Original subtitles

Narrator: In all the oceans of the world,

this shark is known as most dangerous to people.

It has a jaw full of razor-sharp teeth.

Man: It just came out of the water and bit my arm.

Narrator: And a nasty disposition.

(shouting)

man: Whoa!

Narrator: The bull shark hunts where we play.

(muffled scream)

and now, it's on the move.

Man: Bull sharks have no trouble being upriver in freshwater.

(scream)

narrator: Coming soon to a shore near you.

Man: I don't think they realize that the sharks are here.

♪ ♪

♪ ♪

narrator: Great whites may have a fearsome reputation.

But out of more than 400 species of shark,

there's one that is considered even more dangerous.

It's the bull shark.

A creature with a reputation

for being exceptionally aggressive.

Mike heithaus: I kind of think of bull sharks

as the pit bulls of the oceans.

They are probably more impressive predators

than other sharks that are the same length.

Most sharks will only attack prey

that's maybe 10%, 15% of their own body size.

For bull sharks, all bets are off, because they are so strong.

Narrator: Aggressive...

Fast...

And fearless.

Bulls are a threat wherever they're found.

Charles bangley: The distribution of the bull shark is worldwide.

If I had one word to sum up the bull shark,

it would be adaptable.

That makes them kind of unique among a lot of shark species.

Narrator: The bull shark favors warm, shallow waters,

making it a danger to swimmers around the world.

And it's likely responsible for more attacks than we realize.

♪ ♪

♪ ♪

♪ ♪

June 2015.

16-year-old hunter treschl enjoys a day at the beach.

Hunter treschl: I was in oak island for a family vacation.

We'd just taken like a day trip down there.

Me and my cousin and my grandma.

And we had been there for probably like three, four hours.

So, I was just kind of walking out,

getting ready to wash off.

And I stop about waist-high water.

And the water was like super murky at this point

because there was a storm offshore.

So, I could see kinda my upper thighs and that's it.

♪ ♪

♪ ♪

I knelt down, crouched down, maybe 50 feet from shore.

I felt this solid bump on my ankles.

♪ ♪

I assumed it was a stingray.

That's like a pretty normal thing to have happen

down in north carolina.

I started backing up.

♪ ♪

♪ ♪

and that's the first moment when I realized

that it wasn't a stingray.

It was a shark.

It just came out of the water and bit my arm.

Grabbed me toward the bottom of my arm,

took the arm below the elbow in that first bite.

And then it was just gone, just like that.

I was awake through this whole thing.

There was a crowd around.

There were people with towels trying to stop the bleeding.

Narrator: Hunter couldn't identify the kind of shark

that attacked him.

But based on the size of his wounds,

experts make a pretty good guess:

A bull shark.

Hunter: They estimated it being

about seven and a half to eight and a half feet long.

Prior to the attack,

I didn't actually know much about bull sharks.

Now after my attack, I feel like I've learned a lot more.

They are one of the more aggressive breeds of shark.

I'm super lucky to have gotten out from that experience alive.

Narrator: Researchers have confirmed

100 bull shark attacks.

But the real number may be much higher,

because the bull shark is so difficult to identify.

Mike: When you first look at a bull shark,

it doesn't really jump out at you that it's a bull shark.

It just kind of looks like other sharks, you know,

kind of grayish-brown on top, white below.

That's really different from an iconic species

like the tiger shark that has that really square head

and those stripes that set it apart from any other species.

Then you also have white sharks,

nobody's gonna mistake a white shark,

this is a really iconic look.

You have the torpedo shape, the tail,

the bright white belly, kind of slate gray above.

Narrator: The bull shark's looks aren't showy or iconic.

But if you know what to look for, you'll never forget it.

Mike: When you really start to look closer at the bull sharks,

you see some features that differ from typical shark shape.

They almost look like swimming mouths at times.

They're really thick from those pectoral fins forward,

you know, huge jaws,

and then they've got the musculature to back that up.

Narrator: June 2005.

16-year-old craig hutto and his brother, brian,

are fishing in waist-deep water 30 yards from shore.

Craig hutto: We were making our way kinda in the gully.

I really didn't have any worries or anything.

Something came up underwater, I didn't see anything.

Something bumped me on my left leg.

Something grabbed me on my right leg and took me underwater.

It's just like that going into shock right then,

is kinda my whole body just went numb.

Brian hutto: That's when I saw its back come out of the water.

There's this fin that just kinda sweeps up and grabs him

and rolls over on top of him.

Craig: My first real instinct was

I need to get this shark off of me.

I've heard from somebody saying that a shark's tooth is so sharp

that it can bite you and you not even feel it.

And I think that's what happened to my hands

'cause in a split second I put my hands down.

I looked up at my hands and it was just,

my hands were just cut open, just torn to pieces.

Narrator: The shark releases craig for a moment,

giving his brother enough time to drag him to shore.

It takes five months for craig's hands to heal.

But his right leg is too damaged to save.

The only warning he had for the attack was a bump on his leg.

Mike: Now a lot of times when we think about sharks,

we think about, you know, maybe mindless eating machines

just charging in to grab things right away.

But that's not always what they do.

Narrator: The bull shark uses its bump to test

whether its victim is going to fight back.

Mike: When they see something and they're not sure

if it's prey or not, they might do something like this,

which is just give it that little bump

so they can figure out, you know, is this something

I want to eat or something I want to just leave alone?

Narrator: If the bull shark's bump isn't challenged,

it then moves in for the kill.

George burgess: They'll come back to do the bite,

which usually is in the lower quadrant of the body.

Narrator: Making the bull shark's bite so devastating:

An arsenal of razor-sharp teeth.

George: On each of these teeth,

there's little serrations on each side,

so when the animal bites,

it not only uses the pointed tips to cut,

but those serrated teeth get into the flesh

and then they literally cut off what they want.

Mike: As they shift their jaw,

it can kind of cut and slice as well

and cut out big chunks of their prey.

Narrator: The bull shark has 50 functional teeth,

with up to 6 replacement teeth in each row.

That's up to 300 teeth in its mouth at any given time.

A bull shark might grow as many as 65,000 teeth

in its lifetime.

But as soon as it loses one, another rises in its place.

George: You can see the replacement teeth.

Behind each tooth there's a row of other teeth.

And every two weeks or so a new tooth comes in from behind

and it keeps making teeth for its entire life.

Narrator: It's not just the teeth that make

a bull shark's bite so killer.

Its power comes from its jaw structure.

Mike: Their mouth is kinda back in under the snout a little bit,

so if it just opened the lower jaw,

it would be really hard for it to get something big.

But the bull sharks kinda protrude their jaw forward

when they open their mouth.

And so then they can clamp on to prey, including really big prey.

Narrator: Like tarpons,

turtle shells,

other sharks,

and sometimes, people.

Biologist dr. Brady barr has tested the bite force

of some of the world's biggest predators,

including sharks.

Brady barr: Oh, look at that!

Narrator: Now he's after a great white

off the coast of south africa.

Brady: Whoa, come on, baby.

Narrator: They've got one,

about 4,000 pounds and 16 feet long.

Brady: Whoa!

Got it, got it, we got a bite, we got a bite!

Narrator: He reads the pounds of force per square inch.

Brady: I mean, 669.

That is a heck of a bite!

Narrator: Next up: Testing the bite force

of a much smaller bull shark off the coast of florida.

Brady: Careful!

Oh, look at the size of that!

That is a monster bull shark!

Narrator: Which bite is stronger?

The great white or the bull shark?

Brady: Whoa!

Narrator: Biologist dr. Brady barr is off the coast

of florida to test the bite strength

of a fearsome bull shark.

Brady: So the idea is you're just gonna pull the shark's head

up out of the water,

and I'll stick the bite force meter down in there.

I'm using the bite force meter

that I normally use for crocodiles.

I'm gonna get a digital read-out here of pounds of force.

And this shark is angry and it's a bull shark.

I have a feeling we're gonna get a huge bite!

Come on, open your mouth!

Look at those teeth!

Oh, 989!

989 pounds!

That's literally half a ton of bite force

from a 300-pound bull shark!

Narrator: The bull is less than half the length

and only a third of the weight of a great white.

But its bite is more than 300 pounds of force stronger.

The bull's head is wider than most other shark heads.

That extra width means more muscle,

which means more jaw strength.

George: There's a great deal of weight

used in the biting process,

simply because of the mass of the head.

Narrator: The bull shark's bite is greater

than any other shark.

It can exert 1,300 pounds toward the back of the jaw

and over 450 pounds up front.

How it deploys all that force is also unique,

with terrifying savagery.

George: What makes bull sharks distinct from other species

of sharks is the aggressiveness of their attacks.

Narrator: July 6, 2001.

8-year-old jessie arbogast and his cousins

play in the shallow waters off pensacola, florida.

(screaming)

suddenly, an enormous bull shark bites down

on jessie's right arm

and begins to shake.

♪ ♪

it tears the arm from his body,

and goes on to rip off a large piece of his thigh.

♪ ♪

jessie's uncle grabs the 7-foot animal by the tail

and drags it onto the beach.

A park ranger shoots the shark.

They find jessie's arm still in its mouth, intact.

Surgeons reattach the arm.

But severe blood loss leaves jessie brain damaged.

In just a few seconds, his life has been changed forever

by two bites from this aggressive bull shark.

George: Bull sharks will come back for second and third bites.

In many cases will finish off their victim one way or another.

We very frequently hear that the shark was following the victim

right up to the shoreline.

Mike: If you're a bull shark and you're attacking something big,

you're likely to make bites in fairly rapid succession

because if it starts to get too far away,

it may maneuver enough to avoid that killing bite.

Narrator: An attack can be lightning quick.

A bull shark cruises slowly near the bottom.

It's capable of achieving a burst up to 11 miles per hour.

Mike: If you're prey, a bull shark's on top of you

before you know it.

Narrator: In August 2000,

69-year-old thadeus kubinski and his wife anna

decide to go for a quick swim in the inlet behind their home

in boca ciega bay, florida.

Thadeus jumps in first.

He swims in five feet of water, yards from the dock.

♪ ♪

♪ ♪

♪ ♪

suddenly, he's attacked by a shark.

It kills kubinski with a bite into his chest,

15 inches across.

Authorities recover a shark tooth from kubinski's body.

It belongs to a bull,

estimated to be nearly 9 feet long and 400 pounds.

As big as it was,

kubinski never saw it coming.

Mike: So, you can see here, that shark is almost invisible,

and it just kind of materializes out of nowhere.

Narrator: In the murky water,

the quick-swimming bull shark can sneak up on anyone.

Even the most experienced swimmers.

♪ ♪

shark biologist greg skomal knows firsthand

the dangers of swimming with bull sharks.

Greg skomal: My name's greg skomal. I'm a shark biologist.

I'm affiliated with

the massachusetts division of marine fisheries.

I've been studying sharks for over 30 years.

Narrator: Skomal's latest project:

Tagging a variety of sharks

to see if their movements are impacted by weather.

Greg: Gotcha, gotcha!

It's on, woo-hoo!

Narrator: He tags a dangerous tiger shark.

Now skomal wants to tag an even more aggressive shark,

a bull.

Greg: Bull sharks arrive here every day,

so I'm hoping to get a tag on one of these animals underwater.

Narrator: Skomal has decades of experience.

He knows tagging a bull shark is risky business.

Greg: Now I've got to admit that getting in the water

with bull sharks, I've got my concerns.

I'm certainly going to be keeping my eye open.

Narrator: But today skomal just may be

putting his life on the line.

Just because you can't see a bull shark

doesn't mean it can't see you.

Narrator: Research scientist dr. Greg skomal

swims in the bahamas,

hoping to find a bull shark before it finds him.

Skomal swims just below the surface.

♪ ♪

greg: I can't see anything down here.

Wait, wait! Whoa, whoa! Whoa, whoa! What is that?

Is that a bull shark coming at me?!

I'm coming up, I'm coming up!

♪ ♪

♪ ♪

♪ ♪

narrator: Skomal's experiment has to wait.

In such poor visibility,

the risk of an attack is far too great.

Greg: Frankly, I'm not super comfortable

with bull sharks in places where I can't see them!

Narrator: It's a good call.

In murky water, the bull shark's super senses

give it a clear advantage.

Mike: Bull sharks have incredible sensory systems,

so murky water for them is no trouble.

George: The bull shark is pre-adapted

for these conditions

where it can rely on other senses

other than just pure eyesight.

Narrator: Sharks are literally wired for hunting.

Special pores around their faces detect

the electrical currents coming from other animals,

allowing bull sharks to hunt

without relying on their eyesight.

George: Bull sharks, they have tiny little eyes,

and they rely more on their senses of smell and hearing

in detecting movements.

And so, they do particularly well in turbid water,

which is the norm at the mouths of rivers and in estuaries.

Mike: For a predator like a bull shark,

an estuary is really great

because you've got all those nutrients coming out of rivers

and off the land, lots of plankton, sea grass,

and that feeds tons of fish.

George: Bull sharks instantly become

the largest predator in the area.

And they're able to find ample food supplies

that others cannot.

Narrator: Unlike other sharks, the bull shark doesn't

just swim outside the mouth of a river.

It can swim into the river itself.

That's because bull sharks are armed

with an astonishing adaptation:

They can survive in saltwater and freshwater.

Mike: Bull sharks can actually change their physiology enough

to survive under these two incredibly different

sets of conditions.

Narrator: Sharks need salt inside their bodies to survive.

As they enter freshwater,

the internal salt levels become diluted.

The lack of salt causes the shark's cells to expand

and their bodies to bloat,

killing them.

But the bull shark has a gland toward the tail

that shuts down to hold salt in.

While its long, specialized kidneys work

to reuse the salt already in the body.

Mike: So unlike other sharks, the bull sharks can switch

back and forth between being good in freshwater

and being good in the ocean.

Narrator: This supreme adaptability allows

these wandering sharks to use more waterways

where they encounter people.

George: The bull shark likes to live in the areas

where we like to go in the water.

So, as a result, the number of attacks involving bull sharks

is pretty high,

and the results can be quite catastrophic.

(scream)

mike: When people think about sharks,

they tend to think about deep water.

But some of these predators get into really shallow waters.

Bull sharks will hunt in water

that looks like it's just barely deep enough for them to swim in.

That's where prey are found, and when you lock on to it,

the prey has less dimensions to try to escape.

Narrator: Bull sharks don't just live

in the world's tropical oceans.

The bull shark's invasion into freshwater expands its range

beyond that of other sharks,

to rivers, lakes, and freshwater streams.

Man: Oh!

Mike: Bull sharks get found in what are amazing places

to people all around the world.

You've got populations in lake nicaragua,

they probably live there their whole life there.

Couple thousand miles up the amazon river.

Heck, in northern australia, they had some bull sharks

that were living for a fairly long time in a golf course pond

after they'd gotten swept in in a flood.

The zambezi river in south africa,

where you have animals that are 12, 13 feet long,

just huge predators.

Narrator: Here in south africa,

bull sharks aren't afraid to spar with creatures

more than twice their size.

Narrator: The estuaries of south africa's

isimangaliso wetland park

support some of the world's most imposing creatures.

Elephants,

black rhinos,

nile crocodiles,

and hippos.

Upriver from the indian ocean,

10 massive adult hippos take a swim.

Then notice an intruder.

Mike: If there's an animal in africa not to mess with,

hippos are right at the top.

But, you know, this shark is just kind of swimming around

and checking out hippos.

Narrator: Hippos kill more humans

than any other african animal.

This smaller bull shark isn't fazed by their size.

Mike: You can see the shark just kind of circling around here

and the hippos are definitely keeping an eye on this shark.

♪ ♪

♪ ♪

narrator: Suddenly, the shark makes a bold, aggressive move.

But moves on when the hippos gang up.

Mike: This is incredible.

You would never expect to see bull sharks and hippos,

but you do because those sharks can get into freshwater.

Narrator: Signs of the bull shark are found in rivers

all around the world, including the united states.

♪ ♪

♪ ♪

for the past 40 years, waterman john "willy" dean

has made his living fishing the tidal waters

of the potomac river, a mile from the chesapeake bay.

Every morning, he checks his nets for menhaden, croakers,

and anything else that swims in.

Willy: It's like a grab bag.

You never know what you're going to have.

That's what makes it so interesting.

Just hold her there, greg.

Greg: I'm holding it.

Willy: A lot of crabs in there.

Greg: Mm-hm.

Narrator: On a routine haul in August 2013,

willy and his son greg pull up the catch of their lives.

Willy: We were coming out to fish the net that day,

doing just what we're doing now,

and when we got pulling this side up here,

we noticed some thrashing in the water.

And I told the boys, I said, "we got something in here today.

And it ain't little."

as we started getting the net up, we got a glimpse of it.

And we realized we had a shark in here.

First thing I think is, how can I get him out of this net

as quick as possible, so he doesn't eat the net up?

He would hit the net so hard he was shaking the poles.

His tail section, he was flipping!

That's a lot of power.

Don't want to let your guard down.

Narrator: Just when the shark is under control,

the deans notice they have another problem.

Greg: As we were pulling the one in the boat,

we saw the second one.

We all looked at each other and realized, yo, hey,

we got to get ready to get this second one now, too.

I weigh about 225, and, yeah, it was a struggle that day.

The tail was pretty scary because of the force behind it.

The entire time, all we heard was just him chomping his jaws.

Narrator: Each bull is over 8 feet

and weighs in at 300 pounds.

Greg: I never would imagine to think there would be one

right here, so close, you know, where I grew up at.

Never in a million years would have thought it.

Narrator: Two enormous bull sharks.

Not in the ocean, but up a freshwater river,

just a quick swim from beachgoers.

Willy: This is where everybody comes to go swimming.

This park is usually packed.

I don't think they realize that the sharks are here.

Kind of makes you reluctant to want to go swimming very much.

Narrator: Since the deans pulled in

their two bull sharks, scientists have recorded

other bull shark sightings along the chesapeake.

Charles: In the chesapeake bay,

most of the bull sharks that are sighted,

particularly in the potomac river,

tend to be very large individuals,

8 or 9 feet or greater.

Narrator: There's a good reason why bull sharks head inland

up waterways like this.

And it's not for prey.

The sharks are here to make more sharks.

Narrator: Each year, the waterways of the southern united states

get some dangerous visitors:

Bull sharks...

Coming to breed.

Mike: A pregnant female bull shark

will swim into coastal waters,

maybe into the mouth of a river and estuary,

and she'll have her pups.

Those pups have been growing inside her for about a year.

Narrator: Bulls give birth to around eight pups per litter

in the safety of these nurseries.

George: By definition, nursery areas are rich in food

so the young can grow.

And they also are areas where the danger is lower

of being eaten by larger predators.

♪ ♪

narrator: River fish expert and national geographic explorer

zeb hogan has traveled to australia's outback

to see if he can find proof of baby bulls in freshwater.

Zeb: We're at our fishing spot and what a nice spot to fish!

Narrator: Zeb's daytime attempts are a bust.

But after sundown, something shifts.

Zeb: Oh, something pulling.

It's coming towards us.

Whoa! This is big, this is big!

Whatever this is, it's big!

It really was pulling line at the beginning there.

I haven't seen it break the surface yet,

but might be a shark!

Little bull shark!

Man, long time coming, finally got one.

Look at this thing!

Wow!

♪ ♪

small bull shark, probably about a meter long.

World record size would be about 800 to 1,000 pounds.

So, this is a very young shark.

Narrator: Zeb has discovered a bull shark nursery.

One day the babies here may threaten swimmers far away.

Mike: They'll be in these freshwater systems

for maybe three to five years.

Then once they're big enough, they'll leave the river systems

and start living in coastal waters.

Narrator: Bull sharks have always lived in rivers

and close to the coast.

A bull shark may have been responsible for a string

of the deadliest inland attacks in history.

Mike: You had so many attacks clustered

in such a short period of time,

that started to get the public perception of sharks

as dangerous, and ultimately was an inspiration for jaws.

(scream)

narrator: More than a hundred years ago,

shark attacks were virtually unknown in america.

George: At that time, there was a school of thought

that sharks don't attack humans.

In fact, a person put a high reward out for anybody

who could prove that sharks attack humans.

Narrator: July 1, 1916.

Just off the coast of long beach island, new jersey,

a shark attacks and kills 25-year-old charles vansant.

Five days later and 45 miles north,

27-year-old charles bruder is attacked not far from shore.

His abdomen is ripped open and both legs are severed.

The unprecedented back-to-back killings

leave the public shaken.

Eleven days later, there's a third attack,

but not in the atlantic ocean.

Matawan creek, new jersey.

15 miles inland from the jersey shore.

A group of boys are playing

when a shark grabs 11-year-old lester stilwell

and pulls him under.

(screams)

a good samaritan tries to recover the body.

But a shark kills him, too.

30 minutes later, a shark attacks another boy.

This teen manages to escape with his life.

Mike: One of the things that to me is really interesting

about the 1916 attacks in new jersey

is the attacks that occurred so far upstream.

That's the kind of habitat you wouldn't really think

a great white would be in.

I mean, that seems more like a bull shark.

Narrator: The river attacks in new jersey were lethal...

But rare.

In another part of the world,

people risk their lives every time they enter the water.

Narrator: The ganges river basin,

west bengal, india.

For many of the 400 million people living here,

the murky river is an important source of income.

It also holds a danger:

Bull sharks.

Mike: When you see a big bull shark in the caribbean

or the atlantic, they are big, impressive predators,

but get over to the indian ocean,

and they get three feet longer and way more massive.

So, you get from an impressive predator

to a truly amazing apex predator.

Narrator: The sharks clash with humans in these river systems.

And leave their signatures on the unlucky.

George: Victims oftentimes reach down and go to try to defend

themselves from whatever is biting them.

And in doing so, they often get defensive wounds.

And they're analogous to what we see in stabbing incidents

where the victim reaches out to defend themselves.

If one examines the wounds, one often can find telltale signs

that a bull shark has attacked.

The serrated teeth often lead to injuries

on particularly the long bones of the leg or arm.

And as the tooth hits the bone,

it leaves very distinctive serrated marks.

Narrator: Now you understand the power of the bull shark,

beware.

There's more chance than ever you'll encounter one.

Charles: There are a number of nursery habitats for bull sharks

that have been identified in us waters.

A lot of them are in the gulf of mexico,

ranging from texas up to louisiana,

over to western florida.

On the east coast, probably the most heavily used

nursery habitat is the indian river lagoon

that stretches along a lot of the east coast of florida.

And more recently, there have been an increasing number

of juveniles born in pamlico sound, north carolina.

Narrator: Bull sharks favor the tropics.

And climate change is inviting them

to more waterways than ever.

They're on the move.

Mike: Climate change is going to affect the oceans profoundly.

As waters warm, what that's going to do is expand the range

over which a lot of tropical species can live.

So, animals like bull sharks that like warm water,

they're going to be able to move

into those higher latitude areas.

They're going to be able to move north along the us coast

as the conditions become more favorable.

Narrator: As that happens,

swimmers off the northeast coast may soon see

two apex predators in their waters.

George: We're going to be seeing the bull shark range impinging

on what was traditional white shark territory.

More humans in the water,

more sharks in those particular waters

is a formula for more bites.

Narrator: It seems we're already seeing the signs

of increased activity.

George: Anybody who spends time in the seas,

in certain areas have had a shark

within 6 to 10 feet of them at one time or another,

without knowing it.

Realistically, we're going to see more shark bites

from the bull shark in years ahead,

as long as we don't contain the climate change.

Narrator: Powerful...

Stealthy...

Adaptable...

And aggressive...

With a deadly bite.

The bull shark swims where we do.

If you get into the water,

you do so at your own risk.

(scream)

george: The sea does not belong to us.

It's a wilderness experience.

As you enter the sea, you're an ecotourist.

You need to understand there's risk.

Mike: If you see bull sharks in the water,

I would suggest getting out.

I'm getting out!

(muffled scream)

captioned by side door media services