the tuna, sharks ride the South Atlantic current to Ascension in terrifying numbers.
[8:09]Tigers, hammerheads, and mako to the ever increasing sightings of Galapagos sharks. Each is locked in an evolutionary arms race with the tuna, and right now, no one knows who's winning.
[8:30]The sharks patrol the beaches.
[8:36]The rock is under siege.
[9:18]Tuna are jam-packed with some of the richest, fattiest meat in the ocean, and an 800-pound yellowfin is the jackpot.
[9:32]But how on Earth will these sharks successfully catch and kill such formidable prey?
[9:46]Yellowfin tuna are unbelievably fast, powerful predators, and for a shark, incredibly hard to catch. There are only a handful of contenders up for the tuna challenge. To hunt these superfish, you need extraordinary predatory powers.
[10:10]Meet the resident bad boy, the Galapagos shark. Ascension is their local hunting ground, and unlike the tuna and migrant sharks, they know this terrain like the backs of their hands. Most of them grew up here, learning to hunt in the shallow nurseries, and in the last two years, Galapagos sightings have increased dramatically. Despite reaching 12 feet in length, this welterweight is only half the size of the giant yellowfin. Its streamlined and slender frame does give this shark agility and speed like the tuna. But like its cousin, the tiger shark, the Galapagos has more powerful jaws and sharper serrated teeth. This allows for a highly varied diet from bony fish and iguanas to sea lions and even each other.
[11:18]But here at Ascension, yellowfin remain a number one prize. Oily prey like tuna leaves a scent signature up to two miles away. In the open blue water, this Galapagos shark's incredible sense of smell could give it the edge. Almost two-thirds of their brain is dedicated to smell.
[11:57]All the better to smell you with, 10,000 times better than humans. Where the Galapagos shark matches the tuna is in numbers. Most sharks hunt alone, but the Galapagos move in a mob, a veritable street gang of aggression.
[12:22]They investigate anything that may potentially become prey.
[12:30]Like a school of piranhas, competition drives them to frenzy.
[12:44]The Galapagos may be fast, agile, and aggressive, and they may have the numbers, but one-on-one, they hardly stand a chance.
[12:57]In the open ocean, the giant tuna are just too fast, too strong, and too big. This underdog would have to do something spectacular to sink its teeth into one. To win a giant tuna, you need to put more on the table. A heavyweight enters the ring, the tiger shark.
[13:30]Like its namesake, its striped camouflage allows the tiger to silently stalk prey virtually undetected.
[13:45]Their stripes may fade with age, but killer instincts and voracious appetites stay with them for life.
[14:16]It has an arsenal of weaponry to track, hunt, and devour massive prey.
[14:28]These super-fast yellowfin are no easy target. So the tiger shark will be on the lookout for struggling young, injured, and old fish.
[15:44]This built-in tracking device helps distinguish large from small prey, individual from school, as well as the distance and speed of its target.
[16:02]Once the tiger gets within range, the tuna doesn't stand a chance.
[16:12]This juggernaut has the power to crush a car.
[18:07]It's all tasty nutrition if you've got the stomach for it. The tiger pulverizes the turtle's bones and shell to unlock marrow, proteins, and fats. It can eat anything from dolphins, rays, and seals to whatever falls into the water, like birds, trash, and even people.
[16:38]The tiger shark is responsible for the most attacks against humans, second only to the great white.
[16:52]This indiscriminate diet is largely thanks to their highly specialized teeth.
[20:46]Tuna swim nearly 20 miles a day in search of large schools of prey, but here at Ascension, the food is on tap. They track prey by the smell of the oil on its skin, and once spotted, the attacks are so fast, if you blink, you'll miss it. Maneuvering at such pace requires military precision. The tuna's bright yellow finlets help reduce turbulence, while its fins retract into modified grooves to minimize drag, and unlike any other creature, the tuna uses its lymphatic system like hydraulics to stiffen its fins, which allows for sharp turns when chasing prey. Life at super speed requires fuel, lots of it.
[20:33]Squid, mackerel, octopus, and even other tuna are all on the menu.
[20:42]To satisfy this insatiable hunger, the yellowfin swim nearly 20 miles a day in search of large schools of prey.
[32:46]With chum in the water, the diver knows he only has a short window of opportunity before the sharks find him. Every minute he stays here, the more he puts his life at risk.
