Mount Fiji is Japan's highest and most famous landmark...
..but it's just the tip of an extraordinary landscape
that stretches far beyond the Japanese coast
and leads to the deepest underwater gorges in the world.
Deeper even than the Grand Canyon,
they're one of the most spectacular features
of the planet's ocean floor
and a century and a half ago,
a group of extraordinary fish were discovered living there.
Scientists, among them those on a British research vessel
HMS Challenger,
were shown specimens of creatures
unlike any they had ever seen before - deep-sea sharks.
Even today, few of these creatures had ever been seen alive
and no-one really knows how they live and what they do.
This most intriguing of underwater kingdoms is about to be
explored afresh.
State-of-the-art equipment is going to take scientists
to the furthest reaches of these deep gorges.
Their aim is to find and film the bizarre species of shark
that have lived down here almost unchanged
for dozens of millions of years.
Oh, look, big shark on him!
Where? Right there. Oh, my God!
Sixgill on him already. Oh, my God!
Giant sharks that dominate large territories on the sea floor.
Sharks with extraordinary extendable jaws.
Yes, yes, that's it!
And one of the most elusive of all inhabitants of the deep sea.
Just outside Japan's leading marine science laboratory,
a valuable specimen is coming out of cold storage.
It's a young sperm whale which died of natural causes
and was then washed up on the beach in 2008
and now, it's setting off on its last and very unusual mission.
Dead whales usually drop to the ocean floor
where their flesh is stripped to the bone by the animals
which live down there.
A single whale's huge carcass can be a source of food for several years.
This particular sperm whale is now being taken out
to one of the deep sea gorges and dropped to the bottom.
For the very first time,
scientists will record right from the start what happens to it.
It could be that this huge meal will attract those mysterious,
rarely seen deep-sea sharks.
It's a bold experiment that's being masterminded
by Dr Yoshihiro Fujiwara.
He's a world authority
on what happens to the bodies of dead whales.
A large team of researchers and support staff has been assembled.
They have two submersibles,
each capable of diving to 1,000 metres.
The researchers who sit in them have an almost unobstructed view.
This is especially important for the camera crew who must be ready
to film sharks speeding in from any direction.
The Japanese film-makers will be using a specially developed camera
that is several hundred times more sensitive than normal.
Dr Sho Tanaka is Japan's leading shark expert.
He will identify animals if and when they appear.
They plan to drop the sperm whale carcass in Sagami Bay,
east of the Izu Peninsula.
Just 20km off shore, the ocean floor plunges down to 2,000 metres,
making Sagami and its neighbouring bay
two of the deepest in the world.
These two canyons lead to two even deeper trenches.
It's a very dynamic part of the ocean floor
which may be why it contains so many rare animals.
HE SPEAKS JAPANESE
This is the first time an experiment quite like this has been attempted.
No-one can be sure that it will go to plan.
While they prepare the whale for the drop,
the team on the nearby research vessel
make the final adjustments to the observation subs.
We're going to take Triton here at the surface.
Dr Fujiwara is first to board.
They will time the submersible's descent to match that of the whale.
Dr Fujiwara wants to get underwater as quickly as possible.
Sharks have an acute sense of smell and might be attracted
to the whale carcass as soon as it gets to the bottom.
He doesn't want to miss the first visitors.
A concrete block will stop the whale drifting in the current.
As the whale sinks, the clock on the experiment begins to tick.
Comms check, comms check.
It takes 30 minutes
for the submersible to reach the bottom, 500 metres down.
It's a desolate site
the sea floor is like a desert,
there's little here to sustain life.
But, unfortunately, there's no sign of the whale
and they're in trouble.
I've got quite a current.
A strong current has pushed the submersible off course
and they've lost their bearings.
We are better to go...
What does that say? South-east?
So, OK. Guys, I guess what I'm looking for is some direction.
'You can see me, I've lost the mooring line and so forth.'
Yeah, Troy, just stand by one minute.
And now the intercom isn't working,
so they can't get directions from the control room.
And the direction there...
coming from the top is...
I can't believe it.
So we just decide which way...
Dr Fujiwara pulls out his map of the ocean floor
to help them locate the whale.
I need you to watch for bottom for me.
The whale is going too deep for us, I think. No.
It's a frustrating hour before they're back on track.
I can see something. Oh... What is that? Is that it? I don't know.
That's it. Yeah, yeah, that's it!
Oh, yeah! Yeah. Good job. Hey, boys, we got us a whale.
But the whale carcass is moving very strangely.
Oh, yeah, he's dancing all around in the current. Yeah.
Is it the current that's lifting the dead whale's head?
He's moving, still moving.
Oh, look, big shark on him! Where? Right there! Oh, my God!
There's a sixgill on him already. Roger that. So that is moving.
A shark has its jaws clamped on the whale.
Wow, it's crazy.
Yeah, I got about a 30ft sixgill in front of me, probably.
It's a bluntnose sixgill shark
and it's nearly six metres long, as large as they come.
It jerks its head vigorously back and forth
to hack off a piece of meat and then swallows it.
Its teeth are serrated, like those of a saw.
As it tears into the flesh, its eye rolls back into its head
so that it is protected.
The shark's bite has cut an enormous hole in the whale,
47 centimetres across.
But after taking no more than this single mouthful,
the shark moves away and then swims off into the darkness.
Why would it abandon such a feast?
A few moments later...
Holy crap!
The same shark reappears right above the submersible.
This is menacing behaviour.
Perhaps it views the sub as a competitor for its meal
but eventually, it backs off.
The film crew leave a remote camera trained on the whale carcass,
finish their observations
and return to the surface and the research ship.
It's been a long day, but Dr Fujiwara is pleased with the way
things have gone so far.
APPLAUSE
Sharks are among the most famous animals on the planet.
Yet over half of the 500 species live in deep water,
below 200 metres, and little is known about them.
We only learned of their existence in the late 19th century.
Long research voyages, such as that made in the 1870s
by the British research ship HMS Challenger,
pioneered the science of oceanography
and collected specimens of marine life
that had never been seen before.
But it was off the coast of Japan that the Challenger collected
some of the strangest deep-sea sharks of all.
One of them, the frilled shark,
may have inspired seamen's stories of monstrous sea serpents.
Another, the velvet dogfish, was found to have skin as soft as silk.
Since the 19th century,
40 different species of deep-sea shark
have been discovered in Japanese waters.
Some of them are found nowhere else.
The underwater canyons stretching away from Mount Fiji
appear to be a very special place for them,
but they're rarely seen alive.
In the last few years, Japanese film-makers have mounted
a huge effort to capture deep-sea sharks on camera.
They've been helped by the people who know this part of the ocean
more intimately than anyone else - deep-sea fishermen.
Under their guidance, the film-makers work out
the most likely places to find deep-sea sharks.
They load fish into a container mounted in front
of a special camera.
The whole assembly will then be left on the seabed for a day
and record anything that comes for the bait.
There's also a robot camera with a remotely controlled lens
which can track an animal's movements,
even so, it's a tough challenge.
Over a four-year period,
the two cameras are lowered to the sea floor more than 200 times.
They're dropped at 20 promising locations.
Each is a hot spot identified by a number of fishermen
as the places where they've accidentally pulled up a shark
from the depths.
Some of these cameras produced very valuable pictures.
It takes a while for the mud on the seabed to settle.
But then, out of the darkness, drawn to the smell of the bait,
comes a roughskin dogfish.
It's nearly 1.5 metres long.
Food here is scarce,
so it's keen to get to the bait.
Its intense eye-shine reveals one of the secrets of its success.
It's the reflection from a mirror-like membrane
which lies behind the eye
and which enables them to see,
even in extremely low levels of light.
This is how it survives at such extreme depths,
finding its prey in almost total darkness.
In an even deeper part of the ocean canyon,
they find a very different deep-sea shark.
It's so huge, the camera can't get it all in picture.
It's a Pacific sleeper shark
and it's at least five metres long.
Bait appears to stimulate it to start hunting.
And it appears to be doing so by sucking up mud,
perhaps searching for prey hidden there.
A shark as big as this has never been seen doing such a thing before.
Having left a remote camera trained on the whale experiment,
the research team decide to investigate the seabed
close to where HMS Challenger meet its original discoveries.
Its images of the desert-like conditions
on this part of the ocean floor
show how tough it is to live down here,
but they also reveal some of the traits
which give deep-sea sharks an edge over their competitors.
Perhaps none is stranger than this -
a goblin shark.
This long snouted shark was first described
about the time of the Challenger's expedition,
but it was some time before researchers discovered
how these strange sharks find their prey.
The skin just behind the long snout
is covered with pores that contain special sensors.
These detect the tiny amounts of electric current
that flow across cell walls of all living things.
They can register as little as 1 ten millionth of a volt,
so even if prey attempts to hide in the mud on the sea floor,
it is not safe.
The goblin shark's extra-wide snout
carries hundreds of these sensors
and the fish uses it like a metal detector, sweeping the seabed,
waiting for the electric impulse which tells it to strike.
And what a strike!
It certainly lives up to its other name - demon of the deep.
In less than a second,
its jaws shoot out of the rest of its skull to engulf its prey.
It's the first time this remarkable bite has been seen so clearly.
The extra reach gives the goblin shark
a better chance of catching its food
and that might make all the difference down here.
The team is now looking for another shark
which has evolved a different but equally effective feeding technique.
Where the gorge falls away steeply,
it's believed to live in the water just above the ocean floor.
The frilled shark.
When it was first discovered, it caused a sensation
since it looks so like the sea serpents described in legend.
Perhaps its face does look more like that of a snake than a shark.
Needle-like teeth are arranged in lines,
unlike those in any other shark,
and may perhaps be particularly suited to snaring squid.
The red frills which give the shark its name
are extensions of its gills.
The water at this depth and pressure
contains half the amount of oxygen as water at the surface.
These gills extending outside the shark's body
expose a greater surface area of tissue to the water
and so increase uptake of oxygen.
These conditions within Japan's deep-water canyons
have created peculiar forms of shark
and that would be extraordinary enough,
but, equally remarkable, is that the shark's appearance
has changed little over tens of millions of years.
Dr Henri Cappetta of Montpellier University in France
has studied shark fossils
and Earth history to work out how this could have happened.
About 100 million years ago, dinosaurs dominated the land.
This fossil dates from that period
and it's an ancestor of the goblin shark.
It looks very similar to its living descendant.
TRANSLATION:
In the 100 million years since then,
the Earth's climate has changed.
There were periods of great volcanic activity and meteor strikes...
..which led to the mass extinctions of animals living on land
or at the surface of the sea.
But deep ocean canyons may have provided a stable sanctuary,
where animals were under less pressure to evolve.
In their various ways, the deep-water sharks were already
well adapted to conditions in these deep-sea canyons,
so now they appear to belong
to another altogether more ancient world, as indeed they do.
Although the team has now filmed many interesting species,
one deep-sea shark remained a mystery.
It was first discovered as recently as 1976,
when one became tangled in the anchor ropes
of a United States research vessel near Hawaii.
It measured an astonishing 4.5 metres,
but its mouth was an even bigger surprise at over a metre wide.
It was called the megamouth shark.
First to examine the shark's body was Dr Leighton Taylor.
He remembers very well the impression it made on him.
Wow! That's a mega-sized mouth!
So Megamouth, big-mouth shark.
I knew it was a shark,
but it didn't fit into any group of sharks that I had ever seen before.
This huge creature captured popular imagination
and news of the find spread instantly around the world.
It was confirmed as a new species of shark,
a very rare discovery even then.
But as Dr Taylor examined the carcass in more detail,
he found something he had not seen in any other shark.
When we first looked into the mouths of Megamouth,
it was obvious it was different from the lining of other sharks' mouths.
It was very silvery, very reflective.
People were taking flash photographs
and we noticed that the flashes would kind of light up this silvery lining,
like a mirror or something.
The upper jaw,
that flap of skin,
has those...
what we think are bioluminescent organs on them.
So it's kind of like baiting your trap with bright lights, you know,
they attract things in.
And we just don't know it for sure,
but we think that's probably what likely happens.
Dr Taylor suggested that organs along the Megamouth's upper jaw
produce this light,
which is reflected and amplified
by the silvery skin that lines its mouth.
Prey animals are attracted to the light, like moths to a flame,
and then swallowed.
But no-one knows for sure
because hardly anyone has ever seen a megamouth alive.
If you get a picture of a megamouth, I think you're all heroes!
You know, automatic Academy Award.
It's a tough call.
Since the megamouth's discovery in 1976,
only around 50 have been reported worldwide.
But a third of these finds have been made near Japan...
..and most of them were close to the deep sea canyons
beyond Mount Fuji.
If the team is to film such an elusive animal,
then this, surely, is the best place to try.
But how will they find even a giant shark in such a large area of sea?
Shark expert Dr Sho Tanaka
calls a meeting to work out the best plan.
Possible three to four feet... AM and PM at the moment...
Dr Tanaka knows more about the habits of Megamouths than anyone.
Every time a specimen has been found,
he has joined the investigating team to learn a little more about them.
His years of painstaking research tell him that, to find a megamouth,
he must first look for its prey.
This expedition in a submersible
is likely to be his best chance of seeing a megamouth alive.
OK, coming up.
Air is released from the tanks and the submersible descends.
Soon they're almost beyond the reach of the sun's rays
and the submersible switches on its searchlights.
COMPUTER: Depth one-five-zero metres.
They continue down to 200 metres
and beyond into the rarely explored world
known as the Twilight Zone.
Surface, surface, this is Trident.
We are passing two-zero-zero metres.
Course is good...
Here Dr Tanaka hopes to find the prey animals
that will lead him to the megamouth.
They see amazing creatures with translucent bodies...
..but they are not what Dr Tanaka is looking for.
The dive time is ticking past.
Soon they will have to return.
Oh!
What's that one?
Ah, it's beautiful.
Be careful. There you go.
Then a single Sakura shrimp darts in front of the sub.
This is what he's been hoping to see.
Sakura shrimps are small crustaceans
that live a few hundred metres below the surface.
One of these shrimps was discovered in the stomach of a Megamouth
that Dr Tanaka was dissecting and this made him think
that these shrimps might be an important element in their diet.
The world's biggest concentration of Sakura shrimp
is found in the deep seas around Mount Fuji.
When Dr Tanaka superimposed the locations where megamouths
have been discovered, on the habitats of the shrimp,
he found a match which confirmed his idea.
Now he hopes that the shrimp will lead him to the shark.
The shrimp they just found has now disappeared,
but Dr Tanaka thinks he knows where it's gone.
The sub follows the shrimp up towards the surface.
Depth 100 metres, over.
And there they are.
50 metres below the surface, there's a large school of them.
Just as Dr Tanaka thought -
the shrimp remain at depths during the day when surface predators
are active and then, under the cover of night,
they rise upwards to feed on plankton.
He's hoping that a megamouth shark may follow them.
On repeat dives, they do the same.
They stay deep during the day
and rise closer to the surface in the evening.
But there's no sign of a megamouth.
The chances of seeing one alive seem to be as slim as ever.
But the team IS getting results from the sperm whale carcass
which they dropped into a deep sea canyon
at the start of the expedition.
It's nine days since the drop
and Dr Fujiwara is retrieving the remote camera
which he left trained on the dead whale.
Oh!
I need 16 hands!
It's a fiddly job,
but the camera will have recorded how the carcass has changed
and what have visited it.
There will be a glimpse of a world no-one has seen before.
The images from day seven
show huge numbers of eels feasting on the whale.
THEY SPEAK IN JAPANESE
Oh!
A giant bluntnose sixgill shark comes into view...
..but to everyone's surprise,
it takes just a nibble and then drifts away.
An hour later, it returns.
From the body markings, the team recognise it to be the same individual
they discovered feeding here on day one.
It keeps returning to the whale
and taking the smallest of bites.
Dr Tanaka thinks it may have established a territory
around the whale and is guarding the prize,
especially when, a little while later,
it's seen circling the carcass.
It's the first evidence we have
that deep sea sharks are territorial
and it might explain why it's the only shark to appear on the scene.
The shark's behaviour has hidden benefits,
for under the protection of this huge bluntnose sixgill,
the carcass becomes a pit stop for other animals of the deep sea.
A Japanese spider crab is the largest known arthropod in the world
and only found here and at these depths.
Watching these visitors, Dr Fujiwara learns something else.
Without the bluntnose sixgill first ripping into the whale's skin,
the flesh would not have been as accessible to the crabs,
eels and urchins which have gathered here.
These time-lapse images reveal this vital process
for the very first time.
It begins with that important first bite,
taken by a large deep sea shark.
The carcass then becomes a kind of temporary oasis,
attracting smaller creatures.
The shark takes bites from its meal when it needs to,
but, like a big lion on a savanna,
it keeps other voracious predators away.
The experiment reveals that deep sea sharks
are a cornerstone of life in the oceans.
Meanwhile, Dr Tanaka has received some promising news.
Local fishermen have reported a large, unusual shark
swimming in shallow water near the coast.
It could be a megamouth, so he hurries to the site.
Evening.
He's naturally curious.
The full moon is illuminating a remarkable natural event.
Dr Tanaka can see a seething mass of krill at the ocean's surface.
Krill behave like Sakura shrimp.
At night, they migrate to the upper layers of the ocean
in order to feed on phytoplankton.
Individual krill may be tiny,
but in great numbers,
they are the sort of food that would encourage a megamouth
to swim from the deep sea almost to the surface.
The underwater cameraman gets into the water
and, soon after, something huge enters the pool of light.
It is most definitely a megamouth.
At last, we are face-to-face
with this mysterious creature of the deep.
This first meeting is taking place in very shallow water,
but the megamouth appears unfazed by the attention,
inquisitive even,
and propels its five-metre body through the water
at a leisurely pace.
Perhaps it has every reason to feel relaxed.
This is an animal that has pursued its ancient way of life
unchanged through an immense segment of the Earth's history.
It's teeth are no more than 5mm long.
Since it has specialised on eating small creatures,
such as Sakura shrimp and krill, it has no need of anything larger.
Suddenly, it accelerates away,
heading for a school of krill.
It swims into the school
and with a slight adjustment of direction
turns to where the krill are most densely packed.
So now the researchers can see how it feeds.
For an instant, we can even see inside its huge mouth.
A slow replay confirms Dr Taylor's original observations.
Light carried by the camera operator
is reflecting off the lining of the mouth
so that the whole inside of the mouth glows.
We can't be sure that it creates its own bioluminescence,
but this glow is probably what attracts prey.
It's taken over 30 years,
but this is a very big step towards understanding this rare deep sea shark.
If a creature as large as this can remain unknown until so recently,
what other sharks could remain hidden out there in the deep?
The encounter is a humbling reminder
of how relatively little we still know about the oceans.
Where the slopes of Mount Fuji extend down into the Pacific
lie dramatic oceanic gorges
that shelter a remarkable community of deepwater sharks.
Their body patterns have scarcely altered over millennia.
It's as if they've been living in a time capsule,
while the earth has changed around them.
They successfully adapted long ago to a harsh environment
where food is hard to find
and have been under little pressure to change ever since.
They may look primitive,
but they are highly specialised and successful.
Nothing since has been able to compete with them.
And they may yet lead us to further revelations about this,
the least explored part of our planet.