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In a remote corner of Australia...

Oh no!

...a group of bull sharks
is targeting sports fishermen

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with unprecedented ferocity.

Holy ****!

Showing evidence of
a sophisticated new hunting behavior.

- You need to hook 10-15 fish...
Oh, look out!

...just to get one to the boat.

Now, a research team
is launching an ambitious investigation

using ground-breaking technology...

Oh, he's got it! How good was that?

...to find out if one of the
world's most dangerous sharks...

Oh, there it is!
Ah! Look at the size of it!

... just got smarter.

Weipa, a remote mining town located
on the edge of northeastern Australia.

Each year,

hundreds of sports fishermen are drawn to
its shores by seasonal fish migrations.

But more and more,

their catch is being stolen
in audacious underwater raids.

Some fishermen even claim
the sharks have learned

how to recognize
and follow individual boats.

Shark biologists Dr. Johan Gustafson

and Dr. Mariel Familiar Lopez
are here to investigate.

What's actually happening here
is a behavior called depredation

and that's when a fisherman's
caught a fish and they're winding it in

and then a shark will come
and take that fish.

Locals claim they are losing as
much as 80% of their catch to the sharks.

The level of depredation
described by the fishermen

hasn't been seen anywhere else
in Australia or even the world.

Johan and Mariel
have timed their arrival

with the height
of the tuna fishing season.

But with a weather front moving in,

they have just 10 days until strong
winds whip up a powerful swell

and force their research
vessel back to port.

We have a variety of equipment
we're going to utilize.

We've got acoustic tags, cameras,

and for the first time ever,
a new cage design.

If what the fisherman are saying is true,

I want to know why.

Johan and Mariel team
up with local fisherman, Wade Alleyn.

Together, they're heading
to one of his favorite fishing spots.

What's your experience
with the sharks versus the anglers?

Definitely have an
issue with the bull sharks.

I believe they've definitely tuned in on
the boats. They relate the boats to food.

Bull sharks are often depicted
as mindless, opportunistic killers.

But they're armed with an array
of high-performance senses

they could be using
to target the fishermen.

Smell many times
more powerful than humans.

Vision that pierces
through the murkiest waters.

And hearing that can pick up
sound from over a mile away.

Do you think they're mainly bull sharks,
the ones that are taking the fish?

I mean, it's hard for us
to identify all the time

because they'll eat our fish out of sight.

But there are definitely
a lot of bull sharks down here.

To find out for sure,

and see if the situation in Weipa
is as bad as the fishermen claim,

Johan and Mariel
go fishing for themselves.

We're using a fishing line
camera to be able to ID the shark.

Is it a bull shark?

Also, we're going to be able
to see a bit more information

about the behavior that's occurring.
When does the shark come in?

There we go. Let's get it in the water.

Right, we'll send this
all the way to the bottom.

How's my technique, Wade?

Spot on, mate.
I couldn't do it better myself.

Yep, yeah. (grunts) Oh!
Oh, it's a fish! I got a fish!

It's taking it down.

Alright, I'll try
and bring it up.

Oh, it's gone!

You got bitten off!
Yep. I think we got sharked.

Within moments of snaring a fish,

Johan's catch is stolen by an
unmistakable underwater raider,

a bull shark.

Wow. That's a big shark.
Over three, three and a half meters.

The fishing line camera did a great job.

Alright? We were able
to confirm the species

and the first fish we caught,
it was taken by a shark in 20 seconds.

That gives more weight to what
the fishermen are claiming up here.

This is the first time I've been able to
actually capture a depredation event

so close-up, underwater. This is amazing.

Yeah. It is really amazing footage.

Now we've seen one shark under
the water from the view of a camera.

We want to see more. We want to
see are there other sharks around?

So we need to get in the water with them.

In a place as remote as Weipa,
that's a significant challenge.

You need to remember, we're diving in an
area where sharks have never seen a cage.

Sharks have
an acute sense of hearing.

They use it to locate their prey,
but also keep themselves out of danger.

Loud, unfamiliar noises
can put them on edge.

Sound is an important
thing in an aquatic environment

because it travels four
times faster than in air.

The thing with sharks is loud,
sudden, sharp noises tend to spook them.

The team has come
prepared with a radical prototype

designed and built by underwater
cinematographer Colin Thrupp.

A noise canceling cage
made entirely of plastic.

So how do we reckon this is
going to go when we get in the water?

Do you reckon these joins
are going to hold?

I mean, a cage made out
of polyethylene pipe

sounds a bit nuts
when you first talk about it,

but when you actually get these
things together, it's pretty strong.

A world-first,
the cage has been forged

using cutting edge electro-fusion welding,

a technique that bonds plastic
by super-heating it

to over 200 degrees Fahrenheit.

I've been told that an earth mover
can hit this and then bounce off.

Okay.

But I haven't heard what
happens if a bull shark hits it.

Well we'll test it.
- That's what we're here to do.

We're here to test it. We'll see.

What I'm hoping
is that these sharks

become more accustomed
to this plastic cage,

which is quieter and a
little bit more stealthy.

It's going to minimize the noise
and hopefully get us closer to the sharks.

If the plastic cage works
and sharks do come closer,

this could be a game-changer
of how we study shark behavior,

not just up here at Weipa
but around the world.

Topside, topside.
Please begin lowering the cage.

Monitoring the descent
of the experimental cage

is divemaster, Che McGuiness.

So, can you give us
an indication of the cage?

JOHAN
The cage is sitting fine, over.

On the surface, Wade casts out.

The water visibility is unseasonably poor

but his on-board sonar reveals
there are big animals lurking below.

COLIN
I have a big bull shark, 10 meters out.

They're staying right
on the edge of our periphery.

We can only just see them.

The sharks move in closer,

and there's more than expected.

There's at
least six, maybe seven bull sharks

directly beneath us
right on the edge of the murk.

They're not sure what
we are. They're keeping a safe distance.

Encountering this big pack of bull sharks

is the first clue something different
is happening in the waters around Weipa.

A lot of the times I've
seen them just by themselves.

But here I'm seeing a group
of bull sharks together.

Bull sharks are normally
solitary and fiercely territorial.

They're even known to be cannibalistic.

Do these sharks
hang out here all the time?

Do they hang out together all the time?
What's the pecking order in this group?

We have a lot of work ahead of us
to answer these questions.

COLIN
This is great!

All we need now
is for Wade to get a fish on his line.

Divers, divers. Just letting you know.

The swell and wind has increased
swell and wind has increased.

If it becomes unsafe or
unworkable, let us know. Over.

Another challenge the team
must deal with has reared its head.

JOHAN
Copy that. Let's just see how we go.

This year, the whole of
Australia is suffering from La Niña,

an atmospheric phenomenon
that plays havoc with the weather.

Recent rainwater has been pouring out of
nearby rivers, reducing ocean visibility.

Whilst unpredictable winds on the surface

are churning up
the coastal currents below.

Johan. Johan. Does the cage feel steady?

JOHAN
The cage is bouncing a lot.

We are concerned
because this is a plastic cage.

It hasn't been really used a lot of times,
and we haven't really tested it that much.

The lightweight plastic cage

is being pushed and pulled
by the turbulent water.

If the ropes connecting it
to the boat snap,

Colin and Johan could be swimming
unprotected from the sharks.

Johan, Johan, copy?

Johan, Johan, Johan, do you copy? Over.

JOHAN
Topside, topside can you hear me?

I can hear you now.
I can hear you now.

The current's getting stronger.

Tipping the experimental cage on its side.

Has the cage stabilized, over?

COLIN
The cage is buckling under the pressure.

You need to get us up now, over.

Coming up now. Coming up now. Over.

COLIN
Copy that.

We got you at the surface.
Just wait there for a second.

Safely alongside the
mothership the damage becomes clear.

We had raging current
by the end of that,

you could just see this
thick plume of just muck

just come through and sweep
us and really tip the cage.

The plastic cage didn't like it at all
it was really bowing under that pressure.

We were getting a
little bit banged up underwater,

but the plastic cage did do
what it was supposed to do.

We did get close to those sharks,
and they did seem to not be spooked by us.

I think we had around six to
ten sharks at any one time

swimming around us up nice and
close. We could almost touch them.

Johan and Mariel still need
to observe sharks raiding the fishermen

from underwater.

But it will take several days for the
cage to be repaired and strengthened.

Yep! Grounded.

It gives them time to
investigate a different question.

According to the fishermen,

it's the noise of their vessels
or the shape of their vessels

that's attracting sharks
to these fishing grounds.

Some locals claim
an even more radical sea-change,

that the bull sharks have learned

how to distinguish and follow
individual fishing boats.

Johan and I have
devised a little experiment

to see if we can prove or disprove
what the fishermen are telling us.

Are the sharks really
following their boats?

To find out how shrewd the sharks are,

they need to be tagged
with acoustic transmitters.

These will monitor their movements.

But to fit them, the sharks must
be brought alongside the boat.

In my experience, rod and reel has
always been the best option just for us,

but also for the welfare of the shark.

We're there the whole time with it.
We can bring it in quickly.

We can handle it faster
and we can release it faster.

Johan straps in.

Landing a shark means going head-to-head
against its power and strength.

Oh, were on! Were on!
Yep, we got one!

It's a fair bit of weight.
That's a decent shark.

You can feel a strong head movement.

Oh! We are gaining ground, boy!

Once we get the
shark up close to the boat,

we're going to be putting in
a head rope and then a tail rope

and then we're going
to flip it upside down.

So, belly up, to try to put
him in tonic immobility.

To roll the shark over, the
team need to bring it closer to the boat

and maneuver it with a rope
attached to its tail.

It's definitely a bull.
Oh, it's a female.

She's feisty.
She's feisty.

Tail rope is on.
Good work!

It's upside down,
and she's getting calmer.

Tonic immobility is when
a shark is put belly up.

Basically, they go into
a transient sleep state.

They're not completely asleep or unaware.

They can snap out of this,
so we have to be quite cautious still.

The quicker the team works,

the better it will be
for both them and the shark.

First up, the acoustic tag.

It'll allow us to map
the movement patterns

and behaviors of bull sharks in this area,

and it's extremely pivotal
to this experiment.

Okay. Tag is on.

Measuring in at over eight feet,

this bull shark is a prize catch.

The decision is taken to fit
an additional fin camera.

It can tell us so much
about that shark's behavior.

How fast is a shark swimming?

Are they swimming really close to the
surface or are they going really deep?

This treasure trove of data
will pop off the shark automatically

in a few days.

It's time to release the hook.

Alright, let's get rid
of this thing. Yep, off.

Let her free?
Let it go.

Let it go.
Woo-woo!

Perfect. Good release, guys.

Before they run their experiment,

Johan and Mariel need to fit
as many acoustic tags as possible.

Working like a well-oiled machine,
and with the sharks' welfare in mind,

they catch and swiftly release
four more bull sharks.

Done!

All these tags that we're putting

is getting us closer to an answer
of what's going on here.

We're going to give
them 24 hours to relax

and go back to a more natural behavior
before we start our experiments.

The tagging experiment
is designed to prove or disprove

the fishermen's claims that sharks
are following their fishing boats.

Johan and Mariel
split up into two boats

and both deploy hydrophone receivers.

We can detect the pings
that are coming off those tags.

Two of the sharks
they tagged are quickly located,

still lurking together
in the same fishing spot.

Yes Johan.
I've got two of our tagged sharks here.

How about you?

Uh, hold on.
We're going to come to you. Over.

The experiment can begin.

Johan is in Wade's fishing boat. He'll
cast out to get the sharks attention.

Once they're stealing fish off his line,

the fishing boat will move
several miles down the coast.

Mariel will track the tagged sharks from
the second boat to see if they follow.

Johan is going to start
fishing from the other boat

and he's going to wait
for a depredation event.

Yeah. We're hooked up.

Wow. That's a good-size one.

Oh. No, no, I'm getting
shut. No, that's changed.

I think that's a shark.
That's a shark. Oh!

Oh! Oh, no. It's off.

Mariel, Mariel? Got bitten
off by a shark. So, it is happening here.

I still got our two tagged sharks here.

Okay.
Let's pack up everything here.

We're going to move down to the other site
and we're going to see they follow. Okay?

MARIEL
Roger that.

The big question is:

have the sharks followed?

MARIEL
Johan, Johan, do you copy?

Yes, I read you.

I don't pick up any
tagged sharks over here. Over.

Well look,
we've been here for 30 minutes now.

I think that if they were
following us from there,

we would have picked them up
on the hydrophone by now.

That's a result for us. It means they
haven't followed us from that site.

The tagged bull
sharks are nowhere to be seen.

But at this new site.
even without fishing,

the on-board sonar reveals a school
of different sharks lining up below.

That's a shark there.

That is interesting.
What does this mean?

The experiment
has delivered an unexpected result.

We don't think that
sharks are following the boats.

What's more likely is this depredation
behavior is much more widespread

in the population of bull sharks
up here at Weipa.

Rather than being
followed by specific sharks,

all the bull sharks in the region may have
learned how to carry out these raids

and could be ambushing the
fishermen wherever they go.

We need to remember that this
was just one small experiment

with only a few tagged sharks.

But what it does indicate is that the
scale of these depredation behaviors

could be occurring far more widespread and
intense than what the fishermen realize.

It could explain why such
a huge proportion of the fishermen's catch

is being taken.

But why do so many bull
sharks in these waters

appear to be conducting these raids?

Forces beyond Weipa's shores
are likely playing a role.

Australian fish stocks have decreased
by 31% over the past decade.

Scientists believe this pressure
could be forcing sharks

to alter their natural hunting behavior.

But it still leaves
many questions unanswered.

We want to know,
why is it so concentrated here in Weipa?

Now halfway through
their time in northern Australia,

the team has just five days until strong
winds will force them back to port.

Colin has fixed and strengthened
the plastic cage.

It's ready for him and Johan
to go back in the water.

So far we've only seen the depredation
behavior from the fishing-line camera.

But what we want to do
is see it from the plastic cage

and that's the intention of this dive.

We know that there is
multiple sharks down there.

Wade's up top. He's going to be fishing,
and hopefully we'll be able to see,

is there a hierarchy
between different sized sharks?

What's the etiquette at this dinner table?

On this dive, a 360-degree
drop camera will help fight back

against the unpredictable
water visibility.

We're really hoping to get
a lot of information from it.

The cage is lowered into position.

On the surface, Wade casts out.
Shadows emerge deep in the water.

JOHAN
I've got two bull sharks.

Two bull sharks. Approximately
five meters below us. Over.

COLIN
The sharks are coming in closer.

They're getting more confident with us.

We've got three
bull sharks around us now.

Topside, Wade has a fish on.

JOHAN
They're just circling.

COLIN
Not coming in too close to take the fish.

The sharks are biding their time.

But as the fish on Wade's
line tires, they strike.

JOHAN
Big bull coming up, big bull.

Here he comes. He's going for the fish.

COLIN
Oh! He's got it! How good was that!

We were expecting to see
the shark come really fast

and just snap it from the line.
But that's not what we saw.

It came in slow.
No sense of urgency at all

and just basically plucked
the fish off the hook.

I've never seen that before.
It was incredible.

Another thing I noticed
was the biting tactic.

So, the sharks took out
the propeller of the fish.

It bit off the tail section first.

And then they came swooping around again,
slow and calm, and they took out the rest.

The general perception about bull sharks

is that they are just
mindless, aggressive hunters.

And that is not what we're seeing here.

What we are seeing is a calm,
more intelligent approach.

It's strikingly similar to a
tactic used by a legendarily smart hunter.

Killer whales also patiently
stalk fishing boats

striking with intelligent,
surgical precision

once trawlers start
to bring in their catch.

Scientists believe Orcas do this
to deliberately save energy.

Are sharks now rivaling
this clever thinking?

Think of it
from a shark's perspective.

When they hunt,
they expend a lot of energy.

So, a hooked fish presents an opportunity

for a more efficient way
of getting a feed.

Back beneath the boat,

underwater cinematographer Colin
catches a glimpse of something unusual.

COLIN
I think I can see a smaller bull shark.

Yeah, definitely a young
bull shark. That's really weird.

Col reckons that
he saw a juvenile bull shark.

To me, that's unusual.

Why would there be
a small juvenile bull shark

out in the open ocean in adult territory?

Bull sharks have a really
interesting reproductive cycle.

The females come from the ocean up rivers

to lay their pups
in freshwater environments.

Rivers offer protection
and security for bull shark pups.

Only once they reach six to seven feet
or around eight years old,

will they head to the ocean.

If Colin did actually see a juvenile
bull shark this far out offshore,

that's quite a significant find.

It means there could be a bull
shark nursery somewhere nearby.

If that's true, that means juvenile
bull sharks are leaving their nursery

and they're mingling in with these
adults on these fishing grounds.

I think that's something that
needs further investigation.

To prove that there is a nursery,

we need to go and catch
juvenile bull sharks.

And in order for us to do that,
we need to go upriver.

Located just 30 miles
from the offshore fishing site,

the Mission River runs through Weipa

and is one of the largest
nearby sources of freshwater.

Searching for baby sharks in an
open river is notoriously difficult.

The trick is to follow the food.

We've got a bunch of birds
just hanging off under the bridge.

It's good. A lot of birds are a good sign.

The birds are taking
advantage of a crowded ball of fish

near the surface of the water.

It's a sign that normally means
there are predators lurking below.

Where we get little fish
big fish follow, right?

That's right.

Maybe we should start
to get our gear together.

What do you think
we should put down first?

- Let's go drum lines first.
- Good idea.

In these silty, low-visibility
waters diving is not an option.

The team needs to bring
whatever's hunting the fish up to them.

This is really actually quite exciting

because we think that we found a location
where there are juvenile bull sharks.

We're going to set up some drum lines.

Just think about
a really long fishing line.

Okay?

Got it?
Line.

- Perfect.
- Here's your way.

Bring us a little bull shark, please.

Once those yellow floats
are no longer visible,

or if the entire
big float bobs underwater,

we're "shark on."

They back off the boat,

and wait for something to bite.

Guys. I think the floats are down.

All right, cool. Yep, the floats are down,

we can't see the yellows. That's great.

He's definitely on.
He's still on. He's still on.

There he is. Here he is.
Here he is. Alright.

Oh, yes. That's a nice little belly.

It looks like-- oh, that could be a bull.
That looks like-- that looks like a bull.

Bull shark!
This is great. I think we're on.

This is exactly what we came here for.

Genetic analyses of this juvenile

could provide vital details
about Weipa's bull shark population,

but only after it's brought
alongside the boat.

Guys, get that tail rope on.

- Thank you.
She's strong.

Hang on, hang on she's come
back around. Swing back round.

Baby bulls are born
with a mouth full of razor-sharp teeth.

And they're even more agile than adults.

He's going--
he's going too far forward.

- Just keep this in gear, in back here.
You got it.

They might be small,
but they still can bite.

Fighter, yeah. I lost it.

Whoa!
He's a fighter.

That's great.

Towing, off. Ready?
Yes!

Grab that rope.

Oh, it's a female.

Hello, cutey.

The shark is under control.
It's one meter 40.

I would say she's been here,
for about five years.

Measuring under five feet,

it's highly unlikely this shark
traveled here by sea.

She's definitely from this river system.

So, I'm pretty confident there's
even smaller ones around.

Capturing this juvenile bull shark

indicates that there is
a nursery in this river.

This means that there is
an easy connection

between this nursery
and the offshore population.

An easy connection
means more opportunities

for juveniles to mingle
with adult sharks out at sea.

Bull sharks don't have parental care,
and they're usually solitary animals.

So, seeing them interact together,
we get a lot of questions.

Previous research has shown
that a lot of species, including sharks,

have the ability to learn new
behaviors in a social setting.

Is that how bull sharks in Weipa

are actually picking up
this depredation behavior?

Catching a juvenile bull shark

also allows Johan and Mariel
to test another theory.

Alright, were going to
need a biopsy sample.

Bull sharks tend to migrate
with the seasons

because the water temperature changes.

So as it cools, bull sharks will move
into the more constant warmer waters.

But that rule might not apply in
this tropical part of northern Australia.

Up here in The Top End,

the water temperature doesn't
really fluctuate as much.

The sharks around Weipa

could be resisting their migratory
instincts and putting down roots.

If that's true and they
are staying in the one area,

that means social learning behaviors

could be offloaded
to younger sharks more often.

Proving this theory
will take years of field work and tagging.

But cutting-edge genetic analysis
could offer a sneak-peek at the results.

DNA can tell us
a lot of interesting stuff.

We can test it against other
populations around Australia.

It can tell us if there's
any genetic differences.

It can also tell us how related
sharks are to each other.

I think we're good here.

I think we can get ready to release,
so we're going to take off the tail rope.

Okay, tail's out.

Off she goes.

Whew! How good?!

- Oh, nice. That was great.
- Yes! What fun!

To complete their investigation

and find out if the bull sharks around
Weipa are putting down roots,

Johan and Mariel need to get DNA samples
from adult sharks back out at sea.

On the way, there's a temporary diversion.

A ping from the fin cam

they attached to a big bull shark
several days ago.

We're trying to find it
by tracking its signal

so we can download and get the data.

I think it's coming near the shore.

There it is.

Oh yeah, I can see it.

The data from the fin cam
showed us some amazing information.

Generally, bull sharks that I've tagged

spend more of their time
at the ocean floor during the day.

Normally they use the
cover of night to patrol at the surface.

That's not what we're
seeing here in Weipa.

We're seeing the bull shark
spending time at the water's surface

and then going all the way back down
to the sea floor during the day.

The fin cam
captures the shark repeatedly diving

and then returning to the surface.

This is what we call "yo-yo diving."

The yo-yo behavior is generally associated
with a type of patrolling behavior.

Basically, the shark's looking for food.

But why is this bull shark doing it during
the day when they're generally nocturnal?

That is a significant question.

It's yet another anomaly
amongst the local bull sharks.

Is it somehow related
to the recreational fishing?

Are they looking for
recreational fishing catches?

This is a good piece of the puzzle,

but we have to remember
that it is only one animal,

one incident in one video shot so far,
but it does start to raise questions.

To conclude something,
we really need to get more data first.

It's the team's final day in Weipa.

Strong winds will soon force
the mothership back to port.

This is our last dive here.
And we need to get more DNA samples.

Basically, the higher the number
of biopsy samples we have

is the greater our strength in our
conclusions that we can come up with.

To collect the DNA,
Johan is armed with a modified spear gun.

This will maximize his chances of getting
multiple samples from one dive.

Wade fishes topside once again
to draw the sharks in.

Yes, we've got two
sharks below us. Two sharks. Over.

Although we're seeing the bull sharks,

we still need to get them
a little bit closer

so that we can get
a biopsy sample from them.

The cage is positioned closer to Wade

to increase Johan's
chances of a clean shot.

COLIN
Bull shark at 12 o'clock.

six or seven meters out.

It's high-noon for Johan,

but before he's had a chance
to pull the trigger, disaster.

COLIN
There's this murk coming through.

A cloud of silt envelopes the cage.

JOHAN
We're right on the edge of visibility.

Giant bull sharks
just meters away from the divers

have become invisible.

The visibility
is getting worse and worse.

With fish in the water,

an unseen shark could easily
collide with the cage.

Surface to divers,
we have a 20-minute bottom time

due to conditions have just started
to creep up, up here.

Okay divers, you've got 20 minutes,
20 minutes, 20 minutes.

Time is running out
to get the DNA samples.

COLIN
Johan. Bull shark to your left.

Coming in closer.
Take the shot! Take the shot!

Got him! Yes!

It's the perfect shot.

The shark is none-the-wiser
and disappears as if nothing's happened.

Divers. Divers. Five
more minutes. Five more minutes. Over.

There's still
a few more minutes on the clock.

COLIN
We've got another one coming in.

Yes! A second biopsy
in the bag. Nice shot.

It's another crucial sample.

Divers to surface.
You can start bringing us up.

Mission success.

Copy, copy.
We'll bring you close to the surface.

COLIN
That was a better dive, wasn't it?

That was awesome. That
was great. It actually worked really well.

I don't know about you,
but I count that as a win.

I think we've done well.

Despite the unpredictable
weather, the team have what they need.

We got several biopsy samples from
a range of different sizes of bull sharks

that we've sent
to the laboratory to analyze.

The DNA results are in.

It's a small sample size, but they've
delivered truly intriguing data.

What the DNA has shown us,
is that the shark we sampled upriver

is half related to the large female

that we sampled offshore
in that last cage dive.

Further analysis
indicates that the third sample

is also related to both these sharks.

Due to the small sample size
that we have, I'm completely surprised,

and I did not expect any of these sharks
to be in any way related to each other.

We don't know
if it's a mother or a father

but we do know that they're sharing
an ancestor in-between them.

It's a strong family link
connecting the bull sharks in the nursery

to the adults raiding
the fishermen at sea.

It may also implicate
that compared to other areas

these sharks may not
be moving in large numbers.

The closer related the
sharks, the smaller the gene pool,

and the less they could be moving away.

If they're not
migrating the large distances

and they're spending
more time in this one area,

that could explain why
the depredation events

are so much higher
and concentrate here in Weipa.

If the populations of bull sharks
up here at Weipa are localized,

they would be exposed
constantly to fishing activities,

increasing their likelihood
of depredation behaviors.

Together with the presence
of the nearby bull shark nursery,

it could put Weipa at the
epicenter of a perfect storm.

It's definitely possible
that juvenile bull sharks

could be learning
the behaviors from adults.

We've seen smaller
sharks leaving the river earlier...

JOHAN
Definitely a young bull shark.

...and potentially
starting the social interactions

and learning procedures at a younger age.

Seeing this bull shark
behavior has been amazing.

However, it's also been surprising.

The raids on
fishermen have been exposed

as the work of a methodical,
calculated hunter.

They're highly intelligent.

They're analyzing their environment
before they do anything.

These smart bull sharks
might be at the vanguard

of an adapting shark behavior
that could soon spread elsewhere.

Recreational fishing
is increasing worldwide.

We're starting to see a lot
more anger towards sharks,

and that could lead to a downward
spiral towards shark conservation.

That's why it's important when we get
opportunities like up here in Weipa

that we grab them with both hands.

There's a lot more to uncover.

And I am looking forward to coming back
and spending a lot more time here.