Ocean Odyssey Britain's Treasure Islands

My name's Stewart McPherson, I'm an explorer and naturalist.

I've climbed dozens of unexplored mountains

and discovered many new species.

And yet the journey I've always wanted to make

is to the most remote parts of Britain.

And I mean remote.

Not the islands of Scotland or the mountains of Wales,

but the UK overseas territories.

14 islands and archipelagos

scattered all across the seven seas.

They have seven times the land area of the UK.

Some are uninhabited

but 350,000 people live on the others.

People who have voted to remain part of the United Kingdom.

I read about these far-flung places when I was a child

and this was my treasure map.

Not to hoards of gold and silver,

but something even more special -

untold riches of wildlife and unique cultures.

I wanted to stand on the biggest penguin colonies on the planet.

I wanted to dive on the world's richest coral reefs.

And I can do all that without leaving Britain.

No single person has ever explored all 14 overseas territories

and that is just too much of a challenge

for any explorer to resist.

So, I'm going to follow my childhood treasure map

right the way across the globe

to discover the furthest reaches of Britain.

My first journey will take me right around the world,

through the tropics and subtropics

and across three oceans...

..to visit Pitcairn in the Pacific ocean...

..the Chagos Archipelago in the Indian Ocean...

but first, the oldest of all the overseas territories

in the Atlantic Ocean, Bermuda,

1,000km from the shores of the United States.

The English found Bermuda by accident

after a ship trying to cross the Atlantic ran into it...

literally.

That vessel was carrying supplies to Jamestown,

England's first permanent colony in America.

HORN TOOTS

The year was 1609,

just two years after Jamestown was founded.

The wreck of that ship, the Sea Venture, became famous

and probably inspired Shakespeare to write The Tempest.

The shipwreck was a happy accident

and not just for Shakespeare.

The British realised the strategic importance of Bermuda

and built forts to protect it.

This is the oldest.

Fort St Catherine.

A stone fort was built here in 1614

followed by many others across the island.

Some of those buildings are still standing.

The earliest surviving buildings

built by the English in the New World.

This small island has been settled for 500 years -

long enough to be developed from shore to shore.

Even so, it's a beautiful place...

..with its history visible on every street.

I've always wanted to come to Bermuda,

but not for its human history.

It's natural history is just as fascinating.

The British weren't the first to come here.

The islands were discovered by the Spanish.

By Juan de Bermudez,

just a few years after Columbus first arrived in the New World.

But the Spanish didn't stay.

As they dropped anchor offshore

and the sun began to set,

the air was filled with terrifying, unearthly noises.

The Spanish were convinced of the islands of Bermudez

were the abode of devils

and they never came back.

When the British settled here, over 100 years later,

they realised that there were no devils here,

just a huge colony of sea birds.

They named them cahows,

imitating their strange cries,

and instead of being afraid of them,

the British simply ate them,

every last one...

aided by rats and hogs that roamed the island

since the Spanish first anchored here.

Bermuda was the only place where these birds nested.

And by the 1630s, the cahow was declared extinct.

Then, in 1951,

something amazing happened.

A few pairs of cahows were found on a group of tiny, rocky islets

off the main island.

No-one had seen this bird for more than 300 years.

It was like finding a living, breathing dodo.

But their tiny, rocky homes were exposed to high seas

and Atlantic hurricanes.

They needed somewhere more secure to nest.

'I'm travelling out with Jeremy Medeiros

'to a place I read about as a child.'

This is Nonsuch Island

and it's been cleared of rats and cats.

It's now the Nonsuch Living Museum.

But it still lacked Bermuda's charismatic devil bird...

..partly because of a problem from another bird...

..the tropicbird.

These are also a protected species...

..but they evict cahows from their burrows and they even kill them.

How could tropicbirds and cahows be persuaded to live as neighbours?

This is the answer.

Luxury apartments for the tropicbirds.

Tropicbirds love these artificial burrows,

which also makes it easier

to monitor the progress of this important population.

OK, here's one of the artificial tropicbird nests

that I've been monitoring for...

'Now, with less competition for nest sites,

'an ambitious plan to reintroduce cahows could begin.'

Starting in 2004, cahows were moved from their tiny islets to Nonsuch.

When they're fully grown,

the parents abandon the chicks

so that hunger drives them to fly out to sea to find their own food.

If they're moved to a new burrow on Nonsuch before they fledge,

it was hoped that they'd return to their new home when they matured.

It seems to have worked

and cahows are now returning to Nonsuch to breed.

This huge, ungainly-looking chick

will soon fledge

to soar far and wide over the Atlantic.

And yet, when it's ready to breed,

it can still find this tiny pinprick of land in the vast Atlantic.

Across the UK overseas territories,

I'm going to find many such stories

of battles to save rare and strange species

living on tiny islands.

Such small, isolated islands - like Bermuda -

have been too easily damaged by development

and by the introduction of alien plants and animals,

and many of the territories face another threat.

I can find the evidence of this by going deep underground

into the limestone foundations of Bermuda,

where there are spectacular caves.

This is Fantasy Cave,

decorated with amazing displays

of stalagmites and stalactites.

These formations take thousands of years to form

as rainwater filters through the porous limestone

and deposits calcium carbonate...

drip by single drip.

But these formations only form in air.

Here, in Fantasy Cave, many of these structures are underwater.

The cave records a history of sea level change

from the end of the last ice age.

When the ice melted, sea level rose by more than 100 metres,

flooding many of the caves.

These caves offer irrefutable evidence of sea level change,

but there's even more evidence just offshore.

Now under ten metres of water,

these are the roots of trees

that once grew on dry land.

Wind back the clock to a time when these trees were still growing

and we'd see a very different world.

After the ice age, rising sea levels created many of the small islands

that now make up the UK Overseas Territories.

It also isolated them from other landmasses,

allowing their unique species to evolve.

But these species are now threatened by a new rise in sea level -

this time, caused by us.

As climate change warms the planet, so sea levels rise.

Sea level change is still a major threat today -

especially on flat, low-lying islands such as these.

Normally, if the water level would rise,

these mangrove forests would retreat inland to higher ground.

But the problem today is that there's nowhere for them to go.

Some of the islands of the UK Overseas Territories

are so low-lying that the predicted rise in sea level

over the next few hundred years

will have a huge impact on them.

That's certainly true of where I'm going next -

half a world away, the British Indian Ocean Territory.

It's made up of the Chagos Archipelago,

a series of coral atolls

that lie more than 600km to the south of the Maldives.

These atolls are so remote,

my journey to the British Indian Ocean Territory

will have to start in the Maldives...

in Male, the island's capital.

I can't imagine anywhere more different

from the unspoiled tropical islands I'm trying to reach.

Crammed with people, cars, bikes, scooters -

this is urban chaos at its most extreme.

HORN BLARES

So, this whole island is one massive concrete jungle,

but there's not one square metre of forest or natural vegetation

and no wildlife here at all.

I'm only here to catch a boat,

but that took me nearly a week to organise.

And we're off.

Not bad. We're still checking out.

I can't believe we're actually going now.

It's taken me three years of planning just to reach this stage.

Getting permission to travel to the Chagos Archipelago

is nearly impossible.

But now, I'm just two boat trips away.

Nice to meet you, my name is Stu.

Chagos really is one of the hardest places on the planet

to get to.

We've charted this dhoni, this Maldivian dhow,

and we're going to sail in her down south from Male

right the way down to Gan,

the island at the southernmost part of the Maldives.

From there, hopefully a charter boat has been arranged to meet us.

HORN BLARES

Well, that was the plan -

but we were still sitting on the boat until after sunset.

Yay! We're finally off.

We had to wait a few more hours.

The captain didn't actually show up. We had to wait for someone else.

But now, as you can see,

we're casting off and, after three years,

on our way to Chagos.

Bye-bye.

Bye-bye. See you later.

It's such a relief to escape Male.

It'll take three days to get to Gan -

with nothing much to do, but enjoy the ride and soak up the sun.

The only boat I could find to take us

from Gan to the Chagos Archipelago

was based in South Africa - but if the plan worked,

they'll already be in Gan waiting for us.

These guys have travelled for seven weeks,

halfway across the globe.

It's almost like Dr Livingstone meeting them here.

Jeremy, I presume.

-It's good to see you again.

-It's so good to see you both.

There's hardly enough room for all of our film kit and dive equipment,

let alone us.

It's going to be very cosy in here over the next few weeks.

But now we start the final part of the journey.

Almost right away, we're joined by a school of dolphins.

Oh, man.

An excuse to take the dinghy out and race with them.

I'm not sure who's enjoying it most.

At last, our first glimpse of the British Indian Ocean Territory.

Coming here is one of my life ambitions

and I know it's going to live up to everything I imagined.

This is simply one of the most beautiful places

I have ever had the privilege of going to.

The water is just crystal clear,

the reefs come right up onto the beaches

and, well, the landscape speaks for itself.

It's just stunning.

Who would have thought this is a British Territory?

The Chagos Archipelago is made of seven huge coral atolls,

each, the tip of an extinct volcano.

The summit of each volcano

reaches to just below the surface

where it's colonised by coral.

Each atoll is a roughly circular coral reef,

which sometimes breaks the surface

to create a ring of islands enclosing a sheltered lagoon.

The reefs and islands of this archipelago are vast.

They cover an area twice the size of the UK.

In 2010, this was declared a marine reserve.

This is the biggest, fully-protected marine reserve on earth.

These reefs and islands are largely unexplored.

One island doesn't even have a name.

Where else in the world can you travel

and find an island that hasn't even been named yet?

This has surely got to be one of the last in the Indian Ocean,

or maybe even on the whole planet.

It truly isn't an exaggeration

to say that Chagos is one of the least explored

and least known places on the entire planet.

I mean, just look at these charts.

This is where we're going, the Northern Atolls.

And all across this chart,

look, it says, "Unsurveyed",

"Unsurveyed", "Unsurveyed".

So, where else can you see that in the world?

The charts aren't very helpful,

so we'll have to go very carefully.

There are massive reefs and rocks just below the surface.

We're slowly picking our way

towards the largest atoll,

the Great Chagos Bank.

This is the largest coral atoll on the planet...

..and I'm really keen to see what lives down there.

OXYGEN HISSES

This place is a world record breaker for all sorts of reasons.

I'm about to dive onto the most pristine coral reef on earth.

There's up to six times more fish on this reef

than any other in the Indian Ocean -

perhaps even the whole world.

The diversity of life down here is breathtaking...

..and no-one has ever filmed here before.

It's very likely we are the first people ever

to have dived on this site.

It's an enormous area, completely unexplored reefs.

No-one really knows what's down here.

We know more about the surface of the moon

than we do about these coral systems.

There are dozens of different types of coral growing here

and they completely cover the seabed.

Staghorn corals...

table corals...

..and pillar corals.

And it's not just the diversity of the corals,

but their sheer size.

Diving on these reefs,

it's amazing to see the size of some of these coral growths.

This is a Porites coral

and this one clearly represents

hundreds and hundreds of years of growth.

This demonstrates that the reefs here are healthy

and have remained stable for a very long time

and continue to do so today.

All the corals grow in different ways,

building up a complex structure -

providing homes for different fish.

This city of coral,

with its varied living space,

is one reason for the diversity of fish down here.

Table coral provides a roof over the head of an oriental sweetlips...

..and shelter for an emperor angelfish.

Schools of green chromis rarely venture far from the staghorn coral.

At the slightest hint of danger,

they disappear into the branching arms.

These reefs fringe the summit of a huge extinct volcano

and, while I've got air left,

I'm going to the edge of the reef

where the volcano's slopes plunge into the depths.

This is the drop-off of the reef.

It falls away for hundreds of metres.

No-one has ever been down there...

..and we have absolutely no idea

what lives down in the darkness.

The years of planning to get here seemed endless,

but every day of that time was worth it.

Those are the most incredible reefs I've ever seen.

It's stunning down there.

And the scattered islands should be just as interesting.

They're fringed by coconut palms,

which are well adapted to life on remote islands.

Coconuts are huge seeds that can float on the ocean

for a very long time.

They're borne by winds and currents for great distances...

..and a lucky few will wash up on one of these coral sand beaches.

The flesh and milk of the coconut provides the plant with food

as it grows in the sterile sand.

But that same food is valuable to us.

Coconuts are big business

and these palms have been taken to tropical islands

right around the world.

In the past, they were also planted on this island.

As well as fringing the beach, their natural habitat,

they now grow in the island's interior as well.

The people who managed this coconut plantation

were resettled in the late 1960s

and the plantations abandoned.

Nature has been left to itself for nearly half a century,

which is one reason why the reefs are so rich.

But these plantations aren't the only legacy

of the island's settlement.

Rats.

They still thrive on the islands that used to be inhabited.

Rats eat seabird chicks,

so there aren't many seabirds on rat-infested islands.

But some native creatures do survive -

land hermit crabs.

The reefs offshore are so diverse,

all shapes and sizes of empty shells are washed up -

homes for the crabs.

Some extravagant...

..and some just plain homely.

And the crabs are everywhere,

feeding on scraps of carrion or fallen fruits.

But there is one crab that rules supreme on these islands.

It's called the coconut crab

and it's the biggest land arthropod that exists on the planet today.

And it's actually as big as arthropods can get

in the current atmosphere and the current oxygen levels.

They're mostly nocturnal, but if we have a look around here,

we might just find one.

Ah.

This...

This is a coconut crab nest.

If you look down here, you can see very clearly,

the crab's burrowed down into the ground

and this is where he would have lived - down in this hollow.

There's no-one at home here now,

but this is a good sign, so we'll keep looking.

Ah, here we go.

Yep, I can see claws peeking out.

OK, this obviously isn't a natural nest.

There's a crab under here,

under a sheet of metal -

but, opportunistically, he's just found this

and thought it's obviously made a good nest.

So, let's delicately lift it up and have a look.

Wow!

What a whopper!

Hello, crab.

Oh! God, that's a big one!

Look at this specimen.

This is enormous!

What a beauty. Look at those claws.

Wow!

Let's gently...

Oh!

..gently try and pick him up.

Wow, look at this guy.

This...

Oh!

This is pretty much a full-size coconut crab.

They can get up to a 90cm leg span to leg span.

But this one, I'd say, is getting on for that size.

They can reportedly weigh up to 4kg

and this one would be a good three, I suppose.

So, this is near for the maximum for this species.

And you can easily see why they've become so rare.

Just with a piece of wood, you could kill them

and people have killed them for hundreds of years.

And as a consequence, it's been wiped out

from many of the islands from the Indo-Pacific.

But here, at least, on the Chagos Archipelago, this species is safe,

and here is one of the last places in the world

where you get these really large, full-sized, adult specimens.

What an absolute beauty.

Let's put him back in his home.

There we go.

Coconut crabs are relatives of land hermits.

And when they're young, they also use old shells for protection.

But they grow so big, an adult wouldn't find a big enough shell.

But by then, they don't need one.

They have their own tough body armour

and claws that can do a lot of damage.

Adults and young both love coconuts -

so they thrive in these abandoned plantations.

The youngsters need to find coconuts already broken open,

but adults can use their powerful claws

to rip through the tough outer shell.

And once they've broken into a coconut,

those big powerful claws

become precision instruments.

They're also very good at climbing.

They scale the tallest coconut trees...

..and when they reach the top,

they use their versatile claws

to cut down more coconuts.

These islands do seem to belong to crabs.

Land hermits venture out onto the beach

to see what the tide has brought them.

But they're soon put in their place.

These coral sand beaches really belong to ghost crabs.

These idyllic beaches are built from tiny fragments of coral skeleton...

..but how it gets here is an interesting story.

Much of it is generated by one particular group of reef fishes.

Parrotfish.

Many different species live on this reef,

but all have powerful jaws,

armed with a razor-sharp beaks

which they use to bite off chunks of coral.

Underwater, the reef is really noisy...

..and most of the rasps and clicks

come from untold numbers of parrotfish eating the reef.

They digest the living, fleshy parts of the coral,

but every mouthful is mostly just the chalky skeleton

of the coral polyp -

not very nutritious.

So, the parrotfish have a simple solution.

They just excrete the inedible bits as coral sand

in unbelievable quantities.

Sometimes, curtains of fine sand

hang in the clear water.

It builds up on the floor of the reef

and, eventually, is washed ashore.

So, next time you're relaxing on a white, tropical beach -

remember where the sand's come from.

Some of the species here are found nowhere else

but the reefs of the Chagos Archipelago.

Like Chagos anemonefish.

They live amongst the tentacles of these huge anemones,

somehow immune to their stings.

This keeps them safe from most predators

and the anemone makes use of the fish excretions.

This anemone also shelters a porcelain crab.

When it's sure it's safe,

it comes out to filter particles from the water

with legs modified into sieves.

The Chagos anemonefish is just one unique species here.

Less than 1% of these reefs have been explored by scientists.

There must be hundreds of other new species here,

all living their own lives,

completely unknown to us.

Although the reefs here are totally unspoilt,

the islands I've visited so far

have been touched by humanity.

But now, we're sailing towards

a really remote part of the archipelago,

to a group of islands as untouched as the coral reefs.

For any explorer or naturalist,

this is the ultimate experience.

We don't reach the island until nightfall,

so I'll have to wait until morning before I can explore.

At first sight, this island doesn't look very different

from the islands I've already visited.

Coconut palms growing at the top of the beach.

But step through the coconuts...

and there's a whole new world.

A native forest of hardwood trees and ferns.

How on earth did they get to such a remote place?

Some of these trees have big floating seeds, like coconuts.

Others, have seeds that stick to birds.

And these hardwood forests are full of birds,

like fairy terns.

Some seabirds nest high in trees,

but there's nowhere secure to build a nest on a coconut palm,

so these huge seabird colonies

depend on the hardwood trees for their nest sites.

But there's another reason why there are so many birds here.

This is an island that's never had rats on it.

The birds are able to nest on the bushes

or directly on the ground.

And just look at the difference. It's deafening.

The air is full of birds.

Red-footed boobies...

..and sooty terns.

They nest on the ground,

so can only live in such numbers where there are no rats.

Visiting the British Indian Ocean Territory

has been a real privilege,

and discovering its natural treasures

has been a unique experience.

The Chagos Islands feel incredibly remote...

..but that's nothing to where I'm going next -

into the centre of the biggest ocean of them all, the Pacific.

The British Territory of the Pitcairn Islands seems lost

in the vastness of this ocean.

And it's another very difficult territory to reach.

I have to start in Mangareva, in French Polynesia,

and, from here, the journey to Pitcairn will take three days.

Getting to Pitcairn Island,

one of the most remote inhabited islands on the planet, isn't easy.

This vessel behind me is the MV Claymore II.

She's the official supply vessel that supports the islands,

and she's the only vessel in the world

that visits the islands on a regular basis,

and she calls just four times a year.

I've been lucky to secure passage on her

and she leaves in about an hour, so I'd better get on board.

HE CLICKS TONGUE Hello. Hello.

Even on a modern cargo vessel,

the scale of this ocean is daunting.

For those first explorers, at the mercy of the wind and the weather,

it must have been overwhelming and disheartening.

And sometimes, it was all just too much.

In 1789, the Bounty sailed these waters

to collect breadfruit plants from Tahiti

and to take them to the West Indies to feed slaves.

They spent five months in Tahiti

and loaded up 1,000 or so breadfruit plants.

But as they sailed west, many of the crew mutinied,

casting Captain Bligh and his followers

adrift in an open boat.

The crew sailed the Bounty into the Pacific

looking for somewhere no-one could find them.

Their leader, Fletcher Christian, knew just the place.

The tiny island of Pitcairn

was the perfect place to hide from the harsh justice

of the Royal Navy.

It's easy to find today, but in the 18th century,

it was misplaced on the Admiralty charts,

so the Navy could only find the mutineers by chance.

This was to be their new home.

'I was fascinated by the story as a child

'and now I can hardly believe

'I've finally arrived at the mutineer's remote hiding place.'

The Pitcairn islanders come out to meet the Claymore

and pick up vital supplies.

HORN BLARES

So I can hitch a ride to shore.

'First, I check in with the authorities.

'Then, I pick up the island's standard form of transport.'

The island is roughly 4km long and this is the only way to get around.

And it doesn't take long to feel at home.

I'm heading to the island's museum

to see what remains of the infamous Bounty.

But on the way, I can't resist popping into the only shop -

a great place to find out more about life on Pitcairn.

So, this is the Pitcairn shop.

It's supplied just four times a year -

when the Claymore, the ship, comes in.

It's got everything you'd find in a normal supermarket.

I can't believe how full it is.

Oh, my God.

My wife searched everywhere for a yoghurt maker.

In London and when we went to Sydney.

Every shop she found, she looked for this and couldn't find one.

And now you come to Pitcairn Island and find a yoghurt maker.

That's absolutely unbelievable, so there you go.

At the end of the world, one of the best shops in the world.

Now, back to where I was going -

to find the museum.

It turns out to be a treasure trove of artefacts from the Bounty.

The ship's anchor.

Even the ship's Bible.

And this is the actual bell from the Bounty.

And by ringing it, we can actually hear what the ship sounded like.

BELL TOLLS But what happened to the Bounty herself?

The ship that brought the mutineers here.

To find out, I'll have to venture offshore.

The water around Pitcairn is teeming with fish.

It's tempting to stop and study the fish,

but I'm here to find a ship.

There are several spectacular wrecks down here,

but my guide knows exactly what he's looking for.

This is all that is left of the Bounty -

ballast stones from her hold.

They don't look like much,

but to touch these last remnants of such a famous ship

really brings history alive.

Now, it's time to head back to the surface.

It's Bounty Day on Pitcairn

and I don't want to miss the celebrations.

Once they'd arrived at Pitcairn,

the mutineers knew that a large sailing ship, anchored offshore,

could be seen by any Navy vessel passing by.

So they set fire to the Bounty and scuttled her.

And every year, the islanders commemorate the event

by building a model of the ship out of old boxes and bits of wood,

and setting fire to it.

It's a great excuse for all the islanders to get together,

and it's a great chance for me to meet everyone...

..because the story of the mutiny on the Bounty

is more than just history here.

CAMERA SHUTTER CLICKS All of these people are direct descendants

of the mutineers.

I'm Jackie Christian, I'm a seventh-generation descendant

from Fletcher Christian and Maimiti.

I'm Sean Christian, eighth-generation

from Fletcher Christian.

Why do you think the mutiny happened? Who was to blame?

Well, I think it was a combination of things -

but being on Tahiti for much longer than expected

and then going back to the discipline on ship,

it was hard work and they missed all the fun and free time

and wine, women and song in Tahiti.

And I guess the harsh treatment aboard the Bounty

and no-one will tolerate the leadership that William Bligh...

And how he treated his crew and so, I guess that led...

-like, a big part of the mutiny on the Bounty.

-Yeah.

I've been invited to the Bounty Day party - a cook-out, Pitcairn-style.

But first, we have to collect the food up here.

So, I'm wondering what's on the menu.

Perhaps it's some local bird.

No. This is a first for me.

Somewhere you have to shoot the plants.

That's a tiny target. That's an awesome shot.

These are breadfruits,

probably descended from those on the Bounty

that never made it to the West Indies.

Now, everyone lends a hand

to prepare a gigantic feast.

Their style of cooking is Polynesian.

When the mutineers left Tahiti,

they brought with them Polynesian men and women.

When they got here, Pitcairn was uninhabited -

but, in the distant past,

native Polynesians had lived on this island.

This type of cooking takes a while

so, while I'm waiting, I'll find out more

about the original inhabitants of Pitcairn.

The island had been discovered

long before the Bounty mutineers landed here,

and the evidence for that is just over here.

These strange markings are evidence of early Polynesians

but, as of yet, no-one's been able to decipher them

and we have no idea what they mean.

When you were down there, did you see much of this?

'Reynalda Warren has been painting these symbols for many years...'

They're just so huge.

'..but even she's not sure what they mean.'

What do you think they meant? What do you think they signified?

I always called that thing...

Course, that one's a little bit out of perspective there, but...

-..the pie.

-Maybe this wheel could be...

'The only people who could answer those questions

'seem to have vanished from Pitcairn

'some time in the 14th century, long before the Bounty arrived.'

If the meaning of the symbols has been lost in history,

Polynesian cooking techniques certainly haven't.

Dinner is ready.

I'll try a bit of breadfruit.

-Richard, breadfruit?

-I'll have a breadfruit with this.

Oh, lovely.

'There are only 47 people on the island.

'I'm not exactly sure who's going to eat all this.'

So, this is some of the breadfruit that came off the Bounty,

that's been growing here on Pitcairn for 200 years.

Mm.

It tastes like, um...

Like a sweet potato, like a starchy potato. It's beautiful.

At first, it seemed that the mutineers had arrived in paradise...

..but nothing could be further from the truth.

Confined to a small island,

tensions began to rise

between the mutineers and the Polynesians -

and amongst the mutineers themselves.

They still worried about being found

and executed by the Royal Navy,

and so kept a constant lookout from this cave high in the cliffs.

But soon, tensions turned to violence

and Polynesians and mutineers alike were murdering each other.

Fletcher Christian retreated up to these massive caves

to live in isolation.

But within just three years of the Bounty landing in Pitcairn,

Christian had been murdered

along with all but two of the other mutineers.

One reason such brutal violence erupted on Pitcairn

was the size of the island.

It didn't take long for the mutineers

to eat their way through most of the island's resources.

These tiny islands are incredibly fragile

and Pitcairn is still suffering from the impact of those early settlers.

Even these spectacular banyan trees are not native here.

Neither are these shrubs.

All these alien species outcompete native ones

and push them into extinction.

But some parts of the island

have been completely stripped of vegetation.

Now, just barren slopes of dry sand.

These are the culprits.

GOATS BLEAT Goats.

Some of them could even be descended

from the animals brought here on the Bounty.

Many of the Pacific Islands were so fragile and tiny,

it was even a problem for the original Polynesian inhabitants.

Not every island contained everything needed to survive.

The Polynesians' answer was to open up trade networks

across the vastness of the Pacific.

The length of these journeys was amazing.

The one I'm about to make would be like, for them,

popping round to the local shop.

I'm setting off to Henderson Island,

nearly 200km away.

It's a very big ocean

and a very small boat...

but the Polynesians often made this journey

in far more flimsy boats than this.

The Polynesians were the greatest navigators the world has ever seen.

At a time when the European explorers

were just skirting round the edges of the continents,

and they were afraid of falling off the edges of the maps,

Polynesians were travelling thousands of kilometres

between the Ocean islands of the Pacific.

They didn't have any charts

or any technology as we understand them today -

they used the stars to navigate.

The clouds, the reflection of the land onto the clouds

and also other signs, such as the birds,

which they could follow to their destinations.

We view the oceans as barriers,

they saw them as means of communication,

as highways to communicate between these ocean islands.

Just imagine their journeys.

I mean, this journey today is just one day,

but their ones could take weeks or even months

to travel across the island systems.

Henderson was once inhabited by Polynesians

but, as on Pitcairn,

they vanished before Europeans discovered the island.

It's been uninhabited for about 400 years.

So, I'm hoping that I'll get a glimpse

of what Pacific islands once were like.

This is Henderson Island.

It's virtually the last example

of a raised coral island in the Pacific,

with an entirely pristine and intact ecosystem.

It's about as remote as you can get on the surface of the planet.

Henderson's forests shelter birds found nowhere else on earth

but this tiny speck of land.

The Henderson fruit dove and the Henderson lorikeet

are tiny species of parrot.

It's also home to seabirds,

like fairy terns and masked boobies.

Both of these occur right around the tropics.

But this seabird, the Henderson petrel,

only nests on this one single island -

at least, as far as we know.

Many of the more remote Pacific islands

are almost impossible to reach.

Henderson's forest is impenetrable in places - at least, for me.

It's no problem for these land hermit crabs,

built like miniature tanks.

Henderson is larger than Pitcairn

and there was abundant food here.

The flightless land birds would have been easy prey for the Polynesians

and these land hermit crabs, that live all over the ground,

would also have been easy pickings.

And, of course, the reefs that surround the island teem with fish.

About 20 major habitation sites have been found

mainly in the cliffs that surround the island.

That indicates that a population of about 100 Polynesians

could have once lived here.

But all of the settlements faced one major problem -

the island is made out of coral

and this means there was none of the hard, volcanic stone

that the Polynesians needed in order to make the tools to survive.

But Henderson Island Polynesians solved that problem

by trading with Pitcairn Island,

and the evidence for that success story is inside this cave.

This is one of the caves where the Polynesians lived.

They're thought to have inhabited the island for up to 900 years -

all the way from the eighth century,

right the way to as late as the 17th.

Let's go inside and see what it's like.

Oh, God. It's a bit of a squeeze.

The presence of the Polynesians can actually still be seen

inside this cave.

If you just look down at the ground,

you can see layers of ash

where they used to burn... make fires inside the cave

and outside, there are big heaps, big middens, of discarded shells.

Well, actually there's lots of oyster shells

just littered around inside this cave.

That could be coincidence, they could have washed in,

but I don't think so. I also, just a minute ago, found this tool.

And if you look at it, it fits perfectly into your hand,

and this edge here is cut razor sharp,

so this looks like it's been worked by the Polynesians.

But the most compelling evidence is that, in this very cave,

many stone tools have been found -

some of which are made out of volcanic stones

that are known to have originated from Pitcairn Island

and other islands hundreds of kilometres away.

Now, what that proves is that

there was an immense trading network between the islands.

It's easy to imagine that the Polynesians, here on Henderson,

could have traded turtle eggs and bird meat,

particularly things like bird feathers that were highly valued,

for these volcanic stones that were then brought across

on these vast, inter-island canoes.

The waters surrounding Henderson were also harvested

but, like the island itself,

these reefs have had a few hundred years to recover.

Now, they're breathtaking.

Colours and diversity to make your head spin.

A longnose butterflyfish, with mouth parts like tweezers.

The diversity of fish rivals the Chagos Archipelago.

The ocean here looks like it's never been affected by humanity...

but the truth is more sobering.

This land hermit crab has found itself a plastic shell.

It's certainly one that won't wear out, but that's the problem.

Plastic is virtually indestructible.

The whole beach is littered with plastic.

We're 4,500 kilometres from the nearest major landmass

and hundreds of kilometres from any other island,

and there's bits of plastic boxes,

toys,

I don't know what that is, and some foam.

Basically, everything that floats can be washed ashore

after years at sea and just accumulates along these beaches,

polluting an otherwise pristine island.

Plastic now pollutes all of the world's oceans...

and, as it breaks up into smaller pieces,

it's eaten by marine creatures.

Even on islands as remote as Henderson and Chagos,

many of these birds will have plastic in their stomachs.

But Henderson and Chagos also show how resilient nature can be,

if given the chance.

This is a rare glimpse at the state of the world

before the impact of man,

and a benchmark by which to measure our impacts

across the rest of the world.

The sad thing is that all of the world's reefs should be like this,

with an intact ecosystem.

But it offers hope because, if we act now

and conserve the world's reefs, they can recover,

and one day they might look like this once again.