Secrets of the Deep Galapagos

In the vastness of the Pacific,

a once-in-a-lifetime expedition is underway.

We're on a voyage of discovery,

covering over a thousand kilometres through the Galapagos Islands.

Galapagos.

One of the greatest treasures of the natural world.

This place is just incredible.

Over 1,000 species here are found nowhere else on Earth,

and they've evolved in extraordinary ways.

But this paradise is under threat,

as our planet changes faster than ever before.

He's such a beautiful specimen. What health checks are you carrying out?

We've embarked on one of the most ambitious expeditions

ever attempted in Galapagos.

This just changes everything.

Everything.

'I'm Liz Bonnin.

'I'm a wild animal biologist

'and I'm helping to carry out

'a series of ground-breaking research missions in the field.

'With me is a team of world-renowned scientists.'

-How's that look?

-That looks perfect.

'On this leg of our journey,

'equipped with cutting-edge technology...

'..we're going beneath the waves...

'..to study the most endangered marine life in Galapagos...'

I have a green board.

'..in search of a giant of the deep...'

-ALL GASP

-It's massive!

'..to reveal how young sea lions are fighting for their lives...'

Mama's gone fishing. Look at this little munchkin!

'..and to discover why hammerhead sharks gather here in huge numbers.'

Oh, my God! Look at this!

'But on such an expedition...'

Toby, you're drifting onto us. Turn left, turn left...

'..we're at the mercy of the mighty Pacific Ocean.'

Oh, God! That was close.

'This is Mission Galapagos.'

We're one third of the way through

our 1,000-kilometre voyage of discovery around the Galapagos,

travelling on the scientific research vessel, the Alucia.

Our expedition is continuing 1,000 kilometres west of South America,

in the Pacific...

..where the Galapagos Islands lie.

So far, our journey has revealed

how animals here are adapting on land.

These animals are getting shorter to survive.

It's like a magic trick.

Now, we want to discover how animals are finding ways

to survive in the ocean.

Our first mission is taking us to the north-west tip

of the largest island, Isabela.

We're going in search

of one of the world's most elusive marine creatures...

..the mola, or ocean sunfish.

They've been studied near the surface here,

but never at depth.

RADIO CHATTER

Using Alucia's state-of-the-art submersible,

we're hoping to observe one in the deep...

This is Control, over.

..and set down a receiver

to track the movement of sunfish in the future.

-Yeah, I'll make my way across.

-Roger, Captain.

There's a real buzz on board this morning.

Everyone is excited about our plans for the day,

particularly because this animal is just so rare,

even here in the Galapagos.

Marine biologist Dr Tierney Thys is leading our mission.

She studies sunfish when they come to the surface.

It's thought they do this to warm up in the sun, giving them their name.

But no-one knows what sunfish do in deeper waters.

You've got your standard hypothesis,

that it's the food,

and maybe, it's the finding mates.

So, until you're down there with your own...

you know, your own observational capabilities,

you don't know the answer.

They could be doing all sorts of different things.

Taking us to the ocean floor is submersible pilot Buck Taylor.

He's been a sub captain for almost 20 years.

We couldn't be in safer hands.

Galapagos is exciting on the way down.

The last sort of 20, 30 metres, you've got everything running -

sonars, lights - trying to see what the seabed's like.

Touchdown and landing's definitely the bit that gets your heart going.

For this mission, we'll be diving along the flanks of the volcano

to a depth of 80 metres

where Tierney thinks we might find sunfish.

We'll then descend a further 20 metres,

to the sea floor, to drop the receiver.

The Nadir submersible will be our office for the next few hours.

OK.

It might be small,

but it weighs a mighty eight tonnes.

Just getting it into the water is a major operation.

Nadir. That's swimmer clear. Am I clear to vent?

-Roger. Venting now.

-He vents a lot, that guy.

BUBBLING

Control, Control, Nadir. Depth - ten metres. Life support, OK.

Vent secure. Descending. Over.

'Copy, Nadir.'

We begin to descend down the wall of the volcano.

The water is clouded with nutrients and plankton.

It's teeming with life.

This is a real hot spot.

-Sea lion. Right in front of us. Look!

-Oh.

-Look at how beautiful they are in the water.

-He's so graceful.

We reach a depth of 80 metres. This is the spot where Tierney thinks

we're most likely to see sunfish.

How much is known about the mola,

particularly the mola that hang out in the Galapagos?

Well, not a lot.

Not a lot. So, we're covering a lot of new ground.

Ah! Mola! Deep! Coming right in.

-Oh.

-Oh, my gosh!

-OK, so...

-Mola, guys. Right in front of us.

-82 metres. 82 metres.

Oh, my gosh! It's massive!

Just an hour into our dive and we've found a sunfish.

Tierney has never observed one this deep before.

-It's the most odd shape for a fish.

-So elegant.

It's really elegant despite the fact

that it looks like a big dinner plate with two fins on either side.

It just looks so unusual.

I mean, how big can they get?

Well, the sunfish can get to be over three metres long,

-two and a half tonne.

-Two and a half tonne?!

That's the weight of a big car.

-Two big cars.

-A small truck.

-Yeah, easily.

The sunfish is the world's largest bony fish.

As it grows, it gains an incredible one kilogram per day.

Its main food is jellyfish,

so Tierney thinks that sunfish might be venturing down here

to feed on them. But today, they're after something else.

Oh!

-It's getting cleaned. It's getting cleaned!

-It's getting cleaned!

Sunfish skin carries as many as 40 different parasites.

The tiny organisms are removed by cleaner fish.

Hogfish are one of several species which do this here.

Without this cleaning service,

the sunfish would become infested with parasites,

compromising its health.

Is this the first time, then,

that you can categorically say that Galapagos mola

-are being cleaned at this depth, then?

-Yes.

-Yes, because this is below our diver depth.

-Right, so that's a first.

This is a first.

It looks like it's sort of in another world right now.

It doesn't seem like it's very aware of what's going on around it.

By taking that unusual attitude,

it's saying to everybody who could potentially clean it,

"I'm ready for my spa treatment.

"Come in and exfoliate me..."

-"I'm not going to eat you."

-"..and I'm not going to eat you.

"I'm at peace, and come do your thing."

For me, they underscore how everybody plays a role,

Even the tiniest little fishes are of service to the big ones.

The big ones are of service to the little ones,

and you need everyone.

Everyone is what makes this system tick.

But our dive isn't over yet.

After two hours underwater,

we reach a depth of nearly 100 metres.

We've got one last thing to do before returning to the surface.

-It's a good spot.

-OK, Rover.

We're going to set up to deploy.

Very little is known about this incredibly rare species.

This receiver will help to further Tierney's research,

enabling her to monitor the movement and behaviour of sunfish

tagged at the surface with tracking devices.

-Look at that.

-Good luck.

Control, control - Nadir!

Mark this waypoint, transducer deployment site, over.

This is the first-ever deep-water receiver in Galapagos.

-It's a special moment, Tierney.

-Yes, it is.

It's powerful enough to run for 14 months.

Being able to deploy listening stations below diver depth,

it allows us to keep our finger on the pulse of a changing ocean.

'You are clear to surface.

'Clear to surface. Over.'

That was a brilliant dive.

Amazing.

All right! That was a great dive!

That was epic!

That was amazing!

Dream come true.

I'm not going to get this grin off my face in a hurry.

I get it. I totally get it now.

-I know.

-I'm beginning to understand your obsession with sunfish.

It's easy to be enchanted by them.

ALL LAUGH

WHOOPING

Our next task is to study

some of the most playful characters in Galapagos - sea lions.

This group live on the coastline of Fernandina Island.

They're one of the most endangered populations

of sea lions on the planet.

This is due in part to a regular weather phenomenon called El Nino.

Its effects can be devastating for this population.

And scientists believe that El Nino events are becoming more severe

because of climate change.

Marine biologist Dr Pelayo Salinas De Leon

studies how El Nino affects sea lions.

On this map,

we can look for specific features of El Nino.

For Galapagos, El Nino is really bad news,

because it brings warm water from the Western Pacific

that stops the production of food,

you know, the basic levels, like plankton.

Two cold currents are critical

to all marine life in Galapagos.

They're its lifeblood.

These currents come from thousands of kilometres away

and force nutrients up to the surface...

..kick-starting a rich, marine food web.

But El Nino disrupts these currents,

raising water temperatures by up to two degrees

which can severely affect the entire food chain.

I'm getting an opportunity to observe first-hand

how sea lions here are faring.

So, we're just off the coast of Fernandina.

It's nice and calm.

The water's at its clearest, so we need to get going.

The dive team has been out since first light,

scouting the waters where the sea lions swim.

We've had a quick recce in the little bay.

-That's where we're going to go, in there.

-OK. Perfect.

It's incredibly shallow, maybe one metre,

and there's juvenile sea lions in the bay.

Monitoring young sea lion numbers like this

can provide evidence of how well the entire colony is doing.

If females can't find enough food,

fewer pups will be born.

And because pups feed on their mothers' milk for up to three years,

those that ARE born can easily starve.

Scientists are seeing evidence of the effects of the last El Nino.

Numbers of sea lion pups have plummeted.

But in the water, there are clues

as to which pups still might fare better in tougher times.

The vast majority are females and there is a good reason for that.

Both male and female sea lions can catch food from six months old,

but because males are bigger,

they need to suckle their mother's nutritious milk

for longer than the females.

Daughters, meanwhile, are more independent,

learning to hunt for themselves at an earlier age.

This can give them an advantage when El Nino hits and times are hard.

It's been shown that, in harsher years,

when there isn't a lot of food around,

more females are likely to survive

because they've got all that practice in,

so there's this balance with nature.

The males get more milk when they're younger,

but when things get tough out here,

the females do a little bit better.

Galapagos sea lion numbers

have dropped by more than 50% in the last 30 years -

but it's not all bad news.

Scientists are finding signs

that these sea lions are adapting

by foraging at different depths...

..or moving to other parts of Galapagos

where the food supply is more plentiful.

Thanks to their intelligent and resourceful nature,

it's hoped their numbers will bounce back.

Adaptation is vital for survival in Galapagos.

And this species of cormorant,

one of the world's rarest birds,

tells one of the most extraordinary adaptation stories of all.

It, too, has responded to the challenges

this unique island chain presents.

Over millions of years,

this bird has lost its ability to fly.

Instead, the flightless cormorant is a superb swimmer.

It's developed a larger body and strong leg muscles

that make it a powerful diver.

And it's evolved denser, down-like feathers

that trap tiny air bubbles,

preventing them from getting waterlogged during deep dives.

Cormorants don't have any large land predators

that require them to fly off at a moment's notice

and also, all of their food is beneath the surface.

And so, evolution

has allowed the cormorant to spend all of its energy

in becoming a better, sleeker diver,

and for that, it doesn't need its wings.

The flightless cormorant hunts a variety of prey,

including octopus, eels and crustaceans.

A diverse diet which helps it to survive harsh times

when the food supply might be disrupted.

Oh, no. Look!

Mama's gone fishing.

Look at this little munchkin!

Hi, baby.

Bye, sweet thing.

Severe El Ninos can threaten the survival of the animals here...

..but the cold currents are returning,

bringing with them a bountiful food supply.

This year is going to be amazing.

With such cold water, there's going to be life everywhere.

These cold currents will deliver the all-important nutrients

that all life in Galapagos relies on.

Orca pod just sighted...there!

Right there! That's the male!

A huge dorsal fin.

There's about three or four of them.

It just goes to show how rich these waters are.

There's the male!

The ocean here is heaving with food,

all the way up the food chain. The orcas are here.

There must be a lot of fish.

I just saw a sea lion, there, in the background

and it's all down to this current bringing all those nutrients,

and then, the whole food chain just benefits from that bounty.

INDISTINCT RADIO CHATTER

For the next part of our expedition,

we're focusing on the sharks of Galapagos.

I've had such an incredible time

getting to know the west of the Galapagos, but I am keen to see more

and we are now heading to the two most northerly islands

in the archipelago - the frontier islands of Wolf and Darwin.

These two rugged islands are located 160 kilometres north of us.

The journey takes the entire night.

By daybreak...

..we're anchored in the centre

of the now extinct volcano, Wolf Island.

The waters beneath us boast

one of the highest concentrations of sharks in the world...

..and 33 different species have been recorded here.

Today, we're interested in a particular one...

..the endangered scalloped hammerhead shark.

They congregate here in vast numbers.

Our task is to assess just how many.

Shark expert Dr Alex Hearn is leading this mission.

He's been studying hammerheads there for the past 11 years.

The scalloped hammerhead shark is classified as endangered,

and this is because it's been subject to overfishing,

especially in this region.

Over the last 20 years,

there's been a huge increase

in the demand for shark products,

and in particular, shark fins for shark fin soup,

and hammerhead sharks in particular,

because of their large fins, are a desirable species to catch.

In many parts of the world, hammerhead numbers have decreased

by a staggering 99% in the past 30 years.

Alex believes that the gathering here

is now the biggest remaining one on the planet.

If he's right, this will help the cause to protect them.

But how do you count hammerheads when they're always on the move?

The answer is by fitting them with tags

that will be detected by an underwater receiver.

The man responsible for this daunting task

is Dr Cesar Penaherrera.

His research group is the only one in the world

with permits to tag hammerheads like this.

So, this is one of the tags that we use. It's an acoustic tag

that sends a sound signal in the water.

In a normal dive, you can count probably, I don't know, 80 sharks.

But there are not 80, there are more sharks moving around the area

and that amount of the sharks that we tag,

it helps us to refine and get more accurate estimates.

The good that we are getting out of this information is vital,

not only for protecting sharks here

but to show what do we need to know about them.

Hammerheads are disturbed by the noise and bubbles

of scuba-diving gear.

So Cesar has to free-dive and tag them by hand.

He can hold his breath for an incredible two and a half minutes

and dive to depths of 15 metres.

Is there any other way to tag a shark other than free-diving?

Well, there are, but particularly with hammerhead sharks,

this is the fastest way to get most of the data that we need.

Hammerheads have eyes on either end of their wide heads.

This gives them superb depth perception,

allowing them to accurately track and catch fast-moving prey.

But it also means that they have a large blind spot

in front of their heads, which Cesar is only too happy to exploit.

I'm getting butterflies for you.

HE LAUGHS And I commend you.

Well, you should join me one of these days.

There is no way in heck I would ever do it!

You can see the hammerheads, the water is so clear.

That's mad.

Cesar aims for the thick skin at the base of the fin.

If he's not certain he'll hit the target,

he won't take the shot.

Did you get it?

-That was exciting! But, yeah, we got it.

-That's amazing!

Wow! I could see you for quite a distance, the water is so clear.

That's amazing.

He sets off to tag another shark.

As risky as this might seem,

the hammerheads are highly unlikely to attack Cesar.

Aggressive behaviours towards humans are incredibly rare.

Can you manage?

-Wow!

-Let me catch my breath.

That was quite something.

It's amazing to watch, Cesar.

It really is.

-Yeah. It is. It is...

-HE PANTS

Sorry, I have to catch my breath!

I don't know how you do that.

With ten hammerheads tagged,

these new individuals can be added to Alex's data-set,

and by analysing it,

he can begin to get an idea of the size of these congregations.

Preliminary estimates would suggest

maybe there's 500 or 600 hammerhead sharks here at any given time.

We are very happy.

Alex's calculations show

that this may be the biggest known congregation

of hammerheads on the planet.

This research helps to highlight just what an essential refuge

these waters are, and how important it is to protect them.

Darwin and Wolf are really among the last outposts in the world

where we have these huge numbers of sharks.

It's the front line of conservation.

Alex has studied sharks here for many years, but never on this scale.

Some of his previous data from GPS tags

is revealing another remarkable discovery...

Look how we've tagged them here and they've moved off...

..the distance hammerheads are travelling.

So, these are some tracks of the hammerheads

that we've tagged with satellite tags.

And so we can pinpoint their location at different times,

and we can see, first off, that they've moved incredible distances.

And so, we have these two sharks that headed out

about 200, 300 kilometres north-east,

and then we have this other one that headed over 500 kilometres out

and back again to Darwin and Wolf.

So, it's almost like Darwin and Wolf are the central hub.

Alex's research reveals

that hammerheads consistently return here.

But why do they gather in such large numbers?

Answering this is the second part of our mission.

Alucia is a hive of activity

as we prepare to dive with hammerheads.

Alex has chosen a prime location nicknamed "Shark Point".

It's full of large swells and strong currents.

The perfect place for us to observe hammerhead behaviour.

Yeah, roger that. Thanks very much.

The target location is nearly 50 metres down.

It's reachable with scuba gear,

but we want to study the hammerheads for as long as possible

without running out of air.

So, for this mission, we need Nadir.

We know where they are,

but we don't know exactly what they are doing.

The only way we can do that is by observation.

We're really limited by scuba,

which is why being able to jump into one of these

and get down there and really spend some quality time with the sharks

is going to give us so much more insight.

This gathering in large groups is a behaviour called "schooling".

But Alex doesn't know why hammerheads do it.

So, how common is this behaviour and what is it exactly?

Not all sharks school.

Hammerheads are perhaps the most iconic of the ones that do.

It basically means when you have a large group of sharks

that stick close together for an extended period.

Here, if we're lucky, we'll see schools of several hundred,

which is just... And it will blow your mind!

It really will!

At the spot where the hammerheads prefer to gather,

a huge current splits into two.

So, we'll have to battle turbulent waters

to get our sub into the right position.

We're going to need the second submersible,

Deep Rover, as a safety backup.

It's actually called Shark Point,

-because it's so sharky?

-Because it's so sharky, yeah.

-OK. OK.

And then the hammerheads like to sit in that spot

where the currents split,

so it's like this little sweet spot that they sit in.

That's where they want to be.

'Deep Rover has just dropped.'

As soon as we touch the water, we've got company.

Inquisitive silky sharks have come to investigate.

Two silkies. They love it. Oh, look at that.

Are they sort of renowned for being the most curious sharks?

-They are very curious.

-Look at that! They are loving it.

They seem to be fascinated by us.

They're more fascinated by us than we are of them.

INDISTINCT CONVERSATION

Venting now.

Oh, here we go.

Control, Control. Nadir.

Life support OK. Vents secure. Descending.

Because of the difficult conditions,

it's paramount that we work as a team

with Mission Control on board Alucia.

Once the subs get past about probably 80 metres,

visibility starts to go.

So, they're just going down, descending down,

so they need us to tell them in which direction to go to.

Together, we begin the dive

and reach the sea floor relatively quickly.

So far, no hammerheads.

But in Galapagos, you never know what surprises might lie in store.

I thought that was rubble,

but it's all...it's all crabs.

Wow!

These spider crabs are most probably gathering in large numbers to mate.

Grouping together like this

also helps to protect them from predators such as octopus.

From claw to claw, the largest males are over half a metre in length.

I think we should move further along.

I think we should move further to the Point, over?

We're edging closer to Shark Point.

But as we do, we're becoming more exposed to the currents.

They're starting to push all eight tonnes of our sub.

Yeah, affirmative. I don't think we'll go much further.

-The current's starting to pull quite hard.

-OK.

So, we'll just hold it on this point.

Come on, now, hammerheads.

Starting to get in the zone now.

Eyes peeled.

You can see the currents coming in from either side,

so we're right on the point now.

Holding our position in these strong currents is proving difficult.

Watch yourself, Toby. You're drifting onto us.

Turn left. Turn left.

We're being pushed dangerously close together.

A collision could spell disaster.

Stay away, Toby.

Keep coming to port.

OK, that's good there.

Fall down.

The current keeps getting stronger and stronger,

now pushing our sub towards the rocks.

ENGINES WHIR

Come on, baby! Hold it!

We're going backwards!

-ENGINES WHIR

-Come on, come on, come on...!

-Is that the current pushing you?

-Yeah.

-Oh, my God!

Nadir is no match for the surging water, even on full power.

-Jesus Christ!

-Look behind you. It's just mad.

Are you used to this? Does it happen a lot?

Er, no...

On board Alucia, the team is unaware of the problem.

We've lost communication.

Control, Nadir. Do you copy my last, over?

Turbulent water can disrupt comms,

as well as the tracking of our sub.

Comms, at the moment, are poor.

We'll move to clearer water

and, hopefully, get a better comms angle to them.

We finally spot some hammerheads,

but they're the last thing on our minds

as we're forced towards jagged rock.

Oh, God! That was close!

At last, Buck gets Nadir back under control.

Control, Nadir.

Over. Strong current.

Seeking permission to ascend back to the surface. Over.

Bottom depth, 116 metres. Over.

I'm kind of relieved to be going to the surface, I have to say.

Just this once.

Buck releases bubbles to help Alucia find us at the surface.

DEEP SPLOOSHING

On the scale of one to ten with things you've had to deal with,

-with respect to currents, what was that?

-That was up there.

I would say nine and three quarters.

It was taking us from 15 metres down to about 45.

Just pumping us up and down.

And I tell you what, as much as I've had an amazing time in the subs

and then really beginning to appreciate the oceans,

this experience has made me realise we've got to still respect it.

She's the boss, and every now and then, she lets you know it.

-Thank you for getting us out of the soup.

-Thank you.

And thanks for being part of the adventure.

-I loved it.

-When do we go back down?

-Half an hour?

-I'm going for a gin and tonic!

ALL LAUGH

Our failed sub dive is a setback.

We managed to catch a brief glimpse of hammerheads gathering,

but not long enough to be able to study them properly.

And now, with time running out before we need to move on,

we only have one more chance to observe their behaviour.

The team regroup to discuss the plan...

..and it's decided that the currents at Wolf Island

are just too strong to risk another sub dive.

We choose to relocate 20 kilometres north

to nearby Darwin Island.

Not much can live on this barren rock...

..but beneath the waves,

it's brimming with life and, hopefully, hammerheads.

Alex is keen to get into the water as soon as possible.

Now, we've got to get the sub in,

because hammerheads tend to move offshore at night to feed,

and come back at dawn. What I'm hoping is,

over the morning, as the hammerheads come back,

they'll build into a nice school

and then we can go down and start looking at their interactions.

So, let's really hope we can get the sub down there.

The bulk of the hammerheads are due back

from feeding out in deeper water at any moment.

This is the ideal time and place to see them school.

But Buck and dive master Steve have been assessing the site

and there's a problem.

Conditions, visibility-wise, are lovely.

Very blue. Lots of fish.

Lots of hammerheads. However...

-Currents, don't tell us.

-The current is strong.

-It's a definite no.

-At the moment.

It's just too dangerous to use the sub.

With time running out, we decide to attempt a dive with scuba instead.

Remind me again why it's not OK for the sub,

but it's OK for us, even though the currents are so strong?

A sub is very big and lumbering, and we find it hard to hide.

Whereas, you're small, agile, nimble. You can tuck into the rocks.

I don't know about the agile bit...

It would be crazy to waste this time.

It would. We need to observe more hammerheads.

We need to see what it's all about down there.

-And the action's happening now.

-So, they're there now?

-Are they schooling?

-They are schooling.

-Oh, right.

-Let's go.

-Wet-suit time?

-Yes.

-OK, perfect.

-Let's do it.

Scuba isn't an ideal way to observe hammerheads,

as the noise and bubbles spook them.

But, at least for a short time, at a safe depth,

we might get to watch them as they school.

To maximise his chances of studying this behaviour,

Alex has asked the dive team to construct an array of cameras.

They will be left unmanned,

recording on the sea floor,

and retrieved later.

I'm covering 360 degrees, basically.

So, towards you. Behind me.

Left and right.

Alex hopes this will help him

to better understand the sharks' behaviour.

INDISTINCT

This location is an iconic dive site at the tip of the island.

Darwin's Arch.

With dangerous rocks and strong currents,

it's a testing dive location for even the most experienced of divers.

You get big seas. There's strong currents.

You get counter currents. You get up-wellings,

and what we don't want to do is get into a situation

whereby we start drifting,

because there's a place further on known as the "Meat Grinder".

It will be the most advanced dive I've ever attempted.

But I'm in safe hands.

Bobby, my dive buddy, has a plan.

Liz, so what we're going to do

is I'm going to actually get behind you and push you down by your tank,

just to assist you to get down on the rocks as quick as possible.

So, then we'll proceed with the dive,

so we'll just bounce along the rocks. Get a little closer.

Right at the edge and then, hopefully,

we'll get the school of hammerheads right over the top of us.

Okey dokey. So, I'm not going to see you beside me,

but I'm going to feel you shoving me down into the water?

I'll be right there with you the whole time.

I'll just be right behind you.

Conditions above the surface are intense.

Beneath, it looks almost serene.

But powerful swells and currents are in force.

To avoid them,

we descend quickly, looking for shelter among the rocks.

The filming team has the added difficulty

of taking the camera rig with them.

Underwater cameraman Mike Pitts

is able to communicate with the rest of the team with a special mask.

There's such a strong

surging current here.

But we're going to get down.

As predicted, the hammerheads are startled by the noise

and bubbles of our scuba gear.

The unmanned cameras will be vital

for observing their natural, undisturbed behaviour.

Jorge, can you hear me? Yo!

Let's go!

Only the team deploying the camera rig venture beyond the reef.

This could be quite good here, I think.

The camera is positioned, weighted down

and switched on to record for four hours.

Well, I hope nothing happens to it...

..and the sharks don't bite it.

Alex and I find a position to anchor ourselves at the reef's edge,

just out of the currents.

Beyond us, the ledge drops off hundreds of metres.

The hammerheads should come right past this point, so, in theory,

we're in the perfect spot to see them gathering.

All we can do now

is watch and wait.

And then it begins.

The hammerheads are gathering

and our cameras are rolling.

It's just like being in an aquarium.

The only difference with this aquarium is it's for real.

Oh, my God! Look at this!

OK, we're just going to go up now gently.

Finally, just before we hit the surface,

Galapagos has one more surprise for us.

I can't believe it!

Whale shark! Whale shark!

A passing whale shark,

the biggest fish in the ocean.

Whoo!

Whoohoo! That is unbelievable!

Something on the surface, port side, 15 metres.

Good dive. Good dive.

Oh, my God! That was amaz...!

Hammerheads, fireworks and fish.

Shark everywhere.

That was totally worth it.

It's like a dream. Like the best dream you would ever have,

except it's real.

That was a good morning at the office!

HE LAUGHS

By observing these hammerheads school,

Alex is closer than ever before

to explaining why they group like this.

The hammerheads. They were coming in. They were circling.

What it appears to be is that the largest females

tend to dominate the centre of the school,

and the smallest ones are around the outside.

And then the males are kind of trying to mate

with the females that are at the centre.

It was a stunning dive.

It really was.

Alex believes this behaviour

is part of a complex courtship ritual.

The largest, more sexually mature females

place themselves at the centre of the school.

This means that only the strongest males,

capable of making their way through, succeed in mating with them.

Footage from our locked-off cameras supports this theory...

..shedding light on our understanding

of hammerhead behaviour.

That's just opened my eyes to... this extraordinary world

that we hardly understand, beneath the waves. It's just...

It's just shifted something in my brain.

It's more glorious than you can possibly imagine.

On this leg of our journey,

Alucia and her technology have helped us to understand

the rapidly changing oceans here like never before.

We've found a rare ocean giant in the deep...

..learned more about the survival strategies of sea lions...

..and we've come closer to revealing why hammerheads gather here.

Our responsibility to protect these waters

has never been more important.

'Next time on Mission Galapagos...

'we'll explore what the future holds for this last, great wilderness.'

We're heading to a lush, green world, unlike any other.

'What does the magma chamber, deep beneath Galapagos...'

This place is just incredible.

'..reveal about the future of these volcanic islands?'

It feels pretty special to sit here imagining

that lava used to rush through here.

'How are scientists protecting the ancient migration routes

'of the Islands' most iconic creatures?'

Tortoises will definitely suffer the consequences.

'And how can deploying the latest drone technology

'help us to save an enchanted forest?'

This place is so completely different

to anywhere else I've been on these islands.