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're vital for our future survival.
0:00:18 > 0:00:23But the secrets of our oceans have remained largely undiscovered.
0:00:23 > 0:00:25I'm with a shark.
0:00:25 > 0:00:28Yes! 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 > 0:00:43For a year, the team has voyaged across the world to build up a global picture of our seas.
0:00:43 > 0:00:46We are doing some pretty uncharted research here.
0:00:46 > 0:00:49This is psychedelically colourful!
0:00:49 > 0:00:54We're here to try and understand the Earth's oceans and put them in a human scale.
0:00:56 > 0:01:00Our oceans are changing faster than ever.
0:01:00 > 0:01:04I've never seen ice like this before.
0:01:04 > 0:01:10There's never been a better time to explore the last true wilderness on Earth.
0:01:16 > 0:01:18It's that way. Something quite big.
0:01:18 > 0:01:21Yes, look! Woo-hoo!
0:01:21 > 0:01:23It's a whale, here.
0:01:25 > 0:01:30The team is exploring a unique corner of the Pacific Ocean, the Sea of Cortez.
0:01:30 > 0:01:35- Oh, my goodness. - This is SO beautiful, isn't it?
0:01:35 > 0:01:37Those are whales.
0:01:37 > 0:01:40- And this is the first day!- I know!
0:01:40 > 0:01:44- It feels good, doesn't it? - It certainly does.
0:01:47 > 0:01:50The Sea of Cortez is a rich, fertile gulf,
0:01:50 > 0:01:56separating the peninsula of Baja California from mainland Mexico.
0:01:58 > 0:02:02This sea is an exceptional marine environment,
0:02:02 > 0:02:08home to the greatest variety of whales and dolphins found anywhere in the world.
0:02:09 > 0:02:12Look at them go!
0:02:15 > 0:02:17But today, this ocean paradise is under threat.
0:02:17 > 0:02:20In the last 50 to 100 years,
0:02:20 > 0:02:21humans have had a growing impact
0:02:21 > 0:02:25on the systems that make the sea so interesting -
0:02:25 > 0:02:30the health of sea lions, sharks and sperm whales,
0:02:30 > 0:02:34you know, all these big animals that are found here in this young sea.
0:02:34 > 0:02:39Fishing, tourism and industry have triggered complex changes here,
0:02:39 > 0:02:42and it's these that the team has come to investigate.
0:02:50 > 0:02:52This is definitely on the edge.
0:02:52 > 0:02:58Environmentalist Philippe Cousteau will examine the shifting balance of this delicate ecosystem.
0:02:58 > 0:03:01Woah, look at that!
0:03:01 > 0:03:09If you're seeing an explosion of squid, that is at the cost to some other species.
0:03:09 > 0:03:16Maritime archaeologist Dr Lucy Blue discovers how local people have found a way to protect our seas.
0:03:16 > 0:03:21They are very aware that the seas only have a limited resource.
0:03:21 > 0:03:25They have to be farmed in a way that is sustainable.
0:03:26 > 0:03:31There's five sperm whales down there.
0:03:31 > 0:03:34Marine biologist and oceanographer Tooni Mahto
0:03:34 > 0:03:36explores how life is responding
0:03:36 > 0:03:40in a rare encounter with one of the largest carnivores on Earth.
0:03:40 > 0:03:45I got sonar boomed. I felt that boom going right through my body.
0:03:48 > 0:03:51The Sea of Cortez is a sea under change,
0:03:51 > 0:03:54and we're going to witness those changes.
0:03:54 > 0:03:56That's a fantastic mission for a diving expedition.
0:03:56 > 0:04:02This will be a voyage of discovery into a sea of change.
0:04:06 > 0:04:11Expedition leader Paul Rose will head up their first mission -
0:04:11 > 0:04:16the search for an ocean predator that once dominated this sea.
0:04:16 > 0:04:22Hammerhead sharks - as soon as we put together the Sea of Cortez diving expedition,
0:04:22 > 0:04:25hammerhead sharks was the only image that came to mind.
0:04:25 > 0:04:26Is this the hammerhead video?
0:04:26 > 0:04:30Yeah, this is filmed right here, right underneath us.
0:04:30 > 0:04:36These pictures were taken 16 years ago, in a spot directly beneath the expedition boat.
0:04:36 > 0:04:37- That was here?!- Yeah, right here.
0:04:37 > 0:04:39Right here, that's spectacular.
0:04:39 > 0:04:43- And the research...- Across the world, sharks are in decline.
0:04:43 > 0:04:47Tens of millions are caught each year.
0:04:47 > 0:04:52The team has come here to see how that's effecting this once-thriving hammerhead population.
0:04:52 > 0:04:56- That's a fantastic shot. - That's a great shot, good lord.
0:04:56 > 0:05:01There's no real evaluation of how many there are left and what their habits are and how they're changing,
0:05:01 > 0:05:05and the scientists need more information, and the way we can do that
0:05:05 > 0:05:09is get sightings, study their behaviour and that all contributes.
0:05:09 > 0:05:10It's all gold dust.
0:05:14 > 0:05:16Hammerhead sharks are easily spooked,
0:05:16 > 0:05:20so Paul is using special kit that doesn't produce bubbles.
0:05:22 > 0:05:25Rebreathers allow you to stay underwater much longer,
0:05:25 > 0:05:30but you need to be an experienced diver to use them safely.
0:05:30 > 0:05:36There's a few different ways to kill yourself with these, and they're all instant.
0:05:36 > 0:05:39You don't seem... There don't seem to be near-misses with them.
0:05:39 > 0:05:43If you haven't set something up right, it's going to kill you.
0:05:43 > 0:05:46Serious business!
0:06:11 > 0:06:15This is the El Bajo Seamount, an extinct volcano.
0:06:16 > 0:06:21It was once one of the best places in the world to see hammerhead sharks.
0:06:28 > 0:06:32Now, this looks like hammerhead territory.
0:06:32 > 0:06:35These are Cortez stingrays, which hammerheads eat,
0:06:35 > 0:06:40and these are barberfish, that clean parasites off their skin.
0:06:40 > 0:06:43So, we're definitely in the right place.
0:06:46 > 0:06:49Hammerheads are vital to the health of the ocean.
0:06:49 > 0:06:55They weed out the sick and injured and help keep marine life in balance.
0:06:55 > 0:07:00But they've been heavily fished, so Paul doesn't know how many he'll find.
0:07:00 > 0:07:07Our plan is to sit here, still and quiet, and hopefully the hammerheads will come by.
0:07:11 > 0:07:13Paul, surface. Paul, surface.
0:07:13 > 0:07:17Unknown to Paul, he's gone silent for another reason.
0:07:17 > 0:07:21- The boat has just lost radio contact. - Paul, surface. Paul, surface.
0:07:21 > 0:07:26With Paul 40 metres underwater, this could be a serious situation.
0:07:26 > 0:07:27Obviously,
0:07:27 > 0:07:30We've seen the kind of equipment he's working with.
0:07:30 > 0:07:33If there is a problem, we've got no way of knowing.
0:07:33 > 0:07:35Paul, surface. Paul, surface.
0:07:35 > 0:07:42For the time being, we don't know where he is or what he's doing, which is not great.
0:07:42 > 0:07:45Richard Bull is in charge of dive safety.
0:07:45 > 0:07:49It makes me very, very nervous, it really does.
0:07:52 > 0:07:54If I can relax at all during the dive,
0:07:54 > 0:07:58it's when I can hear them talking and they're calm,
0:07:58 > 0:07:59and I haven't got any of that now.
0:07:59 > 0:08:02Paul, surface. Try PTT. PTT.
0:08:02 > 0:08:04Paul, surface.
0:08:10 > 0:08:11Yeah, yeah!
0:08:11 > 0:08:13A sea lion. Woo-hoo!
0:08:13 > 0:08:16RADIO STATIC
0:08:16 > 0:08:18- BROKEN SPEECH OVER RADIO: - 'It's beautiful.'
0:08:18 > 0:08:21HE LAUGHS
0:08:21 > 0:08:23That's a nice surprise!
0:08:23 > 0:08:26Oh, oh! Laughter!
0:08:26 > 0:08:32LAUGHTER OVER RADIO
0:08:32 > 0:08:35Well, something's very good.
0:08:38 > 0:08:40I thought it was a shark.
0:08:40 > 0:08:42The Rose chuckle!
0:08:42 > 0:08:45We like that.
0:08:47 > 0:08:52Paul's now been diving for hours, but still no sign of sharks.
0:08:52 > 0:08:57This nutrient-rich current should help bring in the hammerheads,
0:08:57 > 0:09:00but where the heck are they?
0:09:14 > 0:09:18- And?- It was an exciting dive, but no hammerheads.
0:09:18 > 0:09:21- Not a single one?- Sadly, no.
0:09:26 > 0:09:28I really felt that we would find them.
0:09:28 > 0:09:32It felt like hammerhead territory, it was all there.
0:09:32 > 0:09:34But no hammerheads.
0:09:39 > 0:09:46Paul dives the Seamount again and again, but still no sightings.
0:09:46 > 0:09:51Just 20 years ago, this was a hammerhead hot spot.
0:09:51 > 0:09:57It's becoming clear this shark population is in severe decline.
0:10:00 > 0:10:05'Three days of expedition time and, you know, didn't get a sniff of one.'
0:10:05 > 0:10:08No hammerheads.
0:10:08 > 0:10:11There used to be hundreds of them on the Seamount like this,
0:10:11 > 0:10:14and now we'll be very lucky to find one or two.
0:10:14 > 0:10:20There is a sense in me that says, well, maybe there's none here.
0:10:21 > 0:10:23In the Sea of Cortez,
0:10:23 > 0:10:26thousands of hammerhead sharks are caught each year,
0:10:26 > 0:10:30mostly to satisfy the demand for shark fin soup in the Far East,
0:10:30 > 0:10:35and there's further evidence of how destructive this trade can be,
0:10:35 > 0:10:37as Dr Lucy Blue has discovered.
0:10:37 > 0:10:44One of the boat crew found this skull on a beach on one of the islands here, and, as you can see,
0:10:44 > 0:10:50this is the hammerhead of the shark, and it's actually quite a small one.
0:10:50 > 0:10:52It just shows that they're not fussy about what size,
0:10:52 > 0:10:55they'll take them small or big, juvenile or adult.
0:10:55 > 0:10:58Once they've chopped off all the fins,
0:10:58 > 0:11:00which is what they're after, they discard the rest.
0:11:00 > 0:11:06The fins can reach something in the region of like 100 for one kilo,
0:11:06 > 0:11:08so you're talking big business, really.
0:11:08 > 0:11:14And this is happening on a large scale, so, yeah...
0:11:16 > 0:11:20In this sea, hammerhead numbers have been dramatically reduced.
0:11:20 > 0:11:24Some estimates suggest only 10% are left.
0:11:24 > 0:11:27It's the demand for shark fin soup.
0:11:29 > 0:11:31You know, it's barely credible.
0:11:31 > 0:11:34For someone from England, you think, well, shark fin soup?
0:11:34 > 0:11:36But that's what's happened.
0:11:36 > 0:11:39Shark fin soup's supposed to have some fantastic properties,
0:11:39 > 0:11:44but it's not worth decimating a whole species for, is it?
0:11:46 > 0:11:51The decline in the number of sharks is shifting the balance of life in the sea.
0:11:51 > 0:11:55Later in the expedition, the team will explore
0:11:55 > 0:11:58the surprising consequences which that's having here.
0:12:03 > 0:12:04Did you see that?!
0:12:04 > 0:12:11Next morning, this corner of the Pacific Ocean offers the expedition a welcome lift.
0:12:11 > 0:12:13There's a whole pod of them.
0:12:13 > 0:12:15Look at them go!
0:12:15 > 0:12:19- We're seeing a pod of common dolphins, but there's quite a lot of them.- There are.
0:12:19 > 0:12:24They seem very small, so I don't know if they're young teenagers who are out for a laugh!
0:12:24 > 0:12:25Showing off.
0:12:25 > 0:12:29More than 30 species of whales and dolphins are found here.
0:12:32 > 0:12:39The loss of sharks has reduced competition for food, so dolphins are actually doing well.
0:12:39 > 0:12:45It shows how the balance of life is more complex and surprising than it first appears.
0:12:45 > 0:12:48Man, they're so lovely!
0:12:54 > 0:12:58For the next dive, environmentalist Philippe Cousteau,
0:12:58 > 0:13:05grandson of explorer Jacques Cousteau, hopes to investigate another part of the puzzle.
0:13:05 > 0:13:08We're headed off to Los Islotes to go diving with sea lions,
0:13:08 > 0:13:12which I have to say is one of my favourite things to do in the world.
0:13:12 > 0:13:17Large breeding colonies of California sea lions are found here.
0:13:17 > 0:13:23But as commercial fishing increases in this sea, it's starting to affect them.
0:13:23 > 0:13:27Now, there's been a lot of overfishing of their traditional food, like sardines,
0:13:27 > 0:13:33in the Sea of Cortez, so a lot of the sea lions are suffering because of that.
0:13:33 > 0:13:36The animals of Los Islotes are a mysterious exception.
0:13:36 > 0:13:39Somehow, these animals are thriving.
0:13:42 > 0:13:47Marine biologist Tooni Mahto will be helping to unearth their secret.
0:14:01 > 0:14:05The first aim is to check out how healthy this colony is.
0:14:10 > 0:14:12He came close!
0:14:12 > 0:14:16Woo! It's like speeding bullets.
0:14:16 > 0:14:19Their manoeuvrability underwater kind of puts us to shame, I feel.
0:14:24 > 0:14:26That one over there is a bit of a big boy.
0:14:26 > 0:14:28I think he's one of the males.
0:14:28 > 0:14:32Oh, and he's certainly coming round to check me out.
0:14:32 > 0:14:36Yeah, that is a big male, that's for sure! He's awesome.
0:14:36 > 0:14:40You can see that huge, bony crust on their head.
0:14:40 > 0:14:44They use that to reverberate sound so that everybody can hear them
0:14:44 > 0:14:48and let them know that they're in the territory and they're in charge.
0:14:48 > 0:14:52Blowing bubbles is a way of saying, "keep your distance".
0:14:57 > 0:14:58Hello!
0:15:00 > 0:15:05This looks like the nursery area to me, with all the juveniles.
0:15:05 > 0:15:09So, apparently, the pups here, in is this particular population,
0:15:09 > 0:15:14spend an awful lot longer with their mothers than pups of the same species in different areas.
0:15:14 > 0:15:18So they go and fish with their mothers so they learn that behaviour.
0:15:20 > 0:15:24The number of pups in the water is a sign this colony is doing well,
0:15:24 > 0:15:29as it means the females are healthy enough to breed regularly.
0:15:29 > 0:15:34There were about 30 pups a year in the early '90s, and now there are more than 100 a year.
0:15:34 > 0:15:37It's a real success story, which is good news.
0:15:39 > 0:15:45But with many fish stocks declining, the mystery is why this colony's doing so well.
0:15:45 > 0:15:47Something else must be going on.
0:15:59 > 0:16:00Oh!
0:16:06 > 0:16:09They look so incongruous on land, don't they?
0:16:09 > 0:16:14And then as soon as he's in the water, he's absolutely perfectly streamlined.
0:16:14 > 0:16:17Amazing. Master of his environment.
0:16:24 > 0:16:29Gathering sea lions' droppings, or scats, might give Tooni clues about their diet.
0:16:29 > 0:16:32Sea-lion poo number two.
0:16:36 > 0:16:43Essentially, I'm doing the scientific equivalent of panning for gold.
0:16:43 > 0:16:46I'm looking at the sea-lion poo,
0:16:46 > 0:16:51and what we're looking for are the fish otoliths,
0:16:51 > 0:16:53which are the ear bones of fish,
0:16:53 > 0:16:57and from the otoliths, we can identify what the sea lions have actually been eating.
0:16:57 > 0:17:00Oh, there's one.
0:17:02 > 0:17:05Gold! I've found gold!
0:17:05 > 0:17:08These ear bones could reveal the answer.
0:17:08 > 0:17:14And it seems Tooni really has struck gold.
0:17:14 > 0:17:18What we've found here is the fish otolith from a deep-water sea bass
0:17:18 > 0:17:21that lives pretty much between 75 and 265 metres,
0:17:21 > 0:17:26so that instantly shows that this population has, at some stage,
0:17:26 > 0:17:30adapted to fishing at much deeper depths.
0:17:31 > 0:17:38California sea lions normally hunt at depths of around 70 metres, catching fish such as sardines.
0:17:40 > 0:17:44But the ear bones Tooni's found prove the animals at Los Islotes
0:17:44 > 0:17:47have been able to change their hunting patterns.
0:17:47 > 0:17:51And that is the reason why that population seems to be doing so well.
0:17:53 > 0:17:58Because of this crucial adaptation, the Los Islotes sea lions
0:17:58 > 0:18:02no longer have to compete with fishermen, and they're flourishing.
0:18:04 > 0:18:08The fact that this particular colony has been able to adapt to the threats
0:18:08 > 0:18:12and challenges that are facing it, and thrive, is a great story.
0:18:12 > 0:18:16Hopefully, if this colony can exhibit this kind of behaviour,
0:18:16 > 0:18:22then others can follow suit and there may be a bright future for the California sea lion.
0:18:35 > 0:18:43Although life is changing fast here, change itself is nothing new to our seas and oceans.
0:18:43 > 0:18:46In fact, their size and shape are constantly shifting.
0:18:49 > 0:18:53Oceanographer Tooni has brought the team west, to the Bay of Conception,
0:18:53 > 0:18:57because here, you can actually see that process in action.
0:19:01 > 0:19:05Beneath these calm waters is a giant fracture in the Earth's crust.
0:19:05 > 0:19:09It's part of the infamous San Andreas fault line,
0:19:09 > 0:19:12and it created this sea.
0:19:14 > 0:19:17The Sea of Cortez is quite young in geological terms.
0:19:17 > 0:19:22The peninsula split away from the main coast line of Mexico about five million years ago,
0:19:22 > 0:19:25so it basically started tearing apart,
0:19:25 > 0:19:28and the great thing I like so much is the fact that it's still moving.
0:19:28 > 0:19:35The whole of the Baja peninsula is moving pretty much west at a rate of five centimetres a year.
0:19:37 > 0:19:43This bay offers Tooni the chance to look for evidence that this sea is getting bigger.
0:19:43 > 0:19:48And Paul's hoping she'll cook a snack in the process.
0:19:48 > 0:19:54Could we have six eggs - huevos? Would that be OK?
0:19:54 > 0:19:57Good man. Thanks very much, thank you!
0:19:59 > 0:20:01There we go. Don't forget these!
0:20:01 > 0:20:05- Mind your head! Good luck, happy cooking.- Thank you.
0:20:18 > 0:20:23Tooni and Lucy are swimming over part of the San Andreas fault line.
0:20:24 > 0:20:28As the Earth's crust is being ripped apart beneath them,
0:20:28 > 0:20:34heat and gas from the centre of the planet are escaping through crack called hydrothermal vents.
0:20:34 > 0:20:38Oh, look! Look at all these bubbles coming though.
0:20:38 > 0:20:40Oh, God, yeah.
0:20:40 > 0:20:45It's rare to see a hydrothermal vent in five metres of water.
0:20:45 > 0:20:49They're normally found deep beneath the surface.
0:20:49 > 0:20:53Oh, look, you can see the heat shimmer.
0:20:53 > 0:20:56This is the shimmering water,
0:20:56 > 0:21:03where the hot water is coming out of the ground and mixing with the colder seawater around it,
0:21:03 > 0:21:08and that's the evidence of all the hydrothermal activity, accompanied by all the bubbles.
0:21:08 > 0:21:12Oh, that's hot! That's really hot.
0:21:12 > 0:21:15It's actually burning my fingers.
0:21:15 > 0:21:20This hot water is over 90 degrees Centigrade.
0:21:20 > 0:21:26It once trickled down though cracks in the Earth's crust, towards the furnace of the inner earth.
0:21:26 > 0:21:31There, it was super-heated and forced out into the Sea of Cortez.
0:21:35 > 0:21:39Right. We brought our eggs with us,
0:21:39 > 0:21:44and we're going to bury them here, cos it's really, really warm here,
0:21:44 > 0:21:48and then we're going to take them back on board for lunch.
0:21:48 > 0:21:53We're cooking in the sea floor - it's not right!
0:21:54 > 0:22:02Hot mineral-rich water like this is only found in places where fault lines are tearing the Earth apart.
0:22:02 > 0:22:04It proves that directly below the team,
0:22:04 > 0:22:10the Earth's crust is slowly moving and this sea is steadily growing.
0:22:10 > 0:22:16Seas and oceans are thought of as immovable features of our planet.
0:22:16 > 0:22:19This dive has shown they're anything but.
0:22:19 > 0:22:22It's quite amazing to think
0:22:22 > 0:22:28that this action of the tearing apart of these two land masses is a continuum.
0:22:28 > 0:22:31It's been going on for five million years.
0:22:34 > 0:22:40But although this process created the Sea of Cortez, it will also destroy it.
0:22:40 > 0:22:43As Baja California continues to move north-west,
0:22:43 > 0:22:48it will eventually break away from the mainland to become a giant island.
0:22:49 > 0:22:56Then the Sea of Cortez will disappear for ever, engulfed by the rest of the Pacific Ocean.
0:23:00 > 0:23:03Hey, hey! I know what you're holding behind you.
0:23:03 > 0:23:06You can't fool me. Boiled eggs. Hard-boiled eggs, soft-boiled eggs?
0:23:06 > 0:23:08I'm struggling with soldiers.
0:23:08 > 0:23:11I don't know what Spanish is for "soldiers"!
0:23:15 > 0:23:19- That looks perfect.- It does look good.- That's a hard-boiled egg.
0:23:19 > 0:23:24That's a perfect, perfect, hydrothermal vent boiled egg.
0:23:24 > 0:23:28Is it OK to eat? Of course it's all right to eat. It's blooming great.
0:23:28 > 0:23:32- You could do it like an oyster, couldn't you?- I could.- What? In one?
0:23:32 > 0:23:34Ohhhh.
0:23:34 > 0:23:36That's absolutely brilliant.
0:23:36 > 0:23:38Did you just down an egg in one?
0:23:38 > 0:23:41It's brilliant. Well, I thought it was worth a go.
0:23:41 > 0:23:43You're disgusting!
0:23:43 > 0:23:49- Sea of Cortez, eating eggs cooked by Lucy and Tooni on a hydrothermal vent.- Awesome!
0:23:49 > 0:23:50Oh, cheers, mate.
0:23:56 > 0:24:03At the start of the expedition, the team saw how hammerhead sharks were being decimated.
0:24:03 > 0:24:09Now they plan to investigate a surprising knock-on effect.
0:24:09 > 0:24:12The invasion of another fearsome predator.
0:24:12 > 0:24:15They are ugly creatures.
0:24:15 > 0:24:20A few decades ago, there were no Humboldt squid in the Sea of Cortez.
0:24:20 > 0:24:22Now there could be over 20 million.
0:24:22 > 0:24:27'They've taken over in a really short space of time,'
0:24:27 > 0:24:30and that's to do with the amount of fishing that's gone on in this sea.
0:24:30 > 0:24:32They've taken out the top predators,
0:24:32 > 0:24:38'and now the Humboldt squid have basically filled in the giant empty space.'
0:24:38 > 0:24:43Growing to over two metres long, these are ferocious cannibalistic hunters.
0:24:43 > 0:24:46Look at the beak. They're so strong.
0:24:46 > 0:24:48- You see it overlaps?- Yeah.
0:24:48 > 0:24:53That is kind of hooked over, so, you know, if your finger's in there, it's gone.
0:24:53 > 0:24:59- Yeah, and look at the eye. - Ooh, that's too eerie!
0:24:59 > 0:25:02Humboldt squid are thought to have excellent vision
0:25:02 > 0:25:06and are armed with over 30,000 barbed hooks inside their suckers.
0:25:06 > 0:25:11I mean, you can feel them. They are properly sharp, these hooks.
0:25:11 > 0:25:14The team wants to find out what impact the squid invasion is having.
0:25:14 > 0:25:19- Honestly, that is nasty. - And that means seeing them hunt.
0:25:23 > 0:25:26Humboldts live in the depths of the ocean.
0:25:28 > 0:25:32Local fishermen say catching one tempts others up from the deep.
0:25:37 > 0:25:40- I've caught a squid! - We've got a squid here!
0:25:44 > 0:25:46- Oh, my God!- Well done.
0:25:46 > 0:25:48We've got squid in the area!
0:25:48 > 0:25:53'We've been fishing about two hours, and we've run into a huge pile of squid,
0:25:53 > 0:25:57'and what's really interesting is that every single time'
0:25:57 > 0:26:03we put a hook down, it brings up a squid that's got marks and rips and bites all over it.
0:26:04 > 0:26:07A number of the ones we pulled up have actually been eaten,
0:26:07 > 0:26:11so this is demonstrating the sort of cannibalistic habits of the squid,
0:26:11 > 0:26:14which is really quite unnerving.
0:26:14 > 0:26:17Watch your mate get caught on a line and then eat him on the way up.
0:26:20 > 0:26:25To see how they hunt, there's only one option - to dive in.
0:26:25 > 0:26:32I don't particularly want to get in there with a whole load of arms and suckers and teeth.
0:26:32 > 0:26:36Dive safety supervisor Richard Bull is also worried.
0:26:36 > 0:26:43There are some very serious reports of people getting grabbed by them, divers getting grabbed by them.
0:26:43 > 0:26:45One grabs them, another one grabs them,
0:26:45 > 0:26:48and then another one grabs them, and if you don't react quickly,
0:26:48 > 0:26:50then you are on your way down to the deep.
0:26:52 > 0:26:55This is to keep us safe.
0:26:55 > 0:26:58In case something goes wrong, the rest of the crew can grab...
0:26:58 > 0:27:02There'll be a line tied to this and they can grab us and bring us up.
0:27:02 > 0:27:07It's now past midnight and the weather has started to deteriorate.
0:27:07 > 0:27:09The waves are coming in strong.
0:27:09 > 0:27:12It's really rough. The wind is picking up.
0:27:12 > 0:27:15This is definitely on the edge.
0:27:15 > 0:27:19If you're not in in five minutes, it's off.
0:27:21 > 0:27:24Watch the line.
0:27:28 > 0:27:31Cor, look at that current.
0:27:31 > 0:27:34OK...
0:27:40 > 0:27:46- Flipping heck!- That was a very rough entry in the water.
0:27:46 > 0:27:49Woah! Look at that.
0:27:49 > 0:27:50I can see squid.
0:27:50 > 0:27:52They're right here.
0:27:52 > 0:27:55There are loads of them.
0:27:55 > 0:27:57Look, there's one.
0:27:57 > 0:27:59Oh!
0:27:59 > 0:28:01Oh, my goodness!
0:28:03 > 0:28:09We can see the squid, which are kind of racing and pulsing out of the darkness.
0:28:09 > 0:28:14As they come closer, the squid seem to be doing something peculiar.
0:28:14 > 0:28:18There are several of them flashing their colours,
0:28:18 > 0:28:23and we can see these ghostly white shadows that are flashing red.
0:28:26 > 0:28:30You see the colour of him? That red flash.
0:28:32 > 0:28:34These flashes may be a form of language
0:28:34 > 0:28:40that could possibly help groups of squid to communicate as they hunt.
0:28:40 > 0:28:43They are definitely attracted to the lures.
0:28:43 > 0:28:46Yeah, there it is.
0:28:46 > 0:28:48God, they move quick.
0:28:48 > 0:28:52The squid have started to attack the team's bait in a pack.
0:28:52 > 0:28:55There's, like, 10 or 20 out here.
0:28:57 > 0:29:01Invertebrates don't normally hunt together like this.
0:29:01 > 0:29:04But Humboldt squid are intelligent.
0:29:04 > 0:29:11By flashing, they might be organising themselves into a hunting pack.
0:29:11 > 0:29:19And that's helping them to devastate local fish stocks, eating an estimated 10,000 tons a night.
0:29:21 > 0:29:27Underwater, Tooni and Philippe are unaware of how windy it's become on the surface.
0:29:27 > 0:29:31It's kicking up, it's getting very rough.
0:29:31 > 0:29:32It's deteriorating more.
0:29:35 > 0:29:37I'm thinking we're on the edge.
0:29:37 > 0:29:40- It's my job to say no.- Agreed.
0:29:40 > 0:29:47We've put our men at the edge of our capability and the seas have picked up
0:29:47 > 0:29:52and the weather is obviously getting worse, so time to bring them back.
0:29:52 > 0:29:55The rough seas will now make for a dangerous exit from the water.
0:30:16 > 0:30:18Get him over that ladder quickly.
0:30:24 > 0:30:25Well done, mate.
0:30:25 > 0:30:27Too rough, really, wasn't it?
0:30:30 > 0:30:34It was one heck of a dive, that's for sure.
0:30:34 > 0:30:36Are you all right, mate?
0:30:36 > 0:30:37I'm pooped.
0:30:40 > 0:30:42What time is it?
0:30:42 > 0:30:48- Ten past three.- So we've been squid jigging since eight o'clock, eight o'clock this evening?
0:30:50 > 0:30:53The success of the Humboldt squid
0:30:53 > 0:30:57is having a radical effect on this ecosystem.
0:30:57 > 0:31:01If you're seeing an explosion of squid,
0:31:01 > 0:31:04that is at the cost to some other species.
0:31:04 > 0:31:07They'll eat their way down the food chain
0:31:07 > 0:31:09till there's nothing left down there.
0:31:10 > 0:31:14And this problem isn't just affecting the Sea of Cortez.
0:31:14 > 0:31:18Many invertebrates, like squid, are booming throughout our oceans.
0:31:20 > 0:31:23The expedition has witnessed one of the great changes
0:31:23 > 0:31:26affecting life in our oceans today.
0:31:38 > 0:31:41After the late night, Paul gives the team some time off.
0:31:44 > 0:31:47It's a very good part of the expedition,
0:31:47 > 0:31:50right in the middle of it, and in the thick of it.
0:31:54 > 0:31:56I'm loving this sea.
0:31:56 > 0:32:00Just looks like it holds those hidden jewels
0:32:00 > 0:32:03that, essentially, we are all here to try and find.
0:32:03 > 0:32:07Now I have this real sense of ownership and it saddens me to think
0:32:07 > 0:32:12that anything at all is being done to harm this special, beautiful place.
0:32:14 > 0:32:17The team has already seen some of the surprising effects
0:32:17 > 0:32:18of man's impact here,
0:32:18 > 0:32:22but there's more to explore in this remarkable sea.
0:32:22 > 0:32:24There's still a lot of challenges ahead.
0:32:24 > 0:32:27We've got sperm whales coming up here, all these great things
0:32:27 > 0:32:31we've still got to do in the northern part of the Sea of Cortez.
0:32:40 > 0:32:43For maritime archaeologist Dr Lucy Blue,
0:32:43 > 0:32:47oceans aren't just about the creatures living within them.
0:32:47 > 0:32:51For me, it's the connection between the people in the past,
0:32:51 > 0:32:53their relationship with the sea and what
0:32:53 > 0:32:55that can tell us about people living today.
0:32:57 > 0:33:01Lucy's been researching a shipwreck that tells a tragic story
0:33:01 > 0:33:03of man's relationship with the ocean.
0:33:03 > 0:33:07It's a boat that was smuggling migrant workers with the aim
0:33:07 > 0:33:11of trying to get into the Unites States of America.
0:33:11 > 0:33:14'It is a bit like an investigation into, you know,'
0:33:14 > 0:33:15the lives of these people
0:33:15 > 0:33:19as they took this treacherous journey across the sea.
0:33:19 > 0:33:22- It was a transport ship or what? - Exactly, of people.
0:33:22 > 0:33:25'And there will be clues left within the shell of that boat'
0:33:25 > 0:33:29to give us an indication of what life on board was like.
0:33:48 > 0:33:52You can just see it emerging out of the bottom of the sea.
0:34:03 > 0:34:06This is the wreck of the Fang Ming.
0:34:06 > 0:34:09Sort of eerie as you swim around
0:34:09 > 0:34:13these abandoned pieces of decking and rotting ropes.
0:34:21 > 0:34:25The Fang Ming was formerly a working vessel in China,
0:34:25 > 0:34:28possibly a fishing vessel,
0:34:28 > 0:34:32and then she subsequently crossed the Pacific,
0:34:32 > 0:34:35carrying this cargo of Chinese migrant workers.
0:34:38 > 0:34:40Lucy wants to find out
0:34:40 > 0:34:43where the Chinese workers were kept during the crossing.
0:34:49 > 0:34:51Wow!
0:34:51 > 0:34:53You first!
0:34:58 > 0:35:02It's like walking into a deserted building.
0:35:04 > 0:35:09It feels a little bit like a slavery ship or a prison.
0:35:10 > 0:35:14This was meant to carry boxes of fish.
0:35:16 > 0:35:19Instead, in this tiny dark space,
0:35:19 > 0:35:2388 men and seven women were kept for weeks at sea.
0:35:26 > 0:35:30Imagine what it would have been like, all crammed in here.
0:35:31 > 0:35:34It must have been quite horrific.
0:35:34 > 0:35:38Apparently, there were actually people employed on the boat
0:35:38 > 0:35:42to control them, to keep them crammed in these confined quarters.
0:35:44 > 0:35:48The Chinese workers were just hours from their destination
0:35:48 > 0:35:51when the Fang Ming was seized by the authorities.
0:35:52 > 0:35:56Everyone on board was sent back to China.
0:35:59 > 0:36:02In 1999, the Fang Ming was sunk
0:36:02 > 0:36:06to become the first artificial reef in Latin America.
0:36:06 > 0:36:11All these old pipes and walls have just been colonised by marine life.
0:36:11 > 0:36:14It's just completely taken it over.
0:36:20 > 0:36:22But for Lucy, the Fang Ming
0:36:22 > 0:36:27will always be a reminder of a deeper human story.
0:36:27 > 0:36:29You start to think about, you know,
0:36:29 > 0:36:33they had reasons to put their lives at risk in that way,
0:36:33 > 0:36:36to endure that experience and it's sort of representative
0:36:36 > 0:36:40of migrant workers, illegal immigrants, you know?
0:36:40 > 0:36:45The sea is providing an access for people to move around the globe
0:36:45 > 0:36:48for reasons that we wouldn't have necessarily seen in the past.
0:36:53 > 0:36:55For anyone navigating these waters,
0:36:55 > 0:36:58the weather can be dangerously unpredictable.
0:37:05 > 0:37:08The expedition arrived just after a hurricane
0:37:08 > 0:37:11and now the weather's threatening again.
0:37:16 > 0:37:18Wahey!
0:37:18 > 0:37:21That's a bit of bolt!
0:37:21 > 0:37:26- Yes, first time we've seen this weather, isn't it?- Absolutely.
0:37:26 > 0:37:27Is the hurricane coming back?
0:37:27 > 0:37:29I checked with the captain
0:37:29 > 0:37:31and he said the weather would be all right.
0:37:31 > 0:37:35"The wind's going to pick up but no hurricane," he said.
0:37:35 > 0:37:38What about the thunder and lightning, where does that fit?
0:37:38 > 0:37:41He didn't mention it, he just talked about wind!
0:37:42 > 0:37:44So there's going to be no wind,
0:37:44 > 0:37:47but we're going to be struck down by lightning?
0:37:47 > 0:37:49Yeah, I don't know, I'd better check again.
0:37:49 > 0:37:52I didn't think it rained here... Oh, my goodness!
0:37:53 > 0:37:57It's funny. I was just thinking about a passage-making brief,
0:37:57 > 0:38:01you know, get ourselves organised for the big crossing.
0:38:01 > 0:38:05I'd better incorporate some severe weather briefing, I think.
0:38:08 > 0:38:10Paul was hoping to move north,
0:38:10 > 0:38:13but because of the weather, the team is stuck here.
0:38:15 > 0:38:17We really are, you know,
0:38:17 > 0:38:21squeaking every possible thing into this expedition.
0:38:21 > 0:38:24We don't really need too much bad weather, that's for sure.
0:38:26 > 0:38:31So we're gonna anchor for, probably, at least five hours
0:38:31 > 0:38:35and then set out at three or four in the morning, make way again.
0:38:44 > 0:38:48Once the storm has blown through, they set sail again.
0:38:52 > 0:38:54The team is heading north
0:38:54 > 0:38:57to meet one of the most isolated tribes in Mexico.
0:38:57 > 0:39:00They're known as guardians of this sea,
0:39:00 > 0:39:03and Lucy's keen to find out why.
0:39:03 > 0:39:05This is the area where the Seri Indians live,
0:39:05 > 0:39:08so they're basically indigenous people who live here
0:39:08 > 0:39:12and fish the seas, so it's that sort of symbiotic relationship
0:39:12 > 0:39:16between what's happening around the edges of the ocean
0:39:16 > 0:39:17and the people that live there
0:39:17 > 0:39:21and how they sort of work with the oceans and fish the seas, etc.
0:39:26 > 0:39:29Just over 450 Seris exist today.
0:39:31 > 0:39:36Lucy's been invited to see their approach to managing this sea.
0:39:38 > 0:39:40That must be Chapo then, yeah?
0:39:40 > 0:39:43Chapo? Hello, Chapo.
0:39:43 > 0:39:46- My name is Paul.- Lucy.
0:39:46 > 0:39:48Chapo, thank you so much for your help.
0:39:48 > 0:39:5383 year-old Chapo Burnett is the village shaman, or holy man.
0:39:53 > 0:39:56He still fishes with his son Raimundo.
0:39:56 > 0:39:57OK, thank you.
0:40:01 > 0:40:05They work in a notorious area called Hell's Channel,
0:40:05 > 0:40:08so Chapo asks the sea gods for a safe passage.
0:40:08 > 0:40:12PERCUSSIVE CHANTING
0:40:19 > 0:40:23Chapo and Raimundo are going to collect scallops.
0:40:23 > 0:40:25Lucy wants to see how they go about it.
0:40:38 > 0:40:42He's actually walking along the seabed with the bag between his legs
0:40:42 > 0:40:47and he's gathering them in the way that you might harvest crops.
0:40:47 > 0:40:49Quite a nice comparison.
0:40:49 > 0:40:52Harvesting of the land and harvesting of the sea.
0:40:55 > 0:40:59In just a few minutes, Raimondo has almost filled his bag,
0:40:59 > 0:41:03but the Seris are careful to manage the stocks.
0:41:03 > 0:41:05When I talked to Raimondo,
0:41:05 > 0:41:08he implied that they basically do crop rotation.
0:41:08 > 0:41:11If they feel that they're over-harvesting one area,
0:41:11 > 0:41:15they move to another area and maybe fish octopus,
0:41:15 > 0:41:18so the principles are sustainable.
0:41:18 > 0:41:21This approach clearly works.
0:41:25 > 0:41:27In Hell's Channel, the scallop beds
0:41:27 > 0:41:30are productive and healthy year after year -
0:41:30 > 0:41:33a stark contrast to the rest of the Sea of Cortez,
0:41:33 > 0:41:36where shellfish production is collapsing.
0:41:41 > 0:41:44- For you.- Oh, thank you, Sir.
0:41:44 > 0:41:45Eat!
0:41:49 > 0:41:52Mmm, that is delicious!
0:41:52 > 0:41:57I'm never going to cook a scallop again, that was absolutely gorgeous.
0:41:57 > 0:42:02- Oh, yeah, no kidding. Muy bien, thank you.- Thank you.
0:42:05 > 0:42:08The Seri Indians demonstrate a technique
0:42:08 > 0:42:13that balances the needs of people with the health of the sea.
0:42:13 > 0:42:15OK, anchor?
0:42:15 > 0:42:17They are living in a modern world.
0:42:17 > 0:42:22They have to compete with large commercial fishing operations,
0:42:22 > 0:42:24and yet they're also very aware
0:42:24 > 0:42:27that the seas only have a limited resource,
0:42:27 > 0:42:31they have to be farmed in a way that is sustainable.
0:42:41 > 0:42:43For the last target of the expedition,
0:42:43 > 0:42:46the team aims to carry out pioneering research
0:42:46 > 0:42:49on one of the planet's largest carnivores.
0:42:50 > 0:42:54I've asked a couple of sperm whale scientists who work around here
0:42:54 > 0:42:56to come and join us for a few days on board.
0:42:59 > 0:43:01How are you?
0:43:01 > 0:43:07Dr Karina Acavido Whitehouse and Dr Diane Gendren are experts on whales.
0:43:07 > 0:43:10Welcome. Thanks for joining our expedition.
0:43:10 > 0:43:12With the scientists on board,
0:43:12 > 0:43:14the team prepares for the challenge ahead.
0:43:14 > 0:43:18I'll show you around. 'Sperm whales, that's all we care about.'
0:43:18 > 0:43:22We can't even speak or think or do anything clearly
0:43:22 > 0:43:25because we're full of sperm whales.
0:43:25 > 0:43:26There are certain experiences
0:43:26 > 0:43:30that could stay with you for the rest of your life,
0:43:30 > 0:43:35and I think if we do manage to snorkel with the sperm whales,
0:43:35 > 0:43:39I don't think I'd ever, ever forget that.
0:43:39 > 0:43:41Ever.
0:43:42 > 0:43:46Next morning the search begins.
0:43:46 > 0:43:49Relatively little is known about sperm whales.
0:43:49 > 0:43:53They live far off shore and are hard to find.
0:43:53 > 0:43:56Locating them is the first task.
0:43:56 > 0:43:59So our plan is to go about another hour north-east
0:43:59 > 0:44:03and begin our search pattern, and see what we can find.
0:44:06 > 0:44:09Sperm whales dive for up to 40 minutes at a time.
0:44:09 > 0:44:13Diane and Philippe are using a directional microphone
0:44:13 > 0:44:15to try to track them under water.
0:44:15 > 0:44:19Anything within this spectrum of the cone, it's going to pick up.
0:44:19 > 0:44:21Anything outside, like here, like my voice,
0:44:21 > 0:44:24which is quite loud right next to it, it doesn't pick up.
0:44:24 > 0:44:27It's pretty cool. Let's see what we can hear.
0:44:37 > 0:44:40Sperm whales are amongst the loudest animals in the world.
0:44:40 > 0:44:46Their clicks reach 220 decibels - louder than a shotgun blast -
0:44:46 > 0:44:49so they can be heard for many miles under water.
0:44:49 > 0:44:51So you can hear the sperm whales clicking.
0:44:51 > 0:44:54As soon as I turn it off of where the sperm whales are,
0:44:54 > 0:44:56the sounds - the clicks - go away.
0:44:56 > 0:44:58So that way, we know which way to go, right?
0:44:58 > 0:45:00Yeah, they are this way.
0:45:00 > 0:45:02Roger, that's all copied.
0:45:02 > 0:45:05So do you have an estimate on numbers in the group, over?
0:45:05 > 0:45:07Got a pretty broad sweep all along the port side.
0:45:07 > 0:45:11- It seems like there would be more than one group.- That's great news.
0:45:11 > 0:45:17Whales, we've actually come right onto a really large group,
0:45:17 > 0:45:20so we're timing this pretty perfectly.
0:45:20 > 0:45:23Very exciting times.
0:45:23 > 0:45:27Lucy catches the first glimpse.
0:45:27 > 0:45:31Oh, is it gonna turn? It's going, it's going, it's going!
0:45:42 > 0:45:43Here we go, look.
0:45:43 > 0:45:47Woo-hoo, did you see that?
0:45:47 > 0:45:49I hope these guys saw it as well.
0:45:56 > 0:45:59You couldn't book him, could you?
0:45:59 > 0:46:04This is the team's chance to take a closer look.
0:46:04 > 0:46:07Learning more about sperm whales is important
0:46:07 > 0:46:10because they're a vital part of the ocean's food chain,
0:46:10 > 0:46:13particularly here in the Sea of Cortez
0:46:13 > 0:46:17where their main diet is Humboldt squid.
0:46:17 > 0:46:20We've decided to pop in the Panga and kind of get a bit closer
0:46:20 > 0:46:23and see how they respond to us being around them
0:46:23 > 0:46:25and maybe getting in the water with them.
0:46:25 > 0:46:29And we got some dolphin escorts here that are swimming next to us.
0:46:29 > 0:46:31You could almost touch them.
0:46:36 > 0:46:38Then the moment Tooni's been waiting for.
0:46:38 > 0:46:41Oh, my goodness, look at these!
0:46:41 > 0:46:44The whales rise up to breathe.
0:46:45 > 0:46:48Part of the challenge in studying these animals
0:46:48 > 0:46:52is that you really only get the briefest glimpse
0:46:52 > 0:46:55of their life cycle by witnessing them only on the surface,
0:46:55 > 0:46:58so the opportunity to try and get underwater and film them
0:46:58 > 0:46:59is very important.
0:47:01 > 0:47:03But that's not going to be easy.
0:47:03 > 0:47:05- No, he's diving.- No, he's diving.
0:47:09 > 0:47:12Seeing as it's the deepest diving mammal on our planet,
0:47:12 > 0:47:14we could be here for some time.
0:47:16 > 0:47:20Sperm whales can dive to over 2,000 metres,
0:47:20 > 0:47:22so until they re-surface,
0:47:22 > 0:47:26studying them underwater will be out of the question.
0:47:28 > 0:47:32Right, we do our absolute utmost to get to swim with sperm whales
0:47:32 > 0:47:35and as soon as they see us they're just like,
0:47:35 > 0:47:37"You know what? I'm not interested today,"
0:47:37 > 0:47:41and that's it, one flick of the tail, gone.
0:47:47 > 0:47:52Lucy and Karina want to find out how healthy these whales are.
0:47:54 > 0:47:58Their sheer size makes taking blood virtually impossible,
0:47:58 > 0:48:02so Karina's the first scientist to try to capture
0:48:02 > 0:48:04a sample of the whale's breath in the wild.
0:48:10 > 0:48:13So we take the lids off once we are really close?
0:48:13 > 0:48:16Well, actually, we are very close.
0:48:19 > 0:48:21Germs in the whales' breath
0:48:21 > 0:48:24will tell Karina if they have any infections in their lungs.
0:48:31 > 0:48:33But taking a sample is easier said than done
0:48:33 > 0:48:37as the sample dishes have to be held right over the whale's blowhole.
0:48:41 > 0:48:42Oh, no!
0:48:48 > 0:48:49No!
0:48:53 > 0:48:59Please, please, don't. Don't go. No, no, no, no, no!
0:48:59 > 0:49:03Oh, how very disappointing!
0:49:03 > 0:49:07Reel her back in. Yes, next time.
0:49:09 > 0:49:13They fail to capture a single sample,
0:49:13 > 0:49:16but Karina has an ingenious Plan B.
0:49:19 > 0:49:22Oh, wow! What a superb looking thing.
0:49:22 > 0:49:26It is a fabulous idea to link science collecting
0:49:26 > 0:49:29with a small, miniature helicopter, wow!
0:49:31 > 0:49:33With sample dishes attached,
0:49:33 > 0:49:36the helicopter can fly straight through the whales' breath
0:49:36 > 0:49:38without disturbing them.
0:49:40 > 0:49:45But pilot Augustine Paen has strong winds to contend with.
0:49:52 > 0:49:54Oh, the wind, the wind, the wind, the wind!
0:49:54 > 0:49:56No problem.
0:49:59 > 0:50:01It's a very tricky thing to fly, this.
0:50:01 > 0:50:04We're moving up onto the whales right now,
0:50:04 > 0:50:06nice and slowly, to parallel their course,
0:50:06 > 0:50:08and then he can swing this in
0:50:08 > 0:50:13and collect a sample of the blow, so it's all a matter of timing.
0:50:13 > 0:50:15Go, Augustine, it's perfect, man!
0:50:19 > 0:50:21Go, buddy!
0:50:21 > 0:50:25Just a bit further out, Augustine.
0:50:27 > 0:50:30He's gonna dive, yeah, can you believe it?
0:50:33 > 0:50:37Tooni and Philippe aren't having much luck, either.
0:50:37 > 0:50:40I think there's a whole load of sonar conversations
0:50:40 > 0:50:42going on down there at the moment
0:50:42 > 0:50:45which is basically the sperm whales telling each other
0:50:45 > 0:50:48that there's a bunch of wannabes knocking around on the bay
0:50:48 > 0:50:51and to get the heck out of here.
0:50:51 > 0:50:55You can just see them. They're all, just diving all around us.
0:50:55 > 0:50:57OK, Augustine. Get in there, buddy.
0:50:59 > 0:51:01Despite the strong winds,
0:51:01 > 0:51:04they're finally getting closer with the helicopter.
0:51:04 > 0:51:05Good man, get in there!
0:51:05 > 0:51:08Forward, mate. That's it - now, now!
0:51:10 > 0:51:12Woo!
0:51:14 > 0:51:16That's the sample, he's got it.
0:51:16 > 0:51:20The germs caught in the dish will help reveal more information
0:51:20 > 0:51:24about the health of the sperm whale population here.
0:51:24 > 0:51:27Well done, that's perfect.
0:51:28 > 0:51:30And with each sample so hard to collect,
0:51:30 > 0:51:34this one will be important for Karina's research.
0:51:34 > 0:51:38- Thank you.- Perfect, thanks very much.
0:51:38 > 0:51:40OK, that was a good sample.
0:51:40 > 0:51:42And what is it that you're specifically looking for?
0:51:42 > 0:51:46Microbacteria, for example, the agent that can cause tuberculosis.
0:51:46 > 0:51:51There's a very common germ that causes infection in the lungs.
0:51:51 > 0:51:53It can cause severe problems, even meningitis.
0:51:53 > 0:51:56It's just a list of germs to start with.
0:51:56 > 0:51:58Karina's early findings
0:51:58 > 0:52:02suggest whales could have caught some of these bacteria from humans,
0:52:02 > 0:52:06perhaps through activities like whale watching.
0:52:07 > 0:52:09Her groundbreaking work
0:52:09 > 0:52:12has highlighted this problem for the first time.
0:52:12 > 0:52:16It might be an important development in protecting sperm whales.
0:52:17 > 0:52:22Look, look! One two, three, four...
0:52:22 > 0:52:24After almost five hours,
0:52:24 > 0:52:27the whales finally seem to be staying at the surface.
0:52:27 > 0:52:31Philippe and Tooni are desperate to observe them underwater.
0:52:31 > 0:52:33I'm off!
0:52:59 > 0:53:04There's five sperm whales down there!
0:53:13 > 0:53:17The large females in this group are over nine metres long
0:53:17 > 0:53:19and can weigh more than 12 tonnes each.
0:53:35 > 0:53:40Now you can see how they just turn around and touch other
0:53:40 > 0:53:42and they're so, so social.
0:53:44 > 0:53:48The whales are socialising. This is a rare sight.
0:53:50 > 0:53:53It suggests their food stocks are plentiful
0:53:53 > 0:53:56as they can afford to take time out from hunting.
0:54:00 > 0:54:03It shows the explosion of Humboldt squid
0:54:03 > 0:54:06might actually be benefiting these animals.
0:54:11 > 0:54:14Suddenly, Diane spots something astonishing at the surface.
0:54:14 > 0:54:20Woo-hoo! That's a big male. This is amazing.
0:54:21 > 0:54:24A large, mature male has joined the group.
0:54:26 > 0:54:31This giant in the centre of the pack could weigh over 40 tonnes.
0:54:31 > 0:54:34Male sperm whales have the largest brain
0:54:34 > 0:54:37of any animal that's ever lived.
0:54:37 > 0:54:39We don't see that every day.
0:54:39 > 0:54:42No, seriously, this is...
0:54:42 > 0:54:44you're lucky. It's a treat.
0:54:57 > 0:55:00Adult males usually live in small groups
0:55:00 > 0:55:03in the cold waters around the Poles,
0:55:03 > 0:55:06so this one has probably come here to breed.
0:55:09 > 0:55:10After a short time,
0:55:10 > 0:55:14he grows sexually aroused and starts courting the females.
0:55:17 > 0:55:21This behaviour is seldom seen and it shows
0:55:21 > 0:55:23how important the Sea of Cortez is
0:55:23 > 0:55:26as a breeding ground for sperm whales.
0:55:35 > 0:55:39More than any other, this dive has illustrated
0:55:39 > 0:55:43why the health of this sea is so vital to the life within it.
0:55:57 > 0:55:59I'm blown away.
0:55:59 > 0:56:02I'm one of the luckiest people on the planet.
0:56:02 > 0:56:06There just aren't words to explain how incredible that feeling is.
0:56:06 > 0:56:08I got sonar boomed.
0:56:08 > 0:56:13I heard and felt that pulse just that boom going right through my body
0:56:13 > 0:56:16as it was doing the kind of X-ray scan of what the heck I was.
0:56:16 > 0:56:18I want a hug!
0:56:23 > 0:56:27Oh, man! I felt like crying. It was a really strange reaction,
0:56:27 > 0:56:30but you feel like crying when you're watching.
0:56:33 > 0:56:37It's a spectacular end to the expedition...
0:56:37 > 0:56:38How was it?
0:56:38 > 0:56:40- Oh, my god, it was fantastic! Paul, Lucy...
0:56:40 > 0:56:43A voyage that's offered a remarkable window
0:56:43 > 0:56:46into the world of our changing oceans.
0:56:46 > 0:56:48Well done, well done indeed.
0:56:51 > 0:56:53The Sea of Cortez is a place in flux
0:56:53 > 0:56:56and there's so many things we don't know
0:56:56 > 0:56:59and so many things that we're doing carelessly,
0:56:59 > 0:57:03and what is that doing to the natural balance?
0:57:03 > 0:57:07This sea has revealed how destructive man's impact can be,
0:57:09 > 0:57:13but it's also shown us we can live in harmony with the ocean,
0:57:18 > 0:57:21and that in the face of great change,
0:57:21 > 0:57:24life can adapt and even thrive.
0:57:26 > 0:57:28The Sea of Cortez, at the moment,
0:57:28 > 0:57:33still seems to be an incredibly rich place, so yes, it's changing,
0:57:33 > 0:57:39but I personally feel like the sea finds its own equilibrium.
0:57:41 > 0:57:46This shifting balance will create winners and losers
0:57:46 > 0:57:49but as yet it's impossible to predict who they'll be.
0:57:57 > 0:58:02Next time, the team braves the wild Southern Ocean...
0:58:03 > 0:58:07..and explores its unique underwater world.
0:58:07 > 0:58:10Very, very strange creatures, aren't they?
0:58:10 > 0:58:13Parts are warming twice as fast as other oceans,
0:58:13 > 0:58:15pushing marine life to the brink.
0:58:15 > 0:58:19The expedition sees what can be done.
0:58:19 > 0:58:21Oh, it's lobster everywhere!
0:58:40 > 0:58:43Subtitles by Red Bee Media Ltd
0:58:43 > 0:58:46E-mail subtitling@bbc.co.uk