0:00:02 > 0:00:05They cover two-thirds of our planet.
0:00:07 > 0:00:11They hold clues to the mysteries of our past.
0:00:11 > 0:00:15And they are vital for our future survival.
0:00:18 > 0:00:23But the secrets of our oceans have remained largely undiscovered.
0:00:23 > 0:00:28I am with a shark. Yes! Yes!
0:00:28 > 0:00:32Explorer, Paul Rose, is leading a team of ocean experts
0:00:32 > 0:00:36on a series of underwater science expeditions.
0:00:36 > 0:00:41For a year, the team has voyaged across the world to build up
0:00:41 > 0:00:43a global picture of our seas.
0:00:43 > 0:00:46We are doing some pretty uncharted research here.
0:00:46 > 0:00:49That is psychedelically purple!
0:00:49 > 0:00:51We are here to try and understand
0:00:51 > 0:00:54the Earth's oceans and put them in a human scale.
0:00:56 > 0:00:59Our oceans are changing faster than ever.
0:00:59 > 0:01:02I've never seen ice like this before.
0:01:04 > 0:01:07There has never been a better time to explore the last true
0:01:07 > 0:01:10wilderness on earth.
0:01:18 > 0:01:21Tanzania, east Africa.
0:01:22 > 0:01:24The team has come to the edge of a continent,
0:01:24 > 0:01:27where the full force of the Indian Ocean
0:01:27 > 0:01:29collides with the African coast.
0:01:36 > 0:01:40The Indian Ocean links Africa and Asia.
0:01:40 > 0:01:44It has over 44,000 miles of shoreline.
0:01:46 > 0:01:49And its coastal waters support habitats
0:01:49 > 0:01:53that are home to an enormous diversity of marine life.
0:01:58 > 0:02:01But its coasts throng with people.
0:02:01 > 0:02:0440 million live along its western edge alone,
0:02:04 > 0:02:08making the vibrant coastal waters of this ocean
0:02:08 > 0:02:11particularly vulnerable to man's impact.
0:02:11 > 0:02:12The sea can never
0:02:12 > 0:02:15be considered a discreet entity from the land.
0:02:15 > 0:02:17The two are completely interconnected
0:02:17 > 0:02:20and nowhere more so than the coastal zone.
0:02:22 > 0:02:26So the team has come to the rich waters of the Spice Islands,
0:02:26 > 0:02:29an intense meeting point of man and sea.
0:02:31 > 0:02:36They are here to explore this fragile relationship and to discover
0:02:36 > 0:02:39what this ocean can do for man.
0:02:39 > 0:02:41We know so little about these animals.
0:02:41 > 0:02:44And what man might be doing to this ocean.
0:02:51 > 0:02:54Marine biologist and oceanographer Tooni Mahto will take part in a
0:02:54 > 0:03:00pioneering experiment, to see how a coastal creature could help predict
0:03:00 > 0:03:01natural disasters.
0:03:03 > 0:03:07All of this is data of what's been happening in the ocean
0:03:07 > 0:03:12and the atmosphere over the past 40 years or so.
0:03:12 > 0:03:18Maritime archaeologist, Dr Lucy Blue, will dive a sunken medieval village,
0:03:18 > 0:03:24to search for evidence that these waters brought wealth and prosperity.
0:03:24 > 0:03:29I can't get over how much stuff's here, look at this.
0:03:31 > 0:03:36And environmentalist Philippe Cousteau, grandson of ocean pioneer
0:03:36 > 0:03:42Jacques Cousteau, will discover how man is threatening a coastal giant.
0:03:42 > 0:03:46The world's largest fish.
0:03:46 > 0:03:50I think it's one of those things like erm...the polar bears, that
0:03:50 > 0:03:54I want to see before they're gone.
0:04:08 > 0:04:12Their first mission is to dive the submerged cliffs
0:04:12 > 0:04:14around the Island of Pemba.
0:04:14 > 0:04:19These rise steeply from the seafloor 800m below,
0:04:19 > 0:04:22and are the collision point for the mighty tides
0:04:22 > 0:04:25and currents of the Indian Ocean.
0:04:30 > 0:04:32This is a very old island,
0:04:32 > 0:04:35it broke away from the mainland over 10 million years ago.
0:04:35 > 0:04:39So in that 10 million years it's been attacked from all sides by the water currents.
0:04:39 > 0:04:42It seems like the perfect place to sort of have a look
0:04:42 > 0:04:49at how currents and tides and geology all interact in one location.
0:04:49 > 0:04:52And, er, you know, feel the full force of the ocean.
0:04:54 > 0:04:59Tooni and Paul are going to explore a geological feature here,
0:04:59 > 0:05:03a submerged fracture, scored into the rock.
0:05:06 > 0:05:11They want to discover what happens when land and sea collide.
0:05:13 > 0:05:15How you doing Tooni, all right, mate?
0:05:15 > 0:05:17Man, feel those currents, eh?
0:05:21 > 0:05:23They dive down the edge of the island,
0:05:23 > 0:05:25an underwater cliff-face,
0:05:25 > 0:05:29to see how the power of the Indian Ocean can shape the land.
0:05:30 > 0:05:33This is a rare opportunity.
0:05:33 > 0:05:36Behind me and 800m down
0:05:36 > 0:05:39is the bottom of the Pemba African Rift,
0:05:39 > 0:05:44which separates this from the continent of Africa.
0:05:48 > 0:05:51They soon find the fissure.
0:05:53 > 0:05:58A vast crack, 30m long and 30m deep.
0:06:14 > 0:06:17This is an erosional feature, this particular fissure.
0:06:17 > 0:06:22And what it is is a weakness in the rock that has been forced in
0:06:22 > 0:06:25by the continual movement of water over the years.
0:06:25 > 0:06:29The current is just taking us in here.
0:06:29 > 0:06:32We...we're working quite hard to not be pushed
0:06:32 > 0:06:35too deep into this deep fissure.
0:06:35 > 0:06:39And it feels very different to the wall outside.
0:06:39 > 0:06:42Even just a casual glance, you can
0:06:42 > 0:06:46just see that it's a different life-form inside this fissure.
0:06:51 > 0:06:54They've entered an oceanic recess,
0:06:54 > 0:06:57an ecosystem teaming with life.
0:07:01 > 0:07:06Shoals of sea goldies, darting mimic blennies
0:07:06 > 0:07:08and two bar anemone fish.
0:07:11 > 0:07:13The same currents that carved the land
0:07:13 > 0:07:15have brought life to this fissure.
0:07:15 > 0:07:19Currents that have travelled thousands of miles
0:07:19 > 0:07:21across the Indian Ocean.
0:07:22 > 0:07:26A lot of these organisms may have arrived on one of
0:07:26 > 0:07:28the giant Indian ocean currents.
0:07:28 > 0:07:30So say for example a larvae
0:07:30 > 0:07:34started off in Indonesia, it would have taken about 5 months to cross
0:07:34 > 0:07:37the entire Indian Ocean right to the east coast of Africa
0:07:37 > 0:07:40and then smacked up against this vertical wall face.
0:07:40 > 0:07:45And that's led to this amazing diversity of creatures and colours
0:07:45 > 0:07:47and life forms that you can see.
0:07:49 > 0:07:51Deep inside the fissure,
0:07:51 > 0:07:55they can see the extent of this stunning vertical reef.
0:07:55 > 0:07:58Look at these tree corals.
0:07:58 > 0:08:01Normally, sunlight is vital for a healthy reef,
0:08:01 > 0:08:06but life here is especially adapted to living in the shadows.
0:08:07 > 0:08:12This is the green tree coral, aptly named because it's very dark green.
0:08:12 > 0:08:14And the reason why it can grow here
0:08:14 > 0:08:19and do so well here is because it doesn't contain any algae at all.
0:08:19 > 0:08:22Most corals are half-plant, half-animal
0:08:22 > 0:08:27whereas this one is purely animal and it's absolutely beautiful.
0:08:28 > 0:08:30Because it contains no algae,
0:08:30 > 0:08:34this coral doesn't depend on sunlight for survival.
0:08:36 > 0:08:38Like the rest of the life here,
0:08:38 > 0:08:42it feeds on the organisms brought in by the currents.
0:08:44 > 0:08:48Most of them are filter feeding, which means they're grabbing
0:08:48 > 0:08:51particles out of the water and feeding on them.
0:08:51 > 0:08:55And the reason why there are so many filter-feeding organisms is
0:08:55 > 0:08:58because there's so much water being forced in,
0:08:58 > 0:09:02food and nutrients are racing past it.
0:09:02 > 0:09:06Which is kind of like pizza delivery in an oceanic context.
0:09:09 > 0:09:14In contrast to the deep and largely barren open seas, the
0:09:14 > 0:09:19collision of land and ocean currents creates the rich ecosystems
0:09:19 > 0:09:22that characterise these coastal waters.
0:09:23 > 0:09:28You can actually see the currents in action and how important they are to
0:09:28 > 0:09:32the marine life of the area because without that bringing the larvae of
0:09:32 > 0:09:35- those encrusting organisms, there'd be no life forms there at all.- No.
0:09:35 > 0:09:37These currents help sustain
0:09:37 > 0:09:41one of the most important ecosystems in the ocean -
0:09:41 > 0:09:43the coral reef.
0:09:54 > 0:09:57Coral reefs support a quarter of all fish species
0:09:57 > 0:10:00and help support the coastal people here.
0:10:00 > 0:10:06But fishing, tourism and pollution are putting reefs under pressure.
0:10:07 > 0:10:12So environmentalist Philippe Cousteau wants to find out
0:10:12 > 0:10:14if the corals here are healthy.
0:10:16 > 0:10:19And one of the best ways to do that is to dive at night.
0:10:19 > 0:10:23It brings the coral alive at night in a way the daytime can't.
0:10:23 > 0:10:27I mean, one of the biggest challenges we always face is trying
0:10:27 > 0:10:30to get people to understand that coral reefs are alive,
0:10:30 > 0:10:31They're not just rocks.
0:10:31 > 0:10:34If you dive the same reef in the daytime and the same reef
0:10:34 > 0:10:38at night time, it's like diving on two completely separate reefs.
0:10:43 > 0:10:46But diving at night can be hazardous.
0:10:46 > 0:10:48A night dive is a lot more dangerous.
0:10:48 > 0:10:51You can't see your partner, if something goes on with lights.
0:10:51 > 0:10:54And at night, when it's pitch black underwater, you can get even,
0:10:54 > 0:10:58you know, confused and turned around about which direction is up.
0:10:58 > 0:11:01So if you're running low on air and don't have lights,
0:11:01 > 0:11:04you end up going in wrong direction, it's a bad thing.
0:11:04 > 0:11:07They have to prepare quickly for the dive.
0:11:07 > 0:11:10In the tropics, night falls fast.
0:11:10 > 0:11:14The sun's going down, it's gonna... and at this latitude, it just drops
0:11:14 > 0:11:19like a stone. So I need to get the night dive away right now.
0:11:19 > 0:11:22Very messy, boats along the side here and er...
0:11:22 > 0:11:24loads of activity and it's all been sorted out at once,
0:11:24 > 0:11:28so I'm in a big push to get everybody off and things happening.
0:11:28 > 0:11:29OK?
0:11:36 > 0:11:41At dusk, Tooni and Philippe set off to examine the reef.
0:11:57 > 0:12:00When you point your torch out left, all you see
0:12:00 > 0:12:03is inky, murky blackness.
0:12:19 > 0:12:22Just look at size of these table corals, they're so big,
0:12:22 > 0:12:24- it's awesome!- They're huge!
0:12:24 > 0:12:28It really is. I have never seen table corals this big in my life.
0:12:28 > 0:12:31But you just, you just look up and they're everywhere.
0:12:33 > 0:12:35Seeing so many large corals
0:12:35 > 0:12:39is a positive sign that this reef is healthy.
0:12:41 > 0:12:46This, right here, is such a perfect example...
0:12:46 > 0:12:51of just how vibrant and thick and diverse this whole area is.
0:12:51 > 0:12:54I mean, look at this different grouping of corals.
0:12:56 > 0:13:00Coral reefs are the most bio-diverse ecosystem on the planet,
0:13:00 > 0:13:04even more so than a rainforest.
0:13:06 > 0:13:09They're surrounded by many different varieties of coral,
0:13:09 > 0:13:11from this favia...
0:13:12 > 0:13:14..to acroporara.
0:13:17 > 0:13:20And by diving at night,
0:13:20 > 0:13:23Philippe and Tooni can gauge the health of the coral,
0:13:23 > 0:13:28because the animal part, the polyp, emerges to feed.
0:13:28 > 0:13:33One of the reasons I love night dives is because
0:13:33 > 0:13:36you can really see all these little arms, these little tentacles,
0:13:36 > 0:13:39that open up during the night-time, and during the day
0:13:39 > 0:13:44those are completely encircled, completely closed,
0:13:44 > 0:13:46pulled back into the coral polyp.
0:13:51 > 0:13:55Many corals have tentacles, armed with stinging cells,
0:13:55 > 0:13:58that reach out at night to hunt their prey.
0:14:11 > 0:14:16Nutrients are transported from the depths by the currents.
0:14:25 > 0:14:27But the tidal currents are about to change,
0:14:27 > 0:14:29and that's worrying Paul.
0:14:29 > 0:14:33Dive team, dive team, Kairos here, copy?
0:14:33 > 0:14:36There are communication problems.
0:14:36 > 0:14:38Dive team, Kairos, how copy?
0:14:40 > 0:14:42It's a strong, strong current and
0:14:42 > 0:14:48it's shortly due to change back the other way, so we'll all be affected.
0:14:48 > 0:14:51You know, my divers and this ship are all going to be affected
0:14:51 > 0:14:53by these changing currents.
0:14:53 > 0:14:57Err, with bad communication as well, and the risks that occur with
0:14:57 > 0:15:01night-diving, it just gives me the willies a bit, you know?
0:15:01 > 0:15:05I do need decent regular, reliable communication, I haven't got it
0:15:05 > 0:15:06at the moment.
0:15:06 > 0:15:12Underwater, Tooni and Philippe are unaware of Paul's concerns.
0:15:12 > 0:15:15They've spotted something that could be part of the
0:15:15 > 0:15:17secret of this reef's success.
0:15:18 > 0:15:22So there's two different species of coral growing here,
0:15:22 > 0:15:25one of which is the much slower growing species,
0:15:25 > 0:15:27which is the big coral in the middle.
0:15:28 > 0:15:32These two corals are engaged in battle.
0:15:32 > 0:15:36What the slower growing coral is doing is emitting toxins
0:15:36 > 0:15:38via it's stinging cells
0:15:38 > 0:15:43that prevent the much larger, faster growing table corals overgrowing it.
0:15:46 > 0:15:51Corals use chemical and biological warfare.
0:15:51 > 0:15:52By reaching out with their
0:15:52 > 0:15:58stomachs from within the polyps, the aggressors can digest their rivals.
0:16:02 > 0:16:07During the night, conflicts like these are fought across our oceans,
0:16:07 > 0:16:11as corals compete for position and maximum exposure to the sun.
0:16:15 > 0:16:19In a coral reef, it's location, location, location.
0:16:19 > 0:16:23It's all about where you are and so these corals are literally battling
0:16:23 > 0:16:25it out over prime real estate.
0:16:25 > 0:16:28To, to try to get access to sunlight.
0:16:28 > 0:16:31I love this reef, I love this reef.
0:16:31 > 0:16:35It is one of the most incredible reefs I've ever seen,
0:16:35 > 0:16:37no question about that.
0:16:41 > 0:16:44The nightly battles between different species prevent
0:16:44 > 0:16:46any one coral from dominating.
0:16:48 > 0:16:53This creates diversity, which helps this reef remain healthy.
0:16:54 > 0:16:59A healthy diverse reef is home to many marine species,
0:16:59 > 0:17:03which in turn, help feed the people who live on the coast.
0:17:08 > 0:17:10- Ahhh, it's just so rich and diverse.- I know.
0:17:10 > 0:17:15All the different types of coral and you could really see them coming out
0:17:15 > 0:17:18with their little tentacles in the water and there's crinoids
0:17:18 > 0:17:20and, oop, you just got a fish in the face!
0:17:20 > 0:17:23They're jumping all over the place.
0:17:26 > 0:17:30With everyone back on board, Paul leads the expedition south.
0:17:33 > 0:17:37They're going to Zanzibar, to carry out a pioneering experiment
0:17:37 > 0:17:40that could help protect people from the destructive forces
0:17:40 > 0:17:44of the extreme weather than can rage in the Indian Ocean.
0:17:46 > 0:17:48So all the dive stuff is gonna go here...
0:17:48 > 0:17:49Dive stuff'll be all right there,
0:17:49 > 0:17:52doesn't need to be lashed down, cos the forecast is good.
0:17:55 > 0:17:58The Indian Ocean is the engine for some of the most
0:17:58 > 0:18:01unpredictable weather on the planet.
0:18:01 > 0:18:05It can trigger floods, droughts and famine.
0:18:07 > 0:18:12Heavy rains are caused as warm water evaporates from the surface
0:18:12 > 0:18:16of the sea, which can reach 28 degrees centigrade.
0:18:17 > 0:18:21The rapid changes in air pressure create spiralling winds.
0:18:21 > 0:18:25In extreme conditions, this can produce cyclones.
0:18:27 > 0:18:31The waters off Zanzibar might hold information that could help protect
0:18:31 > 0:18:37millions of people against these potentially catastrophic storms.
0:18:40 > 0:18:46But as the team arrives, their boat is stopped by the port authorities.
0:18:46 > 0:18:48The climate study is forced to wait.
0:18:49 > 0:18:52We're under pressure to move our boat, the Kairos,
0:18:52 > 0:18:55into the harbour and the reason for that is
0:18:55 > 0:18:57the port authorities want to check
0:18:57 > 0:19:01we've got all our permits and all our paperwork straight.
0:19:01 > 0:19:04It's gripping stuff really, because if they don't like us
0:19:04 > 0:19:09or they've had really, really bad day and then don't like anybody,
0:19:09 > 0:19:13that could put a stop on the expedition I think, dead easy,
0:19:13 > 0:19:17they could certainly impound the, this ship and that would
0:19:17 > 0:19:19effectively stop the expedition.
0:19:19 > 0:19:21It's a problem.
0:19:22 > 0:19:26The authorities escort the team into the harbour at Stone Town -
0:19:26 > 0:19:28the capital of Zanzibar.
0:19:29 > 0:19:31Their boat is detained.
0:19:36 > 0:19:41They can't continue unless it's released, so, expedition leader
0:19:41 > 0:19:44Paul will have to go ashore to confront the authorities.
0:19:56 > 0:20:00Paul and ship's captain Fabrice have no idea what to expect.
0:20:00 > 0:20:03It's the old story when you do these trips.
0:20:03 > 0:20:08Some of them just go like clockwork, some look like hell but they all went brilliantly.
0:20:08 > 0:20:10And there's others the other way around.
0:20:10 > 0:20:15You know, there's no control over these situations, and that's difficult. We've got no control.
0:20:15 > 0:20:17Oh, we've got to wait, that's bad news.
0:20:17 > 0:20:19Ok, show the permit.
0:20:28 > 0:20:34Time's getting on, if he doesn't get an answer in a few minutes...
0:20:35 > 0:20:36then let's just walk in.
0:20:36 > 0:20:38Because at least we're in.
0:20:38 > 0:20:40Yeah.
0:20:43 > 0:20:46Without the harbour master's stamp on the papers,
0:20:46 > 0:20:48the expedition is going nowhere.
0:20:50 > 0:20:56The enforced stopover means maritime archaeologist Dr Lucy Blue
0:20:56 > 0:21:01can investigate how this ocean's been used by man for centuries.
0:21:01 > 0:21:06For trade, transport, and as a source of food.
0:21:09 > 0:21:11I mean, this has been like this for,
0:21:11 > 0:21:14since, since the Muslims arrived, since people have
0:21:14 > 0:21:17been trading through Zanzibar, this is what you'd expect to see.
0:21:17 > 0:21:20It is so rare to find a harbour where, effectively,
0:21:20 > 0:21:24the majority of boats here are just entirely made out of wood,
0:21:24 > 0:21:27they don't have engines in them, they go out of this harbour
0:21:27 > 0:21:30and they go up the coast of east Africa and over to Arabia
0:21:30 > 0:21:32completely under sail.
0:21:36 > 0:21:38Hey, we're in, thank you.
0:21:38 > 0:21:42Now the whole expedition hangs on Paul's meeting
0:21:42 > 0:21:44with the harbour master.
0:21:55 > 0:21:58Nine crew, huh?
0:21:58 > 0:22:03- She will tell me. - We pay, and she will tell you?
0:22:03 > 0:22:04Ok, you can go, bye.
0:22:06 > 0:22:09Thank you very much.
0:22:10 > 0:22:12Freedom!
0:22:17 > 0:22:20The expedition is back on course
0:22:20 > 0:22:23and the team can finally begin the climate study.
0:22:26 > 0:22:30They're about to take part in ground-breaking research,
0:22:30 > 0:22:34to try and predict the violent storms that strike this coastline.
0:22:39 > 0:22:41Welcome, hi, you're Jens.
0:22:42 > 0:22:46They'll be working with an international group of coral scientists.
0:22:48 > 0:22:53Surprisingly, coral holds a unique record of climate information.
0:22:53 > 0:22:57What we're really looking for is to get his boat
0:22:57 > 0:22:59just as close in as possible.
0:22:59 > 0:23:05So they're going to drill samples of the coral here for the first time.
0:23:05 > 0:23:10We have a lot of data from the open ocean, but we haven't got much data
0:23:10 > 0:23:12from the African coast.
0:23:14 > 0:23:16All seated up and ready to go.
0:23:16 > 0:23:18Tooni's on the way here.
0:23:25 > 0:23:28Scientists have realised that as coral grows it's affected
0:23:28 > 0:23:30by different weather conditions,
0:23:30 > 0:23:35so its growth pattern over the years creates a record of past climate.
0:23:36 > 0:23:40And that could be used to predict future weather.
0:23:41 > 0:23:44- I'll go low.- OK, mate.
0:23:44 > 0:23:48Coral grows at about one centimetre a year.
0:23:48 > 0:23:51So the larger it is, the older it is.
0:23:51 > 0:23:53Yeah, got it Tooni.
0:23:54 > 0:23:56It's 3m 10cm.
0:23:56 > 0:24:01So that lump there is over 300 years old.
0:24:04 > 0:24:06Locked inside this coral
0:24:06 > 0:24:10is a detailed record of three centuries of local weather.
0:24:11 > 0:24:15We've got a perfect 300 year data set.
0:24:18 > 0:24:20And to get that information,
0:24:20 > 0:24:24they need to drill a core to the heart of the coral.
0:24:24 > 0:24:29Yeah, we've got to steady this drill here or it's just going to run around.
0:24:29 > 0:24:32Once we get er...a couple of inches down it will steady itself,
0:24:32 > 0:24:34but we've gotta steady it now.
0:24:38 > 0:24:39Coral has growth bands within it.
0:24:39 > 0:24:43Like tree rings, each band is a year's growth,
0:24:43 > 0:24:46so the coral can be aged accurately.
0:24:48 > 0:24:52That's the first coral core out.
0:24:52 > 0:24:54There's the first one.
0:24:54 > 0:24:57This is the only live bit of this whole section.
0:24:57 > 0:25:02All of this is dead material, so you can see, that's why this coral
0:25:02 > 0:25:06can recover quite quickly from a process that looks quite destructive.
0:25:06 > 0:25:11And all of this is data of what's been happening in the ocean
0:25:11 > 0:25:16and the atmosphere, over the past roughly 40 years or so.
0:25:16 > 0:25:18And in the end,
0:25:18 > 0:25:23they'll have a whole three metres worth and a whole 300 years of data.
0:25:23 > 0:25:26Shall we get this darkened up?
0:25:27 > 0:25:32Back on the ship, Lucy and Philippe are preparing a dark room to examine the coral.
0:25:32 > 0:25:34So apparently this is best if we lay it out,
0:25:34 > 0:25:37because you can see the coral.
0:25:41 > 0:25:47So far, they've drilled out a 40 year record of the climate.
0:25:47 > 0:25:51But to predict the future weather accurately they need to
0:25:51 > 0:25:53go much further back in time.
0:25:56 > 0:26:00Right, that is the second piece of core that we've got.
0:26:00 > 0:26:05Hey, here's our number 2, that's our second one, there's the top.
0:26:10 > 0:26:14They'll begin to analyse the centuries of climate information
0:26:14 > 0:26:16on board the expedition ship.
0:26:23 > 0:26:27Oceanographer Craig Grove is using a new technique
0:26:27 > 0:26:32to "read" the weather data from this core with ultra-violet light.
0:26:32 > 0:26:37When you get the monsoon coming over, a large amount of rainfall,
0:26:37 > 0:26:40you get these luminescent bandings that occur.
0:26:41 > 0:26:47The UV light reveals bright bands which are formed during heavy rains.
0:26:47 > 0:26:51Well, the brightest bands indicate the most extreme wet weather
0:26:51 > 0:26:53and that's what we're looking for.
0:26:53 > 0:26:59And by counting these bands we can date these climate events
0:26:59 > 0:27:01and when they occur.
0:27:01 > 0:27:06So you can find the Ras Kisimani event. So we want 1872.
0:27:06 > 0:27:081872.
0:27:08 > 0:27:13Lucy is keen to see if she can identify one particular cyclone
0:27:13 > 0:27:17that wiped out an important trading settlement here.
0:27:17 > 0:27:22So they count back almost 140 years along the core.
0:27:22 > 0:27:25And we're going to see a wider band or a denser band?
0:27:25 > 0:27:28Yeah, well it depends on the intensity of the rain.
0:27:28 > 0:27:31If it was a cyclone it would be quite bright and if it was
0:27:31 > 0:27:33prolonged it would be quite wide.
0:27:33 > 0:27:38- But, well already, you can see a glow coming right from that.- Yeah.
0:27:38 > 0:27:39That's exactly it, yeah.
0:27:39 > 0:27:41That's a really bright, wide band.
0:27:41 > 0:27:47You can see it can't you? That means there was intense rainfall that year.
0:27:47 > 0:27:49Now that could well be a cyclone.
0:27:53 > 0:27:57By studying the coral record to find patterns of extreme weather
0:27:57 > 0:28:01in the past, they hope to develop more accurate computer forecasting.
0:28:04 > 0:28:08That will help the people living here by enabling them
0:28:08 > 0:28:12to prepare for potentially devastating weather.
0:28:24 > 0:28:28After hours in a dark room, with no air conditioning,
0:28:28 > 0:28:30the whole team gets a chance to cool off.
0:28:33 > 0:28:35But Paul's mind is elsewhere.
0:28:35 > 0:28:38We're gonna go early because the crabs come at sunset.
0:28:40 > 0:28:43He's heard the biggest land crabs in the world
0:28:43 > 0:28:47live on a nearby island, so he and Tooni are going to see them.
0:28:47 > 0:28:50But he's far from relaxed.
0:28:50 > 0:28:53He's got this unbelievable fear of beasties.
0:28:53 > 0:28:55Doesn't like tentacles or legs.
0:28:55 > 0:28:59And, ha-ha - there's these very, very large land crabs
0:28:59 > 0:29:02and we're gonna go and have a look, and see if we can find any of them.
0:29:02 > 0:29:07Do you have...um, a big machete would be ideal.
0:29:07 > 0:29:10A big, an axe or something...
0:29:12 > 0:29:14Perfect, that's perfect!
0:29:15 > 0:29:18Thanks very much, that's great.
0:29:20 > 0:29:25Coconut crabs begin life in the ocean before moving onshore.
0:29:25 > 0:29:30They weigh up to four kilograms and can have a leg-span of over a metre.
0:29:32 > 0:29:34Hey, Paul. I think we should stop here.
0:29:34 > 0:29:38- Good a place as any.- This looks like good crab-hunting territory.
0:29:38 > 0:29:42Because they're a prized local delicacy,
0:29:42 > 0:29:45on some islands, they've been hunted to extinction.
0:29:47 > 0:29:53So Paul and Tooni want to find out how healthy this population is.
0:29:53 > 0:29:56Hey! Right, get some coconut milk spread around
0:29:56 > 0:29:59I reckon because they'll love that.
0:29:59 > 0:30:02Now we're using these because this is their preferred food.
0:30:02 > 0:30:05- Yeah, they love it. They can smell it.- They can scent it.
0:30:05 > 0:30:09They'll use infra-red light to film undetected.
0:30:09 > 0:30:12Can you hear them creeping up on you though?
0:30:12 > 0:30:16Well, of course, now we've turned our lights off
0:30:16 > 0:30:19- there's a lot of noise.- Oh, man, I can hear, I can hear rustling close.
0:30:19 > 0:30:21- Hang on then, hang on.- Shh...
0:30:27 > 0:30:30I tell you what, it's a bit spooky actually.
0:30:30 > 0:30:33Can you hear that creeping? Can you hear the rustling?
0:30:33 > 0:30:36Oh! Oh my, there's a crab!
0:30:36 > 0:30:40There's a crab! Look at the size of that beast.
0:30:40 > 0:30:42You're dead right. Is it worth getting up there
0:30:42 > 0:30:45- with our torches and getting it? - Yeah.- Shall we go for it?
0:30:45 > 0:30:49- OK. They're sharing it. - That's so so neat.
0:30:49 > 0:30:52They're scraping it out with their claws
0:30:52 > 0:30:56and then passing it to their feeding parts.
0:30:56 > 0:30:59The way it's actually wedging itself into the fossilised coral.
0:31:01 > 0:31:04The largest of these creatures
0:31:04 > 0:31:08can lift weights of up to 28 kilograms.
0:31:08 > 0:31:11- They are prehistoric looking creatures.- Here it goes!
0:31:11 > 0:31:13Go on... They're just pulling that, look.
0:31:13 > 0:31:19Their respiratory organs are in-between gills and lungs.
0:31:19 > 0:31:24They're a species in mid-evolution, halfway between land and sea.
0:31:24 > 0:31:28They've obviously evolved into land crabs, but originally
0:31:28 > 0:31:31they were brought here on Indian Ocean currents.
0:31:31 > 0:31:35But there's still a direct connection between these and the sea, because
0:31:35 > 0:31:40when they deposit their larvae, they need to deposit them in the sea.
0:31:40 > 0:31:42And the larvae grow and develop,
0:31:42 > 0:31:46and when the time is right, when they reach a certain maturation point,
0:31:46 > 0:31:49they'll come back onto land, and that's where they'll grow
0:31:49 > 0:31:51- into these that we see here.- Got it.
0:31:51 > 0:31:53There are two kinds of these crabs.
0:31:53 > 0:31:58There are the blue coloured ones and the slightly reddish ones...
0:31:58 > 0:32:02- Like this guy.- ..a distinctive orange. Their presence shows
0:32:02 > 0:32:05- that it's a healthy population, so they're doing well here. - That's great news.
0:32:05 > 0:32:11The presence of both varieties here means the population is thriving.
0:32:11 > 0:32:16That could be a good sign for the species, because the larvae produced
0:32:16 > 0:32:20by this population will be spread by the Indian Ocean
0:32:20 > 0:32:23and could help repopulate other islands.
0:32:23 > 0:32:25It's friendlier than I imagined in my nightmares.
0:32:25 > 0:32:27Paul Rose, I'm very proud of you.
0:32:41 > 0:32:44Land crabs are just one of the species threatened
0:32:44 > 0:32:48by increasing human pressure along these densely populated coastlines.
0:32:51 > 0:32:53The team is now heading south
0:32:53 > 0:32:55to search for one of the most vulnerable
0:32:55 > 0:32:59coastal species.
0:32:59 > 0:33:03One that lives in shallow mangrove lagoons.
0:33:03 > 0:33:08A species at the mercy of an immense global trade -
0:33:08 > 0:33:10the seahorse.
0:33:10 > 0:33:15Seahorses are getting wiped out in many cases. All around the world, wherever they can be caught.
0:33:15 > 0:33:21So to explore the issue and also contribute a little bit to science
0:33:21 > 0:33:26and to conservation science, is really special.
0:33:26 > 0:33:28In one year, it was estimated
0:33:28 > 0:33:32that as many as a quarter of a million seahorses
0:33:32 > 0:33:36were exported from Tanzanian waters. The trade is driven
0:33:36 > 0:33:39by the huge demand for them in traditional Eastern medicines.
0:33:39 > 0:33:44Seahorses are highly prized around the world for multiple different reasons.
0:33:44 > 0:33:47Eastern cultures use them for aphrodisiacal properties,
0:33:47 > 0:33:51they use them for medicinal reasons.
0:33:51 > 0:33:54So they're being heavily hunted still around the world.
0:33:56 > 0:33:58The team will assess the impact of the trade
0:33:58 > 0:34:03by collecting information about this seahorse population.
0:34:03 > 0:34:08Very little is known about the species that exist here or the numbers that exist here.
0:34:08 > 0:34:12And obviously with lack of baseline data, it's then therefore difficult
0:34:12 > 0:34:16to assess if these populations are in any way endangered.
0:34:16 > 0:34:22Their first task is to find a boat big enough to take them and their equipment into the shallow lagoons
0:34:22 > 0:34:25where the seahorses live.
0:34:28 > 0:34:30This sort of thing would be quite good.
0:34:30 > 0:34:33- About the right size? - Yeah, I think so, don't you?
0:34:33 > 0:34:36The waters around the Spice Islands are home to one of the largest
0:34:36 > 0:34:39traditionally made boating fleets in the world.
0:34:43 > 0:34:47For maritime archaeologist Lucy, it's like stepping back in time.
0:34:47 > 0:34:51It's the sort of thing you'd find in medieval shipyard. I'm not belittling this
0:34:51 > 0:34:56activity at all. But this whole tool kit in fact is very akin
0:34:56 > 0:35:01to what you'd find in a medieval shipyard. And the great thing is that they're still building
0:35:01 > 0:35:04a lot of boats here, and there's obviously a lot of demand.
0:35:10 > 0:35:14With the boat arranged, the team can begin their search for seahorses.
0:35:19 > 0:35:23They'll have to bring them out of the water to take accurate measurements -
0:35:23 > 0:35:24a sensitive operation,
0:35:24 > 0:35:27but important to help protect them.
0:35:27 > 0:35:32I'm not a huge fan of taking things out of their environment into an artificial environment.
0:35:32 > 0:35:38Yet without taking that seahorse out of its environment, you can't take the measurements that are essential
0:35:38 > 0:35:40to look at population and numbers,
0:35:40 > 0:35:44and therefore you can't go on to make any conservation assessments.
0:35:51 > 0:35:55As the divers descend, the lagoon comes alive.
0:35:57 > 0:35:59It's a nursery
0:35:59 > 0:36:01for juvenile scorpion fish,
0:36:01 > 0:36:03yellow boxfish,
0:36:03 > 0:36:07tiny squid, hermit crabs,
0:36:07 > 0:36:11and a host of mysterious micro-wildlife.
0:36:11 > 0:36:15The perfect environment for seahorses.
0:36:19 > 0:36:22A few centimetres tall and perfectly camouflaged,
0:36:22 > 0:36:25they're not easy to spot.
0:36:31 > 0:36:35Back on shore, Paul and Lucy are building a temporary lab.
0:36:39 > 0:36:43Here, they'll identify the species of any seahorse they find.
0:36:43 > 0:36:49The main objective is to to shelter it from the sun, so we need tarp.
0:36:49 > 0:36:52Perfect, and of course the wind's from that way as well.
0:37:02 > 0:37:05- Ok, OK, you can let go. - It's a tall order, this.
0:37:05 > 0:37:11We've got half a day roughly, got about four hours from now.
0:37:11 > 0:37:17And then we've gotta join Kairos and sail north, so, it is a long shot.
0:37:17 > 0:37:18There's no doubt about that.
0:37:23 > 0:37:26Underwater, the search continues.
0:37:30 > 0:37:32Oh, my God!
0:37:32 > 0:37:35Tooni, over here...
0:37:35 > 0:37:38To give you an idea of how hard they are to find,
0:37:38 > 0:37:40it is right here.
0:37:45 > 0:37:47To disguise themselves,
0:37:47 > 0:37:50seahorses allow small organisms to grow on them.
0:37:50 > 0:37:52For such a slow-moving fish
0:37:52 > 0:37:56their camouflage is an essential defence against predators.
0:37:59 > 0:38:02The only thing that gives her away
0:38:02 > 0:38:06is the slight movement of her gills
0:38:06 > 0:38:08as she's pumping water through to get oxygen.
0:38:08 > 0:38:11And that is pretty much it.
0:38:11 > 0:38:14I just think they look so sad.
0:38:14 > 0:38:17He's got his little head drooped down.
0:38:17 > 0:38:18I know!
0:38:20 > 0:38:23She's having a damn good look around though.
0:38:24 > 0:38:29I'm carefully, carefully going to lift up this seahorse here.
0:38:30 > 0:38:33Very gently.
0:38:33 > 0:38:36Seahorses almost have a mythical quality.
0:38:36 > 0:38:38They look as if...
0:38:38 > 0:38:41they come out of some storybook.
0:38:41 > 0:38:43And it might be for this reason
0:38:43 > 0:38:48that they're so prized in traditional medicines in the East.
0:38:50 > 0:38:54Seahorses are in a lot of trouble.
0:38:54 > 0:38:56Look at this beautiful creature -
0:38:56 > 0:38:58people capture these in their millions.
0:38:58 > 0:39:00Not sure if I can get him
0:39:00 > 0:39:01to hold onto my finger...
0:39:01 > 0:39:03There we go.
0:39:06 > 0:39:09Need to be very gentle and delicate with him.
0:39:09 > 0:39:14What's really key is that we get this one onto shore,
0:39:14 > 0:39:16back to its location
0:39:16 > 0:39:20within 20 minutes, because we don't want to stress it.
0:39:20 > 0:39:23Seahorses are monogamous.
0:39:23 > 0:39:26So if this one is not returned right here,
0:39:26 > 0:39:30its mate isn't going to know where it is and it'll be lost.
0:39:32 > 0:39:35Once the spot is marked, there's no time to waste.
0:39:36 > 0:39:37Precious cargo.
0:39:47 > 0:39:50Yeah, got it.
0:39:50 > 0:39:52There's a tarpaulin there for your gear.
0:39:55 > 0:39:59- Come on!- Flippin' well done! Got to be really careful.
0:39:59 > 0:40:03- Ah, she's gone down, great.- She's quite big. - Yeah, yeah, she's beautiful.
0:40:03 > 0:40:08They have just minutes to identify the species.
0:40:08 > 0:40:10Here you go, she's in there.
0:40:10 > 0:40:14- Right have you started the clock? - Yeah.- Really quiet, really quiet, yeah?
0:40:14 > 0:40:18So I think she's a female - you can see the bands on her.
0:40:18 > 0:40:21- Man, she's feisty!- She's great.
0:40:21 > 0:40:24Males have a smooth pouch that broods the young.
0:40:24 > 0:40:26Females have bands all down their bodies,
0:40:26 > 0:40:30and the number of these bands helps to identify the species.
0:40:30 > 0:40:36...5, 6, 7, 8, 9, 10... 11...
0:40:36 > 0:40:3811.
0:40:39 > 0:40:42- We're half way through. It's 10 minutes.- 14mm.
0:40:42 > 0:40:45That's spot on.
0:40:45 > 0:40:48Some species of seahorse are traded more than others.
0:40:48 > 0:40:50So identifying this one
0:40:50 > 0:40:54will help determine how endangered the population here is.
0:40:56 > 0:40:59- It's going to be hard in the water. - Can you get this down? Quickly.
0:40:59 > 0:41:01- The whole height.- Tooni,
0:41:01 > 0:41:04- gotta get in-between your fingers. - Well, you'll have to...
0:41:04 > 0:41:07I'll hold her head and you'll have to hold her tail.
0:41:07 > 0:41:09Time is slipping away.
0:41:09 > 0:41:14- Let's take her out of the water.- You can do it in the water.- All right.
0:41:14 > 0:41:16You've only got about five minutes left, guys.
0:41:16 > 0:41:19I think we try and get the length.
0:41:21 > 0:41:25The length of the seahorse is a crucial final measurement.
0:41:25 > 0:41:27It will confirm the species.
0:41:27 > 0:41:31- Quick, get in there. - I can't with your fingers there.
0:41:33 > 0:41:35That's perfect.
0:41:35 > 0:41:37Can you straighten that baby tail out?
0:41:37 > 0:41:41That's perfect, you can run it round bottom. Nearly.
0:41:41 > 0:41:44I think you've got it.
0:41:44 > 0:41:45That's it, right.
0:41:45 > 0:41:49- Good.- 164, is that about right?
0:41:49 > 0:41:52Shall we go for the upper end then?
0:41:52 > 0:41:58Combining these measurements reveals that this is a Hippocampus Borboniensis,
0:41:58 > 0:42:01a species prized in the medicinal trade.
0:42:01 > 0:42:04Get your dive gear and we'll bring her out. Call when you're ready.
0:42:04 > 0:42:09Selling for as much as £500 per kilogram, this seahorse is at risk
0:42:09 > 0:42:13from a global trade estimated to capture
0:42:13 > 0:42:1730 million seahorses a year across 80 countries.
0:42:17 > 0:42:19My heart is still going though.
0:42:32 > 0:42:36So small and yet really, really strong.
0:42:36 > 0:42:37Yeah.
0:42:40 > 0:42:45As Tooni and Philippe return the seahorse to its exact location,
0:42:45 > 0:42:48Lucy and Paul discover something.
0:42:48 > 0:42:52Ours is 16.4.
0:42:52 > 0:42:55Well, it says maximum height 14.
0:42:55 > 0:42:58I reckon it's a world beater.
0:42:58 > 0:43:00We've got a record!
0:43:00 > 0:43:01They've just found
0:43:01 > 0:43:07the largest Hippocampus Borboniensis ever recorded.
0:43:11 > 0:43:15This vital data will be sent to conservation organisation,
0:43:15 > 0:43:16Project Seahorse.
0:43:16 > 0:43:19Identifying where it might be at risk
0:43:19 > 0:43:22will be the first step in helping to protect
0:43:22 > 0:43:25this enigmatic but vulnerable creature.
0:43:31 > 0:43:35Earlier in the expedition, the team found evidence of a cyclone
0:43:35 > 0:43:37that hit this region over 100 years ago.
0:43:37 > 0:43:42Paul and maritime archaeologist Lucy
0:43:42 > 0:43:46want to explore the remains of a village that could hold clues
0:43:46 > 0:43:48to man's long relationship with this sea.
0:43:48 > 0:43:51- All we need is just one or two... - Yeah, I know.
0:43:51 > 0:43:53We're not gonna find great big things.
0:43:53 > 0:43:59- No, no, it's just clues.- Something to indicate what's going on.- Yeah.
0:44:03 > 0:44:09In 1872, a cyclone pulverised a coastal village and dragged it into the ocean.
0:44:12 > 0:44:16This is Ras Kisimani, once a vital trading hub.
0:44:23 > 0:44:26They'll be looking for evidence of its rich trading history.
0:44:31 > 0:44:35There's been limited archaeological work, but the site has been identified.
0:44:35 > 0:44:40A lot of material, because of the effects of the cyclone in 1872,
0:44:40 > 0:44:43has been washed into the sea.
0:44:43 > 0:44:47So a lot of the material is actually now under the water.
0:44:47 > 0:44:51There's very little known about the site, so I don't know what we'll find.
0:44:51 > 0:44:57I'm hoping that we'll find some bits of masonry and maybe even some pottery,
0:44:57 > 0:45:01to indicate who was here and when they settled and you know the people they were trading with.
0:45:01 > 0:45:08- Be great just to find something, wouldn't it?- Absolutely. Just a small piece of pottery
0:45:08 > 0:45:12will be able to give us some idea of the nature of activities here.
0:45:16 > 0:45:20These underwater remains have never been studied.
0:45:20 > 0:45:23They don't know what, if anything, they'll find.
0:45:23 > 0:45:27It's the challenge to the archaeologist in a way. Often you don't see
0:45:27 > 0:45:29a huge amount left on the seabed.
0:45:29 > 0:45:31It's like a puzzle.
0:45:31 > 0:45:35You have to take bits of the puzzle and through those clues try to build up a picture,
0:45:35 > 0:45:39enough to give us an indication or who was settled there,
0:45:39 > 0:45:44- who they were trading with.- Right, you guys, ready? I'll hand you scooters when you're in there.
0:45:44 > 0:45:51Five, four, three, two, one... Divers in!
0:45:56 > 0:46:00The cyclone scattered the remains across a wide area.
0:46:00 > 0:46:04- Are you getting anything there? - No, not a thing at the moment.
0:46:04 > 0:46:09So the best way to cover the ground is to use underwater scooters.
0:46:09 > 0:46:11See this, um...?
0:46:14 > 0:46:19- Oh, here, Lucy - stop. What's this? - Yeah.
0:46:19 > 0:46:23At first, it looks like debris and rubble.
0:46:23 > 0:46:26Ah, look - see there?
0:46:26 > 0:46:30That shows you the profile of a bowl.
0:46:30 > 0:46:32This is like the local coarseware,
0:46:32 > 0:46:37so this identifies the people that were settled at the site.
0:46:37 > 0:46:40They've found pottery, probably 19th century -
0:46:40 > 0:46:43evidence this is the site of a sunken village.
0:46:43 > 0:46:45Shall we go for a scoot around, Lucy?
0:46:45 > 0:46:47Yeah, what we need to try to do
0:46:47 > 0:46:50is have a look where the main concentration is.
0:46:58 > 0:47:01Hey, Paul, Paul, Paul - look!
0:47:02 > 0:47:04Oh wow, what's that?
0:47:04 > 0:47:06Wow, look at that!
0:47:06 > 0:47:09That is beautiful.
0:47:11 > 0:47:14Now that is a clear import.
0:47:14 > 0:47:18I think this is material that was coming from Persia.
0:47:20 > 0:47:24The foliage and glaze in this design date it not to the 19th century,
0:47:24 > 0:47:26but to the 15th -
0:47:26 > 0:47:31evidence that Ras Kisimani had a much older trading history.
0:47:32 > 0:47:35This is such an identifying piece of ceramic.
0:47:35 > 0:47:37This really gives an indication
0:47:37 > 0:47:41of the scale of Indian Ocean trade
0:47:41 > 0:47:44and the range that people were travelling.
0:47:48 > 0:47:52If you just do a little bit of hand fanning...
0:47:52 > 0:47:56I can't get over how much stuff's here. Look at this!
0:47:56 > 0:47:59I think it's a piece of celadon ware, which would have come from
0:47:59 > 0:48:03sort of Southeast Asia, maybe even China.
0:48:04 > 0:48:07This discovery takes them even further back in time
0:48:07 > 0:48:11and further across this ocean.
0:48:11 > 0:48:13That's a beautiful piece.
0:48:13 > 0:48:17Celadon is a type of ancient Chinese pottery.
0:48:17 > 0:48:18See this design here?
0:48:18 > 0:48:21That's got to be oriental.
0:48:21 > 0:48:24This piece could date to the 14th century, and shows that
0:48:24 > 0:48:30this village was a trade hub between China and Africa over 600 years ago.
0:48:30 > 0:48:34This was a major stopping point on a trading system
0:48:34 > 0:48:36along the East African coast.
0:48:36 > 0:48:40This particular little site worked as a stopover,
0:48:40 > 0:48:41a service station in a way.
0:48:41 > 0:48:43People would come here,
0:48:43 > 0:48:46there was a good supply of water,
0:48:46 > 0:48:50and it all worked as part of this system of trade along the coast...
0:48:50 > 0:48:52It makes a lot of sense.
0:48:52 > 0:48:56..exploiting and extracting the goods that Africa had to offer.
0:48:57 > 0:49:01Laid out on the sea bed is the long history of this village
0:49:01 > 0:49:03and the vital role of the Indian Ocean
0:49:03 > 0:49:05in uniting cultures through trade.
0:49:05 > 0:49:10From 14th century China to ancient Persia, they have found evidence
0:49:10 > 0:49:14that man has been working with this sea for hundreds of years.
0:49:22 > 0:49:26This is the first time that I've ever dived off off an island in the Indian Ocean
0:49:26 > 0:49:30and found such a wealth of material, particularly of this period.
0:49:30 > 0:49:35I mean the Islamic ceramics are really rich and colourful - their glazes, their colours -
0:49:35 > 0:49:39and so well preserved. I just cannot get over that.
0:49:44 > 0:49:50Across the centuries, the people here harnessed monsoon winds to drive trade in spices,
0:49:50 > 0:49:53gold and even slaves, up and down this coastline.
0:49:56 > 0:50:00But these waters also control the movements of marine life.
0:50:03 > 0:50:04Tooni and Philippe
0:50:04 > 0:50:09are on the look-out for the whale shark, the largest fish in the sea.
0:50:10 > 0:50:14We know very, very little about whale sharks,
0:50:14 > 0:50:17so this is really an attempt, a global attempt at trying to get
0:50:17 > 0:50:20an idea of how many whale sharks are out there.
0:50:20 > 0:50:22We don't even know that. How they migrate,
0:50:22 > 0:50:25where they go - we don't know really anything.
0:50:27 > 0:50:33These marine giants are still killed for their meat and fins, and are officially threatened.
0:50:33 > 0:50:37Philippe wants to gather information that can help protect them.
0:50:39 > 0:50:41They are still being hunted.
0:50:43 > 0:50:48I hope they won't get wiped out, but I think it's one of those things like
0:50:48 > 0:50:53the polar bears that I want to see before they're gone.
0:50:57 > 0:51:01Giant African river deltas feed this region of the Indian Ocean
0:51:01 > 0:51:04with vast quantities of nutrients.
0:51:04 > 0:51:08These wash into the waters and create feeding corridors
0:51:08 > 0:51:11that draw the whale sharks to the coastal regions.
0:51:13 > 0:51:16Philippe spots what he's looking for.
0:51:16 > 0:51:20There it is! We got whale shark!
0:51:20 > 0:51:23Oh, yeah, yeah, yeah.
0:51:23 > 0:51:29Just keep seeing a little fin come out of water, because they stay near the surface when feeding.
0:51:29 > 0:51:33Come to take big mouthfuls of krill. There it is - good heavens!
0:51:33 > 0:51:38My goodness, It's just come right out of the water. You can see it.
0:51:38 > 0:51:40Good Lord!
0:51:42 > 0:51:47Whale sharks are normally seen travelling alone, but here a group has gathered.
0:51:47 > 0:51:51My goodness, we are surrounded.
0:51:53 > 0:51:57To see six sharks circling like this is very rare.
0:51:57 > 0:52:00Look at the size of it!
0:52:00 > 0:52:04These vast creatures are almost as big as the team's boat.
0:52:09 > 0:52:11Your face, man!
0:52:11 > 0:52:15Thing is, you read like eight metre whale shark in the book,
0:52:15 > 0:52:18but then you see an eight metre whale shark and it's...
0:52:18 > 0:52:20That thing was huge.
0:52:22 > 0:52:28Tooni and Philippe want to take photographs of the whale sharks to identify individuals.
0:52:28 > 0:52:34This information will be used to track whale shark movement around the globe.
0:52:35 > 0:52:39The sharks pose no threat to humans, and as they seem relaxed,
0:52:39 > 0:52:42the team can go after the information they need.
0:52:48 > 0:52:52The water is clouded with life.
0:52:52 > 0:52:57Shoals of fish pulse, shimmer and pool together for protection.
0:53:02 > 0:53:08Mobula rays glide in to take advantage of plentiful prey.
0:53:13 > 0:53:17An entire food chain is active here.
0:53:17 > 0:53:21And these huge creatures are cutting swathes right through its centre.
0:53:43 > 0:53:47Whale sharks can weigh up to 35 tonnes.
0:53:51 > 0:53:54They've been known to travel distances of up to 8,000 miles
0:53:54 > 0:53:57to recharge at feeding grounds like this.
0:54:06 > 0:54:11The gills filter the water of its content.
0:54:11 > 0:54:14A cough helps to clear trapped food particles.
0:54:18 > 0:54:22Tiny eyes and poor sight mean it's their sense of smell
0:54:22 > 0:54:26that enables them to track down their prey of fish and plankton.
0:54:52 > 0:54:56Their skin is the thickest of any animal on earth,
0:54:56 > 0:54:59and it's the markings on it that Philippe needs to photograph.
0:55:13 > 0:55:18Like a fingerprint, the spots on the side of each shark are unique.
0:55:21 > 0:55:24The photographs will go into a database to help track the sharks,
0:55:24 > 0:55:30so conservationists can find out where they need to be protected.
0:55:40 > 0:55:44That was... That was incredible!
0:55:44 > 0:55:46- They are so beautiful. - That was incredible.
0:55:46 > 0:55:50A giant, gaping, wide mouth.
0:55:50 > 0:55:54It was just magical, just awesome.
0:56:00 > 0:56:05The team moves to land to get a stable communications platform.
0:56:06 > 0:56:11They need to upload the whale shark photos into an international database.
0:56:11 > 0:56:14This is how they identify them.
0:56:14 > 0:56:17The spots on the side of them are similar to fingerprints.
0:56:17 > 0:56:22In every single whale shark the spot pattern is different. It will compare these spots
0:56:22 > 0:56:29with a photographic database of at least 1,000 other whale sharks.
0:56:30 > 0:56:33If this shark has already been identified
0:56:33 > 0:56:36in other parts of the world, the database will show where it's been travelling.
0:56:38 > 0:56:42If it's a new shark, then one more can be tracked.
0:56:44 > 0:56:47Right, so here we go. Results just came up, and...
0:56:47 > 0:56:50we've got a new whale shark.
0:56:50 > 0:56:52- That's cool.- Well done.
0:56:52 > 0:56:55And the great thing about this is that we'll find out,
0:56:55 > 0:57:00- we'll be e-mailed if this whale shark is sighted again and where it was sighted.- Great.
0:57:00 > 0:57:05It's a final success and a fitting end to the expedition.
0:57:07 > 0:57:14The interaction of land and sea created the feeding corridors that support the whale sharks.
0:57:15 > 0:57:19But it also brings the human activity that threatens them.
0:57:21 > 0:57:25The Indian Ocean has shown how much it has to offer those around it...
0:57:25 > 0:57:28- That's a really bright band. - You can see it, can't you?
0:57:28 > 0:57:32..but also how these people are threatened...
0:57:36 > 0:57:40..people who've developed ways of exploiting this sea for centuries.
0:57:40 > 0:57:45It's a case of the sea not dividing but uniting
0:57:45 > 0:57:47the different cultures around its shores.
0:57:49 > 0:57:53But we may now be learning how to work with our coastal waters,
0:57:53 > 0:57:57strengthening our fragile relationship with the ocean.
0:58:02 > 0:58:08Next time, the team explores the blue waters of the Mediterranean Sea.
0:58:09 > 0:58:13They'll brave perilous caves for proof of its turbulent past.
0:58:13 > 0:58:16This cave is like a time capsule.
0:58:16 > 0:58:21They'll search for evidence of one of Europe's first superpowers.
0:58:21 > 0:58:22I'm going in.
0:58:22 > 0:58:26And they'll search for the feared great white shark.
0:58:42 > 0:58:45Subtitles by Red Bee Media Ltd.
0:58:45 > 0:58:48E-mail subtitling@bbc.co.uk