0:00:42 > 0:00:47This is a blue whale, the largest animal on the planet.
0:00:49 > 0:00:53In fact, the largest animal that has ever lived.
0:01:04 > 0:01:10It's 100 foot long and weighs nearly 200 tonnes.
0:01:16 > 0:01:21For millions of years, these giant whales
0:01:21 > 0:01:25and their super-intelligent cousins, the dolphins,
0:01:25 > 0:01:29have ruled the world beneath the waves.
0:01:38 > 0:01:42Sadly, our relationship with them has not always been a friendly one.
0:01:42 > 0:01:45In the past, we persecuted them.
0:01:45 > 0:01:48But today we are reaching out to them
0:01:50 > 0:01:55and experiencing a sense of wonder that's hard to explain.
0:02:02 > 0:02:06As we explore the seven seas, we'll come face to face
0:02:06 > 0:02:10with the world's most extraordinary whales and dolphins.
0:02:11 > 0:02:13Uncovering their secrets
0:02:13 > 0:02:15alongside the scientists
0:02:15 > 0:02:18who dedicate their lives to understanding them.
0:02:18 > 0:02:21The great mystery is, what are the whales doing here?
0:02:21 > 0:02:25These killer whales demand respect. They've taken out a minke whale
0:02:25 > 0:02:28that probably weighs more than ten tonnes.
0:02:28 > 0:02:32I think we could talk to dolphins within five years.
0:02:33 > 0:02:36Sharing these breathtaking encounters,
0:02:36 > 0:02:39two of the world's top underwater cameramen.
0:02:41 > 0:02:43I've waited a long time to see a blue underwater,
0:02:43 > 0:02:45and that was just magic.
0:02:47 > 0:02:51Fantastic, today is the best day of my life.
0:02:54 > 0:02:55Whales are born to be big.
0:02:59 > 0:03:03Even this newborn baby weighs over a tonne.
0:03:09 > 0:03:15So what is it like to live your life as an ocean giant?
0:03:40 > 0:03:45Part of our attraction to whales has always been their gentle nature.
0:03:48 > 0:03:52But we are beginning to discover a different story,
0:03:52 > 0:03:56one spiced with sex and violence.
0:04:00 > 0:04:05Every spring thousands of humpback whales are drawn to Hawaii,
0:04:05 > 0:04:08the world's most remote island chain,
0:04:08 > 0:04:10to do battle.
0:04:20 > 0:04:25A scientific team heads out over the tropical seas of Maui,
0:04:29 > 0:04:33for a bird's-eye view of one of nature's greatest showdowns.
0:04:39 > 0:04:45Gangs of humpback whales posture, ram, and can even kill each other.
0:04:50 > 0:04:54So what has driven these giants to fight?
0:05:01 > 0:05:03The answer to this question needs
0:05:03 > 0:05:06a close-up view of the action from underwater.
0:05:09 > 0:05:14Jeff Kalbach has spent 15 years watching fighting whales,
0:05:14 > 0:05:18trying to make sense of their belligerent behaviour.
0:05:18 > 0:05:20OK, she is ready to go.
0:05:21 > 0:05:25He's joined by ex-Cousteau cameraman Didier Noirot,
0:05:25 > 0:05:27who's hoping to find more clues
0:05:27 > 0:05:31by going right into the thick of the action.
0:05:31 > 0:05:33Humpbacks are my favourite whales.
0:05:33 > 0:05:37I have filmed them many times before
0:05:37 > 0:05:40but there is one thing I'm really keen to see,
0:05:40 > 0:05:43is to see the fight of the males.
0:05:43 > 0:05:45It's going to be very dangerous,
0:05:45 > 0:05:49you can be hit by the tail end. I guess you can die.
0:05:50 > 0:05:53They go so fast underwater despite their size,
0:05:53 > 0:05:56and that's going to be, like, a challenge for me.
0:06:00 > 0:06:04There's news of some action a mile offshore.
0:06:06 > 0:06:10See that pectoral fin, the white?
0:06:10 > 0:06:13Now it's going up, rolling over.
0:06:15 > 0:06:22A female humpback announces she's here, and she's ready to mate.
0:06:27 > 0:06:30These fin slaps can be heard a mile away.
0:06:34 > 0:06:38And almost immediately a gang of suitors is headed her way.
0:06:42 > 0:06:46One, two, three, four, five, there's definitely six, seven.
0:06:46 > 0:06:47Oh, big guy.
0:06:49 > 0:06:53Before long, she's surrounded by male admirers.
0:06:53 > 0:06:56To help her choose the strongest mate
0:06:56 > 0:06:58she sets the ultimate fitness contest.
0:07:05 > 0:07:07She sets off on a marathon swim
0:07:07 > 0:07:10with the pack of jostling males in hot pursuit.
0:07:14 > 0:07:17Each one is trying to win her affections
0:07:17 > 0:07:19by staying as close to her as possible.
0:07:28 > 0:07:31- All ready to go? - Yes, exactly.- We have to go.
0:07:46 > 0:07:50Underwater, the 40-tonne males might seem relaxed
0:07:50 > 0:07:52but the tension is building.
0:07:57 > 0:08:00They are already sizing each other up.
0:08:01 > 0:08:05These lustful rivals could do battle at any minute.
0:08:09 > 0:08:12Didier must stay alert.
0:08:14 > 0:08:18He can't risk diving with scuba tanks,
0:08:18 > 0:08:20as any dispelled air could be interpreted
0:08:20 > 0:08:24as a challenge by the males, who blow bubbles as a sign of aggression.
0:08:26 > 0:08:28Like now.
0:08:41 > 0:08:44Suddenly, the female comes into view,
0:08:44 > 0:08:49escorted by a bubble-blowing lead male, or "primary".
0:09:00 > 0:09:04It's a good start to the filming.
0:09:06 > 0:09:08There was the two animals right here
0:09:08 > 0:09:11and I could tell that wasn't the female or the primary
0:09:11 > 0:09:14so we were looking and then all of a sudden, Didier was like, ooh,
0:09:14 > 0:09:17he hits me and then right behind us was the primary
0:09:17 > 0:09:19coming with a bubble trail.
0:09:19 > 0:09:23- Bubble trail which I filmed.- Yes.
0:09:23 > 0:09:26Jeff believes the escort uses bubbles
0:09:26 > 0:09:29to produce a 100-foot curtain
0:09:29 > 0:09:32to screen the female from other challengers.
0:09:37 > 0:09:40And, with lungs the size of a car,
0:09:40 > 0:09:45it's the biggest male that can expel the most air.
0:09:52 > 0:09:57This hot pursuit can last all day and cover miles of ocean.
0:09:58 > 0:10:02To stand a chance of catching the action the team must race ahead.
0:10:13 > 0:10:18Meanwhile, the competition escalates to explosive shows of strength.
0:10:18 > 0:10:21Look at that, he's riding contact with her, you can see his pec fin.
0:10:21 > 0:10:24The other animals are colliding into him,
0:10:24 > 0:10:27look at him pushing and shoving.
0:10:27 > 0:10:30See that fluke just flick over like this
0:10:30 > 0:10:34and he's diving down, charging at somebody, pushing somebody away.
0:10:38 > 0:10:43For the dive team, it's like jumping into six lanes of traffic.
0:10:57 > 0:11:02Testosterone-fuelled giants charge by at 20 miles per hour.
0:11:18 > 0:11:22A male upends into the crucifix block,
0:11:23 > 0:11:27a tactic to stop a rival in its tracks.
0:11:46 > 0:11:48As the violence intensifies,
0:11:48 > 0:11:54it becomes more dangerous for the rival whales and for the cameraman.
0:12:19 > 0:12:23A huge male charges straight for his bubble-blowing rival,
0:12:23 > 0:12:25ramming him off course.
0:12:41 > 0:12:45For Didier, it is the dive of a lifetime.
0:12:48 > 0:12:53- It was amazing.- It was perfect, good dropping, thank you, good advice,
0:12:53 > 0:12:56we are just at the right time at the right moment.
0:12:56 > 0:13:02We saw the collision and then that male...with his, all his bubbles.
0:13:19 > 0:13:24Using his weight advantage, the bigger male takes the lead,
0:13:24 > 0:13:30but the female has yet to choose her mate and the marathon continues.
0:13:30 > 0:13:33Let's go. Let's go. Go, go.
0:13:44 > 0:13:48Then, suddenly, the mood changes.
0:14:00 > 0:14:05The female has vanished, perhaps having eloped with her chosen male.
0:14:07 > 0:14:10And without the object of their desire
0:14:10 > 0:14:12the heat has gone out of the battle.
0:14:22 > 0:14:25Minutes after duelling in the high seas,
0:14:25 > 0:14:29the males are caressing each other in a graceful ballet.
0:15:10 > 0:15:15And they stopped, they danced like a ballet, beautiful.
0:15:17 > 0:15:21How beautiful to watch them just moving and turning and touching.
0:15:22 > 0:15:25It was spectacular, very spectacular.
0:15:37 > 0:15:41Despite the scientists' best efforts,
0:15:41 > 0:15:44no-one has ever seen humpbacks mating.
0:15:54 > 0:15:58But everything points to the female choosing the biggest blowing
0:15:58 > 0:16:02and hardest hitting male to be the father of her young.
0:16:15 > 0:16:20It's not just humpback males for whom size really matters.
0:16:26 > 0:16:32Here, off the coast of Argentina, is the biggest whale orgy on the planet.
0:16:43 > 0:16:47In the sheltered bays of Peninsula Valdes,
0:16:47 > 0:16:507,000 southern right whales
0:16:50 > 0:16:53come to mate, give birth
0:16:53 > 0:16:56and raise their young.
0:17:06 > 0:17:10Even for a veteran cameraman, it's an extraordinary spectacle.
0:17:13 > 0:17:17I have never seen that before. So many whales, so close to shore.
0:17:17 > 0:17:21It's probably the only place in the world you can see that.
0:17:25 > 0:17:29Right whales are huge, at least twice the sizes of humpbacks.
0:17:34 > 0:17:38Their tails alone match the wing span of a light aircraft.
0:17:51 > 0:17:53Unlike the aggressive humpbacks,
0:17:53 > 0:17:57male right whales are surprisingly gentle lovers.
0:18:03 > 0:18:08A 40-year project studying the lives of these extraordinary creatures
0:18:08 > 0:18:12offers a unique opportunity to get close to these gentle giants,
0:18:12 > 0:18:14and Didier can't wait.
0:18:14 > 0:18:16I love southern right whales,
0:18:16 > 0:18:19they are probably the friendliest of the whales,
0:18:19 > 0:18:22they are very approachable, they don't mind the divers,
0:18:22 > 0:18:26and here in Patagonia the water is very clear
0:18:26 > 0:18:29so I'm really looking to do something fantastic.
0:18:31 > 0:18:34Exploring the mating habits of these friendly whales
0:18:34 > 0:18:36is Dr Mariano Sironi.
0:18:46 > 0:18:49Tragically, it's their very friendliness
0:18:49 > 0:18:53that made them such easy targets for the early whalers
0:18:53 > 0:18:56and made them the "right" whales to hunt.
0:18:57 > 0:19:01Today, these giants are making a slow but promising recovery,
0:19:01 > 0:19:05thanks to conservationists like Mariano, and to their...
0:19:07 > 0:19:08..amorous nature.
0:19:08 > 0:19:12- You see the male in the right position under the female?- Yeah.
0:19:12 > 0:19:16You can see the flipper of the male hugging the female,
0:19:16 > 0:19:18and they are belly to belly.
0:19:25 > 0:19:28Both sexes are very promiscuous,
0:19:28 > 0:19:30and the males are equipped
0:19:30 > 0:19:34with a particularly astonishing adaptation for mating,
0:19:34 > 0:19:36a pair of giant testicles!
0:19:37 > 0:19:41Their two testicles together can weigh up to one tonne.
0:19:41 > 0:19:45The testes of the right whale are 20 times heavier
0:19:45 > 0:19:47- than those of the blue whale... - 20?!
0:19:47 > 0:19:51..so, that's an indication of a very sexual species.
0:19:54 > 0:19:56Mariano is investigating the link
0:19:56 > 0:20:00between the size of a male's giant testicles
0:20:00 > 0:20:02and his chances of paternity.
0:20:05 > 0:20:10But making sense of this mass of writhing bodies at the surface is difficult.
0:20:10 > 0:20:14To complete the picture, Didier must get in the water.
0:20:16 > 0:20:17Let's go.
0:20:32 > 0:20:36With most whales, getting close to them is the challenge.
0:20:36 > 0:20:41With these whales, the problem is getting TOO close.
0:20:42 > 0:20:44WHALE GRUNTS
0:20:44 > 0:20:47WHALE BELLOWS SLOWLY
0:20:55 > 0:20:59They are so friendly that a diver must be careful
0:20:59 > 0:21:04not to be accidentally crushed by one of these 80-tonne giants.
0:21:16 > 0:21:19Underwater, it becomes abundantly clear
0:21:19 > 0:21:23that males not only boast giant testicles
0:21:23 > 0:21:25but that, at nine foot long,
0:21:25 > 0:21:28they have the biggest penis in the animal kingdom.
0:21:30 > 0:21:33And one which appears to have a mind of its own!
0:21:42 > 0:21:46When they finally mate, it's belly to belly.
0:22:02 > 0:22:04But this is just the start for the female,
0:22:04 > 0:22:08as she goes on to mate with the rest of the males,
0:22:08 > 0:22:10sometimes up to five or six at a time.
0:22:18 > 0:22:24After an hour of being spellbound by this extraordinary courtship,
0:22:24 > 0:22:27Didier's air finally runs out.
0:22:27 > 0:22:29- That was just fantastic.- Good.
0:22:29 > 0:22:34What I have seen just now is the most amazing spectacle
0:22:34 > 0:22:36I have ever seen underwater.
0:22:36 > 0:22:38Ohh, that's good.
0:22:41 > 0:22:43Didier's intimate images of the mating
0:22:43 > 0:22:46will be invaluable to Mariano's study.
0:22:50 > 0:22:53By mating with a variety of males,
0:22:53 > 0:22:58the female ensures that the battle for paternity goes on inside her
0:22:58 > 0:23:00and not in the open seas.
0:23:08 > 0:23:09But it's still the biggest male
0:23:09 > 0:23:12that stands the best chance of winning that battle,
0:23:12 > 0:23:16because by having the longest penis and largest testicles
0:23:16 > 0:23:19he can flush out any competitor's sperm.
0:23:27 > 0:23:32For male southern right whales, size really does matter.
0:23:37 > 0:23:38And in 12 months' time
0:23:38 > 0:23:41this female will give birth to a calf
0:23:41 > 0:23:43that will inherit its father's strength
0:23:43 > 0:23:46and, most importantly, his size.
0:23:54 > 0:23:58But here, off the west coast of Mexico,
0:23:58 > 0:24:01it's the size of the mother that matters.
0:24:16 > 0:24:20These calm, safe waters are ideal nurseries
0:24:20 > 0:24:23for these playful grey whale newborns.
0:24:32 > 0:24:36For the first three months of their lives,
0:24:36 > 0:24:38when they're at their most vulnerable,
0:24:38 > 0:24:42the calves live in peace, feeding only on their mothers' milk.
0:24:53 > 0:24:55The calf has tripled in weight,
0:24:55 > 0:24:59but for his mother there's nothing to eat here.
0:25:01 > 0:25:05For her own survival, she must leave this safe haven
0:25:05 > 0:25:09and lead her calf on a perilous journey,
0:25:09 > 0:25:13the longest made by any mammal.
0:25:16 > 0:25:22From the barren waters of Mexico, they will swim 6,000 miles
0:25:22 > 0:25:25to the rich feeding grounds of Alaska.
0:25:27 > 0:25:30During its 50-year lifespan,
0:25:30 > 0:25:34a grey whale will swim over half a million miles!
0:25:39 > 0:25:43As they head north from Mexico, they hug the coastline,
0:25:43 > 0:25:45hiding in the murky shallows.
0:25:57 > 0:26:00But at Monterey Bay, California,
0:26:00 > 0:26:03they can take a short cut across the deep mouth of the bay,
0:26:03 > 0:26:05and that's a gamble.
0:26:06 > 0:26:08They're now exposed to attack.
0:26:16 > 0:26:19At dawn, a scientific research team heads out
0:26:19 > 0:26:21into the troubled waters of the bay.
0:26:23 > 0:26:26BELL RINGS, SEALS BARK
0:26:36 > 0:26:41John Durban is studying the attacks on grey whales.
0:26:41 > 0:26:44This is one of the most important ambush points
0:26:44 > 0:26:46for grey whales along the coast.
0:26:46 > 0:26:48The grey whales are coming to this point here
0:26:48 > 0:26:51and making the decision whether to tuck round in the bay
0:26:51 > 0:26:55or cut across to the other side and save them some time.
0:26:55 > 0:26:59But what could possibly take on a 30-tonne whale,
0:26:59 > 0:27:02especially one defending her calf?
0:27:03 > 0:27:08No-one knows better than underwater cameraman Doug Allan.
0:27:08 > 0:27:14Ten years ago, he filmed a ferocious attack in this exact spot.
0:27:16 > 0:27:20And what he saw was the oceans' top predator in action.
0:27:20 > 0:27:22Killer whales.
0:27:28 > 0:27:31The intensity of the battle has left a lasting impression.
0:27:33 > 0:27:36It's a very harrowing experience
0:27:36 > 0:27:40watching killer whales take down a grey whale calf.
0:27:40 > 0:27:42The calf tries so hard to survive,
0:27:42 > 0:27:45the mother does all she can, too.
0:27:47 > 0:27:50The killer whales are just so relentless,
0:27:50 > 0:27:53they harry, harry, and they will just take those two apart.
0:28:03 > 0:28:09A male killer whale is ten tonnes of pure power, a cunning mind
0:28:09 > 0:28:10and 60 teeth.
0:28:17 > 0:28:20The killers targeted the defenceless calf,
0:28:20 > 0:28:24its survival dependent on the strength and size of its mother.
0:28:27 > 0:28:32The killer whales' strength is in numbers.
0:28:32 > 0:28:35They launched coordinated attacks to outmanoeuvre the mother.
0:28:39 > 0:28:43But she wasn't going to give up her only calf without a desperate fight.
0:28:44 > 0:28:47Four times the size of her attackers
0:28:47 > 0:28:50and with thick skin protected by barnacles,
0:28:50 > 0:28:54she beat them back with deadly tail swipes.
0:29:01 > 0:29:04But the killer whales had chosen their victim well.
0:29:09 > 0:29:13The mother was neither big enough nor strong enough
0:29:13 > 0:29:14to withstand the onslaught,
0:29:14 > 0:29:18and the killers drove a wedge between mother and calf.
0:29:24 > 0:29:28Eventually, they drowned the isolated calf.
0:29:40 > 0:29:43After six hours, the battle was over,
0:29:43 > 0:29:48the mother exhausted, the calf killed and eaten.
0:29:54 > 0:29:57A decade on,
0:29:57 > 0:30:01John is waiting for this season's killer whale attacks to begin.
0:30:01 > 0:30:04- What's happening, John? - They got killer whales,
0:30:04 > 0:30:08they're about a mile north of the ship over here, the Miller Freeman,
0:30:08 > 0:30:12and the killer whales were chasing something when they arrived, they've stopped.
0:30:21 > 0:30:25John is planning to attach state-of-the-art satellite tags
0:30:25 > 0:30:28to these killer whales for the first time.
0:30:36 > 0:30:37We've got a group of killer whales.
0:30:37 > 0:30:40As we're coming up we can see there are birds overhead,
0:30:40 > 0:30:43and you can smell a really strong fishy smell right now.
0:30:43 > 0:30:46That's a good indication they've killed recently,
0:30:46 > 0:30:49that's the blubber smell of a whale.
0:30:52 > 0:30:53The attack is over
0:30:53 > 0:30:57but the killer whales are now feeding on their victim.
0:30:59 > 0:31:02The bulk of the carcass is probably sinking
0:31:02 > 0:31:03and they're trying to hold it up,
0:31:03 > 0:31:06but we have seen a whale with a big chunk of flesh in its mouth.
0:31:06 > 0:31:09They're probably dismantling it right now.
0:31:09 > 0:31:12These killer whales just demand respect.
0:31:13 > 0:31:18The feasting whales offer John the best chance to secure a tag.
0:31:18 > 0:31:21Right under us here, it's going forwards,
0:31:21 > 0:31:23so if you go forward a little...
0:31:24 > 0:31:27To work properly, the tag must be positioned perfectly
0:31:27 > 0:31:32on the dorsal fin. John's aim has to be spot on.
0:31:32 > 0:31:35I'm waiting... OK, this one's coming up here.
0:31:36 > 0:31:37Perfect.
0:31:38 > 0:31:40Oh, yeah, look at that, it's flush.
0:31:40 > 0:31:43Just the tapes... the antenna looks good.
0:31:43 > 0:31:47With so many killer whales gathered in one place,
0:31:47 > 0:31:51John is eager to secure as many tags as he can.
0:31:53 > 0:31:56That's good, right there, it's good.
0:31:56 > 0:31:59When you tagged those whales they didn't flinch.
0:31:59 > 0:32:02That's the nice thing about small tags, it's an issue of scale.
0:32:02 > 0:32:05We're putting a 40-gram tag on a seven-tonne whale.
0:32:05 > 0:32:07They don't notice it.
0:32:09 > 0:32:11Now we've got some tags on,
0:32:11 > 0:32:14the signals are going to get pinged from the tags up to some satellites
0:32:14 > 0:32:16and we receive the signals on my phone.
0:32:16 > 0:32:20That'll allow us to track them over the next few weeks, hopefully.
0:32:22 > 0:32:26John can now track their movements and, critically,
0:32:26 > 0:32:29work out how often grey whales are attacked.
0:32:35 > 0:32:39Only one week later, some extraordinary results come through.
0:32:40 > 0:32:43Rather than wait in ambush in the bay,
0:32:43 > 0:32:47these killer whales have headed way up the coast.
0:32:47 > 0:32:49Here's Monterey Bay, to give an idea of the scale.
0:32:49 > 0:32:52It looks pretty small on this chart. The first group we tagged,
0:32:52 > 0:32:54in eight days now, no, further,
0:32:54 > 0:32:57have moved all the way to the top of this chart
0:32:57 > 0:33:00to Northern Oregon by the Umpqua River. It's over 700 kilometres.
0:33:03 > 0:33:07The hungry killer whales have had to broaden their search for prey
0:33:07 > 0:33:09way beyond Monterey Bay,
0:33:12 > 0:33:16perhaps because there are far fewer grey whale mother and calves
0:33:16 > 0:33:19undertaking their epic migration this year.
0:33:23 > 0:33:26It's highly likely that this immense migration,
0:33:26 > 0:33:29probably the longest regular migration of any mammal,
0:33:29 > 0:33:32is largely due to the threat of predation by killer whales.
0:33:36 > 0:33:39Grey whales may choose to breed in Mexico,
0:33:39 > 0:33:43thousands of miles away from their northern feeding grounds,
0:33:43 > 0:33:46simply to keep the calves safe from killer whales
0:33:46 > 0:33:48for as long as possible.
0:33:51 > 0:33:53After three months travelling,
0:33:53 > 0:33:56the grey whales finally make it to Alaska.
0:34:00 > 0:34:05The emaciated whales can now gorge themselves.
0:34:08 > 0:34:14Each day they sieve out over a tonne of shellfish from the muddy seabed.
0:34:30 > 0:34:35But it's only the largest, strongest and most determined mothers
0:34:35 > 0:34:37who can save the lives of their calves
0:34:37 > 0:34:40on this most gruelling of migrations.
0:34:53 > 0:34:56Further north, within the Arctic Circle,
0:34:56 > 0:35:00lives a whale three times the size of a grey whale.
0:35:02 > 0:35:07And it's grown massive for even more extraordinary reasons.
0:35:17 > 0:35:20As it stays in the Arctic all year round,
0:35:20 > 0:35:24it doesn't need to be big to survive lengthy migrations.
0:35:28 > 0:35:32And, protected by the maze of shifting pack ice,
0:35:32 > 0:35:35it has less to fear from killer whales.
0:35:52 > 0:35:55It's a bowhead whale,
0:35:55 > 0:35:58named after its enormous curved upper jaw.
0:36:02 > 0:36:04So, why is this whale so big?
0:36:19 > 0:36:22In eastern Greenland, a scientific team
0:36:22 > 0:36:26is attempting to unlock the secrets of this little-known giant.
0:36:36 > 0:36:40Cameraman Doug Allan has 30 years' experience
0:36:40 > 0:36:42filming at the frozen poles.
0:36:44 > 0:36:46Every time I come to the Arctic
0:36:46 > 0:36:50I think, "This is it, never again. Next shoot, Caribbean,"
0:36:50 > 0:36:53but there is something special about this that keeps pulling you back.
0:36:58 > 0:37:02In the last two centuries, bowheads were almost wiped out
0:37:02 > 0:37:07by commercial whalers, and are notoriously wary of humans.
0:37:11 > 0:37:14No-one knows this better than Doug.
0:37:14 > 0:37:18I think if bowheads had personalities they'd be a little bit sad.
0:37:18 > 0:37:22They've had such a lot of bad things done to them, were almost wiped out,
0:37:22 > 0:37:24but somehow I think they're coming back.
0:37:24 > 0:37:27They'd like to be friendlier
0:37:27 > 0:37:29but they just don't yet know how to trust us.
0:37:34 > 0:37:37WHALESONG ECHOES
0:37:40 > 0:37:43During the winter bowheads are impossible to track,
0:37:43 > 0:37:47but in spring they announce their presence with song.
0:37:49 > 0:37:55Eavesdropping on these mysterious giants is scientist Outi Tervo.
0:37:55 > 0:37:59She's one of the very few whale researchers prepared to tough it out
0:37:59 > 0:38:02in this brutally hostile part of the world.
0:38:02 > 0:38:05It's a "Whooo"...
0:38:06 > 0:38:08..and then a "Rughhhh."
0:38:10 > 0:38:14Outi suspects that these are mating calls
0:38:14 > 0:38:18and that the bowheads may be gathering somewhere close to breed.
0:38:18 > 0:38:20- Can I have a listen?- Yeah, sure.
0:38:23 > 0:38:26Ah, "Whooo!"
0:38:27 > 0:38:29"Oooh," says the other one.
0:38:29 > 0:38:30"Oooh, I like you."
0:38:33 > 0:38:37Outi has never been able to see bowheads under the ice before
0:38:37 > 0:38:39and hopes that Doug's camera
0:38:39 > 0:38:44might offer new insights into the world of these secretive whales.
0:38:48 > 0:38:54Unfortunately for Doug, bowheads are the masters of concealment,
0:38:54 > 0:38:58able to hold their breath for up to an hour and a half.
0:39:01 > 0:39:05To make matters worse, the elements aren't exactly inviting.
0:39:05 > 0:39:07Brrrrrr!
0:39:08 > 0:39:11It's minus 20 degrees Celsius
0:39:11 > 0:39:14and Doug hasn't even got in the water yet.
0:39:16 > 0:39:18But at least there's a whale!
0:40:01 > 0:40:03She just heard me coming, I think.
0:40:03 > 0:40:07Bowheads are remarkably alert to danger.
0:40:07 > 0:40:12One small splash and this one simply melted away.
0:40:13 > 0:40:17The only hope is for a whale that is a little less skittish.
0:40:32 > 0:40:37Gosh, these whales... Gee, they're hard to get close to.
0:40:44 > 0:40:50As the game of cat and mouse continues, the Arctic weather closes in.
0:41:00 > 0:41:02Even with his insulated dive suit
0:41:02 > 0:41:06Doug is close to hypothermia after just two hours.
0:41:06 > 0:41:09- LAUGHING:- I must be mad.
0:41:20 > 0:41:26But how do bowheads survive this cold?
0:41:28 > 0:41:32It's all to do with being a giant.
0:41:35 > 0:41:39The bigger and rounder the body,
0:41:39 > 0:41:43the better it is at retaining heat.
0:41:43 > 0:41:47Wrapped in 50 tonnes of insulating blubber,
0:41:47 > 0:41:50these whales are the fattest animals on the planet.
0:41:50 > 0:41:55Indeed, half their entire body weight is fat!
0:42:10 > 0:42:14The team continues to try to film the bowheads underwater,
0:42:14 > 0:42:17this time using a pole camera.
0:42:24 > 0:42:29For the whale, this method of filming may be less intrusive,
0:42:29 > 0:42:33and for Doug, well, it's just a little bit warmer.
0:42:35 > 0:42:38Hold it there, I can see a fluke.
0:42:51 > 0:42:54That was the first underwater shot of the bowhead.
0:42:54 > 0:42:58I'm sure we can improve on it, but at least it's a start.
0:42:58 > 0:43:04Already they're discovering something distinctive about these creatures.
0:43:08 > 0:43:11The footage reveals a patchwork of markings
0:43:11 > 0:43:14all over the whale's body.
0:43:21 > 0:43:25Bowheads use their backs to break through the ice
0:43:25 > 0:43:28to create vital breathing holes,
0:43:28 > 0:43:32permanently scarring their skin in the process.
0:43:32 > 0:43:35These patterns are as unique as fingerprints
0:43:35 > 0:43:37and help identify each individual whale.
0:43:40 > 0:43:42Nice shot, nice shot.
0:43:45 > 0:43:48With the whales so close,
0:43:48 > 0:43:52it's an ideal opportunity for the scientists to collect a DNA sample.
0:43:59 > 0:44:04No more than a pin prick to these fat-coated giants.
0:44:16 > 0:44:19Analysis of bowhead tissue samples is revealing
0:44:19 > 0:44:24some extraordinary links between their size and their age.
0:44:27 > 0:44:32Some estimate they are over 200 years old, so this could be a sample of a 200-year-old whale.
0:44:32 > 0:44:37But that would make that animal one of the oldest living animals on the planet.
0:44:37 > 0:44:40Yes, it would be the oldest mammal we know of right now.
0:44:43 > 0:44:45WHALESONG
0:44:49 > 0:44:52Bowheads can live for over 200 years
0:44:52 > 0:44:56because they have a lower body temperature than any other whale,
0:44:56 > 0:45:01and the lower your body temperature, the slower you age.
0:45:10 > 0:45:15These enormous whales can afford to live life slowly,
0:45:15 > 0:45:18roaming the rich Arctic waters,
0:45:18 > 0:45:20simply opening their mouths
0:45:20 > 0:45:22and filtering all the food they need.
0:45:25 > 0:45:30Uniquely, a bowhead's backbone never fuses,
0:45:30 > 0:45:35so all that time they never stop growing.
0:45:43 > 0:45:46Just think of all the wisdom that's in that whale.
0:45:46 > 0:45:50For 200 years he's swum around the Arctic, slowly finding his way around.
0:45:50 > 0:45:53They are amazing, and still mysterious too.
0:45:57 > 0:46:00Although this gentle giant can grow for centuries,
0:46:00 > 0:46:04there is one whale that is even bigger.
0:46:16 > 0:46:18Only in the vastness of the ocean
0:46:18 > 0:46:21could there live the largest creature on earth.
0:46:29 > 0:46:31The blue whale.
0:46:51 > 0:46:53Before commercial whaling,
0:46:53 > 0:46:58300,000 blue whales cruised the oceans.
0:47:05 > 0:47:08Today, less than 10,000 remain.
0:47:14 > 0:47:17We know almost nothing of their lives
0:47:17 > 0:47:21and for years assumed that, like the other great whales,
0:47:21 > 0:47:25they migrated to cold, rich seas to feed.
0:47:31 > 0:47:35Yet, in the warm tropical waters off Sri Lanka in the Indian Ocean,
0:47:35 > 0:47:39blue whales seem to be living here all year round.
0:47:50 > 0:47:55An international team of scientists, led by Anouk Ilangakoon,
0:47:55 > 0:48:00has pioneered blue-whale research here through the decades of civil war.
0:48:05 > 0:48:10This is a once-in-a-lifetime opportunity for cameramen Doug and Didier,
0:48:10 > 0:48:13who have never managed to film blue whales before.
0:48:13 > 0:48:17They're not easy to approach like southern right whales.
0:48:17 > 0:48:19They're not friendly like humpback whales.
0:48:19 > 0:48:21These are very difficult characters.
0:48:21 > 0:48:25If I get one shot of a blue whale underwater,
0:48:25 > 0:48:27that would be a dream come true.
0:48:29 > 0:48:33They head out into blue-whale territory,
0:48:33 > 0:48:3620 miles into the open ocean.
0:48:40 > 0:48:43Despite Anouk's decades studying blue whales,
0:48:43 > 0:48:48she is still unsure how many there are off Sri Lanka,
0:48:48 > 0:48:50and why.
0:48:50 > 0:48:53Sri Lankan blue whales seem to be pretty unique.
0:48:53 > 0:48:56They seem to stay around here year round
0:48:56 > 0:49:00and the real mystery is what are they feeding on?
0:49:00 > 0:49:04And what is there to sustain them throughout the year in these waters?
0:49:07 > 0:49:14Will it finally be possible to record what these mysterious whales are up to?
0:49:43 > 0:49:45The whales remain elusive.
0:49:52 > 0:49:55Did you get me my shot yet?
0:49:55 > 0:49:57That was the first time! No, be patient.
0:49:57 > 0:50:00This is going to be difficult, you know.
0:50:00 > 0:50:04Those whales were... They didn't stop, they just came towards me.
0:50:07 > 0:50:12Perfectly streamlined, blues are one of the fastest ocean giants,
0:50:12 > 0:50:14powering along at over 30 miles an hour.
0:50:23 > 0:50:26But at least they're sticking around.
0:50:30 > 0:50:34So what holds them to this patch of blue sea off Sri Lanka?
0:50:38 > 0:50:42By measuring how temperature and salinity change with depth,
0:50:42 > 0:50:45scientist Asha de Vos believes she has the answer.
0:50:47 > 0:50:51What I've discovered is that along our coastline
0:50:51 > 0:50:54there are these areas of upwelling, pretty large areas,
0:50:54 > 0:50:57which are bringing all this cold, nutrient-rich water
0:50:57 > 0:50:59from the depths to the surface,
0:50:59 > 0:51:02which might be providing conditions for whale food.
0:51:02 > 0:51:08The upwelling of cold, nutrient-rich water is unusual for the tropics,
0:51:08 > 0:51:11but appears to contain the perfect food for blue whales,
0:51:11 > 0:51:13whatever that is.
0:51:15 > 0:51:20Any images of whales feeding in Sri Lanka will not only be a first,
0:51:20 > 0:51:23but will also help support Asha's theory.
0:51:55 > 0:51:58Ironically, the water is so full of nutrients,
0:51:58 > 0:52:00it's too murky to film in.
0:52:02 > 0:52:05I could see that guy almost coming in. He put his head down.
0:52:05 > 0:52:09But, of course, with an 80-foot whale, when the head goes down,
0:52:09 > 0:52:11it's 80 feet down, and I just lost the head.
0:52:11 > 0:52:15Lovely view of the tail going through. Big, big tail.
0:52:17 > 0:52:21I swum very fast toward the whale, but then, all of a sudden,
0:52:21 > 0:52:26I saw all the massive animal coming to me so quickly...
0:52:26 > 0:52:27What an experience.
0:52:27 > 0:52:31I was lucky not to be hit, but I really want to see it again.
0:52:34 > 0:52:40So far, the footage suggests that, if the whales are feeding,
0:52:40 > 0:52:42it must be at depth.
0:52:47 > 0:52:51Ari Friedlaender, another member of the research team,
0:52:51 > 0:52:56is investigating the duration and depth of each whale's dive.
0:52:56 > 0:52:59OK, I think that's the animal from that third group,
0:52:59 > 0:53:02so that dive time is about seven minutes.
0:53:02 > 0:53:06I'd probably say, just based on that dive time, maybe between about 50 and 200 metres.
0:53:06 > 0:53:09I think it's pretty clear that these guys are feeding.
0:53:09 > 0:53:12They're lunging quite a bit down there too.
0:53:14 > 0:53:18Ari is now convinced the whales are feeding at great depth,
0:53:18 > 0:53:20but on what?
0:53:24 > 0:53:29The whales leave behind crucial evidence floating on the surface.
0:53:30 > 0:53:34- This is whale poo.- Whale poo?!
0:53:34 > 0:53:36That's right. It's red in colour,
0:53:36 > 0:53:40and that gives us a clue to what it is, actually.
0:53:40 > 0:53:43- It's full of krill.- That's what they feed on?- That's right.
0:53:47 > 0:53:51The largest creature in the ocean feeds almost exclusively
0:53:51 > 0:53:53on one of the smallest...
0:53:53 > 0:53:54krill.
0:53:54 > 0:53:57A crustacean just a few inches long.
0:54:01 > 0:54:05Krill are normally found in cold polar seas,
0:54:05 > 0:54:07but the unusual conditions off Sri Lanka
0:54:07 > 0:54:11allow krill to thrive in these tropical waters.
0:54:14 > 0:54:16So is that why the blue whales are here?
0:54:19 > 0:54:21We see these animals diving,
0:54:21 > 0:54:24we're counting how long they're down
0:54:24 > 0:54:28and I've got 100% confidence that these guys are diving deep down
0:54:28 > 0:54:32and they're finding these really dense patches of krill and lunge-feeding through them.
0:54:32 > 0:54:36We've made an animation of how these whales feed at depth.
0:54:38 > 0:54:41The blue whale dives to 600 feet,
0:54:41 > 0:54:44below where the krill are hiding in the gloom.
0:54:47 > 0:54:50The whale then powers up through the swarm,
0:54:50 > 0:54:55gulping its own body weight of water into its ballooning throat.
0:54:58 > 0:55:01It then strains out the nutritious krill
0:55:01 > 0:55:04through its fine mesh of baleen.
0:55:11 > 0:55:14Each lunge requires huge effort,
0:55:14 > 0:55:18but if you have a mouth as big as a blue whale's
0:55:18 > 0:55:20you can catch so much food
0:55:20 > 0:55:24that the whole process becomes extraordinarily efficient.
0:55:28 > 0:55:33Their size is the secret of their success.
0:55:38 > 0:55:43Doug and Didier make one final attempt to get up close
0:55:43 > 0:55:45to the deep-feeding giants.
0:56:40 > 0:56:42It was certainly the biggest whale that I've ever seen.
0:56:42 > 0:56:45It just looked enormous underneath me.
0:56:45 > 0:56:50I've waited a long time to see a blue underwater, and that was just magic.
0:56:50 > 0:56:55Beautiful. Fantastic. Today is the best day of my life.
0:57:00 > 0:57:02Pumped up on tonnes of krill,
0:57:02 > 0:57:05blue whales can grow as long as a jetliner,
0:57:05 > 0:57:08weighing almost 200 tonnes,
0:57:08 > 0:57:11twice the size of the largest dinosaur.
0:57:17 > 0:57:20But, worryingly, the blue's giant size
0:57:20 > 0:57:24and its giant appetite are now putting it at risk.
0:57:24 > 0:57:26We know that climate change is occurring,
0:57:26 > 0:57:31and that in places like Antarctica the temperatures have sky-rocketed.
0:57:31 > 0:57:33We also know that krill has started to decrease,
0:57:33 > 0:57:38and when you don't have enough food blue whales are going to have trouble surviving.
0:57:38 > 0:57:41So as climate change happens, as krill starts to be depleted,
0:57:41 > 0:57:43blue-whale survival could be in jeopardy.
0:57:47 > 0:57:52Blue whales are still endangered, but they are recovering, slowly.
0:57:52 > 0:57:58For their recovery to continue, it's not just the whales themselves that will need protection,
0:57:58 > 0:58:02but the seas and the other creatures they depend on.
0:58:08 > 0:58:14We may have missed the chance to live with the great dinosaurs of the past,
0:58:14 > 0:58:18but we do have the good fortune to be sharing our time
0:58:18 > 0:58:22with the largest creatures that ever lived,
0:58:22 > 0:58:25these magnificent ocean giants.
0:58:33 > 0:58:35WHALESONG
0:58:47 > 0:58:51Subtitles by Red Bee Media Ltd