0:00:05 > 0:00:10Mount Fiji is Japan's highest and most famous landmark...
0:00:13 > 0:00:17..but it's just the tip of an extraordinary landscape
0:00:17 > 0:00:19that stretches far beyond the Japanese coast
0:00:19 > 0:00:23and leads to the deepest underwater gorges in the world.
0:00:28 > 0:00:30Deeper even than the Grand Canyon,
0:00:30 > 0:00:32they're one of the most spectacular features
0:00:32 > 0:00:34of the planet's ocean floor
0:00:34 > 0:00:36and a century and a half ago,
0:00:36 > 0:00:40a group of extraordinary fish were discovered living there.
0:00:44 > 0:00:48Scientists, among them those on a British research vessel
0:00:48 > 0:00:50HMS Challenger,
0:00:50 > 0:00:52were shown specimens of creatures
0:00:52 > 0:00:57unlike any they had ever seen before - deep-sea sharks.
0:01:04 > 0:01:08Even today, few of these creatures had ever been seen alive
0:01:08 > 0:01:11and no-one really knows how they live and what they do.
0:01:25 > 0:01:29This most intriguing of underwater kingdoms is about to be
0:01:29 > 0:01:31explored afresh.
0:01:31 > 0:01:34State-of-the-art equipment is going to take scientists
0:01:34 > 0:01:37to the furthest reaches of these deep gorges.
0:01:41 > 0:01:46Their aim is to find and film the bizarre species of shark
0:01:46 > 0:01:49that have lived down here almost unchanged
0:01:49 > 0:01:50for dozens of millions of years.
0:01:50 > 0:01:52Oh, look, big shark on him!
0:01:52 > 0:01:54- Where?- Right there.- Oh, my God!
0:01:54 > 0:01:57- Sixgill on him already.- Oh, my God!
0:01:59 > 0:02:03Giant sharks that dominate large territories on the sea floor.
0:02:07 > 0:02:10Sharks with extraordinary extendable jaws.
0:02:14 > 0:02:17Yes, yes, that's it!
0:02:17 > 0:02:22And one of the most elusive of all inhabitants of the deep sea.
0:02:55 > 0:02:59Just outside Japan's leading marine science laboratory,
0:02:59 > 0:03:03a valuable specimen is coming out of cold storage.
0:03:03 > 0:03:07It's a young sperm whale which died of natural causes
0:03:07 > 0:03:11and was then washed up on the beach in 2008
0:03:11 > 0:03:16and now, it's setting off on its last and very unusual mission.
0:03:24 > 0:03:28Dead whales usually drop to the ocean floor
0:03:28 > 0:03:31where their flesh is stripped to the bone by the animals
0:03:31 > 0:03:33which live down there.
0:03:33 > 0:03:37A single whale's huge carcass can be a source of food for several years.
0:03:39 > 0:03:43This particular sperm whale is now being taken out
0:03:43 > 0:03:47to one of the deep sea gorges and dropped to the bottom.
0:03:47 > 0:03:48For the very first time,
0:03:48 > 0:03:53scientists will record right from the start what happens to it.
0:03:53 > 0:03:58It could be that this huge meal will attract those mysterious,
0:03:58 > 0:04:00rarely seen deep-sea sharks.
0:04:02 > 0:04:05It's a bold experiment that's being masterminded
0:04:05 > 0:04:08by Dr Yoshihiro Fujiwara.
0:04:13 > 0:04:14He's a world authority
0:04:14 > 0:04:17on what happens to the bodies of dead whales.
0:04:31 > 0:04:35A large team of researchers and support staff has been assembled.
0:04:47 > 0:04:49They have two submersibles,
0:04:49 > 0:04:53each capable of diving to 1,000 metres.
0:04:53 > 0:04:57The researchers who sit in them have an almost unobstructed view.
0:04:57 > 0:05:01This is especially important for the camera crew who must be ready
0:05:01 > 0:05:04to film sharks speeding in from any direction.
0:05:07 > 0:05:11The Japanese film-makers will be using a specially developed camera
0:05:11 > 0:05:16that is several hundred times more sensitive than normal.
0:05:19 > 0:05:23Dr Sho Tanaka is Japan's leading shark expert.
0:05:23 > 0:05:27He will identify animals if and when they appear.
0:05:49 > 0:05:53They plan to drop the sperm whale carcass in Sagami Bay,
0:05:53 > 0:05:55east of the Izu Peninsula.
0:06:01 > 0:06:06Just 20km off shore, the ocean floor plunges down to 2,000 metres,
0:06:06 > 0:06:09making Sagami and its neighbouring bay
0:06:09 > 0:06:11two of the deepest in the world.
0:06:15 > 0:06:20These two canyons lead to two even deeper trenches.
0:06:20 > 0:06:23It's a very dynamic part of the ocean floor
0:06:23 > 0:06:26which may be why it contains so many rare animals.
0:06:33 > 0:06:35HE SPEAKS JAPANESE
0:06:35 > 0:06:39This is the first time an experiment quite like this has been attempted.
0:06:47 > 0:06:50No-one can be sure that it will go to plan.
0:06:54 > 0:06:56While they prepare the whale for the drop,
0:06:56 > 0:06:58the team on the nearby research vessel
0:06:58 > 0:07:01make the final adjustments to the observation subs.
0:07:03 > 0:07:06We're going to take Triton here at the surface.
0:07:08 > 0:07:11Dr Fujiwara is first to board.
0:07:11 > 0:07:15They will time the submersible's descent to match that of the whale.
0:07:21 > 0:07:25Dr Fujiwara wants to get underwater as quickly as possible.
0:07:28 > 0:07:31Sharks have an acute sense of smell and might be attracted
0:07:31 > 0:07:34to the whale carcass as soon as it gets to the bottom.
0:07:34 > 0:07:37He doesn't want to miss the first visitors.
0:07:42 > 0:07:46A concrete block will stop the whale drifting in the current.
0:07:56 > 0:08:00As the whale sinks, the clock on the experiment begins to tick.
0:08:08 > 0:08:11Comms check, comms check.
0:08:25 > 0:08:27It takes 30 minutes
0:08:27 > 0:08:30for the submersible to reach the bottom, 500 metres down.
0:08:35 > 0:08:37It's a desolate site
0:08:37 > 0:08:39the sea floor is like a desert,
0:08:39 > 0:08:42there's little here to sustain life.
0:08:48 > 0:08:52But, unfortunately, there's no sign of the whale
0:08:52 > 0:08:54and they're in trouble.
0:08:55 > 0:08:57I've got quite a current.
0:08:59 > 0:09:03A strong current has pushed the submersible off course
0:09:03 > 0:09:06and they've lost their bearings.
0:09:06 > 0:09:09We are better to go...
0:09:09 > 0:09:11What does that say? South-east?
0:09:11 > 0:09:15So, OK. Guys, I guess what I'm looking for is some direction.
0:09:15 > 0:09:20'You can see me, I've lost the mooring line and so forth.'
0:09:21 > 0:09:24Yeah, Troy, just stand by one minute.
0:09:27 > 0:09:30And now the intercom isn't working,
0:09:30 > 0:09:32so they can't get directions from the control room.
0:09:34 > 0:09:36And the direction there...
0:09:36 > 0:09:39coming from the top is...
0:09:39 > 0:09:41I can't believe it.
0:09:41 > 0:09:43So we just decide which way...
0:09:43 > 0:09:46Dr Fujiwara pulls out his map of the ocean floor
0:09:46 > 0:09:48to help them locate the whale.
0:09:50 > 0:09:52I need you to watch for bottom for me.
0:09:54 > 0:09:58- The whale is going too deep for us, I think.- No.
0:10:00 > 0:10:04It's a frustrating hour before they're back on track.
0:10:06 > 0:10:09- I can see something.- Oh...- What is that?- Is that it?- I don't know.
0:10:09 > 0:10:12- That's it.- Yeah, yeah, that's it!
0:10:12 > 0:10:15- Oh, yeah!- Yeah. Good job. - Hey, boys, we got us a whale.
0:10:20 > 0:10:23But the whale carcass is moving very strangely.
0:10:27 > 0:10:30- Oh, yeah, he's dancing all around in the current.- Yeah.
0:10:31 > 0:10:35Is it the current that's lifting the dead whale's head?
0:10:37 > 0:10:39He's moving, still moving.
0:10:40 > 0:10:45- Oh, look, big shark on him! - Where?- Right there!- Oh, my God!
0:10:45 > 0:10:49- There's a sixgill on him already. Roger that.- So that is moving.
0:10:49 > 0:10:53A shark has its jaws clamped on the whale.
0:10:53 > 0:10:55Wow, it's crazy.
0:10:55 > 0:10:57Yeah, I got about a 30ft sixgill in front of me, probably.
0:11:00 > 0:11:03It's a bluntnose sixgill shark
0:11:03 > 0:11:06and it's nearly six metres long, as large as they come.
0:11:14 > 0:11:17It jerks its head vigorously back and forth
0:11:17 > 0:11:20to hack off a piece of meat and then swallows it.
0:11:34 > 0:11:37Its teeth are serrated, like those of a saw.
0:11:43 > 0:11:48As it tears into the flesh, its eye rolls back into its head
0:11:48 > 0:11:50so that it is protected.
0:12:03 > 0:12:07The shark's bite has cut an enormous hole in the whale,
0:12:07 > 0:12:0947 centimetres across.
0:12:14 > 0:12:17But after taking no more than this single mouthful,
0:12:17 > 0:12:22the shark moves away and then swims off into the darkness.
0:12:22 > 0:12:24Why would it abandon such a feast?
0:12:37 > 0:12:39A few moments later...
0:12:43 > 0:12:46Holy crap!
0:12:46 > 0:12:50The same shark reappears right above the submersible.
0:12:50 > 0:12:52This is menacing behaviour.
0:12:52 > 0:12:56Perhaps it views the sub as a competitor for its meal
0:12:56 > 0:12:58but eventually, it backs off.
0:13:03 > 0:13:07The film crew leave a remote camera trained on the whale carcass,
0:13:07 > 0:13:08finish their observations
0:13:08 > 0:13:11and return to the surface and the research ship.
0:13:11 > 0:13:15It's been a long day, but Dr Fujiwara is pleased with the way
0:13:15 > 0:13:17things have gone so far.
0:13:29 > 0:13:32APPLAUSE
0:13:39 > 0:13:42Sharks are among the most famous animals on the planet.
0:13:47 > 0:13:51Yet over half of the 500 species live in deep water,
0:13:51 > 0:13:55below 200 metres, and little is known about them.
0:14:07 > 0:14:11We only learned of their existence in the late 19th century.
0:14:11 > 0:14:15Long research voyages, such as that made in the 1870s
0:14:15 > 0:14:18by the British research ship HMS Challenger,
0:14:18 > 0:14:21pioneered the science of oceanography
0:14:21 > 0:14:23and collected specimens of marine life
0:14:23 > 0:14:25that had never been seen before.
0:14:29 > 0:14:32But it was off the coast of Japan that the Challenger collected
0:14:32 > 0:14:35some of the strangest deep-sea sharks of all.
0:14:36 > 0:14:38One of them, the frilled shark,
0:14:38 > 0:14:42may have inspired seamen's stories of monstrous sea serpents.
0:14:44 > 0:14:49Another, the velvet dogfish, was found to have skin as soft as silk.
0:14:50 > 0:14:52Since the 19th century,
0:14:52 > 0:14:5540 different species of deep-sea shark
0:14:55 > 0:14:57have been discovered in Japanese waters.
0:14:59 > 0:15:01Some of them are found nowhere else.
0:15:09 > 0:15:12The underwater canyons stretching away from Mount Fiji
0:15:12 > 0:15:15appear to be a very special place for them,
0:15:15 > 0:15:17but they're rarely seen alive.
0:15:22 > 0:15:25In the last few years, Japanese film-makers have mounted
0:15:25 > 0:15:29a huge effort to capture deep-sea sharks on camera.
0:15:35 > 0:15:38They've been helped by the people who know this part of the ocean
0:15:38 > 0:15:42more intimately than anyone else - deep-sea fishermen.
0:15:52 > 0:15:55Under their guidance, the film-makers work out
0:15:55 > 0:15:58the most likely places to find deep-sea sharks.
0:15:58 > 0:16:01They load fish into a container mounted in front
0:16:01 > 0:16:03of a special camera.
0:16:03 > 0:16:06The whole assembly will then be left on the seabed for a day
0:16:06 > 0:16:09and record anything that comes for the bait.
0:16:11 > 0:16:15There's also a robot camera with a remotely controlled lens
0:16:15 > 0:16:18which can track an animal's movements,
0:16:18 > 0:16:21even so, it's a tough challenge.
0:16:43 > 0:16:45Over a four-year period,
0:16:45 > 0:16:50the two cameras are lowered to the sea floor more than 200 times.
0:16:59 > 0:17:03They're dropped at 20 promising locations.
0:17:03 > 0:17:06Each is a hot spot identified by a number of fishermen
0:17:06 > 0:17:09as the places where they've accidentally pulled up a shark
0:17:09 > 0:17:11from the depths.
0:17:18 > 0:17:22Some of these cameras produced very valuable pictures.
0:17:27 > 0:17:30It takes a while for the mud on the seabed to settle.
0:17:37 > 0:17:41But then, out of the darkness, drawn to the smell of the bait,
0:17:41 > 0:17:44comes a roughskin dogfish.
0:17:52 > 0:17:55It's nearly 1.5 metres long.
0:18:01 > 0:18:03Food here is scarce,
0:18:03 > 0:18:05so it's keen to get to the bait.
0:18:07 > 0:18:11Its intense eye-shine reveals one of the secrets of its success.
0:18:12 > 0:18:15It's the reflection from a mirror-like membrane
0:18:15 > 0:18:17which lies behind the eye
0:18:17 > 0:18:18and which enables them to see,
0:18:18 > 0:18:21even in extremely low levels of light.
0:18:25 > 0:18:28This is how it survives at such extreme depths,
0:18:28 > 0:18:31finding its prey in almost total darkness.
0:18:39 > 0:18:41In an even deeper part of the ocean canyon,
0:18:41 > 0:18:44they find a very different deep-sea shark.
0:19:05 > 0:19:09It's so huge, the camera can't get it all in picture.
0:19:12 > 0:19:15It's a Pacific sleeper shark
0:19:15 > 0:19:17and it's at least five metres long.
0:19:30 > 0:19:34Bait appears to stimulate it to start hunting.
0:19:39 > 0:19:43And it appears to be doing so by sucking up mud,
0:19:43 > 0:19:45perhaps searching for prey hidden there.
0:19:45 > 0:19:49A shark as big as this has never been seen doing such a thing before.
0:20:04 > 0:20:07Having left a remote camera trained on the whale experiment,
0:20:07 > 0:20:12the research team decide to investigate the seabed
0:20:12 > 0:20:15close to where HMS Challenger meet its original discoveries.
0:20:21 > 0:20:24Its images of the desert-like conditions
0:20:24 > 0:20:26on this part of the ocean floor
0:20:26 > 0:20:29show how tough it is to live down here,
0:20:29 > 0:20:31but they also reveal some of the traits
0:20:31 > 0:20:34which give deep-sea sharks an edge over their competitors.
0:20:41 > 0:20:44Perhaps none is stranger than this -
0:20:44 > 0:20:46a goblin shark.
0:20:49 > 0:20:52This long snouted shark was first described
0:20:52 > 0:20:55about the time of the Challenger's expedition,
0:20:55 > 0:20:58but it was some time before researchers discovered
0:20:58 > 0:21:01how these strange sharks find their prey.
0:21:05 > 0:21:07The skin just behind the long snout
0:21:07 > 0:21:11is covered with pores that contain special sensors.
0:21:11 > 0:21:14These detect the tiny amounts of electric current
0:21:14 > 0:21:17that flow across cell walls of all living things.
0:21:18 > 0:21:23They can register as little as 1 ten millionth of a volt,
0:21:23 > 0:21:26so even if prey attempts to hide in the mud on the sea floor,
0:21:26 > 0:21:27it is not safe.
0:21:33 > 0:21:35The goblin shark's extra-wide snout
0:21:35 > 0:21:37carries hundreds of these sensors
0:21:37 > 0:21:42and the fish uses it like a metal detector, sweeping the seabed,
0:21:42 > 0:21:45waiting for the electric impulse which tells it to strike.
0:22:11 > 0:22:13And what a strike!
0:22:16 > 0:22:20It certainly lives up to its other name - demon of the deep.
0:22:27 > 0:22:28In less than a second,
0:22:28 > 0:22:32its jaws shoot out of the rest of its skull to engulf its prey.
0:22:36 > 0:22:41It's the first time this remarkable bite has been seen so clearly.
0:22:46 > 0:22:49The extra reach gives the goblin shark
0:22:49 > 0:22:51a better chance of catching its food
0:22:51 > 0:22:54and that might make all the difference down here.
0:23:08 > 0:23:10The team is now looking for another shark
0:23:10 > 0:23:15which has evolved a different but equally effective feeding technique.
0:23:17 > 0:23:19Where the gorge falls away steeply,
0:23:19 > 0:23:23it's believed to live in the water just above the ocean floor.
0:23:34 > 0:23:36The frilled shark.
0:23:36 > 0:23:39When it was first discovered, it caused a sensation
0:23:39 > 0:23:43since it looks so like the sea serpents described in legend.
0:23:52 > 0:23:56Perhaps its face does look more like that of a snake than a shark.
0:24:00 > 0:24:02Needle-like teeth are arranged in lines,
0:24:02 > 0:24:04unlike those in any other shark,
0:24:04 > 0:24:08and may perhaps be particularly suited to snaring squid.
0:24:24 > 0:24:27The red frills which give the shark its name
0:24:27 > 0:24:30are extensions of its gills.
0:24:30 > 0:24:32The water at this depth and pressure
0:24:32 > 0:24:36contains half the amount of oxygen as water at the surface.
0:24:36 > 0:24:40These gills extending outside the shark's body
0:24:40 > 0:24:42expose a greater surface area of tissue to the water
0:24:42 > 0:24:45and so increase uptake of oxygen.
0:24:58 > 0:25:02These conditions within Japan's deep-water canyons
0:25:02 > 0:25:04have created peculiar forms of shark
0:25:04 > 0:25:07and that would be extraordinary enough,
0:25:07 > 0:25:10but, equally remarkable, is that the shark's appearance
0:25:10 > 0:25:13has changed little over tens of millions of years.
0:25:27 > 0:25:31Dr Henri Cappetta of Montpellier University in France
0:25:31 > 0:25:33has studied shark fossils
0:25:33 > 0:25:36and Earth history to work out how this could have happened.
0:25:42 > 0:25:47About 100 million years ago, dinosaurs dominated the land.
0:25:52 > 0:25:55This fossil dates from that period
0:25:55 > 0:25:57and it's an ancestor of the goblin shark.
0:26:02 > 0:26:04It looks very similar to its living descendant.
0:26:08 > 0:26:09TRANSLATION:
0:26:27 > 0:26:29In the 100 million years since then,
0:26:29 > 0:26:31the Earth's climate has changed.
0:26:33 > 0:26:37There were periods of great volcanic activity and meteor strikes...
0:26:39 > 0:26:42..which led to the mass extinctions of animals living on land
0:26:42 > 0:26:44or at the surface of the sea.
0:26:48 > 0:26:53But deep ocean canyons may have provided a stable sanctuary,
0:26:53 > 0:26:56where animals were under less pressure to evolve.
0:27:31 > 0:27:35In their various ways, the deep-water sharks were already
0:27:35 > 0:27:39well adapted to conditions in these deep-sea canyons,
0:27:39 > 0:27:41so now they appear to belong
0:27:41 > 0:27:45to another altogether more ancient world, as indeed they do.
0:27:49 > 0:27:52Although the team has now filmed many interesting species,
0:27:52 > 0:27:56one deep-sea shark remained a mystery.
0:28:03 > 0:28:07It was first discovered as recently as 1976,
0:28:07 > 0:28:10when one became tangled in the anchor ropes
0:28:10 > 0:28:13of a United States research vessel near Hawaii.
0:28:20 > 0:28:23It measured an astonishing 4.5 metres,
0:28:23 > 0:28:29but its mouth was an even bigger surprise at over a metre wide.
0:28:29 > 0:28:32It was called the megamouth shark.
0:28:40 > 0:28:44First to examine the shark's body was Dr Leighton Taylor.
0:28:44 > 0:28:47He remembers very well the impression it made on him.
0:28:51 > 0:28:55Wow! That's a mega-sized mouth!
0:28:55 > 0:28:58So Megamouth, big-mouth shark.
0:29:00 > 0:29:02I knew it was a shark,
0:29:02 > 0:29:06but it didn't fit into any group of sharks that I had ever seen before.
0:29:09 > 0:29:13This huge creature captured popular imagination
0:29:13 > 0:29:16and news of the find spread instantly around the world.
0:29:16 > 0:29:20It was confirmed as a new species of shark,
0:29:20 > 0:29:21a very rare discovery even then.
0:29:30 > 0:29:34But as Dr Taylor examined the carcass in more detail,
0:29:34 > 0:29:37he found something he had not seen in any other shark.
0:29:39 > 0:29:42When we first looked into the mouths of Megamouth,
0:29:42 > 0:29:47it was obvious it was different from the lining of other sharks' mouths.
0:29:47 > 0:29:49It was very silvery, very reflective.
0:29:49 > 0:29:52People were taking flash photographs
0:29:52 > 0:29:56and we noticed that the flashes would kind of light up this silvery lining,
0:29:56 > 0:29:58like a mirror or something.
0:30:02 > 0:30:03The upper jaw,
0:30:03 > 0:30:05that flap of skin,
0:30:05 > 0:30:07has those...
0:30:07 > 0:30:10what we think are bioluminescent organs on them.
0:30:10 > 0:30:13So it's kind of like baiting your trap with bright lights, you know,
0:30:13 > 0:30:15they attract things in.
0:30:15 > 0:30:17And we just don't know it for sure,
0:30:17 > 0:30:20but we think that's probably what likely happens.
0:30:23 > 0:30:27Dr Taylor suggested that organs along the Megamouth's upper jaw
0:30:27 > 0:30:29produce this light,
0:30:29 > 0:30:31which is reflected and amplified
0:30:31 > 0:30:34by the silvery skin that lines its mouth.
0:30:34 > 0:30:37Prey animals are attracted to the light, like moths to a flame,
0:30:37 > 0:30:39and then swallowed.
0:30:39 > 0:30:41But no-one knows for sure
0:30:41 > 0:30:44because hardly anyone has ever seen a megamouth alive.
0:30:48 > 0:30:52If you get a picture of a megamouth, I think you're all heroes!
0:30:52 > 0:30:54You know, automatic Academy Award.
0:30:56 > 0:30:57It's a tough call.
0:30:57 > 0:31:01Since the megamouth's discovery in 1976,
0:31:01 > 0:31:04only around 50 have been reported worldwide.
0:31:11 > 0:31:15But a third of these finds have been made near Japan...
0:31:17 > 0:31:21..and most of them were close to the deep sea canyons
0:31:21 > 0:31:22beyond Mount Fuji.
0:31:28 > 0:31:31If the team is to film such an elusive animal,
0:31:31 > 0:31:34then this, surely, is the best place to try.
0:31:37 > 0:31:41But how will they find even a giant shark in such a large area of sea?
0:31:47 > 0:31:50Shark expert Dr Sho Tanaka
0:31:50 > 0:31:53calls a meeting to work out the best plan.
0:31:53 > 0:31:55Possible three to four feet... AM and PM at the moment...
0:31:57 > 0:32:02Dr Tanaka knows more about the habits of Megamouths than anyone.
0:32:02 > 0:32:04Every time a specimen has been found,
0:32:04 > 0:32:08he has joined the investigating team to learn a little more about them.
0:32:16 > 0:32:21His years of painstaking research tell him that, to find a megamouth,
0:32:21 > 0:32:23he must first look for its prey.
0:32:41 > 0:32:43This expedition in a submersible
0:32:43 > 0:32:47is likely to be his best chance of seeing a megamouth alive.
0:32:52 > 0:32:54OK, coming up.
0:32:59 > 0:33:04Air is released from the tanks and the submersible descends.
0:33:18 > 0:33:22Soon they're almost beyond the reach of the sun's rays
0:33:22 > 0:33:25and the submersible switches on its searchlights.
0:33:29 > 0:33:32COMPUTER: Depth one-five-zero metres.
0:33:32 > 0:33:35They continue down to 200 metres
0:33:35 > 0:33:38and beyond into the rarely explored world
0:33:38 > 0:33:40known as the Twilight Zone.
0:33:42 > 0:33:44Surface, surface, this is Trident.
0:33:44 > 0:33:46We are passing two-zero-zero metres.
0:33:46 > 0:33:48Course is good...
0:33:51 > 0:33:54Here Dr Tanaka hopes to find the prey animals
0:33:54 > 0:33:56that will lead him to the megamouth.
0:34:21 > 0:34:24They see amazing creatures with translucent bodies...
0:34:26 > 0:34:29..but they are not what Dr Tanaka is looking for.
0:34:43 > 0:34:45The dive time is ticking past.
0:34:45 > 0:34:47Soon they will have to return.
0:34:52 > 0:34:53Oh!
0:34:53 > 0:34:55What's that one?
0:34:55 > 0:34:56Ah, it's beautiful.
0:34:58 > 0:34:59Be careful. There you go.
0:35:01 > 0:35:05Then a single Sakura shrimp darts in front of the sub.
0:35:10 > 0:35:12This is what he's been hoping to see.
0:35:13 > 0:35:16Sakura shrimps are small crustaceans
0:35:16 > 0:35:19that live a few hundred metres below the surface.
0:35:29 > 0:35:33One of these shrimps was discovered in the stomach of a Megamouth
0:35:33 > 0:35:36that Dr Tanaka was dissecting and this made him think
0:35:36 > 0:35:39that these shrimps might be an important element in their diet.
0:35:42 > 0:35:45The world's biggest concentration of Sakura shrimp
0:35:45 > 0:35:48is found in the deep seas around Mount Fuji.
0:35:52 > 0:35:55When Dr Tanaka superimposed the locations where megamouths
0:35:55 > 0:35:58have been discovered, on the habitats of the shrimp,
0:35:58 > 0:36:01he found a match which confirmed his idea.
0:36:02 > 0:36:05Now he hopes that the shrimp will lead him to the shark.
0:36:12 > 0:36:15The shrimp they just found has now disappeared,
0:36:15 > 0:36:17but Dr Tanaka thinks he knows where it's gone.
0:36:30 > 0:36:33The sub follows the shrimp up towards the surface.
0:36:46 > 0:36:48Depth 100 metres, over.
0:36:56 > 0:36:58And there they are.
0:37:02 > 0:37:0650 metres below the surface, there's a large school of them.
0:37:17 > 0:37:19Just as Dr Tanaka thought -
0:37:19 > 0:37:23the shrimp remain at depths during the day when surface predators
0:37:23 > 0:37:26are active and then, under the cover of night,
0:37:26 > 0:37:28they rise upwards to feed on plankton.
0:37:31 > 0:37:33He's hoping that a megamouth shark may follow them.
0:37:46 > 0:37:48On repeat dives, they do the same.
0:37:48 > 0:37:51They stay deep during the day
0:37:51 > 0:37:53and rise closer to the surface in the evening.
0:38:01 > 0:38:04But there's no sign of a megamouth.
0:38:04 > 0:38:07The chances of seeing one alive seem to be as slim as ever.
0:38:16 > 0:38:19But the team IS getting results from the sperm whale carcass
0:38:19 > 0:38:22which they dropped into a deep sea canyon
0:38:22 > 0:38:24at the start of the expedition.
0:38:24 > 0:38:27It's nine days since the drop
0:38:27 > 0:38:30and Dr Fujiwara is retrieving the remote camera
0:38:30 > 0:38:32which he left trained on the dead whale.
0:38:34 > 0:38:36Oh!
0:38:37 > 0:38:39I need 16 hands!
0:38:42 > 0:38:43It's a fiddly job,
0:38:43 > 0:38:46but the camera will have recorded how the carcass has changed
0:38:46 > 0:38:48and what have visited it.
0:39:04 > 0:39:08There will be a glimpse of a world no-one has seen before.
0:39:15 > 0:39:17The images from day seven
0:39:17 > 0:39:21show huge numbers of eels feasting on the whale.
0:39:23 > 0:39:25THEY SPEAK IN JAPANESE
0:39:34 > 0:39:36Oh!
0:39:40 > 0:39:44A giant bluntnose sixgill shark comes into view...
0:39:48 > 0:39:50..but to everyone's surprise,
0:39:50 > 0:39:53it takes just a nibble and then drifts away.
0:40:03 > 0:40:06An hour later, it returns.
0:40:06 > 0:40:10From the body markings, the team recognise it to be the same individual
0:40:10 > 0:40:13they discovered feeding here on day one.
0:40:13 > 0:40:15It keeps returning to the whale
0:40:15 > 0:40:17and taking the smallest of bites.
0:40:27 > 0:40:30Dr Tanaka thinks it may have established a territory
0:40:30 > 0:40:32around the whale and is guarding the prize,
0:40:32 > 0:40:35especially when, a little while later,
0:40:35 > 0:40:37it's seen circling the carcass.
0:40:47 > 0:40:49It's the first evidence we have
0:40:49 > 0:40:51that deep sea sharks are territorial
0:40:51 > 0:40:55and it might explain why it's the only shark to appear on the scene.
0:41:05 > 0:41:08The shark's behaviour has hidden benefits,
0:41:08 > 0:41:11for under the protection of this huge bluntnose sixgill,
0:41:11 > 0:41:15the carcass becomes a pit stop for other animals of the deep sea.
0:41:17 > 0:41:21A Japanese spider crab is the largest known arthropod in the world
0:41:21 > 0:41:24and only found here and at these depths.
0:41:27 > 0:41:32Watching these visitors, Dr Fujiwara learns something else.
0:41:32 > 0:41:36Without the bluntnose sixgill first ripping into the whale's skin,
0:41:36 > 0:41:40the flesh would not have been as accessible to the crabs,
0:41:40 > 0:41:43eels and urchins which have gathered here.
0:42:06 > 0:42:10These time-lapse images reveal this vital process
0:42:10 > 0:42:12for the very first time.
0:42:15 > 0:42:18It begins with that important first bite,
0:42:18 > 0:42:21taken by a large deep sea shark.
0:42:21 > 0:42:24The carcass then becomes a kind of temporary oasis,
0:42:24 > 0:42:26attracting smaller creatures.
0:42:34 > 0:42:37The shark takes bites from its meal when it needs to,
0:42:37 > 0:42:40but, like a big lion on a savanna,
0:42:40 > 0:42:42it keeps other voracious predators away.
0:42:49 > 0:42:52The experiment reveals that deep sea sharks
0:42:52 > 0:42:55are a cornerstone of life in the oceans.
0:43:02 > 0:43:06Meanwhile, Dr Tanaka has received some promising news.
0:43:06 > 0:43:09Local fishermen have reported a large, unusual shark
0:43:09 > 0:43:12swimming in shallow water near the coast.
0:43:14 > 0:43:17It could be a megamouth, so he hurries to the site.
0:43:22 > 0:43:24Evening.
0:43:24 > 0:43:26He's naturally curious.
0:43:34 > 0:43:38The full moon is illuminating a remarkable natural event.
0:43:48 > 0:43:53Dr Tanaka can see a seething mass of krill at the ocean's surface.
0:43:59 > 0:44:02Krill behave like Sakura shrimp.
0:44:02 > 0:44:05At night, they migrate to the upper layers of the ocean
0:44:05 > 0:44:06in order to feed on phytoplankton.
0:44:15 > 0:44:17Individual krill may be tiny,
0:44:17 > 0:44:18but in great numbers,
0:44:18 > 0:44:21they are the sort of food that would encourage a megamouth
0:44:21 > 0:44:25to swim from the deep sea almost to the surface.
0:44:40 > 0:44:43The underwater cameraman gets into the water
0:44:43 > 0:44:47and, soon after, something huge enters the pool of light.
0:45:11 > 0:45:14It is most definitely a megamouth.
0:45:14 > 0:45:16At last, we are face-to-face
0:45:16 > 0:45:18with this mysterious creature of the deep.
0:45:37 > 0:45:41This first meeting is taking place in very shallow water,
0:45:41 > 0:45:44but the megamouth appears unfazed by the attention,
0:45:44 > 0:45:46inquisitive even,
0:45:46 > 0:45:49and propels its five-metre body through the water
0:45:49 > 0:45:51at a leisurely pace.
0:46:17 > 0:46:21Perhaps it has every reason to feel relaxed.
0:46:21 > 0:46:25This is an animal that has pursued its ancient way of life
0:46:25 > 0:46:29unchanged through an immense segment of the Earth's history.
0:46:45 > 0:46:48It's teeth are no more than 5mm long.
0:46:50 > 0:46:53Since it has specialised on eating small creatures,
0:46:53 > 0:46:57such as Sakura shrimp and krill, it has no need of anything larger.
0:47:04 > 0:47:07Suddenly, it accelerates away,
0:47:07 > 0:47:09heading for a school of krill.
0:47:21 > 0:47:23It swims into the school
0:47:23 > 0:47:26and with a slight adjustment of direction
0:47:26 > 0:47:28turns to where the krill are most densely packed.
0:47:54 > 0:47:57So now the researchers can see how it feeds.
0:48:22 > 0:48:26For an instant, we can even see inside its huge mouth.
0:48:34 > 0:48:40A slow replay confirms Dr Taylor's original observations.
0:48:40 > 0:48:42Light carried by the camera operator
0:48:42 > 0:48:45is reflecting off the lining of the mouth
0:48:45 > 0:48:47so that the whole inside of the mouth glows.
0:48:54 > 0:48:58We can't be sure that it creates its own bioluminescence,
0:48:58 > 0:49:01but this glow is probably what attracts prey.
0:49:16 > 0:49:18It's taken over 30 years,
0:49:18 > 0:49:23but this is a very big step towards understanding this rare deep sea shark.
0:49:33 > 0:49:38If a creature as large as this can remain unknown until so recently,
0:49:38 > 0:49:42what other sharks could remain hidden out there in the deep?
0:50:01 > 0:50:03The encounter is a humbling reminder
0:50:03 > 0:50:06of how relatively little we still know about the oceans.
0:50:21 > 0:50:26Where the slopes of Mount Fuji extend down into the Pacific
0:50:26 > 0:50:29lie dramatic oceanic gorges
0:50:29 > 0:50:32that shelter a remarkable community of deepwater sharks.
0:50:39 > 0:50:43Their body patterns have scarcely altered over millennia.
0:50:43 > 0:50:46It's as if they've been living in a time capsule,
0:50:46 > 0:50:49while the earth has changed around them.
0:50:59 > 0:51:03They successfully adapted long ago to a harsh environment
0:51:03 > 0:51:05where food is hard to find
0:51:05 > 0:51:09and have been under little pressure to change ever since.
0:51:11 > 0:51:13They may look primitive,
0:51:13 > 0:51:16but they are highly specialised and successful.
0:51:16 > 0:51:19Nothing since has been able to compete with them.
0:51:22 > 0:51:27And they may yet lead us to further revelations about this,
0:51:27 > 0:51:29the least explored part of our planet.