All language subtitles for When Sharks Attack - 6x02_track3_eng

Narrator: For centuries,

native hawaiians
believed sharks

were the reincarnated spirits
of their ancestors,

sent to protect them.

But that was the past.

(scream)

man: There's giant,
just red clouds of blood

just bursting everywhere.

Narrator: Nine mysterious
shark attacks

on the big island
in three years.

Man: I was very close to dying.

Narrator: Investigators
are on the case

of this terrifying anomaly.

Man: This spike
is highly unique.

And we really need to
figure out what's going on.

Narrator: And what they reveal
could send shock waves

across every coastline
on earth.

Man: Whew. I just got attacked
by a tiger shark!

♪ ♪

♪ ♪

braxton rocha:
So, my gear for the day.

I got my speargun, what
we need to get the fish with.

I've got my wetsuit,
got my mask,

and I got my fins for the day.

Narrator: Braxton rocha
has been spearfishing

off the island of hawaii
since he was a child.

Braxton: I always had a strong
connection with the ocean.

I just love to be in the water

to put food on the table
for my family.

Narrator: The big island
is the biggest landmass

in the hawaiian chain.

It's here that sharks
reign supreme.

40 different species
prowl the water,

like oceanic whitetips,
hammerheads, silkies,

and the elusive megamouth,
which can grow to 18 feet long

and live at depths
of up to 15,000 feet.

Historically, the presence
of these predators

hasn't been an issue.

That is, until now.

Braxton: Never in my life
did I ever think

that I'd ever get,
like, bit by a shark.

♪ ♪

narrator: Braxton
and his friend shannon

are enjoying an afternoon
of spearfishing.

Braxton: We were just going
after, like, parrotfish

or like koles, it's like a, like
a black type of fish out here.

It was a really good time.

Narrator: The pair shoot
several fish

and then consider heading back.

But braxton isn't yet happy
with the day's catch.

Braxton: I was like, "nah,"
you know, "one more fish."

maybe I was being
a little greedy that day,

and so I went back out.

Narrator:
It's a fateful decision.

Just minutes later, an ominous
shape emerges from the depths.

♪ ♪

braxton: I've seen sharks,
like, my entire life,

but this one, I mean, it like,
it literally, it blew me away.

It was the size of,
like, a truck.

I was just like,
just like in awe.

And then it happened.

(muffled scream)

narrator: The predator bites
down on braxton's leg.

Braxton: All I could see was
just teeth, just rows of teeth.

And there's, like, giant,
just red clouds of blood

just bursting everywhere.

Narrator: In desperation,

braxton punches the shark
in the nose.

Mercifully, it gives up.

Braxton: She disappeared
and I was just telling myself,

you know,
"maybe she might come back."

narrator: The injured diver
races for shore.

Braxton: I was like
80, 90 yards out.

I was swimming as hard as I can.

I was just, like,
freaking out the whole time.

Narrator: Finally,
he makes it to the rocks.

Braxton: And I'm just, like,
looking down at my leg

and it's like,
it's like, split open,

looks like I got, like,
blown up by, like, a bomb

in, like, in the war
or something.

I was just, like, I could see
everything in my leg.

I could see my bone, like,
everything, like, moving.

And I'm just, like, freaking
out, like, "I'm gonna die."

narrator: But while the reality
of the situation sinks in,

braxton realizes that
his dive partner shannon

is still in the water.

Braxton: And I'm like,
"shannon! Shannon!"

I started screaming his name
as loud as I can.

"shannon! Get out! Shark!"

and he finally sees my leg,
and he's just like,

he starts crying,
he's like, screaming.

He's like, "no! No!"

and I'm like, "bro,
I'm gonna die right now.

I'm (bleep) dying."

narrator: Braxton is rushed
to the hospital.

Braxton: Whew.
I'm going to the hospital.

Wish me luck, guys.

Whew!

Narrator: It takes
nearly 100 staples

to close up the diver's
shredded leg.

He knows he's lucky
to be alive.

Braxton: My surgeon had told me,
if it went any lower

in the inside
of my leg right here,

it would've caught
my main artery,

and I never would've
made it back to shore.

And it's all I ever think about
is, like, how blessed I am.

(muffled scream)

narrator: Attacks are normally
a rare occurrence

on hawaii's big island.

But braxton's encounter
is actually

part of a much bigger problem.

Since 2013, shark bites
have skyrocketed.

In fact, he's
the seventh victim

in just over a year and a half.

And he won't be the last.

In the next three months,

two more people are
savagely bitten.

Nine in total

over a three-year period.

Triple the average

for the past decade.

For marine biologists
like terry lilley,

it's a disturbing trend.

Terry lilley:
In the past here in hawaii,

we had very few shark attacks.

I'm seeing this spike in shark
altercations with humans go up

over the last few years, to
the point I've never seen that

in my entire lifetime
of being in the ocean.

This is highly unique.

Narrator: The cause
must be found,

or the safety of every
beachgoer could be at risk.

Terry: We may have
a much bigger problem.

There's going to be
more shark bites,

so that's incredibly
concerning to me.

Narrator: So what's behind
this alarming surge of attacks?

The first thing
investigators must determine

is the type of shark involved.

And there are a number
of possible suspects.

Hawaii is home
to the three species

most frequently implicated
in attacks on humans.

The massive great white,
the ferocious bull shark,

and the distinctive
tiger shark.

Could one of these
infamous predators

be responsible for
the rise of attacks?

One way to find out is to
examine the victims' injuries.

Dr. Dan huber from the
university of tampa shark lab

investigates.

Dan huber: Right now we're
looking at attack photos

from braxton rocha.

From these photos,
we can see a severe laceration

to the victim's left thigh.

And then less severe lacerations

to the middle and lower portions
of his left calf.

This would indicate that the
victim was attacked by a shark

with a very, very broad
curvature of the jaw,

and the only shark that matches
that in coastal hawaiian waters

is the tiger shark.

Narrator: Tiger sharks
get their name

from the vertical stripes
on their bodies.

Their powerful jaws
mean they can rip through

the shell of their
favorite prey: Sea turtles.

These imposing predators are
one of the most common species

of shark in hawaiian waters.

And when the data is analyzed,

it's clear they play
a key role in the spike.

Dan: Looking at reports
from victims,

witnesses of the accounts,
and some forensic evidence,

it would suggest that most
if not all of the attacks

that occurred
between 2013 and 2015,

were caused by tiger sharks.

Narrator: Despite their
ferocious reputations,

tiger sharks generally
leave people alone.

So why have they suddenly
started attacking

unsuspecting beachgoers?

According to local experts,
in 2013,

reports began to surface
that could indicate why.

Shark sightings near shore
appear to be on the rise.

Terry: In the last couple years,

I'm seeing big tiger sharks

right in the surf zone
where we're surfing.

And this puts them
into more contact with us

out in the water,
surfing, swimming and diving.

And there's going to be more
accidental shark bites

because of that.

Narrator: Tiger sharks
congregating in the shallows;

it's a terrifying revelation.

So why do these
distinctive predators

suddenly seem like they're
showing up near shore?

Local fisherman rick reger
thinks

this frightening occurrence
might be a manmade problem.

Rick reger: This is where
they like to be,

right in the, the entrance

and just right in this
little basin right here.

Narrator: This is
honokohau harbor.

In the late 1960s,
the us army corps of engineers

blasted its 20-foot basin
out of solid volcanic rock,

turning it into
a vital hub for fishing.

But the tiny port
shelters more than just boats.

Near the harbor entrance is
a rich coral reef ecosystem

that's teeming with
fish, manta rays,

and green sea turtles.

But that's not all.

Rick: We see tiger sharks very,
very frequently in this area.

Narrator: This video
was taken in 2019.

It shows a massive tiger shark
inches from land.

Man: Oh, coming straight up
for you.

Narrator: What's more,
honokohau harbor is not alone.

Similar boat basins have sprung
up all over the big island.

And according to experts,
they're full of sharks.

Man: Nine-foot tiger shark!

Narrator: So could
the bountiful habitats

created by these harbors
be drawing tiger sharks

closer to shore and
into areas where humans swim?

It's a scenario that's
played out before.

In recife, brazil,

an incredible string

of 56 incidents over 20 years

has been tied to the presence

of a nearby harbor.

So could the same thing
be happening in hawaii?

According to dan huber,
it all comes down to geography.

Dan: Right now, I'm looking at a
map of the big island of hawaii.

And we're gonna put onto the map

the locations of all of the
harbors around the big island.

You can see that
there's five of them.

Now on top of that, we're gonna
lay on the locations

of the nine attacks that
occurred between 2013 and 2015.

Now, two of these attacks
happened in proximity

to the harbors,

but the other seven attacks are
spread all around the island,

some of them very far
from the harbors.

So it's not likely the presence
of the manmade harbors

was a contributing factor
to this spike in attacks.

Narrator: These manmade ports
are not to blame.

But perhaps
there's another reason

sharks could be congregating
near the shore.

An incredible video
taken in 2019

could point to what
that might be.

Something enormous is lurking
off the coast of hawaii.

In fact, it's the largest
predatory fish...

Ever seen.

Narrator: The jaws of
a tiger shark can slice through

the shell of a sea turtle
like a chainsaw.

But between 2013 and 2015,
on hawaii's big island,

they turn those ferocious teeth
on beachgoers.

Nine vicious attacks have left

experts grappling for answers.

But an increase in sightings
of the predators near shore

could be a vital clue.

Terry: In the last couple years,
I'm seeing big tiger sharks

right in the surf zone
where we're surfing.

Narrator: So why might
these master hunters

be congregating
in the shallows?

And could this increase
in shark traffic

explain the attacks?

In 2019, a monstrous piece of
evidence emerges from the deep.

Off the coast of maui, a group
of snorkelers is investigating

the carcass of a sperm whale,

when they encounter
something extraordinary.

(muffled speech)

a 20-foot-long female
great white shark,

known as deep blue.

♪ ♪

this storied giant

is the largest of her kind
ever recorded.

She was first spotted in 2013,

and her appearance was
a global sensation.

Could her intimidating presence
in these waters

be related to the observations
of the tiger sharks,

which are smaller in stature,
closer to shore?

In deeper waters,
great whites and tigers

have sometimes been known to
seek out similar food sources,

particularly whale carcasses.

So what happens when
sharks of different sizes

are forced to compete for food?

At long island aquarium
in new york,

curator joe yaiullo

and shark keeper
roberto alfieri investigate.

Inside this 120,000-gallon tank
are four sand tiger sharks

of various proportions.

Roberto alfieri: She is
the bigger of the females.

Then we have bumps over there,
is another female.

The two male are
smaller in size.

Narrator: The team
hopes to observe

how these different-sized
sharks interact

when vying for
a single food source.

To do so, roberto places a fish
on the end of a feeding pole.

Joe yaiullo: Yeah.
Well, there's one.

So was that, that was bertha
on the first one?

Roberto: Yeah.

Narrator: Bertha is the biggest
shark in the tank.

Joe: Bertha got pretty excited
about the food

and also grabbed part of the,
the feeding pole itself.

Narrator: The pattern is
immediately clear.

Roberto: Bertha.

Joe: That was bertha.

Narrator: The largest shark is
crowding out the competition.

Joe: So bertha is the biggest
shark in our tank,

and she is pretty much
the one in charge.

So she eats first, and the other
sharks stay on the periphery

until it's their turn.

Narrator:
Joe's experiment shows

that in the world of sharks,
bigger really is better.

Joe: Same thing in the wild,

if there's a whale carcass
or a source of food

that's attracting
a number of sharks,

the bigger great whites
are gonna eat first.

Narrator: So is something
similar playing out

in the waters off hawaii?

Could deep blue
be hoarding prey,

and in turn,
forcing the tiger sharks

to search for food
closer to shore?

It seems possible.

But as investigators
dig deeper,

they find a problem
with the theory.

Between 2013 and 2015,

observations show deep blue
wasn't in hawaii at all.

In fact, the instantly
recognizable behemoth

was spotted numerous times
thousands of miles away

off the coast of mexico.

If tiger sharks are showing up
in the shallows

in greater numbers, then
it's not because of deep blue.

The reason for the attacks
remains elusive.

But while scouring the ocean
for an explanation,

experts come across something
else that also ensnares

large amounts of
a tiger shark's prey.

But it's not another
sea creature.

In fact, it walks on two legs.

Naia rae fox: I think the reason
why we are having

more sharks here actually is
because the amount of fishing

that's been going on.

Narrator: This is one
of the island's

most popular activities:
Sport fishing.

Every year,
recreational anglers haul in

more than 2 million
pounds of fish.

That means that on any given
day off the big island,

there are hundreds of fish
being caught and reeled in.

And for scientists
like dr. Dan huber,

these hooked sea creatures
may be attracting sharks.

Dan: A struggling fish as
its body is twitching a bit,

that motion is giving off
low frequency sounds.

And shark hearing
happens to be tuned in

to low frequency sounds.

This is definitely something
that could attract

a number of sharks
to the same area.

Narrator: So could sport
fishing be drawing tiger sharks

into the shallows,

thereby increasing the risk

of an accidental run-in
with people?

(scream)

according to
fisherman rick reger,

it comes down to where the best
sport fishing takes place.

To demonstrate,
he heads out to an area

well known for
the popular pastime.

Rick: Okay, so this is
our bottom here.

We have some of
the steepest drop-offs

in the whole world right here.

This is where you're gonna see
your tuna, your mahi-mahi,

your ono, your marlin.

Narrator: This location
could hold a vital clue

to solving the mystery.

Called the pelagic zone,

this open-water abyss
extends thousands of miles

between
the continental shelves.

It's home to an array
of large sea creatures:

Whales, manta rays,
big game fish,

and some of the most dangerous
sharks on earth.

Narrator: The island of hawaii
is plagued by shark attacks.

(scream)

nine horrific encounters...

Braxton: Whew, I'm going
to the hospital.

Narrator: ...Between 2013

and 2015 have left locals

and tourists in fear.

The bites appear to be
the work of tiger sharks.

The cause is a mystery.

Some believe that
these dangerous predators

are being lured into shore
by sport fishing.

Fishing guide rick reger
is mapping the island's

undersea geography to
demonstrate exactly where

this activity takes place.

Rick: Right now we're
at about 30,000 feet.

See, we just lose
the bottom here.

Narrator: This steep drop-off
is world-renowned

for its sport fishing,
but it also attracts sharks.

Rick: We'll see oceanic
whitetips, blue sharks,

galapagos sharks, mako sharks.

And at times,
I have seen these tigers.

Narrator: So, could
the presence of sharks

in the same waters
popular with sport fishing

explain the attacks?

Rick is skeptical.

Rick: Right now, we're at
about four miles offshore

not anywhere near
where people are swimming.

A completely different area.

Narrator: It seems that
sport fishing takes place

too far from shore to be
implicated in the surge.

But perhaps by examining
the deepest parts of the ocean,

investigators are getting
closer to the truth.

And when they review
the second attack in the spike,

there is one key detail
lurking in the depths.

James kerrigan:
So this is mahaiula beach.

You got to probably drive
down a road like this

for about half an hour
to get to it.

Narrator: James kerrigan
came to mahaiula beach

with his wife mary in 2013.

James: So these lava fields were
formed hundreds of years ago

from an eruption from mauna loa.

It's crazy how you just go from
this barren, remote,

you know, empty lava field,

and then all of a sudden
you walk through these trees,

and you're on this
idyllic polynesian beach.

It's forever tainted for me.

I can never see it
the same way again.

♪ ♪

it was sunny, probably
a good 85 degrees, low humidity.

The kind of day
you dream about, you know.

Narrator: Around 1:00 pm, james
and mary dive into the ocean.

♪ ♪

♪ ♪

james: I just remember swimming
and having a great time.

My wife was a swim instructor
when she was younger,

so she was teaching me
how to do the side stroke.

Narrator: But the lesson is
about to come to an abrupt end.

♪ ♪

♪ ♪

a shark sinks its teeth
into james' leg.

James: I felt pressure
on my leg, and I felt a pull,

and all of the sudden
my head was underwater.

Everything was kind of a blur.

Narrator: Suddenly
the shark lets go.

James: I was bleeding a lot,

and we just started swimming
as fast as we could.

Narrator: Bystanders drag
james onto the sand.

James: The wound was pretty bad.

Another guy came and wrapped
my leg all up in a towel.

There was a lot of blood.

Narrator: One of
the good samaritans calls 911.

James is airlifted
to a nearby hospital

where he's treated for multiple
lacerations to his leg.

♪ ♪

james: This was the deepest one

that went right down
to the bone,

and then I've got another one
right up here.

So that kind of
gives you an idea

how big the shark's mouth is.

♪ ♪

looking back,
I was very close to dying.

Narrator: James' encounter
is harrowing,

but it does contain a detail

that turns the investigation
on its head.

James: So these lava fields were
formed hundreds of years ago

from an eruption from mauna loa.

Narrator: The big island is
home to four active volcanoes,

including one of the most
explosive on the planet.

Could this subterranean suspect

be behind hawaii's sudden spike
in shark attacks?

Narrator: Hawaii's
magnificent volcanoes

are a draw for millions
of tourists.

But few realize that
they could play a part

in a series of
vicious shark bites.

(scream)

between 2013 and 2015,

the big island is hit

with nine attacks.

Three times the average
for the previous decade.

In each case, the perpetrator
is believed to be

a tiger shark.

Dr. Andrew rossiter from
the university of hawaii

explains this unexpected link
between sharks

and the island's
most unique feature.

Andrew rossiter: Some believe
that tiger shark attacks

may be related to
increased volcanic activity.

Narrator: On the big island,

there are four
active volcanoes,

including what some
consider to be

the most volatile in the world,
kilauea.

This 4,000-foot-tall colossus

has been continually
erupting since 1983.

And all that molten rock
has to go somewhere.

Andrew: The magma comes up to
the surface, lava is formed,

and the lava rushes down
and goes in the sea.

Narrator: The lava
can reach temperatures

of nearly 2,000 degrees
fahrenheit.

And when this scorching hot
torrent hits the ocean,

it creates a plume
of heated water

that can extend more than
a mile offshore.

To some experts,
this oceanic hot zone

could help explain
the spike in attacks.

Andrew: Volcanic fields may lead
to the presence of sharks.

Narrator: In 2015,
off the solomon islands

in the pacific ocean,

a team of researchers studying
underwater volcanic activity

captured video of
something extraordinary.

In the heat of
the spewing lava,

the scientists thought all they
would find would be bacteria,

but they also found...

Sharks.

Dubbed "sharkcano,"

the discovery makes headlines
around the world

and suggests that sharks
cannot only withstand

these extreme environments,
but may even be drawn to them.

Dan: We know that warm water
brings nutrients,

and what that means is
that lots of marine life

will gather in those areas.

Because of this, tiger sharks
might look for prey

in pockets of warm water such as
those caused by lava flows

around the hawaiian islands.

Narrator: But for tiger sharks,
warm water has another effect.

Dan: Tiger sharks are
an ectothermic species,

which means that their
body temperature is determined

by the temperature of
the surrounding environment.

All aspects of their physiology
are gonna change

with the water temperature.

When the water is warmer,

it's gonna increase
their metabolic rate,

which will also increase
their behavior.

This can cause the sharks
to feed more often.

Narrator: So, not only could
heat-seeking tiger sharks

be clustering near
these volcanic outflows,

but they might also
be more active,

making them more likely
to bite beachgoers.

And in 2013,
the year the spike began,

kilauea was especially active.

Dr. Dan huber
explores the theory.

Dan: What we've got here is a
map of the big island of hawaii.

And I'm gonna bring up on it
the location of a lava flow

that occurred in 2013.

But now as we bring up the
locations of all of the attacks,

we see that the attacks are
spread around the entire island,

which would suggest that
the lava flow in 2013

could not have been responsible
for the spike in attacks.

Narrator: Volcanic activity

isn't drawing more sharks
into shore.

But what this theory
does demonstrate

is that environmental factors
may cause tiger sharks

to hunt more often, making them
more likely to bite humans.

This could point to a simpler

but no less frightening
explanation

for the reports of tiger sharks
in the shallows.

Dan: Tiger sharks often hunt
in shallow coastal environments.

So if they're hunting
more often,

in theory, this could be
the reason why

there's reports of
more sharks in the water

in the time surrounding
the spike in shark attacks.

Narrator: So investigators
begin to focus

on one critical question:

Is there something else
that could send sharks

on a hunting spree?

The fifth attack in the spike
offers a clue.

♪ ♪

brian wargo: I've been
in hawaii for 24 years.

You don't get rich
living out here,

but you have
a very rich lifestyle.

Narrator: Brian wargo is
a professional fisherman

and avid surfer.

One of his favorite surf spots
on the island

is a remote stretch of
coastline called kauhola point.

Brian: It's a nice surfing area.

But once you're out there
and you jump off the beach,

you just never know
what's gonna happen.

♪ ♪

it was a typical hawaii day.

It was, you know,
75 to 85 degrees out.

Sunny.

Nice wind conditions.

The water was clear.

There's quite
a few people there.

Narrator: Brian is surfing
with his friend mckenzie clark.

Brian: The first set came in.

I paddled for one,

but I missed the wave.

Narrator: It's then
that brian sees

a surfer's worst nightmare.

(scream)

brian: I heard
mckenzie screaming.

I turned around and saw her
up out of the water

about two to three feet
on top of the shark's head.

♪ ♪

narrator: Brian wargo is
surfing with his friend,

mckenzie clark,

when the unthinkable happens.

(scream)

a tiger shark strikes
mckenzie from below.

Brian: It basically
looked something like

out of a jaws movie.

Narrator: The shark's teeth
slice through

mckenzie's surfboard
and into her hand.

Brian rushes to her aid.

Brian: She ripped her hand
out of his mouth.

I just saw the blood
go everywhere.

(screaming)

narrator: But mckenzie
isn't free yet.

The shark attacks again.

(scream)

brian: She's coming up
and screaming,

trying to get her breath,

and then getting pulled
back down by the shark.

Narrator: In desperation,
brian takes drastic action.

Brian: I grabbed
the shark's dorsal fin,

trying everything to try to stop
the shark from getting to her.

I got one hand free

and I started trying
to punch the shark.

Narrator: Brian hits the shark
a total of five times.

Finally, it releases.

Brian: One finger
was hurt pretty bad,

and there were lots of puncture
wounds throughout the hand.

(siren)

narrator: Mckenzie is rushed
to a nearby hospital.

She's treated for serious
injuries to her left hand

and eventually makes
a full recovery.

But for her savior, brian,
the trauma still lingers.

Brian: Being there and seeing it
has definitely changed my life.

Many sleepless nights
afterwards, you know,

post-traumatic stress syndrome

was in for quite some time
and still is.

Narrator: Mckenzie's attack
is just one part

of a troubling trend.

On the big island of hawaii,

there have been nine savage

encounters with tiger sharks

in just three years.

Investigators suspect that
something may be causing

tiger sharks
to hunt more often.

The question is...

What?

An answer may be hidden
in the details

of brian's harrowing ordeal.

(scream)

the shark that attacked
mckenzie came at her not once,

but three times.

Dan: The vast majority of shark
attacks involve a single bite,

after which the shark
leaves the victim alone.

But in this case,

the shark bumped mckenzie
off of her surfboard,

and then bit repeatedly onto
the board and onto her hands,

and even kept biting
while mckenzie's friend

was repeatedly
punching the shark.

And this indicates that the
shark was extremely aggressive.

Narrator: Investigators wonder
what could push tiger sharks

to behave so violently.

The answer might explain
why the predators

seem to be hunting more often.

Marine biologist
leighton taylor is an expert

on the significance of sharks
in hawaiian culture.

He thinks a clue may be found
not in science,

but in an ancient legend.

Leighton taylor:
The hawaiians' creation myth,

the kumulipo, is
famously coupleted

between the ocean and the sea.

For every land creature,
there's a sea creature.

Narrator:
According to dr. Taylor,

one of these pairings
could help solve the riddle

surrounding the spike in
attacks between 2013 and 2015.

It links one of the island's
most prominent plant species

and its most ferocious
predator.

Leighton: There is
a famous proverb,

"the shark bites when
the wiliwili blooms."

narrator: The adage refers
to the wiliwili tree,

an indigenous species
whose name means

"repeatedly twisted"
in hawaiian.

For centuries, the native
hawaiians revered the plant

for its colorful and
distinctive flowers,

which bloom every fall.

Braxton: Out here in hawaii,
people like to believe

that when the wiliwili tree
out here is blooming,

that's when the tiger sharks
are a lot more active

and more aggressive.

Narrator: So is
the ancient proverb right?

Are tiger sharks more likely
to bite in the autumn?

Dr. Dan huber thinks
there could be some truth

to this timeworn tale.

Dan: When you look at the data
from the attacks in hawaii

between 2013 to 2015,

most of the attacks occurred
from September to December.

Narrator: A critical
piece of the puzzle

has fallen into place.

The majority of the bites
did indeed take place

when the old adage predicts

that tiger sharks might
be more aggressive.

But what's behind this
terrifying change in behavior?

The answer to this deadly
riddle could send shock waves

across countless beachside
communities worldwide.

Narrator:
Between 2013 and 2015,

the island of hawaii
is in the grip

of a disturbing string
of shark attacks.

(scream)

nine incidents.

In each case, the most likely

culprit is a tiger shark.

Investigators have zeroed in
on an ancient proverb

that suggests that
this ferocious predator

might be more aggressive
in the fall months,

the very same time period
as many of the attacks.

Could the old adage be right?

And if so, what could cause

this terrifying change
in behavior?

♪ ♪

biologist dr. Kevin weng
is on an expedition

to catch and study tiger sharks
in the region.

The results of this research
could finally reveal the truth.

And they've just caught
their first subject,

a 14-foot female.

Kevin weng: Still swimming,
swimming good.

Narrator: Kevin and his team
plan to take

various measurements and
samples from the massive shark.

Kevin: Let's get the floats off,
but then you wanna probably

leave that amount of line
in the water.

Okay, I'm gonna move back,
move back.

Dan: Yeah, go ahead.
Kevin: Okay.

Narrator: Before the data
is collected,

they must first immobilize this
potentially dangerous predator.

Kevin: Okay,
I'm gonna move up, dan.

Are you guys ready
with the tail rope?

If we can get the animal flipped
upside down for a few minutes,

typically it will become
very, very calm.

♪ ♪

you got it? Okay.

It's a phenomenon known
as tonic immobility.

Narrator: Tonic immobility
is a reflex

seen in many invertebrates,
including some sharks.

For reasons still not fully
known, when turned upside down,

a tiger shark will enter
a coma-like state,

similar to hypnosis.

This allows researchers
to collect data

without harming the animal
or being bitten.

Kevin: Hannah and brooke
are using

a medical ultrasound machine
to look inside of this animal.

Narrator: Before long, the team
finds what they're looking for.

Kevin: Did you see any eggs?

Hannah: Yeah.

Kevin: Cool.

Narrator: The captured shark is
getting ready to reproduce.

She could soon be carrying

anywhere from 8 to 80 pups
inside her womb.

Studies like this one have
revealed stunning information

about tiger shark
breeding habits.

Kevin: Based upon
the available evidence,

it looks like mating is
happening in the wintertime

in January, February,
kind of a period.

And the giving birth to the pups
is happening in the fall.

Narrator: So could pupping
be causing tiger sharks

to attack bathers?

According to dr. Weng,
an explanation might be found

in the toll
the gestation process takes

on the pregnant shark.

Kevin: They are growing up
all of these young

inside of their uterus.

That's a big job that
takes a lot of energy.

Narrator: By the time
their pups reach full term,

a tiger shark's energy levels
are near exhausted.

And so after
they've given birth,

these tired mothers must eat.

Kevin: You could infer from
having lower energy stores,

they might be more
motivated to feed.

Narrator: As a result,

these hungry mothers
might hunt more often

and may be more aggressive,

meaning that violent encounters
with humans

would be much more likely.

But that doesn't fully
explain the spike.

In hawaii, tiger sharks
have been giving birth

during the fall for centuries.

So what's changed?

The final piece of the puzzle

lies with hawaii's number one
industry: Tourism.

2013 through 2015
saw a dramatic rise

in the number of visitors
to the big island.

A nearly 10% increase
over the previous decade.

That's thousands more swimmers,
surfers and kayakers.

According to dr. Dan huber,
it's a recipe for disaster.

Dan: So the combination
of more people in the water

and tiger sharks
hunting more often

to replenish their energy
reserves after giving birth

increases the chances
of shark attack.

Narrator: It seems that
tiger shark pupping,

combined with
record numbers of tourists,

are the two likeliest reasons
behind the spike in attacks

on the big island
from 2013 to 2015.

These revelations could
have global implications.

While the reproductive cycle
of tiger sharks

is now well understood
in hawaii,

elsewhere in beach communities
such as florida or the bahamas,

much less is known.

And so the aggressive behavior
of this fearsome predator

cannot be predicted.

It's an ominous warning.

But for the residents
and tourists of hawaii,

it's another sign
that our oceans

must be treated with
both caution and respect.

Terry: Sharks are kind of
an indicator species.

We need to spend more time
and effort studying

to see what's going on
out there.

Braxton: We're quick to blame
sharks for attacking us

or being the cause of attacks.

Always know that
that's their home

and that you're a guest when
you're entering the ocean.

Captioned by
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