Atlantic Ocean Oceans

They cover two thirds of our planet.

They hold clues to the mysteries of our past.

And they're vital for our future survival.

But the secrets of our oceans have remained

largely undiscovered until now.

I am with a six gill shark.

Yes, yes!

Explorer Paul Rose is leading a team of ocean experts

on a series of underwater science expeditions.

For a year the team has voyaged across the world to build up

a global picture of our seas.

We are doing some pretty uncharted research here.

That is psychedelically purple!

We are here to try and understand the earth's oceans,

and put them in a human scale.

Our oceans are changing faster than ever.

I've never seen ice like this before.

There's never been a better time

to explore the last true wilderness on earth.

The team is about to explore...

the mighty Atlantic.

This vast sea is the second largest of the world's oceans.

It dominates the western hemisphere

and covers a fifth of the planet's surface,

forty-one million square miles.

Its northern boundary is the Arctic,

its southern boundary is the Antarctic. To the west,

you've got the whole Americas and to the east of course

you've got Africa and northern Europe so I mean, it's a sea of extremes.

It's the youngest of the great oceans but one of the most

influential, with an enormous impact on our climate.

The Atlantic is a critical ocean,

not just because it's such a beautiful vast and varied place,

but because it's so important for the health of the planet.

But it's now under threat.

Increasing commercialisation of its rich resources

is changing it dramatically.

The Atlantic is more than I think many people realise.

It's being lost before we even, I think, grasp its full significance.

The team is here to investigate

how man is endangering our crucial relationship with this ocean.

We are three and a half billion years back in time.

Tooni Mahto is a marine biologist and oceanographer.

On this expedition she'll brave the alien world of our prehistoric seas

to explore how the oceans transformed our planet.

It's dark and gloomy, and just very lifeless by the looks of things.

Maritime archaeologist Dr Lucy Blue

will investigate how conquering the Atlantic helped change our history.

It's clearly a hugely important highway in terms of connecting continents,

but also in terms of the early seafaring activities

in this particular part of the Atlantic Ocean.

And environmentalist Philippe Cousteau, grandson of

ocean pioneer Jacques Cousteau,

will examine how we are threatening the future of this ocean.

It's like seeing a polar bear on the plains of Africa.

It just doesn't belong here.

And he'll become human bait

in an experiment to protect a top predator.

Sharks everywhere!

The team has come to the heart of the Atlantic Ocean,

to the tropical waters of the Bahamas.

Here there are unique marine environments, which can reveal

this ocean's past and its complex future.

So the probe, you'll both be handling the probe.

For their first mission, the team is planning to explore one

to discover what our planet's earliest oceans were like.

We really only know this much about what we're going to find

on this dive. We really, genuinely don't know much about this at all.

They're heading to a strange marine environment, one of the only places

in the world where dark toxic waters mimic the earth's first oceans.

There it is, Tooni.

It's called the black hole.

This could well be the most dangerous dive we make.

It looks like a giant pupil looking up at us.

Formed by chemical erosion over many thousands of years, this

isolated black hole has developed conditions similar to the seas of

three and a half billion years ago.

The team wants to find out what

those early seas were really like by diving deep into these waters.

There's only ever been three scientific expeditions here,

so this is a great opportunity to actually get in the water and try and

glean more understanding about this almost isolated environment.

Though it's relatively unexplored,

there's one thing scientists do know about this deep water pool

- that like our early oceans, parts of it are toxic and dangerous.

I understand there's a layer down there

and this layer is kind of suspended around about twenty metres.

It's a metre deep and in that layer

is very high concentrations of poison - hydrogen sulphide,

and under that I have no idea what to expect whatsoever.

Lucy and Philippe will be at the surface taking

temperature and oxygen readings

to monitor the conditions as Tooni and Paul descend.

We're going to drop the sensor down with the divers, and kind of record

on the way down so we can get an idea, hopefully,

of what's going on down there.

It's a deep dive into toxic chemicals.

Dive safety supervisor Richard Bull is worried.

Quite frankly, I'm a bit twitchy about it, all right?

Don't forget you can bail out at any point.

If you're a bit twitchy, get out of there.

It's better to be stood up here wishing you were in there,

than in there wishing you were stood up here, OK?

Tooni and Paul, you're looking out for each other.

You are each other's standby, all right?

I'm not sure it's going to be that pleasant down there

and if it's not that pleasant, I want my wing man on standby.

I'm yours, don't worry.

Two...one...

Man, that really is looking over the precipice isn't it?

We're just suspended perfectly over this huge black hole

and it, it feels as if it's drawing us down.

Paul and Tooni plan to spend longer in the black hole

than anyone has before.

No-one can be absolutely certain what the effects will be.

Tooni, here's the science kit coming down.

How deep are you right now?

Yeah we're now at fifteen metres, Philippe.

They keep going down. So far,

the dive has been completely normal, but then they reach eighteen metres.

Wow - Philippe, the temperature has just soared

by...by about six degrees.

Yeah Philippe, my head feels quite normal,

but my legs are really, really hot,

and I'm getting some kind of strange layer.

What are you showing up there for temperature?

It's just zipped up to about 30 degrees C.

We're reading some interesting figures here on the probe.

It seems that the temperature has spiked quite considerably.

It's just in a metre.

That's amazing. Usually the deeper you go, the colder it gets.

This is, this is incredible.

-I've never even heard of anything like that before.

-No, nor have I.

To find out what's causing the sudden rise in temperature,

they descend even further.

Oh, my goodness, it's purple!

This is bizarre.

That is psychedelically purple.

It's like being in an outer space chemical soup.

As a marine biologist,

Tooni recognises what the purple cloud must be.

We're right in the middle of a layer of purple sulphur bacteria.

They contain a pigment, which they use to trap sunlight,

and that pigment is purple.

The bacteria absorb the sunlight's energy to photosynthesise,

but not all the energy is absorbed.

And the reason it's warm is because purple sulphur bacterium

are not particularly good for trapping that sunlight so about

70% of the energy of the sun is just dissipated as heat.

Bacteria like these were one of the few life forms that

could survive in our early seas,

but when they photosynthesise, some produce a poisonous byproduct...

hydrogen sulphide.

In high concentrations, that's as deadly as cyanide.

Oh, God, I can smell it in my face mask.

Oh, it really smells.

None of their face is exposed to the water.

What's happening is their skin is actually absorbing the hydrogen sulphide,

and circulating through their body into their sinuses and

that's how they're smelling it.

To discover more about conditions in our early oceans,

Paul and Tooni need to find out what's below this toxic layer.

It can't possibly get any worse.

Let's go down another half a metre or so.

Oh, man, it's absolutely pitch black.

Like somebody's just sucked all the light away.

And the bacteria just above us have actually sucked all the

light out so no sunlight energy reaches this layer.

This is why the black hole appears so dark from the surface.

Then Lucy discovers something else.

The oxygen levels have gone from 7.8 at the surface

all the way down to 0.18.

-Wow!

-I know that's...

-Paul, Tooni, surface.

We're also noticing on the probes that the oxygen level has dropped considerably.

There's almost no oxygen in the water here.

The layer of bacteria acts as a barrier, preventing the sunlight

and oxygenated water above from getting down here.

These are the conditions they have been looking for.

What Paul and I are swimming through

is what the oceans would have once been like - dark and gloomy,

very, very little oxygen and just lifeless, by the looks of things.

With its high concentration of sulphur bacteria

and no light or oxygen,

this body of water is as close as we can now get to our ancient oceans.

We are now three and a half billion years back in time.

The oceans formed when the earth was about two hundred million years old.

They were a series of hot, oxygen-free pools

with very little life, dotted across the barren volcanic landscape.

They remained that way for over a billion years.

I'm getting some weird sensations on my skin.

It's really really tingling.

After just twenty minutes,

their bodies have started to react to this harsh environment.

It's having some weird effect on our skin.

I can almost feel my hair burning.

I need to get this suit off, cos I am itching in here.

These chemicals have really made me itch.

Dive safety supervisor Richard Bull has heard enough.

It's time to get them out.

-Tooni, surface.

-There's too much we don't know about down there.

We don't know how the gas affects them, we don't know

how it affects the equipment, just so many ifs and buts.

We're coming up.

How was it?

Everything about it is weird.

-It's getting warmer and warmer and warmer.

-As you go deeper?

To the point of it being oddly, unhealthily warm.

Oh, look at that!

That's where the metal's been oxidised by the bacteria.

This is a brass clip and this is a brass-bodied pressure gauge.

Just noticed they've both gone off.

But it's no surprise to see some, some other manifestation

of that chemical reaction there, because it's pretty powerful.

That's how our oceans were, not

these wonderful live masses of water covering 70% of our surface.

They were like that weird place. That's where we started.

And so it's fantastic to be in a bit of water that is exactly

the same as our oceans were three and a half billion years ago.

I mean, you know, top that.

Since then, the Atlantic and all our oceans

have changed beyond recognition.

They are now abundant with life.

Divers coming down.

To find out how that happened, Tooni and Paul are about to dive

with the creatures which triggered that great transformation.

Here in the Bahamas

is one of only two places on earth where they still survive.

They are the oldest life form on earth.

I am really looking forward to diving on the organisms that were

instrumental in creating our modern oceans, and so I'm really keen to go

and see almost the seat of all life.

Everyone ready? OK, go!

They may look like lifeless rocks but this

is actually a thriving colony

of the life form that oxygenated our planet's atmosphere...

..stromatolites.

They've been around for three and a half billion years

which is over three-quarters of the earth's history -

quite phenomenal.

It's hard to believe, isn't it? These simple rock-shaped things

are actually one of the engines that turned the planet into the

life-giving place that it is.

Billions of bacteria live on the surface of these mounds

and build up by binding particles in the water.

The bacteria catch the sediment

that's brought with the currents and they just form these large boulders,

and they just lay down more and more of this sandy substance,

and get larger and larger over time.

The stromatolites came to dominate the early seas

and were the first life form to do something extraordinary.

The bacteria are called cyanobacteria, and they

actually photosynthesise in the same way that plants and algae do.

They take carbon dioxide and water and, using the energy from sunlight, they make oxygen.

By producing oxygen, the stromatolites started

to transform the planet, and even now, billions of years later,

they're still producing it as Tooni can prove with a fluorometer.

The fluorometer gives an indirect measurement

of the amount of oxygen that the stromatolites are producing.

Just the skin of this, just the outer layer is the stuff

that's alive and gives off oxygen.

So if you want to hold that bit, arm there, on a flat surface.

And the reading here is 0.5.

This is significantly less than an average plant produces...

..but because there were so many colonies of stromatolites

spread across all our early oceans, they had a huge impact.

The oxygen they produced seeped into the atmosphere

and, after two billion years, reached the levels we have today.

The seas became oxygenated and more complex life could thrive.

It was the fact that they were pumping huge amounts of oxygen into the atmosphere

which meant that modern day life

and very complex life forms such as myself and Paul could evolve.

-We are the ultimate time travellers.

-Yeah, talk about time travel!

We've experienced the ancient ocean and the modern ocean within the space of a day.

Perfect.

For hundreds of thousands of years,

the rich life in the modern oceans has been a vital resource for man,

but today we're increasingly threatening it.

OK guys, white board... we've got it sussed here.

An easy trip, anchor tonight...

Philippe is going to investigate a growing problem

that is changing balance of life here -

an alien species brought to this ocean by man.

Invasive species are having a devastating effect

on more and more of our oceans.

In this part of the Atlantic, the invader is the lionfish.

Probably one of the top five environmental crises we're facing

today is invasive species,

and lionfish is really the poster child of that here,

in the Atlantic ocean.

I love diving with lionfish, you know?

I've done it many times in the Pacific ocean where they belong,

not in the Atlantic, not here in the Bahamas.

Three... two...

one.

Philippe wants to discover

how the lionfish could be affecting the Atlantic ocean.

Native to the warm waters of the Pacific and Indian oceans,

lionfish live mainly around coral reefs.

-Wait, Luce!

-Have you got one?

-Right here.

It's like seeing a polar bear on the plains of Africa.

It just doesn't belong here.

The fish are popular in aquariums

so scientists suspect that unwanted pets may have been released by

their owners into Atlantic waters.

The first sightings began about twenty years ago.

-Here's one here, look.

-They're clearly doing very, very well.

You can see this other one right up here, just sitting on the ledge.

They're everywhere - it's unbelievable.

There's more of them than anything else.

These ornate fish are one of the ocean's most poisonous creatures.

They have spines on their fins.

At the base of these spines are venom glands

containing a neurotoxin.

When the spine punctures a victim, the toxin is released.

Old wives' tales would say

that fishermen who would grab lionfish and try and pull them out

of their nets would get stung

and they would throw themselves overboard and commit suicide because the pain was so excruciating.

But the venomous spines aren't the real danger here.

So far on this dive, the lionfish is the only relatively large fish

that Philippe and Lucy have seen.

These invaders are skilled and efficient hunters

that decimate the native fish population.

He's eyeballing something. He's just kinda sneaking up on it.

Whoa! Did you see that, he just went after something?

Yeah!

Wow! That is so rare.

Typically, lionfish are nocturnal feeders

and for him to have done that, it just shows

just how voracious and deadly these creatures are.

And because they're new here,

the native fish don't yet recognise them as predators.

All the little fish swimming around it, they're just sort of

hanging out, so the idea of identifying it as a predator -

they haven't acknowledged that as yet.

Look at them, they're almost following it at the moment.

Lionfish target young fish, which are easily caught.

The native fish population is in danger of being wiped out.

That was the problem in action.

This is bad news for the health of this ecosystem, bad news for

potentially important fish and for the other creatures that live here

that are part of the natural order of this food chain.

And it's getting worse.

Lionfish have few natural predators in the Atlantic

so their population is exploding.

From just a handful 20 years ago,

there are now countless lionfish

and they've spread from the Caribbean as far north as Rhode Island.

For me, it was just the way that the other fish were just sort of hanging

out around them as if they had no fear or any indication that

-they were their predators.

-They were everywhere.

I was looking for grouper, for parrot fish.

I was keeping my eye out for things that should be here and I didn't see

any of them in the abundancy that I saw lionfish. That's very worrying.

I don't think there's anything we can do about it,

I really don't, except for try and learn so that

if it happens again with another species,

we're a little more prepared to deal with it.

I think that's about all we can... we can hope for, which isn't much.

There's no sign of this Atlantic invasion stopping,

and it's far from the only example of man's impact on this ocean.

Later in the expedition the team will dive with sharks to protect

these top predators - victims of increased commercial fishing here.

These waters are being changed by man, but they brought the

first settlers to these islands, over thirteen hundred years ago.

It's clearly a hugely important

highway in terms of that whole sort of migration of people out of South

America, and slow colonisation of various islands in the Caribbean

and in this part of the Atlantic ocean.

Today, maritime archaeologist Dr Lucy Blue is travelling inland,

in search of the lost civilisation of the Lucayans.

The Lucayans were an ancient people who travelled here

from South America on wooden rafts,

using the ocean currents and prevailing winds.

Lucy will be the first archaeologist to investigate a sea cave

thought to be a Lucayan burial site.

This is the first time in 20 years or so, that anybody's been allowed

to go back and have a look and see if indeed anything still remains there.

Very little is left of the Lucayans' ancient civilisation.

Could this cave hold evidence of their rich history?

This watery state, it's really quite atmospheric,

quite peaceful, actually, isn't it?

Sort of fitting that you bury your dead there, in a way.

Hopefully, my expertise in the archaeological remains will

add something to an understanding - assuming there's anything there.

We're still not sure we're actually going to find anything.

Wow! And into the depths we descend.

That is just like the hand of God touching the cavern.

Finding anything won't be easy.

This underground labyrinth of caverns extends for many miles

and eventually joins the ocean.

The limestone structure of the Bahamas being so porous

and fragile creates these vast cave systems.

The Lucayans' creation legend tells how they were trapped in

a watery cave until the sun and the moon freed them.

So caves were sacred places and used for burial.

What about there?

Ahh! Look at this.

That's really eerie.

Deep within the cave, Lucy spots something remarkable.

Tooni, Tooni, come in, come in.

It's incredible to think this could have been here for over 1,400 years

just lying here...

..in its watery grave.

I can't see any other sort of burial artefacts,

no bits of pottery but unfortunately we can't get too close.

I might just go a little bit closer.

But is this skull Lucayan?

One feature would prove it.

Apparently they used to strap planks of wood on the skull, and this would

give it a very pronounced shape.

It was supposed to be a sign of, you know, beauty. It's a

bit like, you know, when the Japanese bind their kids' feet,

it's the same sort of effect.

And actually it does look like it's had that on its head.

The characteristic flat forehead

shows this really is the skull of a Lucayan.

It's thought the bodies were dropped into the caves from openings above,

but to Lucy, the position of the body suggests another possibility.

The Lucayans themselves were actually really confident free divers,

and so they could've actually carried the body, placed it in this position.

To me it looks very deliberately placed.

But while the Atlantic transported the Lucayan settlers here,

it also brought about their demise

when, hundreds of years later, other races migrated across this ocean.

The Lucayan people lived here quite peacefully until the Europeans

arrived, Columbus and his men.

They took a population of roughly 60,000 people and

enslaved them, and if they refused to be enslaved,

then they shot them.

After Spanish colonisation,

European diseases and mass suicides in response to slavery took their toll.

Within a generation, the Lucayan peoples no longer existed.

I felt very privileged

looking at somebody in their, in their final resting place.

When you find the remains of people that lived, you know, sort of

-1,400 years ago or something.

-A vanished civilisation.

Yeah, that makes it very special.

Today, the Atlantic still has a great influence on our lives.

It's one of the most important oceans for

regulating the planet's climate,

because it carries one of the world's strongest ocean currents...

the Gulf Stream.

Here's the whole huge Atlantic, you know - icebergs either end,

and here's the Bahamas, with the most powerful current on earth.

Originating in the Gulf of Mexico,

it flows north along the east coast of the United States

before arcing away to the north-east

and driving right across the entire north Atlantic.

The Gulf Stream moves a hundred times as much water

as all the rivers on earth.

It gets some of the power to do that right here in the Bahamas.

Where we are in the Bahamas, the Gulf Stream coursing up through that

narrow bit between Florida and us, the gun barrel of the Gulf Stream.

30 million cubic metres of water per second are squeezed

through this narrow channel and forced out of the other end.

And Paul is going to investigate

just what effect that has on this current.

-Ready to rock?

-All set.

We'll all go together, cos with this current if someone gets in first, gone.

It's going that way and there's no force of man that can stop it.

It's here that the current is at its fastest.

The power generated as it's forced through the gap is immense.

This huge current runs right across the Atlantic ocean

and it's one of the great engines

that drives the world's climate.

The Gulf Stream takes warm water

from the southern Atlantic and moves it into the northern hemisphere.

It moves more heat each day than the world's power stations produce in a

year - enough to warm northern Europe

and raise the air temperature in Britain by ten degrees.

The Gulf Stream in the Atlantic ocean is driving our weather.

That gives you an idea of the scale and power of this whole system.

We need to get up there, cos he's going to be low on air by now.

I tell you what, I knew I was going fast,

but I couldn't tell you how fast.

You could sense the power.

Man learned how to harness this current and the winds

to travel around the Atlantic.

For hundreds of years, this ocean was central to the discovery of

new worlds and colonial expansion.

It's clearly a hugely important

highway in terms of connecting continents but also in terms of the

early seafaring activities in this particular part

of the Atlantic ocean.

This ocean has been especially important in shaping the history

of Britain and the United States, bringing settlers, trade, even war.

Lucy wants to investigate a battle between Britain and America by

identifying a significant shipwreck, one that might be the HMS Southampton.

There are so many incidences of shipwrecks in this area.

I mean the Bahamas in Spanish means shallow waters. We don't know...

The war was a dispute over Atlantic trade routes between England

and America in 1812, shortly after the War of Independence.

A shipwreck has been found on a reef near Conception Island.

It's not been mapped at all, not been surveyed extensively.

It certainly hasn't been excavated so it hasn't really been investigated.

Lucy wants to find out if this wreck is the HMS Southampton.

She wasn't actually that big, only about 120-odd feet, carrying 32 guns.

That's a lot of guns for 120 feet.

I know, and a crew of nearly 200 or something. It must have been actually quite cramped.

Awfully close, and they spent a lot of time at sea back then.

I know, totally. It will be interesting to see if that compliment

of guns and anchors and everything actually are reflected on the seabed.

But the weather may scupper their plans.

THUNDER RUMBLES

We should be prepared for some kind of jiggery-pokery with the schedule

-or maybe not even making it.

-Oh, really?

-Yeah, they're talking, you know, gale force.

-Really?

Yeah. So...

And how long is that likely to last?

Well, we don't, well, we don't even need gale force.

If it's on the edge of 20 knots, it'll be on the edge of our diving capability.

The weather moves in and conditions deteriorate rapidly.

This is just not what we want at all.

And, as ever it's a tight schedule, so if we don't get a move on...

As well as the shipwreck, they also need to fit in a

challenging dive with sharks, so they decide to press on.

After hours of forging through choppy seas,

they finally get near the shipwreck.

It's not getting any better and this boat's rocking and it's

blowing like crazy, so it's not making our job any easier.

With the wind, the current and this position,

it's a bit marginal really.

In these conditions,

it's easy to see how a ship could founder on this reef.

Now Lucy can finally try to discover whether it is the Southampton.

Well, there's an anticipation, but also you just don't know

what you're going to find do you? So that's, that's quite exciting really.

Several metres down, conditions are much better

so Lucy and Philippe start their detective work.

I'm just trying to find any clues of the wrecking of the ship.

I'm trying to see if I can find any of the cannon or the anchor.

A-ha, look!

-Philippe, Philippe, Philippe!

-Look at that!

Look, you can see one, two...

there's loads of cannon all over the place.

Any exposed wood will long have rotted away,

but there are artefacts spread over a wide area.

Once you've trained your eyes, there are cannon everywhere.

Another one over there.

They're just lying here.

Here's another one here.

I've never seen so many cannon in such a concentrated area

on a ship before.

Just, just look at the size of this thing.

I mean, it's about as long as I am.

But are these cannons from the Southampton?

The Southampton had 32 guns.

There were 26 of these 12 pounders,

I think this is a 12 pounder. We need to measure it.

The 12 pound guns on the HMS

Southampton were said to be between six-and-a-half and seven feet long.

That's six foot seven.

-So this is the right kind of cannon then, Lucy?

-I think so, I think so.

Ah, the other thing that's quite distinguishing

about this...is that the 12 pounders from this era

have these little sort of rings attached to their ends, so...

which was quite unusual. Not many of the cannons had

these so that looks like one of the

types of cannon that the vessel would have been originally consigned with.

The cannons alone aren't enough for a positive identification.

Lucy needs to find more evidence.

-Philippe, look, look, look, look!

-It's huge! This is just incredible.

I mean you can see this anchor just sitting here.

It's a British anchor.

You can see because of the V shaped arms at the bottom of the

anchor, this is very distinctive of British naval vessel anchors.

If it was from an American vessel, it would have been

more rounded at the base.

It's just another clue, in a way, as to understanding if this is the wreck of the HMS Southampton.

I would have expected maybe

to find a pile of chain or something attached to the anchor that, I mean

that would have been iron that should still be here.

No, no, not for this period, because they would have been using ropes

rather than chains to actually haul the anchor.

She probably would have thrown these anchors aground as she wrecked here during the night.

By the morning they realised there was no saving the vessel

and they had to abandon ship,

so again another clue to confirming this is the HMS Southampton.

The size of the cannons, along with the type and position of the anchors

have convinced Lucy this is the HMS Southampton.

It's a record of the November night in 1812 when, towing a captured

American ship to Jamaica, she hit this reef and sank.

It brings to life an event and a particular battle that has been

forgotten a lot in our, in our histories - both UK and America.

The war was finally resolved with a treaty, signed in 1814.

Neither side was victorious but it confirmed the status

of the United States as a fully independent nation.

You know what this impresses upon me?

I mean the Atlantic played a huge role in that war alone,

not to mention many, many others.

Such a vast, critical ocean.

It is like a snapshot in time which basically the ocean has preserved

for us to come and investigate,

and so in a way the ocean actually holds a story, which

we are very unlikely to find in any other context.

The Atlantic has helped shape our distant and more recent past.

Now the expedition is heading north-west,

to investigate its future.

We're heading for north Bimini, aren't we?

Yeah we're gonna come off the banks so we need to get down here and drop the anchor overnight.

The future of the Atlantic is being shaped by man.

The effects of large scale commercial fishing

are damaging this mighty ocean.

In the last decade, some fish stocks have fallen by 95%.

One fish is particularly hard-hit - the shark.

How many sharks do we catch every year? Who was it who said...

it must have been you, Philippe.

Human beings catch between 70, we estimate between 70 and 100 million sharks every year.

-Million?

-70 to 100 million sharks a year.

Some sharks are caught for their fins, used in shark-fin soup.

But millions of sharks are by-catch,

caught unintentionally by big commercial fishing operations.

Sharks are so critical, and they are the apex predator.

They help to weed out the sick and the diseased, make sure that

the fisheries and the food chain beneath them is healthy and viable.

And when they remove sharks from that, you know, that chain,

it has just disastrous effects on the entire ecosystem.

So the team is going to dive with sharks to investigate

a pioneering technique,

a shark repellent that could help protect these vital creatures.

It's coming up slowly, it's a small one.

Philippe and Tooni are going to team up with scientists from the shark

lab at the Bimini Biological Field Station.

For the last 25 years,

they've been monitoring the population here, catching

and then releasing the sharks once they've collected their data.

There is a shark caught on one of the hooks.

I mean it's giving a good thrash in the water so it's still alive and obviously fine.

To track the diminishing population,

they need to attach an identity tag to this shark.

Philippe is going to monitor the process underwater.

We've got to be very, very careful.

It's gonna be an upset shark and it's happened before that

they can break free from a line so we're going to give a lot of space

and a lot of berth and a lot of respect.

Looks like a tiger shark.

That is a tiger shark all right.

Tiger sharks are known to be one of the more dangerous sharks in the world.

I normally would never get this close to a tiger shark.

Woah!

That was a close call there.

That's why you've got to be really careful.

So we're doing a data tag basically.

As sharks become more threatened,

tags can help identify when and where they are being fished.

Do I push it in?

There you go, pull it out, pull the wood out.

There you go, then the tag stays in, you see?

This shark has been caught deliberately, for research,

but commercial fisheries catch countless sharks unintentionally.

Long lines are set up by commercial fisherman,

miles and miles and miles long, with thousands of hooks laid along them.

Sharks are often left for a long period on those lines and they die.

She wanted to give me a little goodbye present.

And off she goes! She looks good.

Millions of these predators are caught on commercial lines.

So the hunt is on for an effective way of preventing sharks

from getting trapped on them.

Paul and Lucy have joined scientists who've developed a material

they believe will repel sharks.

This is the very stuff right here. It's an alloy, a mixture of metals.

The hope is that hooks made of the repelling metal could

be used on long line fishing hooks, so fewer sharks end up as by-catch.

The metal is electropositive.

It produces a charge that's conducted by salty water.

Well, done.

OK, let him settle down a bit.

So I'll grab him, OK?

Lucy and Paul are going to test the metal on a juvenile lemon shark.

Lucy has been shown a handling technique to help the experiment,

putting the shark in a coma-like state.

I'm going to try and basically

turn him on his back so we've got to try and move him over.

Or her, I don't know.

Be ready for her,

steady as you go.

When the tail becomes immobile...

-Then she's out.

-And basically when she's not moving at all.

OK, so she's totally out of it at the moment.

In this state, the shark is very unresponsive.

Paul is going to bring a small piece of the metal close to its head.

Are you ready, Lucy?

Time to see if the shark will react to the metal.

Holy smoke!

OK, ha-ha! OK, it works.

I think that's definitely a conclusive experiment.

So it works.

Even in a comatose state, the shark sensed the metal, and was repelled by it.

So if you've got a set of fish hooks made of this stuff,

you can do selective fishing.

You're gonna get more of what you do wanna catch

and less, or hopefully none, of what you don't wanna catch.

The expedition is coming to a close.

But there's one final shark mission for Tooni and Philippe.

Chum - a mixture of mashed-up dead fish -

has been spread in the water.

It's attracted blacktip and Caribbean reef sharks.

Oh, we've got sharks.

There are some sharks out here.

We can see their fin tips just going round the water.

They're going to test another shark repellent,

a liquid that could be attached in time-release pouches to long lines.

To make the conditions for the experiment authentic,

it's got to be carried out in open water, teeming with adult sharks.

Philippe and Tooni will dive in amongst the sharks,

and release the repellent by hand.

There are some big sharks down there, actually.

They're a good couple of metres,

which I don't think I was quite expecting.

I was expecting slightly smaller sharks to be honest.

Caribbean reef and blacktip aren't the most aggressive of sharks

but the chumming has attracted quite a few.

One, two, three, four, five, six...

and the small one out the back is seven.

That's bizarre, that makes my heart go a bit funny.

It's quite a bizarre sensation to be sitting on the side of a boat,

about to sort of drop backwards into a pool teeming with sharks.

Safety divers and first aiders are standing by.

Oh!

Oh, my goodness!

Sharks everywhere, all around us.

This is just incredible.

Oh, God, she's having a good look at me.

Whoa! that was close.

That was close.

Shark chaos!

More and more sharks are gathering.

This should be the stuff that really scares them off.

It is essentially distilled tissue from sharks, from dead sharks.

Scientists realised sharks are driven away

by the smell of rotting shark.

As you can see, they're kind of circling us a lot right now.

You can see them getting a

little bit ticked off at each other, a little bit

aggressive towards each other.

Philippe and Tooni decide to release the repellent.

This is the first time this repellent has been tested like this.

This isn't a game, this is serious business.

Sharks have a very acute sense of smell,

but it takes a few minutes for the liquid to disperse.

One by one, the sharks leave.

They keep just swimming further and further away from us.

Clearly they didn't like something.

All the other fish are still here, but the sharks have disappeared.

They're not showing much signs of coming back, either.

The experiment's been a complete success,

and could play a vital role in protecting sharks in all our oceans.

Fantastic!

The sharks kind of do an in, sense something and out again.

Yeah definitely, definitely.

I'd like to say that I smell of shark repellent.

-Oof!

-It's really quite disgusting!

I think it's a great, great piece of science.

It could be impregnated into wet suits or sunscreens and it's just,

it's like widening the gap between sharks and people.

I think this is how science can come together

to have practical applications for conservation,

and ultimately we have healthier more sustainable oceans.

The end of the shark dive is also the end of the Atlantic expedition.

A journey in which this ocean revealed

how all our oceans once looked.

And how they were responsible for bringing life to our planet.

I've spanned three and a half billion years of the ocean's evolution in

one trip and that's quite something.

This ocean has played a critical role in our history, but it's

difficult to assess the impact we could be having on its future.

The Atlantic is just being abused and I don't think anyone knows what the consequences are,

but we know that the consequences, whatever they are, are very serious.

We can't continue to take it for granted.

Next time, the team explores the Indian Ocean.

They'll find out how manta rays survive shark attacks.

There's a shark bite, right there.

Discover the consequences of its treacherous currents.

She hit this reef behind us and broke her back.

And explore an underwater lab that could save coral reefs.

Subtitles by Red Bee Media Ltd

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