Original subtitles

Narrator: Among the ocean's most dangerous predators...

Only one...

Is bold enough to trespass...

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(scream)

...Right where you live.

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Bull shark.

The bad boy of the tropics...

Has earned its reputation...

For aggression.

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Man: Oh, my gosh!

Man: Holy (bleep)!

Woman: Oh, my gosh! (bleep) oh, my gosh!

(screams) oh, my gosh!

(bleep)

Narrator: Like humans, bull sharks prefer warm seas.

The coastlines of brazil, florida, california.

And they don't stop there.

Unlike most sharks, they thrive in fresh water.

Rivers, lakes, harbors, canals.

Bulls will travel miles up the amazon.

They've invaded new orleans,

All the way to lake pontchartrain.

Even 1,700 miles up the mississippi into st. Louis.

And florida, with its network of manmade canals,

Is swimming with bull sharks.

Man: (screams) watch out, boy!

Watch out!

Oh!

Ah, dude, that's 400 pounds, bro.

Look at the size of this shark, guys!

Narrator: They prowl backyards...

Live and hunt among people.

A bull shark will even eat another shark.

Man: Oh, look at the shark trying to eat that shark!

Woman: Oh, my god, look at that.

Man: Holy (bleep)!

Woman: Oh, my god! Oh, my god!

Man: Holy (bleep)!

Woman: (screams) oh, my god!

Man: Holy (bleep)!

Pardon my language, but holy (bleep)!

Did you get that on video?

Narrator: They're mysterious and can be deadly to humans.

Here's what we know.

Like bulls on land, their bodies are muscular and broad.

The biggest, 11 feet long,

700 pounds of muscle,

And brazen enough to steal.

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These spearfishermen are used to competition.

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Trevallies.

Prized game fish and a family meal.

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Bull shark won't let you have it.

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They'll move in at any opportunity

With unpredictable speed.

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Great white, tiger and bull

Are the three deadliest sharks on earth.

The great white shark: All-star cold-water killer.

It can be seven times as heavy as a bull shark, twice as long.

Its favorite food: Seals.

Great whites' hunting method is iconic.

Scout out the weak...

(seals barking)

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Save energy...

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...For the perfect moment.

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Jaws can hack a seal in half.

But the bull shark's bite is even stronger.

Bulls will eat anything

From dolphins to turtles to other sharks.

With over 1,000 pounds per square inch of force...

...It's enough to break a leg.

The next contender: Tiger shark.

The trash cans of the sea.

They'll eat just about anything,

With rows of teeth like a couple of hacksaws.

Bigger than bulls, tiger sharks are travelers.

And a floating whale carcass in a tropical sea

Attracts them in hordes.

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Bull sharks patrol these same warm oceans,

But bulls have an added advantage.

They can hunt where tigers and great whites can't.

Bull sharks don't have to feed every day.

They're opportunists,

Seeking out easy meals that will sustain them for days.

The east coast of south africa

Is one of the most shark-infested coastlines

In the world.

A sardine buffet attracts a throng of a-list predators.

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Gannet dive-bombers assault from the air.

(squawking)

Common dolphins round up the feast.

(dolphins whistling)

Bryde's whales gorge.

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And sharks.

Whalers, duskies and blacktips.

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But the bulls are awol.

There's a reason.

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Unlike most sharks,

Bulls can control the salt levels in their bodies.

They're uniquely adapted to thrive

In estuaries and freshwater environments.

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Meaning they can move freely between salt water and fresh...

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Invade hunting grounds far inland...

Where people live...

...And play.

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No one sees them coming.

(scream)

Man: There she is! (screams)

Narrator: Giant sharks, miles from any ocean.

Bull sharks infiltrate river systems all over the world.

Man: There she goes.

Narrator: The only lethal shark

That's capable of living in fresh water.

They're close to where we live,

Yet we know so little about them.

Dr. Ryan daly studies bull sharks in southern africa.

He's on a mission to find out what makes bull sharks

Such nimble survivors.

Ryan specializes in shark migration,

Where they feed and breed,

And how that impacts their conservation.

A day at the office for ryan means catching bulls

And fitting them with tracking devices.

Ryan daly: We're tagging bull sharks primarily to find out

Where they go, where they spend their time,

So we can balance out the refuges and the risks

That they face as they migrate and move.

Narrator: It's his job to get close to a predator

He wants humans to keep away from, and vice versa.

After eight years of tracking,

He's discovered that bull sharks travel

Almost 1,000 miles each year.

He suspects they often go much farther.

Ryan's main study site is in southern mozambique.

Three miles off the coast of ponta do ouro

Is a global hot spot for sharks.

A healthy reef full of food is a beacon for predators.

And a perfect place to study sharks.

Ryan's looking to identify a few unique individuals,

So he can learn which ones take up residence here.

Ryan: There's so many sharks down there at the moment.

Five blacktips, couple tigers on the outside,

And a whole shoal of hammerheads.

This place is on fire!

Narrator: Ryan's after the bull sharks.

Big ones.

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He records how they hunt,

How they compete with one another.

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Now, ryan's taking his research a step further.

Ryan: Getting an eye, or a perspective of their world

Is almost impossible.

But what recent technology has allowed us to do

Is use cameras to attach to these sharks

And let them collect the data for us.

Narrator: First, he has to catch

His new research assistant.

Ryan: Catching bull sharks is especially difficult,

Because they seem to know that you're after them.

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Narrator: A bite.

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In order for ryan to get a camera on,

The shark needs to be tired out.

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He puts it in a trance-like state and collects data.

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Ryan: We just need to flip her over

And then you can put the camera on.

Okay, looking good.

Narrator: Ryan takes a photo id before the animal disappears.

The fin cam won't start to record

Until the shark's activity returns to normal, in 12 hours.

This will be the first time a bull shark's natural behavior

Is recorded in the indian ocean.

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No human distractions.

Just a window into what a bull shark sees.

Checking out prey.

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Other sharks.

Blacktips.

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Massive tigers.

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And finally, in another first,

A bull shark films other bulls.

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All apex predators,

Instinctively heading towards a massive quarry of food.

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5,000 giant trevallies.

Expert predators and a formidable foe.

At nearly 180 pounds apiece,

They're not afraid of sharks.

Trevallies use a shark's rough skin

To shed parasites from their scales.

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They're fast, too.

Not an easy catch.

Every year, at exactly the same time,

Just before the full moon,

Trevallies gather in southern mozambique to breed.

For ryan, this annual ritual offers a golden opportunity.

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Ryan: So many big fish down there.

Seeing them all in one place

In a massive shoal like that is just mind blowing.

It'll never get old.

Narrator: Thousands of trevallies

Should be an all-you-can-eat buffet.

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So far, ryan sees no predation on the fin camera.

He needs more footage,

And there's an easier way to get it.

Ryan: We've come up with a new camera design

That gives us a unique perspective

Of what the shark's seeing.

We don't have to catch the shark to attach this camera to it.

All we need to do is feed the shark bait

And it'll tow the camera around for about six hours.

Narrator: A blacktip shark is the first to grab the camera

And take off.

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Not what ryan expected.

But a chance to see something brand new.

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Ryan: Footage from the tow cam reveals how these sharks swim

Side by side and sometimes even ram into each other.

Narrator: Sharks are highly competitive.

But also strategic.

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Here come the bulls.

Blacktips and bulls take up position

Around the shoal of trevallies.

The bulls are much bigger.

Higher up the food chain.

Like a police force on patrol.

The blacktips stay close.

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Ryan: You get the feeling that they're all waiting

For something to happen.

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Narrator: Bull sharks, tigers, hammerheads, and blacktips

Converge around a challenging predator:

A shoal of 5,000 fat trevallies.

A bull shark's food of choice.

After almost a decade of research,

Dr. Ryan daly knows that at least 20 bull sharks

Make these mozambican waters a year-round home.

But in summer, when trevallies spawn,

A multitude of sharks move here to feast.

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Scalloped hammerheads outnumber the bulls.

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They're after smaller bonitos, not giant trevallies.

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But blacktips are.

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Bull shark jaws open wide enough

To take much bigger prey, even smaller sharks.

Ryan: It's incredible to see all these sharks,

But when the bulls step in, all the other species step aside.

Narrator: The bulls work the edges of the shoal.

Pick an easy target.

They only need one trevally per week to sustain themselves.

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Nowhere else are this many bulls swarmed

By a potential feast like this.

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Predator versus predator.

Any fish that breaks formation instantly gets eaten.

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It's not a frenzy, but an attack strategy.

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Survival of the fittest.

Marine version.

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Fit trevallies get to breed.

The old and sick get eaten.

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Without mercy.

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Ryan: Wow, seeing a big bull shark

Rip open a fish like that, just so much power.

Narrator: After they spawn, the trevallies dissipate.

So do the sharks.

The question is, where do they go?

Ryan once tagged a bull shark here that traveled 1,000 miles

To the north of mozambique and back.

Another invaded south african waters.

Even these powerful travelers run a gauntlet.

Ryan: As these bull sharks migrate,

They come into contact with so many different dangers,

Ranging from long lines, shark nets,

Which are pretty much designed to cull sharks,

And targeted shark fishing.

There's increasing pressure to catch sharks

Because of their valuable fins.

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Narrator: As with predators on land,

Humans are the bull sharks' greatest threat.

But not the only one.

As these adaptable hunters invade fresh water,

They run into trouble, too.

(hippo bellows)

Narrator: These safari tourists

Are about to get the sighting of their lives.

(people screaming)

Hippo versus bull shark.

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(grunting)

The strongest bite force of all mammals...

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...Faces off with the strongest bite force of all sharks.

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Just 150 miles south of ryan's study site,

At st. Lucia estuary,

One of africa's largest tidal wetlands,

A watery mix of fresh and salt.

Shallow.

Warm.

Just right for bull sharks.

And a once-in-a-lifetime encounter on safari.

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(bellowing)

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(bellows)

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This shark was probably chasing a fish

When it caught the hippos by surprise.

Africa's deadliest large land animal.

And a clue to a mystery.

We know bulls infiltrate rivers like these to feed.

And there's no shortage of rivers

On the east coast of south africa

For a bull shark to invade and disappear.

Tucked away on the wild coast,

A pristine wilderness.

Undisturbed from sea to source.

(birds squawking)

Such a forested retreat

Is an unlikely place to find any marine creature.

(birds cawing)

(bird screeching)

And a long shot for a shark scientist.

But ryan knows there's a visitor from the ocean here

That might bring him closer to bull sharks.

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It's not uncommon to see trevallies in rivers.

They may use systems like this one as a nursery,

Or take advantage of fresh water

To kill off marine parasites.

But seeing 200 of them together is peculiar.

Ryan: Not only do giant trevally occur there,

But they seem to shoal in the unique way

That we just don't see anywhere else.

The reason the giant trevallies are a bit of a mystery,

To be honest.

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Narrator: The mystery goes beyond

Why an ocean dweller adapts to a saline-free habitat.

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To get here, the trevallies battle tides

And swim against shallow rapids 3 miles inland.

It would be impossible

For a big predator to follow the bait.

But not a small one.

They're here.

Baby bull sharks.

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Ryan: This is fascinating, because it is essentially

In the forests, above rapids,

Just right up at the top of this river system.

Narrator: How did juvenile sharks reach so far inland?

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After a 10-month pregnancy,

Female bull sharks drop one to three pups

At the mouth of a river.

Her job is done.

The baby sharks instinctively swim upriver,

Away from ocean predators.

All they have to do now is fatten up.

True to their mysterious nature,

Bull sharks are hard to find.

So this is another first.

Ryan: Yes, I've been studying bull sharks

For over a decade now,

But I've never seen juvenile sharks in a forested river,

Miles away from the ocean, in such a pristine environment.

Just the perfect habitat for them to grow up, grow strong.

Narrator: Ryan has just confirmed

A new nursery ground for his study.

When these baby bulls are big and tough enough,

They will head out to sea.

Where will they invade next?

Narrator: Bull shark.

Among the three deadliest sharks in the world.

The great white and tiger are more famous.

But bull is the only shark

That regularly invades human habitats.

Man: (screams) watch out, boys!

Watch out!

Narrator: Stealing fish...

And growing up in fresh water, miles upriver.

Opportunistic, unpredictable, misunderstood.

Dr. Ryan daly is in the bull shark's corner.

He wants to know where they travel, feed and breed,

So that he can help keep them out of trouble.

Ryan: Bull sharks may be perceived as these

Sort of killing machines,

But they are key predators in our marine ecosystems,

And we need them to keep our ecosystems in balance.

Narrator: He knows bull sharks travel every summer

To mozambique to feed.

But even for a shark, travel comes with risk.

Threats are everywhere.

How are these sharks so successful at moving around?

And what is the bull shark's range?

To find out, ryan travels to the most southwesterly end

Of the bull shark's range in africa.

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The sleepy town of infanta,

On the busy breede river.

Home to at least 30 bull sharks in summer.

People vacation here.

This could be new york's long island

Or the outer banks, north carolina.

Ryan: It's crazy, all these people,

All these sharks in the same place.

It's incredible that everything is so peaceful,

And I hope it continues as it is;

Sharks minding their business, people minding their business.

Narrator: Ryan is here to catch a shark

And fit it with a long-term tracking device.

Ryan: This can stay on the shark for six months to a year.

Pop up on a specified date, come to the surface,

Transmit all the data to us.

So hopefully we're gonna be able to answer some of the questions

Around where they go.

Narrator: Time to go shark fishing again.

Ryan teams up with dr. John filmater,

Marine scientist and local expert.

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They have a tough job on their hands.

Ryan: Yeah, this is pretty much shark food.

So the waiting game begins.

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Narrator: A big shark takes the bait.

Ryan: Ooh, it's nice, putting a bit of extra pressure on him.

Perfect.

Ooh, it might be wrapped a little bit.

It's definitely angry.

Yeah, it's got a lot of energy still.

Narrator: He can't pull it in safely until he's tired it out.

Ryan: Yo.

Narrator: A formidable predator with a temper...

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...That can snap in a second.

Man: Oh, my god!

Narrator: Until the shark is secured next to the boat,

Anything can happen.

Ryan: (laughs) that's right.

John filmater: Think he'll get angry.

Ryan: The head shakes are proper.

Watch, watch, watch!

Male shark.

John: Yeah.

Ryan: Head shakes are violent.

Tail up.

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Yes, it's a monster, this thing.

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(grunts)

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Yes, well done. Very nice.

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We always monitor the shark

And make sure it's got water pumping over its gills.

Narrator: Time to flip it.

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The nearly 10-foot shark instantly calms.

Ryan: It's a big shark.

Ooh, okay. Wait a bit?

John: Yeah.

Ryan: Ah, 297.

John: Okay. Jeez.

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Narrator: A small incision for an internal acoustic tag.

John: Happy?

Ryan: Okay, tag that as well.

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Narrator: And as long as the shark is on its back

It's in a trance.

But if it flips over too soon, there's trouble.

John: Yo. Watch! Watch!

Narrator: A 9 1/2-foot bull shark in a busy river.

Dr. Ryan daly wants to know its migratory patterns

And exactly where it will travel.

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Ryan: It's awake. That's a good sign.

Narrator: A satellite tag on the dorsal fin

Will track his movements for up to a year.

Ryan: It's gonna switch itself on automatically

When it gets to 5 meters deep.

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Narrator: The release is done from the water.

Ryan: Okay, there we go. Turn it over.

John: No, right there.

Ryan: Oh.

John: Don't turn it over. Tell me when to turn it over.

Ryan: Yeah.

Narrator: Ryan guides the shark back.

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John: Watch, watch, watch!

Narrator: Over the course of seven days,

The team successfully tags and releases

Four big male bull sharks.

Ryan: Tagging these bull sharks here has allowed us to discover

That they travel at least 20 miles upriver,

Up and down, almost every day.

Narrator: Bull sharks patrolling a river

Surrounded by farms and vacation homes.

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Triggered by winter's cooler temperatures,

The sharks break for open ocean.

Ryan: We expected them to stop off

At known bull shark aggregation sites as they went up the coast.

In fact, they did the opposite.

Once these bull sharks left the breede river,

They just beelined it for northern mozambique,

Almost 2,000 miles away.

Narrator: Ryan has made a remarkable discovery.

Rather than go it alone,

The sharks leave the river together.

Like bulls on a stampede,

They swim almost 2,000 miles over three months,

All the way to northern mozambique.

This is much farther than ryan thought.

Then, the four sharks turn around in time

To make the trevally feast off the south coast.

The previous record for bull shark migration

Was 2,000 miles.

The four tagged sharks have already covered 3,000 miles

To reach the trevally spawn.

A new record.

Ryan has no idea if his research subjects have survived

Or if they'll return to the breede river

Where they started.

The only way to find out

Is for ryan and john to go back

To where they tagged the sharks 12 months ago...

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...In hopes they pick up a signal

From one of the transmitters.

Ryan: Alright, we're in the spot.

John: See if there's a shark here.

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Narrator: A hydrophone will listen

For acoustic tags nearby.

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John: If there's a shark within 400 meters of us, we'll know.

Ryan: Alright.

Come on, shark.

John: So the tags are pinging every 40 seconds or so.

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Ryan: Oh, is that something?

False alarm.

(clicking)

Oh, there's a detection.

And that's one of the sharks.

John: Five-oh. No ways!

Ryan: What? That's one of the male zambezi sharks.

It was 286 centimeters, so just under 3 meters, or about 9 feet.

So it's one of our big male sharks.

Unreal. Okay, so that means that that shark has gone

At least 1,800 miles up the coast to northern mozambique,

Turned around, swam all the way back to the same place.

Must be a round trip of over 4,000 miles.

Just under a year, it's come all the way back to the same place.

(clicking) there it is again!

John: That is absolutely insane.

Narrator: All four tagged males are detected in the river.

The data reveals that two of them arrived

Within 30 hours of each other.

They traveled 4,000 miles together.

The longest bull shark migration ever recorded.

Double the previously published record.

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Bulls travel from sea to river

And back to sea every day

And in coordinated migratory patterns.

Are bull sharks a species uniquely lethal to humans?

Or an apex predator under threat

In every habitat it invades?

Running the gauntlet of competition

And other predators,

To feed and to breed,

This year and every year, all over the world.

Captioned by side door media services