Episode 2 Shark

This great white shark

is about to attack.

But hunting is only a small part

of any shark's life.

New discoveries are revealing

another side to their character.

They have an intricate social life...

complex courtship rituals....

..surprising ways

of bringing up their young...

..and extraordinary powers of navigation.

They forge relationships

with the strangest of partners...

..even with us.

This...

..is the secret life...

..of the shark.

Some sharks are solitary...

..roaming the ocean alone

for years on end.

But there's one event in every shark's life

where they must come together.

Scalloped hammerheads are travelling to a tiny island in the Pacific.

They're coming here to find a mate.

Of all the sharks, these hammerheads select

a partner in the most elegant way.

Soon, a graceful dance begins.

They swim together in formation,

with the males on the outside

and the females in the centre.

Males seek out the largest females -

the ones most likely to breed successfully.

They pair up,

then swim side by side,

to continue their courtship.

As night falls,

each couple disappears to mate.

Those without a partner can return tomorrow,

to dance again.

Hammerheads are just one of over 500 species of shark...

..but the shark family tree has two branches.

The other half of the family are the rays.

They are flattened sharks.

They share the same flexible cartilage skeleton.

In rays, this has squashed and stretched.

Many still have the tell-tale dorsal fin...

..but their pectoral fins have developed into enormous wings.

Some glide on ocean currents...

..while others "fly",

by undulating their bodies like a wave.

Many species of rays travel the oceans in groups...

..occasionally, in huge numbers.

Just once a year,

off the coast of Baja, Mexico,

Mobula rays gather in the darkness.

They begin by feeding -

fuelling up before the big event.

As the sun rises,

the full extent of their numbers becomes clear.

Like hammerheads, they come together to find a mate.

But with 250,000 in a single shoal,

this is on a completely different scale.

It's the largest aggregation of rays in the world.

But in a group as big as this,

the problem is standing out from the crowd.

Mobula rays have the most extraordinary way

of getting noticed.

As they land,

the impact sends a huge boom through the water.

The higher they leap...

..the bigger the bang.

It's mainly males who jump like this...

..signalling their prowess as a mate.

Females also join in,

drawing attention to themselves.

It's thought that those who make the biggest impact on the spectators

give themselves the best odds of leaving with a mate.

Once the leaping subsides, the rays disperse.

Where they go to mate is still a mystery.

But finding a mate is just the first step.

Port Jacksons come from an ancient order of sharks.

Older than the dinosaurs.

But even these primitive creatures put a huge amount of effort

into giving their young the best start in life.

Each spring, for four months,

they gather here in Jervis Bay, Australia.

At the peak of the breeding season, they can number in their thousands.

Wherever the females go, they're pursued by a male.

Courtship is less seduction,

more a wrestling match.

But, eventually...

..they mate.

The male will have nothing more to do with

caring for the next generation.

It's all down to her now.

Two weeks later, she's ready to lay an egg,

one of just a handful she will lay each year.

It's almost as large as her head,

and shaped like a corkscrew.

She's invested a vast amount of energy,

growing her egg inside her.

Unless she finds a safe place to hide it,

all that effort will be for nothing.

Finally,

the perfect spot.

The egg has evolved this shape to wedge securely under rocks.

A female may carry her egg around in her mouth

until she finds the ideal place to stash it.

It needs to stay hidden for 11 months.

There's an egg thief here,

a wolf in sheep's clothing.

It's a crested horn shark.

They look almost identical to a Port Jackson,

but they are the main predator of their eggs.

The shell is tough, but the horn shark simply crushes it,

squeezing the yolk from inside.

These eggs, hidden in a gulley, are safe from the predators.

The female's work is done.

She can leave now, heading south to feed.

Her developing youngster has everything it needs,

enclosed in the egg's protective casing.

From "corkscrews" wedged under rocks

to mermaid's purses hidden on the sea bed,

or suspended by spiralling fronds...

..shark eggs come in all shapes and sizes.

Inside each armoured capsule is one of the most extraordinary

life-support systems found anywhere in nature.

The embryo is dwarfed by the yolk sac, which will provide

all the nutrients the youngster needs until it's ready to hatch.

For some species, that can take nearly a year.

A few weeks after being laid,

eyes, mouth, fins all begin to form.

Veins drain nutrients from the yolk sac,

feeding the growing shark.

At this stage, their gills are just wavy fronds

sticking out from the side of their head.

Tiny capillaries within

capture oxygen from the water that surrounds the embryo.

The youngster continually beats its body back and forth

to circulate fresh water through the egg.

As they grow, patterns start to form on their skin,

crucial camouflage for the hatchling.

Their gills are now inside their bodies.

Their teeth are formed.

But their food is running out.

The yolk sac has shrunk to almost nothing.

It's time to hatch.

Under the cover of darkness,

this zebra shark slips out of the casing

that has kept it safe for months.

It emerges as a fully formed eight-inch shark...

..ready to fend for itself.

But not all sharks lay eggs.

There's one group that breed more like mammals.

Instead of eggs,

this lemon shark has 15 babies developing inside her.

And, like a mammal,

she feeds each one through a placenta and an umbilical cord.

She's been carrying her young for 12 months.

It's nearly time to give birth.

It's May in the Bahamas,

and high tide briefly gives her access

to the safest place for her pups' birth.

After swimming for days,

she's returning to the same place that she was born.

She finds an isolated spot on the borders of the mangrove forest.

She's ready.

When they're born,

her pups are perfect miniature sharks.

Their umbilical cords break off after birth.

Like us, these sharks have belly buttons.

Their mother can't stay in the shallows to look after her young.

She must leave now before the tide goes out and she's marooned.

From now on,

the newborns will have to fend for themselves.

Instinct tells the pups to head for the refuge of the mangrove forest.

The tangled roots mean predators can't follow them in here.

But the pups aren't safe yet.

They need to find their way through the maze.

Hidden within this twisted forest are clearings,

places of safety for the pups.

This is a shark nursery,

where they will spend the first seven years of their lives.

It's the same secret place their mother knew as a baby.

In here, juvenile lemon sharks have been shown to form friendships.

They can learn from each other.

Even so, with no adults to teach them,

they need time to learn what it takes to be a shark.

Like how to hunt.

At last - success.

After seven years,

it will be time to leave the nursery for good

and head out to sea.

Life as a shark in the open ocean

means facing a whole new set of challenges.

Out here, it's a desert -

vast and empty.

Yet somehow it can support the largest fish in the world.

Whale sharks weigh up to 20 tonnes,

and can live for 60 years.

They feed mainly on plankton,

the tiniest creatures in the sea.

With their enormous mouth and gills,

they filter food from over a million gallons of water every day.

Feeding on such tiny prey means they're always on the move,

constantly searching for food.

A ball of small fish

under attack by a pack of tuna.

It's a chance for the whale shark to change the way she feeds.

From filter feeder...

..to hunter!

She can swallow hundreds of the tiny fish in a single gulp.

It's only the mayhem caused by the tuna

that gives her this opportunity.

Chances like this are few and far between.

Soon she'll return to a life

scouring the vast, featureless ocean.

But when all day long all you can see is blue,

how do you find your way?

Sharks and rays travel the seas with remarkable precision.

Some are thought to be able to navigate

using the position of the sun,

or even the moon.

But in the dark depths

they can't rely on this alone.

Two-thirds of their brain is devoted to smell.

Each nostril works independently,

detecting tiny differences in the strength of an odour,

allowing them to smell in stereo

and track scents over huge distances.

They have tiny sensors on their nose,

which they use like a compass,

allowing them to take bearings from the Earth's magnetic field.

A great white shark was tracked swimming from Africa to Australia,

and found its way back again.

But even this extraordinary journey has been trumped.

One tiger shark was tracked for 27,000 miles.

They can circle the ocean,

yet still return to the same place,

on the same date...

..year after year.

Of all the sharks,

these are the masters of both navigation and timing.

This is Raine Island,

a tiny speck off the east coast of Australia.

It's less than a quarter of a mile across.

She's travelled for weeks to get here.

More green turtles breed on Raine Island

than anywhere else in the world.

65,000 of them come here every year to lay their eggs,

their numbers peaking in the first week of December.

The tiger sharks time their arrival to coincide exactly with that peak.

The turtles may be protected by their armour.

But the tiger sharks wouldn't have come all this way

unless it was worth their while.

They crush through the shells with their formidable jaws.

After the feast, the tiger sharks set off again,

and they know exactly where to go for their next meal.

One thing's for certain -

they won't be late.

Navigating the ocean is as much about intelligence

as it is endurance.

Giant manta rays are perfectly designed for flying

thousands of miles through the sea.

The largest of all the rays,

their huge wings allow them to glide on ocean currents.

But they also have the biggest brains of any fish.

It's thought that mantas find their way using giant signposts

hidden beneath the waves.

This towering undersea mountain rises up from three miles below.

But the visibility of the water means she can only see it

when she's within 100 feet or so of its sheer sides.

So manta rays build up a map in their heads using these landmarks.

When they get to each one,

they can remember the direction to the next.

But the seamounts are more than just waypoints on a journey.

The mantas have come to the island of Socorro,

more than 300 miles off the coast of Mexico,

to visit this group of angel fish,

who pick parasites from the rays' bodies.

When you've got no way of having a scratch on your own,

the services of enthusiastic cleaners like these

are indispensable.

Once they're clean, the mantas head off.

They leave the angel fish behind until their next visit.

Some sharks have formed an even more surprising relationship.

One that requires an extraordinary level of trust.

Normally, grey reef sharks eat anything on the reef they can catch.

Most fish know to avoid them.

But today the grey reefs don't look like they're hunting.

By tilting up their bodies in the water,

the sharks are signalling to these fish.

They want them to clean their teeth.

Eating fish all day means scraps get stuck in their teeth,

and a shark with rotten teeth can't feed.

However, saying "Aah" is quite a challenge for a shark.

They slow down as much as they can,

but grey reefs have to keep swimming to force water across their gills,

otherwise they'd drown.

The brave little cleaner wrasse

are the only fish that can swim right into the sharks' mouths,

and leave with their lives.

Occasionally, the sharks snap their mouths closed

when the wrasse nip a bit of gum.

But they never harm the cleaners.

The sharks need this vital service

from the bravest dentists on the reef.

Sharks have not only learned to take advantage of other fish.

They've learned to take advantage of us, too.

A sheltered bay off West Papua.

Young whale sharks have discovered that, here,

the fishing has been done for them.

At first, they head for the nets,

and try to suck the fishermen's catch out through the mesh.

But there is a simpler way.

Far from trying to scare the sharks away,

the fishermen actually feed them.

Feeding the sharks stops these enthusiastic giants

from damaging the nets.

It started out with just a few sharks,

but over the years more and more have learned to come here

for a free meal.

Encounters like this give us a rare, valuable glimpse into their lives.

But to really understand sharks,

we need to enter their world.

Once a year, around a tiny island in the Pacific,

over 150 great white sharks come together to feed.

This gives divers a unique opportunity

to get closer to the sharks than ever before.

Great whites can reach 18 feet long

and weigh over two tonnes.

Normally solitary, they go for months,

or even years, without seeing another of their own kind.

Now, with so many great whites in one place,

arguments over food or territory could be deadly.

But, by observing them so closely,

it's been discovered that these sharks keep the peace

using body language.

Great whites respect each other's personal space.

They swim directly at each other,

and then both change course,

signalling to one another that they're no threat.

They've been shown to have individual personalities,

and the bigger they are,

the more confident they're likely to be.

With divers, as well as with other sharks.

The language of great whites is based on subtle signals

that we are only just beginning to interpret.

She's lowering and bending her fins,

showing the black tips on the inner edge.

Her mouth is beginning to open in a threat display.

These are clear signals to the diver.

It's time to give her a bit more space.

The more we observe these predators,

the more we realise they're not mindless killers.

They're actually sophisticated communicators

and, when treated with respect,

they'll avoid conflict whenever they can.

However, far too often,

when sharks and humans meet,

it ends badly...

..for the shark.

Oceanic whitetips are used to being at the top of the food chain...

..with very little to threaten them.

Their acute senses allow them to follow sounds and smells

which may lead them to their next meal.

But this can also lead them into danger.

Fishing boats -

towing miles and miles of baited hooks.

Oceanics have learned to follow the boats,

stealing fish from the lines.

Some are caught accidentally.

Others are the targets of specialised shark boats.

This shark is a lucky one.

For many, the outcome is much worse.

100 million sharks are killed every year.

In some places,

99% of the oceanic whitetips have been wiped out.

Even if they escape the hooks,

fishing line can get wrapped around a shark's fins or tail.

They'll jump again and again to try to dislodge it.

This is a dangerous new world.

Sharks simply haven't had time to adapt to being prey...

..rather than predator.

But, despite the threats they face,

it isn't yet too late for sharks.

There are places where fishing, poaching and pollution

haven't sent shark and ray populations plummeting.

In 2006, off the Yucatan Peninsula in Mexico,

local fishermen led scientists to an extraordinary event,

on a scale never seen before.

Here, spawning fish attract whale sharks

from hundreds of miles around.

They're joined by giant manta rays,

flying through the water on wings over 20 feet across.

They're drawn here for just a few weeks each year

to feed on billions of tiny fish eggs.

The food here is so abundant that it brings together the greatest

gathering of sharks and rays anywhere in the world.

Even schools of mobula rays have come to join the feast.

Their numbers build and build.

Around 800 whale sharks and 300 manta rays

converge on an area less than half a mile wide.

Extraordinary places like this allow us to understand

more of the hidden lives of sharks and rays.

Language, courtship and social lives.

They're far more than just hunters.

If a shark gathering on this scale can remain secret until now...

..who knows what else is out there,

still waiting to be discovered?

The Bahamas.

Here there are sharks living in the most unexpected places.

The flooded forests of the island of Bimini.

Living in these mangrove swamps are baby lemon sharks.

Cameraman Duncan Brake's aim was to film these sharks

in their nurseries,

hidden in the heart of this tangled maze.

A glimpse -

but it's off in a flash.

So far, probably done over 200 hours

in and amongst the mangroves.

With almost 3,000 acres of mangrove,

there are a lot of places for the young sharks to hide.

They're in there somewhere.

You can't get frustrated with the wild animals,

they're wild animals at the end of the day, completely unpredictable.

You just have to hope you point the camera in the right direction

and have everything in focus when something happens.

But that's harder than it sounds.

And even when he does get close, with a kick of their tails

the sharks disappear in a cloud of sediment.

Duncan is in this for the long haul.

Meanwhile, the rest of team are trying a different approach.

ROTOR BLADES WHIRR

So just go to your right a little bit, Chuck.

This is good.

This remote-controlled octocopter gives a bird's-eye view

of the sharks swimming through the sunken forest -

revealing secret highways through the maze.

Using the octocopter gives a new perspective on the hidden nursery,

but the team still need the detailed underwater shots.

For the next 11 months,

Duncan perseveres in the mangroves.

At last, he's able to get close to the sharks,

inside their nursery.

These little sharks, they're quite cute, dare to say it.

Um, they all seem to have their own little personalities.

After months in the swamps,

Duncan was finally able to capture the character of these young sharks.

However, these weren't the only sharks

with surprising personalities.

Every year, over 150 great white sharks

gather around Guadalupe,

a remote island in the Pacific.

Here, the sharks use a secret body language to communicate.

Morne Hardenberg's task

is to capture these subtle signals on camera.

I've been doing this for about 15 years now,

it's taken me quite some time

to start understanding their body language.

Morne is willing to do something very few others would dare to...

..swim with a great white shark.

Only by getting out of the cage can the team get close enough

to reveal the details of a shark "conversation".

The biggest challenge is finding the right animal.

You can get an animal that is afraid of you.

An animal that is afraid poses a threat.

Yes, it's dangerous, they're a top predator,

but they're not mindless killing machines.

Surprisingly, the team look for the biggest sharks.

The best animals for us to dive with are the five-metre-plus females.

They've got a presence about them, they are not nervous around divers,

they're actually quite inquisitive.

This shark's pectoral fins are flattened.

She's swimming slowly.

She's not aggressive.

But communication is two-way.

The team must also remain calm.

Their behaviour in the water is crucial for their own safety.

Our body language and knowledge of the animal makes it

where they don't feel like they're in charge of us and we don't feel

like we're in charge of them, and we're all just getting along.

With the relationship established,

the team make their move.

We had to get really, really close to the animals,

sometimes within two feet,

when they allowed us to do it.

And being close to a five-and-a-half-metre white shark

is an amazing feeling.

Sometimes you can see her eyeball actually just turning

and looking at you while you're swimming next to her,

and it's a feeling of acceptance.

The shark is accepting you being there.

But sometimes a shark lets you know you've outstayed your welcome.

A change in her behaviour is often a sign that, listen here,

she doesn't like you entering her space at the moment,

and then the best thing to do

is absolutely listen to what she's telling you!

Her pectoral fins are lowered, with the black tips showing.

Her back is arching.

It's time to say goodbye.

Understanding the social side of sharks

is only one of many recent breakthroughs.

For scientists, it's a golden age of discovery.

And that's what we explore in the next programme.

Scientists are unlocking the secrets of sharks,

and they're finding they've got extraordinary senses.

They're smart and, what's more,

they can help us!

From medical breakthroughs

to making faster cars,

sharks could hold the answer!