"Dwarfed by the vast expanse of the open ocean, the biggest animal that has ever lived on our planet." "A blue whale, 30 metres long and weighing over 200 tonnes." "It's far bigger than even the biggest dinosaur." "Its tongue weighs as much as an elephant." "Its heart is the size of a car, and some of its blood vessels are so wide that you could swim down them." "Its tail alone is the width of a small aircraft's wings." "Its streamlining, close to perfection, enables it to cruise at 20 knots." "It's one of the fastest animals in the sea." "The ocean's largest inhabitant feeds almost exclusively on one of the smallest - krill, a crustacean just a few centimetres long." "Gathered in a shoal, krill stain the sea red, and a single blue whale in a day can consume 40 million of them." "Despite the enormous size of blue whales, we know very little about them." "Their migration routes are still a mystery, and we have absolutely no idea where they go to breed." "They are a dramatic reminder of how much we still have to learn about the ocean and the creatures that live there." "Our planet is a blue planet." "Over 70 per cent of it is covered by the sea." "The Pacific Ocean alone covers half the globe." "You can fly across it non-stop for 12 hours and still see nothing more than a speck of land." "This series will reveal the complete natural history of our ocean planet from its familiar shores to the mysteries of its deepest seas." "By volume, the ocean makes up 97 per cent of the earth's inhabitable space, and the sheer quantity of its marine life far exceeds that which inhabits the land." "But life in the ocean is not evenly spread." "It's regulated by the path of currents carrying nutrients, and the varying power of the sun." "In this first programme, we will see how these two forces interact to control the distribution of life from the coral seas to the polar wastes." "The sheer physical power of the ocean dominates our planet." "It profoundly influences the weather of all the world." "Water vapour rising from it forms the clouds and generates the storms that ultimately will drench the land." "The great waves that roar in towards the shores are dramatic demonstrations of its power." "Waves originate far out at sea." "There, even gentle breezes can cause ripples, and ripples grow into swells." "Out in the open ocean, unimpeded by land, such swells can become gigantic." "It's only when an ocean swell eventually reaches shallow water that it starts to break." "As it approaches the coast, the water at the bottom of the swell is slowed by contact with the seabed." "The top of the swell, still travelling fast, starts to roll over and so the wave breaks." "The ocean never rests." "Huge currents, such as the Gulf Stream, keep its waters constantly on the move all round the globe." "It's these currents more than any other factor that control the distribution of nutrients and life in the seas." "A tiny island lost in the midst of the Pacific." "It's the tip of a huge mountain that rises from the sea floor thousands of metres below." "The nearest land is 300 miles away." "Isolated sea mounts like this one create oases where life can flourish in the comparatively empty expanses of the open ocean." "But all the creatures that swim beside it would not be here were it not for one key factor " "the deep ocean currents." "Far below the surface, they collide with the island's flanks and are deflected upwards, bringing with them from the depths a rich soup of nutrients." "Such up-wellings attract great concentrations of life." "Most of the fish here are permanent residents feeding on plankton - tiny floating plants and animals nourished by the richness brought up from the depths, and they attract visitors from the open ocean." "Tuna." "The plankton feeders are easy targets." "All this action attracts even larger predators." "Sharks." "Hundreds of sharks." "These silky sharks are normally ocean-going species, but the sea mounts in the eastern Pacific like Cocos, Mapelo and the Galapagos, attract silkies in huge groups up to 500 strong." "Silkies seem to specialise in taking injured fish and constantly circle sea mounts on the look out for the chance to do so." "But silkies are not the only visitors." "Hammerheads gather in some of the largest shark shoals to be found anywhere in the ocean." "Sometimes, thousands will circle over a single sea mount." "But these sharks are not here for food." "They have come for another reason." "Some of the locals provide a cleaning service." "Following the last El Niño year, when a rise in water temperatures gave many sharks fungal infections, the number of hammerheads visiting the sea mounts reached record levels." "Nutrients also well up to the surface along the coasts of the continents." "This is Natal on South Africa's eastern seaboard." "It's June, and just off-shore, strange black patches have appeared." "They look like immense oil slicks up to a mile long." "But this is a living slick:" "millions and millions of sardines on a marine migration that in terms of sheer biomass, rivals that of the wildebeest on the grasslands of Africa." "These fish live mostly in the cold waters south of the Cape, but each year the coastal currents reverse." "The warm Agulhas current that flows down from the north has been displaced by cold water from the south, and that has brought up rich nutrients." "They in turn have created a bloom of plankton, and the sardines are now feasting on it." "As the sardines travel north, a whole caravan of predators follow them." "Thousands of Cape gannets track the sardines." "They nested off the Cape and timed their breeding so that their newly-fledged chicks can join them in pursuing the shoals." "Below water, hundreds of sharks have also joined the caravan." "These are bronze whaler sharks, a cold water species that normally lives much further south." "These three-metre sharks cut such great swathes through the sardine shoals that their tracks are visible from the air." "Harried by packs of predators and swept in by the action of the waves, the sardine shoals are penned close to the shore." "Common dolphin are coming in from the open ocean to join the feast." "There are over a thousand of them in this one school." "When they catch up with the sardines, the action really begins." "Working together, they drive the shoal towards the surface." "It's easier for the dolphins to snatch fish up here." "Now the sardines have no escape." "Thanks to the dolphins, the sardines have come within the diving range of the gannets." "Hundreds of white arrows shoot into the sea, leaving long trails of bubbles behind each dive." "Next to join the frenzy are the sharks." "Sharks get very excited when dolphins are around." "They can feed particularly well once the dolphins have driven the sardines into more compact groups near the surface." "As the frenzy continues, walls of bubbles drift upwards." "They are being released by the dolphins working together in teams." "They use the bubbles to corral the sardines into ever tighter groups." "The sardines seldom cross the wall of bubbles and crowd closer together." "Bubble netting in this way, enables the dolphins to grab every last trapped sardine." "Just when the feasting seems to be almost over, a Bryde's whale." "The survivors head on northwards, and the caravan of predators follows them." "Nutrients can also be brought up, though less predictably, by rough weather." "Particularly near the poles, huge storms stir the depths and enrich the surface waters, and here, in the South Atlantic, the seas are the roughest on the planet." "And very rich seas they are, too, for here, the cold Falklands current from the south meets the warm Brazil current from the north, and at their junction is food in abundance." "These black-browed albatross are duck-diving for krill that has been driven up to the surface." "Like all albatross, black-brows are wanderers across the face of the open ocean." "A feeding assembly on this scale is a rare sight." "Most of the time, the birds of the open sea are widely dispersed, but these feeding grounds are close to an albatross breeding colony, and a very special one." "This is Steeple Jason, a remote island in the far west of the Falklands." "It has the largest albatross colony in the world." "There are almost half a million albatross here, an astonishing demonstration of how fertile the ocean can be and how much food it can give even to creatures that do not actually live in it." "Nutrients by themselves are not enough to generate these vast assemblies." "The heat and light from the sun is also essential for the growth of the microscopic floating plants - the phytoplankton." "And it's the phytoplankton that is the basis of all life in the ocean." "Every evening, the disappearance of the sun below the horizon triggers the largest migration of life that takes place on our planet." "One thousand million tonnes of sea creatures ascend from the deep ocean to search for food near the surface." "They graze on the phytoplankton under cover of darkness." "Even so, they are far from safe." "Other marine hunters follow them, some travelling up from hundreds of metres below." "At dawn, the whole procession returns to the safety of the dark depths." "The moon, too, has a great influence on life in the oceans." "Its gravitational pull creates the daily advances and retreats of the tide." "But the moon has more than a daily cycle." "Each month, it waxes and wanes as it travels round the earth, and this monthly cycle also triggers events in the ocean." "The Pacific coast of Costa Rica on a very special night." "It's just after midnight and the tide is coming in." "The moon is in its last quarter, exactly half way between full and new." "For weeks, the beach has been empty, but that is about to change." "At high tide, turtles start to emerge from the surf." "At first, they come in ones and twos, but within an hour, they are appearing all along the beach." "They are all female Ridley's turtles, and over the next six days or so," "400,000 will visit this one beach to lay their eggs in the sand." "At the peak time, 5,000 are coming and going every hour." "The top of the beach gets so crowded that they have to clamber over one another to find a patch where they can dig a nest hole." "A quarter of the world's population of Ridley's turtles come to this one beach on a few key nights each year." "The rest of the time, they are widely distributed through the ocean, most, hundreds of miles away." "This mass nesting is called an arribada." "How it's co-ordinated is a mystery, but we do know that arribadas start when the moon is either in its first or last quarter." "Forty million eggs are laid in just a few days." "By synchronising their nesting, the females ensure that six weeks later, their hatchlings will emerge in such enormous numbers that predators are overwhelmed, and a significant proportion of baby turtles will make it to the water." "But why do the females use a cue from the moon to help synchronise their nesting?" "Part of the answer to that becomes clear at dawn on the following morning." "The day shift of predators are arriving for their first meals." "Vultures have learnt that the returning tide can wash freshly laid eggs out of the sand." "The risk of eggs being exposed by the surf may be partly why turtle arribadas tend to occur around the last or first quarter of the moon." "It's on such days as this when the moon is neither full nor new, that the tides are weakest and the sea is likely to be calmer." "So it's easier for the female turtles to make their way through the surf, and harder for eggs to be washed out of the sand and taken by vultures." "The moon's monthly cycle and its influence on the tides triggers many events in the ocean, from the spawning of the corals on the Great Barrier reef to the breeding cycles of fish, but there's an even longer rhythm" "that has the most profound effect of all - the annual cycle of the sun." "The sun's position relative to the earth changes through the year, and it's this that produces the seasons." "In the north, spring comes as the sun begins to rise higher in the sky." "Off the coast of north west America, the seas are transformed by the increasing strength of the sun." "Here in Alaska, the coastal waters turn green with a sudden bloom of phytoplankton." "Herring that have spent the winter far out to sea time their return to the shallow waters to coincide with this bloom." "They come in vast numbers and initiate one of the most productive food chains in all the oceans." "Humpback whales are at the top of that food chain." "They have spent the winter breeding in the warmer tropical waters off Hawaii, but there was little food there." "This herring bonanza provides the majority of their food for the year." "Stellar and Californian sea lions also return from the open ocean each year to feast off the herring." "The herring, however, have not come here for food." "They are about to breed." "Nothing deters them as they head for even shallower waters." "Now the waters are so shallow that glaucous-winged gulls can snatch live fish from just below the surface." "In spite of these attacks, the herring swim on until they reach the vegetation that the females need if they are to lay." "Each female produces around 20,000 eggs, and they're very sticky." "After the females have spawned, the males release their sperm in vast, milky clouds." "Soon, the excesses of the herrings' sexual spree creates a thick white scum on the surface." "Through the season, curds of sperm clog the shores for hundreds of miles from British Columbia in the south to Alaska in the north." "After a few days, this gigantic spawning comes to an end, and the herring head back out to deeper waters, leaving behind them fertilised eggs plastered on every rock and strand of vegetation." "They time the spawning so that two weeks later, when the eggs hatch, the annual plankton bloom will be at its height, and the fish fry will have plenty to eat." "In the meantime, these eggs provide food for armies of different animals below and above the surface." "Millions of birds arrive to collect a share of the herrings' bounty." "Some of it is easily gathered, for millions of eggs have been washed up onto the shore." "This encapsulated energy is particularly valuable to migrating birds." "These surfbirds are on their way to their breeding grounds in the Arctic and come down to refuel." "Stranded herring eggs are just what they need." "Bonaparte gulls collect the eggs just below the surface of the water." "Further out in the bay, huge flocks of ducks have gathered." "They're mostly surf scoters - diving ducks that can feed off the bottom several metres down." "There are such huge quantities of eggs, that even a big animal like a bear finds it worthwhile to collect them." "The spawning of the herring is a crucial event in the lives of many animals all along the coast." "The whole event coincides with the plankton bloom, and within three short weeks, it's all over." "The migratory birds leave to continue their journey north." "They will not come back until the herring also return next year." "As the herring spawning finishes, other migrants are starting to arrive offshore." "Grey whales." "They have followed the sun north, and they too are seeking the food generated by the bloom of the phytoplankton." "Krill are feeding off it, and these whales are feeding on the krill, skimming it from the surface with the filter plates of baleen that hang from their upper jaws." "Grey whales make one of the longest migrations of any marine mammal - a round trip of 12,000 miles or so from their breeding grounds off Mexico along the entire coast of North America up to the Arctic Ocean." "They travel close to the coast, with the males and non-breeding females leading the way." "The last to start are cows that have just given birth." "They have to wait until their calves are sufficiently strong to tackle such an immense journey." "Their progress is necessarily slow." "The mothers stay with their young, and even a strong calf only travels at a couple of knots." "They stick even closer to the shore, often within just 200 metres." "Killer whales." "They have learnt that grey whales follow traditional routes." "The killers have no trouble in overtaking the calf and its devoted mother." "Normally, they continually call to one another, but now they have fallen silent." "The grey whale and her calf have no idea that they've been targeted." "Catching up with the grey whales is the easy part for the killers." "They have to be cautious for they are only about half the size of the mother." "She can inflict real damage with her tail." "But the killers are after her calf." "As long as the mother can keep it on the move, it will be safe, and she does her best to hurry it along." "At first, the killers avoid getting too close but just stay alongside." "They know that the calf, going at this speed, will eventually tire." "After three hours of being harried, the calf becomes too exhausted to swim any further." "The mother has to stop." "This is the moment the killers have been waiting for." "They start to try and force themselves between mother and calf." "A calf separated from its mother will not be able to defend itself." "Time and again, the black fins of the killers appear between the grey whales." "At last the killers succeed, and now they've got the calf on its own, they change their tactics." "They leap right onto the calf, and try to push it under." "They are trying to drown it." "The calf snatches a desperate breath." "The mother becomes increasingly agitated." "Frantically, she tries to push her calf back to the surface so that it can breathe." "But now it's so exhausted that it has to be supported by its mother's body." "The killers won't give up." "Like a pack of wolves, they take turns in harassing the whales." "Now, the whole pod is involved." "One of them takes a bite." "Soon, the sea is reddened with the calf's blood, and the killers close in for the final act." "The calf is dead." "After a six-hour hunt, the killer whales have finally won their prize." "The mother, bereft, has to continue her migration north on her own." "She leaves behind the carcass of a calf that she cherished for 13 months in her womb, for which she delayed her own journey to find food." "The 15 killer whales spent over six hours trying to kill the calf, but having succeeded, they've eaten nothing more than its lower jaw and its tongue." "Valuable food like this will not go to waste in the ocean." "Before long, the carcass will sink to the very bottom of this deep sea, but even there its flesh will not be wasted." "Over a mile down, in the total darkness of the deep ocean, the body of another grey whale, a 30-tonne adult." "It settled here only a few weeks ago." "Already, it has attracted hundreds of hagfish." "These scavengers, over half a metre long and as thick as your arm, are only found in the deep sea." "They have been attracted by the faint whiff of decay suffusing through the water for miles around." "With their heads buried in the whale's flesh, they breathe through gill openings along their sides." "They're very primitive creatures - not even true fish for they lack jaws." "They feed, not by biting, but by rasping off flesh with two rows of horny teeth." "In just a few hours, a hagfish can eat several times its own weight of rotting flesh." "Next to arrive, a sleeper shark." "It moves so slowly to conserve energy - an important strategy for so large an animal surviving in such a poor habitat." "Sleeper sharks live over a mile down, and grow to over seven metres long." "They can go for months without food, slowly cruising along, waiting for rare bonanzas such as this one to arrive from above." "A whole range of different deep-sea scavengers will feast on this carcass for a long time before all its nutriment has been consumed." "18 months later, all that is left is a perfect skeleton stripped bare." "The sun's energy, that was captured and turned into living tissue by the floating phytoplankton, has been transferred to another link in the food chain, and has ended up as far away from the sun as it is possible to be " "at the bottom of the deep sea." "But some energy also returns from the deep." "Millions of opalescent squid are on their way to the shallows." "They've come up here to mate." "As the males grab the females, their tentacles flush red." "For most of the year, these squid live at a depth of around 500 metres." "They are part of these breeding schools for a few weeks." "Just one school was estimated to contain animals that weigh around 4,000 tonnes." "Wave after wave rise from the depths, and soon the seabed in the shallows is strewn with dense patches of egg capsules several metres across." "As each female adds another capsule to the pile, the males fight to fertilise its contents." "The squid make their huge journey into the shallows because their eggs will develop faster in the warmer water here, and when the young emerge, they will find more food more easily than they would in the ocean depths." "Dawn the next morning, and the seabed for miles around is covered in egg capsules." "The squid have all gone." "Many have died, but some will have returned to their home in the deep." "They will not return to the light of the sun until the next time they are driven up by the urge to spawn." "Over 60 per cent of our planet is covered by ocean more than a mile deep." "That, the deep sea, is by far the largest habitat on Earth and it's largely unknown." "Join us on a journey to the very bottom of the deep sea, to an alien world never revealed before." "It's home to some of the strangest animals on Earth." "Fish flash in the darkness." "New species are discovered on almost every dive." "More people have travelled into space than have ventured this deep." "Come on a journey into the abyss." "A sperm whale takes a breath, its last for over an hour." "It's about to leave the warm, well-lit surface waters and dive far down into the cold, dark depths of the deep ocean." "At the surface it took in air at the same pressure as we breath it." "But it's going to look for food at more than 1,000 metres down, where pressure is 100 times that on the surface, crushing the whale's lungs to just one per cent of their volume." "For us to follow the whale, we need the very latest submersible." "A reinforced acrylic sphere with walls 12 centimetres thick protects a pilot and our cameraman from the enormous pressure below, and allows the submarine to dive to just over 900 metres." "(PIL0T) 900 feet." "With every passing metre, pressure increases and sunlight diminishes." "(PIL0T) 1,000 feet." "By 300 metres, it's already very dark and the temperature of the water is dropping fast." "We are entering the twilight zone, a weird world of gloom where many animals have become completely transparent." "In this twilight, and animal needs to see, and yet, as far as possible, must avoid being seen." "A giant amphipod, 12 centimetres long and almost perfectly transparent." "Its head is completely filled by two huge eyes with which it strains to detect its prey." "Another twilight monster, phronima, the inspiration for the Alien movies." "She and her developing pink offspring live like parasites in the stolen body of a jelly." "This impressive cutlery set and its huge eyes make phronima a powerful predator." "Even really complex animals have become transparent in the twilight zone." "Squids are among the most advanced of invertebrates, but this one never meets a hard surface in its entire life, so its body need not be as robust as that of its shallow water cousins." "There's a rich variety of jellies that live nowhere else but in the deep sea." "Thousands of tiny cilia propel them through a world without walls." "Invisible in the gloom, they grope blindly for their prey." "Comb jellies let out long sticky nets to catch passing copepods." "But the most extensive death trap is set by siphonophores." "This pulsating bell is the head of a colonial jelly that can be 40 metres long." "Millions of tiny stinging cells drifting through the sea." "500 metres down, and in even the clearest tropical waters only the faintest vestige of the sunlight remains - so little that our eyes can't detect it, but others can." "Survival in the twilight zone is all about seeing, yet not being seen." "Hatchet fish are masters of the game of hide and seek." "They have the large, sensitive eyes needed for seeking prey but their bodies are flat... and their sides are highly silvered." "Head on, they are just visible, thin though they are, but as soon as they turn, their mirrored sides reflect the remnants of blue light from the surface, and they disappear into the gloom." "Viewed from the side, whole shoals can hide in this way, but what about from below?" "The tubular eyes of many of the predators, even in this gloom, are able to distinguish their prey silhouetted against the faint glimmer of light from above." "Hatchet fish, however, have a way of confusing any eyes that might be searching for them from below." "Their bellies carry rows of light-producing cells called photophores." "They can use these to exactly match the changing colour of light from the surface far above." "This counter shading breaks up their silhouette, making them almost invisible from below... almost." "But these are no ordinary eyes." "The enormous yellow lenses enable their owner to distinguish between light produced by photophores and sunlight." "So, one device for escape is countered by another equally subtle one for attack in an evolutionary arms race that has been waged for millions of years." "Descend below 1,000 metres, and you enter the dark zone." "No sunlight whatsoever penetrates this deep." "The temperature of the water is below four degrees Centigrade." "The pressure is more than 100 times that at the surface." "Life becomes ever more sparse." "It's a dark, dangerous world." "Relative to body size, these are the largest teeth in the ocean." "They are so big that their owner can't close its mouth." "They belong to the fang tooth." "Unlike most deep sea fish, this has powerful muscles and is an aggressive hunter." "With food in such short supply at this depth, dark zone predators have to be able to deal with a meal of any size." "Many animals here are dark red, like this deep sea jelly." "Caught in the lights of the submersible, it's a spectacular firework display of colour." "Normally, no red light penetrates as deep as this, so animals with red pigment appear completely black down here, perfectly concealed." "Predators here, however, don't just rely on vision - many have tiny eyes." "Instead, their thin, rod-like bodies are lined with organs sensitive to tiny movements in the water." "This monster, half a metre across, is a hairy angler." "This is the first time it's been seen." "It's covered with hundreds of sensitive antennae, which detect the movements of any prey careless enough to stray too close to this motionless predator." "But this, surely, must be the strangest of all the deep sea fish yet discovered." "A highly sensitive metre-long tail hangs down from the head that makes up a quarter of its body." "Its eyes are tiny, but its mouth is truly enormous." "It's called the gulper eel because it can engulf a meal of almost any size." "Hanging motionless in mid-water, its enormous gape enables it to deal with passing prey, whether it's small, or large." "Gulper eels can swallow prey as big as themselves, which is very useful in a world where you never know when the next meal is coming along." "Even in the dark zone, there is SOME light." "Turn off the submersible headlights, and you see a pyrotechnic display outside." "These lights are created by animals." "This is bioluminescence." "A deep sea angler fish flashes in the darkness." "The light is generated by bacteria that live permanently inside the lure which attracts prey to these murderous teeth." "There are all sorts of lures out in the darkness." "Come into my mouth, little fish!" "And what is the purpose of THIS lure, suspended on a long rod, way below its owner's terrifying set of teeth?" "It's difficult to be sure, but then, this monster does have another giant flashing lure much closer to its mouth." "These fish are called anglers because they use their lures in much the same way as fly fishermen use their imitation flies." "For a hunting squid with huge eyes this glimmer is intriguing." "It might just be food." "A satisfying meal for a fish with a highly extendible stomach." "Attracting a mate in this endless darkness can be even harder than finding food." "Flashing lures may be helpful;" "certainly, only female anglers have them." "The tiny males are just a tenth the size of the females." "Their only purpose is somehow to find a mate in the darkness." "She releases chemicals into the water which the males scent with a special white organ in front of their eyes." "Having found a partner, the male bites at her belly with specially designed teeth." "He needs to get permanently attached." "Within a matter of weeks, the male is completely fused to the female, and there he will stay for the rest of his life." "Her blood circulating in his body provides him with all the sustenance he needs." "In return, she gets a continuous, reliable supply of sperm - a brilliant solution to the problem of finding a mate in the vast emptiness of the deep sea." "To help in the constant battle between predators and prey, some fish in the dark zone have developed headlights." "These light-producing photophores beneath their eyes may be used to search out prey in the darkness." "Most bioluminescence in the deep sea is blue or greenish-blue, but a very few predatory fish produce red light." "With this, red prey becomes obvious in the darkness." "Red light is rare down here and most animal eyes can't see it." "Only these fish can do so." "This gives them a sniper scope - a headlight invisible to their targets." "This copepod, unalarmed, takes no avoiding action." "Bioluminescence is useful in escape as well as attack." "A shrimp senses a threat." "It spins in the water, releasing a bioluminescent glue." "This acts like a burglar alarm, startling the attacking fish and leaving it illuminated in the dark, and vulnerable to its own predators." "These twinkling lights in the darkness are produced by copepods." "They probably flash like this to communicate with one another and confuse their predators." "The most sensitive eyes in the ocean belong to an ostracod called gigantocypris." "It's the size of a pea, but that's enormous for an ostracod." "Copepods are a favourite prey, and it actively searches for their flashes in the darkness... but this copepod has a way of confusing a hunting gigantocypris." "It discharges a packet of bioluminescent liquid." "The flash is delayed, like a depth charge." "Spinning, confused, in the water, gigantocypris chases after the flashes... and the copepod slips away unseen into the darkness." "The ultimate bioluminescent defence mechanism has to be the light show created by the deep sea jellyfish, periphylla." "That, presumably, is the way it scares away its enemies." "These bright lights are all produced by firefly squid." "Normally, they live way down at around 300 metres, beyond the reach of these Japanese fishermen's nets... but for a few months each spring, they come to the surface each night." "The brightest lights come from the bioluminescent tips of their two front tentacles, but it's only in the dark of the deep sea, that you can really appreciate the full complexity of their displays." "It's not just their tentacles but their whole bodies that are covered in photophores." "The exact function is not clear." "The bright tentacle tips may be for attracting mates or dazzling predators." "The rest may be camouflage, providing counter shading for the squid as they journey up into the twilight zone." "Every night in the season, hundreds of thousands of squid journey up into the shallow water to spawn." "Before dawn, they will return to the depths, leaving their eggs to develop in the shallows." "The daily cycle of the sun has a profound influence on life in the deep ocean." "As the sun sets, it triggers the largest migration of living organisms on our planet." "One thousand million tonnes of animals travel up from the dark zone into richer, shallower water every night." "Tiny grazers are first up, searching for the microscopic plants that only grow in shallow, sunlit waters." "Predators follow the grazers." "An enormous variety of different animals join the convoy or feed off it as it passes." "Many will travel up hundreds of metres towards the surface, and, at dawn, finding themselves at risk from predators, the visitors return to the safer darkness of the depths." "The sun's rays only have a direct effect in the top 100 metres or so of the ocean." "It's only here that photosynthesis can take place and coral reefs can flourish." "Leave this thin, rich slice of life and travel over the outer face of the reef and you quickly enter a far more demanding world." "Below 150 metres, photosynthesis becomes impossible." "You find no plants, just animals." "Here, the animals are adapted to catch marine snow - particles of dead animals and plants that drift down from above." "So they depend second-hand on the energy captured from the sun by organisms in the surface waters." "Travelling close to the sea floor, we're going to take a journey to the very bottom of the deep sea... to a world completely separate from the mid-water above." "At around 300 metres, the drop-off levels out, and we move out onto the continental slope." "This stretches for about 150 miles from the coast, sloping in a gentle gradient, down to a maximum depth of 4,000 metres." "Water temperatures down here drop below four degrees Centigrade and the pressure can reach up to 400 times that of the surface." "Without the lights of the submersible, it would be completely dark." "The water is crystal clear because there's so little organic matter." "Only three per cent of any food in the surface waters reaches the continental slope." "At first sight, it appears a lifeless desert, but take a closer look and you notice a network of tracks and trails." "There is life even down here." "These animals would die immediately if brought to the surface in nets, so you can only see them behaving normally from submersibles." "Many are new to science." "The deep sea floor is dominated by echinoderms - sea cucumbers, brittle stars and sea urchins." "There are literally millions of them, marching across the sea bed, hoovering up any edible particles in the sediment." "They come in all shapes and sizes, and though they are thinly spread, these are among the most numerous animals on the planet." "Their spikes are good for locomotion and defence, but perhaps not quite so good when it comes to mating." "Finding a mate in this largely empty sea floor could be a problem, so some urchins stay together in herds to be sure that they're never too far from a potential partner." "Rocky outcrops provide good anchorage for animals that rely on food that might drift past." "These crinoids or sea lilies look like plants, but are, in fact, animals." "Their long stalks ensure that their umbrella of feeding tentacles are positioned to best effect in the current." "Particles are swept onto the arms, and carried down to a mouth in the middle of the umbrella." "These sudden movements swat away tiny amphipods that try to steal the sea lily's captures." "Coral reefs are not supposed to exist in total darkness, but recently, a new kind of coral was found as deep as 2,000 metres." "In the cold waters of a Norwegian fjord, there was a deep sea reef 30 metres high and 200 metres long." "This coral gets no energy from the sun, so it has to be very efficient in catching food." "Its polyps are far larger than those of shallow water corals." "These are, in fact, the largest coral polyps in the ocean." "They belong to the deep sea mushroom coral." "Their three-centimetre-long tentacles can catch far larger prey than other corals can." "This necessity to capture every particle of food that comes within reach in this near desert has radically changed many animals." "Most tunicates are filter feeders, but this one has become a predator and its greatly enlarged siphon has been converted into a trap." "Most sea cucumbers stay firmly on the bottom, but not this extraordinary deep sea species." "Its skirts of skin allow it to swim hundreds of metres above the sea floor." "Eventually, it will descend and, with luck, will land on fresh feeding grounds." "This has to be the most extraordinary animal design of all." "It's a polychaete worm and, normally, you would expect the long, pulsating body to be stick firmly in the sediment." "This worm, alone in its group, swims in the open water." "Propelling itself with its yellow frill, it moves about and so finds new sources of food, or maybe succeeds in escaping from a predator." "This is chimaera, a close relative of the sharks, less than a metre long." "Sensory pits on its chin help it hunt prey on the bottom, while its surprisingly large eyes may help it spot bioluminescence." "Large fish are rare down here - there's not enough live prey to sustain them." "Most have become scavengers." "A dead tuna has attracted a deep sea conger eel... and a six-gilled shark." "These monsters grow to eight metres long." "Six gills are living fossils." "For 150 million years, they've existed unchanged, living in water as deep as 2,500 metres." "Very few people have glimpsed these sharks from submersibles, and we know almost nothing about their behaviour." "The body of a tuna is a substantial meal, but just occasionally, a really gigantic corpse drifts down to the deep sea floor." "This is the freshly dead carcass of a 30-tonne grey whale." "It's resting on the sea floor a mile down." "It's only been on the bottom for six weeks, but already it has attracted hundreds of hagfish." "These ancient scavengers are nearly always the first to discover a fallen body, and are attracted from miles around." "They lack jaws and rasp at the flesh with two rows of horny teeth on either side of their sucker-like mouths." "Next to arrive, a sleeper shark - a real deep sea specialist." "They grow to over seven metres long, and have never been filmed at such a depth before." "The gaping wounds in the whale's flank are its work." "Unlike the hagfish, it has powerful jaws, so is able to rip off huge chunks of meat." "Sharks, hagfish and a whole succession of different deep sea scavengers will feast on the carcass for years before all its nutriment is gone." "Eighteen months later, when we returned to this whale, all that was left was a perfect skeleton stripped bare." "It was almost as if a museum specimen had been carefully laid out on the sea floor." "At first, the skeleton seemed totally abandoned, but even after so long, there was still some flesh left in the head." "Hagfish have a skeleton of cartilage and are so flexible that they tie themselves into knots and so get a better purchase on the flesh they feed on." "But smaller organisms had fed here." "A thick band of white bacteria had formed on the mud outlining the original shape of the whale, and on the skeleton itself, colonies of specialised bacteria were extracting energy from the bones themselves." "Most remarkably, and in huge abundance, polychaete worms were collecting the last edible fragments." "These are a new species that so far have only been found on the fallen bodies of whales." "Scientists have discovered 178 different animals on a single whale vertebra, most of which have been found nowhere else." "This whale, lying over a mile down, was not filmed from a submersible with an acrylic sphere." "Such craft can't go as deep as this." "To withstand the pressure here, you need a far stronger submersible." "This is Alvin, a two-metre-wide sphere with just enough room in it for a pilot and two observers." "Its walls are made of titanium." "The viewing ports have to be tiny - any larger, and the submersible would implode under the enormous pressure down here." "Alvin can dive to 4,500 metres, three miles below the surface." "Around 3,000 metres, the continental slope finally flattens out and joins the abyssal plain." "This covers over half the earth's surface." "Mostly it's completely flat, but in places it's gashed by massive trenches hundreds of miles wide." "The deepest of these is the Mariana Trench, which drops to over seven miles below sea level." "There are just five manned submersibles world-wide that can reach the abyssal plain, and between them so far, they have explored less than one per cent of it." "There are a thousand times fewer large animals down here than on the continental slope, but in places, hundreds of brittle stars cross the sea bed in search of food." "Fish have been found right down to the bottom of the deepest trenches." "Most come from one family - the aptly named rattails." "They forage near the sea floor and use their battery of sensory pits to follow odour trails from rotting carcasses." "Rattails can travel long distances across the abyssal plain in search of food, but others down here prefer to sit and wait." "This is a tripod fish." "It supports itself on two specially adapted fin rays and can sit motionless for hour after hour." "It does have tiny eyes, but it's almost totally blind." "It locates potential prey with a pair of fins behind its head which are sensitive to even tiny movements." "We know more about the surface of the moon than we do about the abyssal plain." "Every dive still produces complete surprises." "This deep sea octopus is about the size of a beach ball and has been nicknamed Dumbo." "An umbrella of skin between its tentacles and its extraordinary flapping ears allow Dumbo to hover effortlessly over the sea floor as it searches for food." "Right in the middle of the abyssal plain lie the largest geological structures on our planet... the mid-ocean ridges." "Rising almost two miles off the sea floor, the ridges extend for over 28,000 miles, the largest mountain chain on Earth." "When submersibles finally succeeded in reaching the ridges in the 1970s, they found an extraordinary world with mile upon mile of once molten rock that had welled up from the deep in the past and had now solidified." "They discovered towering chimneys, pouring out water as hot as molten lead." "At the surface, water becomes steam at 100 degrees Centigrade, but here, under the immense pressure of the ocean, it remains liquid at temperatures as hot as 400 degrees Centigrade." "The submersible has to move carefully." "Disaster is very close when surrounded by such enormous temperatures and pressures." "And here, where the very water is loaded with hydrogen sulphides poisonous to normal life processes, they found living creatures." "Some of the chimneys were encrusted with white tubes." "The tubes were inhabited by a new species of polychaete worm that was exposed to temperatures as high as 80 degrees Centigrade." "No other animal on Earth was known to tolerate such high temperatures, so the scientists called these creatures Pompeii worms." "But this was just the beginning." "Nearby, there were chimneys covered by whole communities of different organisms." "The bottom of the vent was encrusted with large mussels." "There were swarms of white crabs, and, most spectacular of all, dominating the chimney were hundreds of bright red tubeworms, each two metres long and four centimetres wide." "Until these creatures were discovered, all life on Earth was thought to be dependent on the sun, but here, in the complete darkness of the deep, they had discovered a rich density of life that derived no energy from the sun." "So what do they live on?" "The answer was found within the tubeworms themselves." "They were packed full of specialised bacteria that are able to derive energy from the sulphides that pour from the vents." "The worms' plumes were bright red with haemoglobin that carries sulphides and oxygen down to the bacteria." "These bacterial colonies are the primary source of energy for all that lives here." "The mussels were packed with them." "Just as green plants are the basis of life for animals living in the sun, so these bacteria and other microbes are at the foot of the food chain on which over 500 species depend." "Crabs and shrimps feed off bacteria and even try to steal pieces of tubeworm plumes." "Since the vents were first visited by biologists in 1979, a new species has been described every ten days." "At the top of the food chain, fish that never stray far from the vents, but they or their descendants will move eventually, for we now know that individual vents are rarely active for more than a few decades." "Such a density of life living in such harsh conditions in the middle of a vast and otherwise barren abyssal plain astounded the biologists who first saw it." "It seemed to them that here was evidence of how life on this planet, which certainly started in the sea, might have begun." "Deep sea submersibles made an even more extraordinary discovery in 1990." "Over half a mile down, at the bottom of the Gulf of Mexico, they came across what appeared to be an underwater lake, over 20 metres long, with its own sandy shore." "Around its edge, there even seemed to be a tide line, but this couldn't be, of course, this was underwater." "In fact, the lapping edge was created by a thick soup of salty brine far heavier than the surrounding sea water, and the sand was made up of hundreds of thousands of mussels." "Once again, in the midst of a totally barren sea bed, an extraordinarily rich oasis of life totally independent of the sun's energy." "The source of energy this time was not sulphides but methane bubbling out of the sea bed, and once again, the mussels carried special bacteria capable of fixing the methane's energy." "Just like the hot vents, a complete ecosystem had developed based on the bacteria." "There was an enormous variety of completely new species - shrimps, weird squat lobsters, and bright red polychaete worms." "These oases were called cold seeps and were surprisingly similar to the hot vents." "The geological processes in the sea floor that produce methane also tend to result in the release of hydrogen sulphides." "It was hardly surprising, then, when, not far from the brine pool, they found tubeworms... extensive fields of tubeworms that stretch for hundreds of metres." "This new species also uses bacteria to fix energy from sulphides, but it extracts them directly from the ground." "Their beautiful gills are only used to supply oxygen to the bacteria." "Amazingly, these tubeworms are over 200 years old." "While hot vent tubeworms may be the fastest-growing invertebrates in the sea, these appear to be far slower - all the more reason to protect your gills from biting amphipods." "The energy sources exploited by the hot vent animals may suddenly fail, but here, life can enjoy a more stable geological future." "To discover within ten years two completely new ecosystems, both totally independent of the sun's energy, has been quite extraordinary." "So far, we have explored just one per cent of the deep ocean floor." "Who knows what is still out there to be discovered?" "These seas, thousands of miles from nearest land, are the most sterile on our planet." "These are marine deserts." "But here live the swiftest and most powerful of all ocean hunters." "Simply finding them is an immense challenge... but we are about to follow them as they search for their food in this little known part of the seas... the open ocean." "Striped marlin - voracious predators that can grow to three metres long." "They hunt mainly in daylight, searching the tropical oceans from close to the surface down to depths of 100 metres or so." "Normally, the fish they feed on are widely dispersed, but sometimes their prey gathers in dense shoals, like these sardines." "This feast may last for over an hour... time enough for other hunters to reach the scene." "Juvenile tuna join in the feeding frenzy." "The noise attracts a giant - a sei whale." "It's 14 metres long and 20 tonnes in weight, and has an appetite to match." "Soon, the only sign that the sardines ever existed are scales sinking down into the abyss." "Such feasts don't last long." "Within a few short days, waters that once swarmed with food will have been cleaned out." "The hunters must move elsewhere and once again search the seemingly featureless open ocean." "A manta ray - immense, five metres across from the tip of one wing-like fin to the tip of the other." "It's travelling Economy, wasting as little energy as possible as it glides through the waters of the tropics." "The remora fish that accompany it travel more economically still by hitching a lift." "Their host is searching for food - plankton, the minute fish and invertebrates that float near the surface." "It needs lots of them and may cruise for days before it finds a good feeding ground." "Dusk, at the edge of a Pacific island, 3,000 miles from the nearest continent." "Here, surgeon fish have assembled to spawn." "As they perform their nuptial dances, they discharge clouds of eggs and sperm into the water." "The manta must have known this was about to happen, for it arrived at exactly this critical moment, and it is not the only one to do so." "Others are here, too." "Now, they just need to sweep the water into their mouths and sieve out the eggs." "Within an hour, the whole event will be over." "Any surviving eggs will be so dispersed that they are not worth collecting." "But other perils await them as they join the clouds of eggs and larvae and tiny fish that drift through the surface waters of the open ocean." "These are the eggs of yellow-fin tuna." "If the hatchlings survive, it will take them two years to become adults." "In three years, they could be nearly two metres long and weigh 200 kilograms." "Perhaps only one in a million will live as long as that." "They and the other animals and microscopic plants of the plankton constitute the basis of all life out on the open ocean." "A storm petrel dancing on the water." "But this is no amiable waltz." "It's a hunt." "As they hover facing into the wind, they pick out morsels from near the surface, including eggs." "Only a tiny percentage of the developing eggs will survive long enough to hatch." "These newly emerged tuna are only three millimetres long, and although they CAN swim, they're still very vulnerable." "It will be many weeks before they can swim strongly enough to make any real headway in the ocean." "After the sun goes down, other predators rise from the depths to attack the floating multitudes." "Darkness shrouds the arrival of battalions of dangerous, drifting predators." "These shimmering comb jellies - sea gooseberries - trap their prey with sticky, net-like webs." "One ill-timed fin stroke could bring certain death to a hatchling fish." "There are many kinds of these comb jellies - all of them very effective hunters." "By dawn, most of the nocturnal feeders will have returned to the depths." "The surviving hatchlings, however, have already started on their travels." "Vast current systems like immense rivers carry them around the ocean basins." "The boundaries between these masses of moving water form invisible barriers that can trap plankton and nutrients carried up from the depths." "So, parts of the ocean become rich with food for days or even weeks at a time." "This attracts vast schools of plankton-feeding fish, like these sardine." "They take in water through their mouths and expel it through their gills, sieving out the plankton which is then funnelled down their throats." "The immense schools travel along the boundaries of the currents, seeking the spots where the plankton is thickest." "As the position of the current boundaries changes constantly, so does both the supply of plankton and the numbers of fish." "A small pod of Pacific spotted dolphin, 20 miles from the coast of Panama." "Like all predators, they seek parts of the ocean where their food is thickest." "They cover as much as 100 miles in a day, and while they travel, they play." "They have detected the sound of schooling fish from hundreds of metres away, and start to track down the shoals using sonar, leaving their toys behind them." "For the hunted, there are few places to hide." "Schooling mackerel." "They have already sensed the sonar beams of approaching dolphin." "Their only defence is to gather into a ball." "Any fish that stayed out of the shoal would be quickly picked off." "Within it, there is at least SOME chance of survival." "The noise of the attack alerts another predator - a sailfish, one of the fastest fish in the ocean." "It has detected rapid vibrations in the water, and is searching for the cause." "Sailfish rely on eyesight for their final approach, so they hunt mainly in daylight." "When sailfish become excited, they change colour, lighting up with blue stripes." "Since mackerel eyes are especially sensitive to blue and ultraviolet, these colours confuse them, making them easier to catch." "Far below, a blue shark returns from a squid-hunting trip in the cold darkness" "300 metres down." "It's heading for the surface to reheat in the warmer water." "As it ascends, it detects the smell of oils and proteins shed into the water by the panicked mackerel." "The trail leads both the shark and its attendant pilot fish towards an easy meal." "Scraps and casualties float in the wake of the passing mackerel school." "Throughout the ocean, predators and prey are locked in a deadly three-dimensional contest of hide and seek, played out over immense distances." "To survive, they must travel." "The huge four-metre-long blue-fin tuna has special blood vessels that enable it to keep its body temperature warmer than the surrounding water." "As a result, they can survive in much colder conditions than any other tuna, and they travel thousands of miles away from their spawning grounds in the tropics to hunt in cold seas where the food supply is richest." "Ocean travellers come in many guises - and few are stranger than this... a crab that spends much of its life afloat." "It's a worrying passer-by for booby birds with delicate toes." "Many floaters are little more than jelly enclosed in membranes but they may drift for vast distances." "And turtles, like these olive Ridleys, migrate thousands of miles every year." "The ocean is full of such wanderers riding the currents and doing their best to avoid enemies while they search for food and a safe place to breed... which is exactly what these rays are doing - forming the two-mile high club," "gathering together for courtship on the wing, far above the ocean floor." "More nomads - flying fish." "They seem to be on every large predator's menu, so their whole life is spent on the run in the open ocean." "They don't scatter their eggs but lay them on pieces of flotsam like this palm frond." "If the quality of water is right, they will attach their eggs to the frond which will then serve as a kind of life-raft for their offspring." "But it's not only flying fish that seek nurseries." "Any piece of floating debris can serve as a shelter under which baby fish can hide." "The only drawback is that predators like this wahoo check up on who's hanging about in the shadows." "The wahoo may trail the flotsam for weeks." "Few bits of flotsam are without their quota of lodgers, even man-made junk attracts them, and some, like this oceanic trigger fish, defend their squatters' rights with vigour." "The triggers, in fact, tend to claim all the prime residences." "Out here, even discarded netting can provide valuable shelter, so, in a bizarre twist, a wrecked trawl net like this can end up as a sanctuary for fish until it finally sinks." "A single large piece of flotsam can be the reason why several square miles of open ocean, instead of being empty, will support a fish population of hundreds of tonnes." "This huge clump of seaweed is doing exactly that." "It's a giant kelp plant, ripped from rocks off the coast of California." "Now, it's floating above thousands of metres of water, held up by its gas-filled floats." "Young rockfish are growing up in the safety of its shadow." "Giants also seek out this algal flotsam." "This is a sunfish." "It can measure as much as four metres from fin tip to fin tip." "Rather surprisingly, it has the record as the heaviest bony fish in the sea." "Sunfish spend much of their time at depth, where they feed on jellyfish, but it's cold and dark down there so from time to time, they seek a little rest and recuperation and warm up near the surface." "They too are looking for floating kelp plants... not for shelter, but because here they can find a particular kind of fish that only lives in such places." "Half-moon fish." "The sunfish form up in an orderly queue." "They have a problem." "Their skin is covered in parasites." "The hungry half-moons will help." "The sunfish turn their heads as a clear invitation to their personal hygienists." "The half-moons nip off and eat every parasite they can find." "If the half-moons don't do the job, there is another rather drastic treatment available here." "Gulls rest on the floating kelp... and if the sunfish send the right signals, the gulls will investigate." "Their beaks can dig out the most stubborn parasites." "But even the very best of health clinics can only trade on a temporary basis." "The seaweed rafts are rotting and will eventually lose their buoyancy." "Then their lodgers will have to find a new home." "If they can't, they will be eaten or die and sink down into the abyss." "But the open ocean is not entirely devoid of permanent shelter." "A volcano is erupting from the sea floor and it's still growing." "It has formed an island some 70 miles from the coast of New Zealand." "Some juvenile reef fish have already arrived, carried here by a lucky current." "Now they are growing up in the shelter of the weeds around the island's fringes." "More plankton and juvenile fish are being swept by currents straight towards the island, but now there's a welcoming committee." "Schools of trevally and blue maomao are patrolling the surface water." "All are in search of a meal." "These one-kilo fish snap up every morsel of plankton they find." "At times, the currents sweeping in from the open ocean bring with them all kinds of small creatures in dense concentrations." "These are mysid shrimps." "Very little that is edible is left after such feasts." "Islands are far from being safe havens for plankton." "The Pacific Ocean, however, is peppered with over 23,000 islands, as well as countless other submerged mountains - sea mounts - whose summits do not break the surface." "Juvenile fish for their first few months would do well to avoid such places." "These yellow-fin tuna, however, are now more than six months old and 40 centimetres long " "big enough to be able to eat fry, so sea mounts for them are promising feeding grounds where they may hunt for several months." "The base of a sea mount." "As currents sweep towards it, they're deflected up its towering walls." "The water coming from the depths carries both nutrients and plankton to the surface." "Numerous reef fish take up permanent residence, feeding where the currents are strongest and the plankton most dense." "Where the cold water mixes with warmer water at the surface, there's a strange, shimmering effect - a clear sign that the currents are running strongly." "But these currents attract more than just coastal fish." "Giants come here from the open ocean - hammerhead sharks, and in great numbers." "During the day, they circle the sea mount looking for small fish at the reef edges... but not in order to eat them." "They, like the sunfish, are looking for cleaners to rid them of their parasites." "White-tip reef sharks gather here, too." "They DO eat reef fish... but they prefer to hunt at night, when the reef fish are sleepy and easier to catch." "Far better to rest by day and allow the cleaners to do their work." "Even swarms of breeding trigger aren't a serious temptation." "These triggers spend much of their time in open water, but they've come to the sea mount to spawn." "Trigger eggs are good food, and the planton feeders gather what they can before the current sweeps them away." "This community is here because of the nutrients and plankton the sea mount deflected into the surface waters." "But ocean-going hunters are never far away." "Silky sharks specialise in picking off injured fish and constantly check over the residents around the sea mount." "At some times of the year, seasonal changes make the currents especially rich in nutrients, and the ocean around the sea mount becomes a virtual soup of plankton." "At such times, hunters gather in astonishing numbers." "Bonito, smaller relatives of the tuna." "They are searching for still smaller plankton feeders that have been attracted by the bloom." "So are these jacks, and their prey is nearby." "A school of anchovetta has strayed up near the surface, even though it's broad daylight and hunters are on the prowl." "These small fish can already feel the vibrations of the approaching predators." "Swimming at speed, they have formed into a ball, and now they must wait for whatever comes." "They've been detected." "At first, the sheer scale of the bait ball seems to daunt the predators... but now the bonito arrive and launch the first attack." "Still the bait ball holds together." "The young yellow-fin tuna move in." "The speed of this attack is so great that groups of anchovetta are splintered from the main fish ball." "Before long, the currents will shift, and the ocean will become once more a blue tropical desert, plankton-free, and the hunters will have to move on." "Spinner dolphins, still searching for food." "Their twisting leaps are, apparently, purely social displays." "Since the hunting has been good, many hundred have gathered together in this exuberant super-pod." "But now the spinners are starting to hunt once more." "Their skill in tracking food is not a secret." "Yellow-fin tuna must be aware of it, for they regularly follow them, but only adult tuna in their second or third year of life have sufficient stamina to keep up with the fast-moving spinners." "These are another kind - common dolphin." "They too are on the move." "As they travel - ever inquisitive - they pay a call on one of their larger relations, a pilot whale." "The whale is not hunting." "It's on its way to its breeding grounds in the Mediterranean." "Pilot whales normally hunt in small family groups, but in mid-summer they head for traditional socialising grounds, where they will assemble in super-herds several hundred strong." "Already, two families have joined together." "The males are competing for the favours of the females." "As the weeks pass by, these group rubbing sessions will become more overtly sexual, but now it's just flirting in the sun." "Timing in the ocean can be crucial." "In summer, the northern Atlantic waters are beginning to warm." "The hunting is good here, and by June, predators from southern waters are heading towards the Azores." "These are more common dolphin." "Like most oceanic dolphins, they too often travel in huge herds containing many different families." "There is seldom enough prey in any one place to feed such numbers... so small groups leave the super-pod and set off on hunting expeditions." "This group will be away from the main herd for many hours." "By midday, they're nearing the islands of the Azores, 900 miles west of the Portuguese coast." "Other hunters are already here - Cory's shearwaters." "Half a million of these birds breed on the Azores every year and scour the nearby ocean for food." "There's insufficient wind to support gliding flight, and since flapping is a waste of energy, they sit out the calm, clustered in rafts and riding the gentle swells." "By mid-afternoon, the dolphin are starting to hunt in earnest." "As the sea breeze picks up, the shearwaters take to the air once more." "Out to sea, the dolphin have found prey." "They are driving a shoal of small mackerel up towards the surface." "The shearwaters crowd the skies, following the dolphins' every turn." "The mackerel are still some metres down... but when the baitfish come sufficiently close, the airborne division makes its move." "Far from being mere bystanders, the shearwaters become underwater predators themselves." "Incredibly, they can dive down to depths of several metres." "The hunting dolphin prevent the mackerel from escaping downwards, and both predators gorge themselves." "Soon, the diving birds outnumber the dolphin and even drive them away from their meal... but another squadron of predators arrives to replace the dolphin - adult yellow-fin tuna." "These are giants, two metres long." "They are heading directly for the bait ball." "Despite the arrival of the giant fish, the shearwater continue to press home their attack unfazed." "Eventually, the tuna move on, leaving the shearwaters to battle among themselves." "As long as a predatory fish or a dolphin remains at the scene, the mackerel can't escape to safety, but when the little skipjack tuna start to move away, gradually the bait ball sinks into the depths towards safety." "The shearwaters follow it down to the very limit of their breath-holding ability, perhaps as deep as 15 metres." "At last, even they are forced to leave their quarry." "However good or bad this summer's feeding may be, within three months, winter will be on its way and the temperature of these waters will drop by a few degrees." "Then the ocean hunters will abandon the Azores once more." "As ever, they will move on, searching for another feeding opportunity - the next pulse of life in the distant reaches of the open ocean." "The frozen seas are worlds unto themselves." "Beneath their ceiling of ice, they have an eerie, almost magical stillness, cut off from the storms that rage above." "In the winter, the feeble slanting rays of the sun bring little warmth and the temperature seldom rises above minus 50 degrees Centigrade." "(HOWLING, WHISTLING WIND)" "For much of the year, it is dark and cripplingly cold." "Yet, there IS life here at BOTH ends of the earth - the Arctic and the Antarctic." "For most animals, whether they live in or out of water, the winters, when much of the sea is frozen, bring the greatest challenge." "The northern hemisphere." "It's February, and as the earth tilts on its axis, the sun's rays creep slowly northwards and the Arctic emerges from its harsh winter." "The Arctic is a frozen ocean surrounded by continents, and when the surface of the sea between the continents freezes from shore to shore, land predators walk out onto it to hunt." "It's early March, and the sea is still covered with ice..." "But there are patches of open water - polynyas - that never freeze over." "Here, where tidal currents are squeezed between islands, the water movement is so strong that ice cannot form." "Walruses spend the winter in polynyas." "Here they have permanent access to the air, but they can also retreat to the sea to shelter, to hunt." "Other sea mammals overwinter in polynyas as well - in this one, a young bowhead whale." "Here, the current is really fast and the shifting ice is dangerous." "This whale became trapped when ice encircled it last autumn." "There is no food here, but a whale must breathe, and the only place it can do so for miles around is in this tiny hole." "It's living entirely on its reserves of fat, but now, they're dangerously low." "It will be some months yet before it can escape." "Elsewhere, other whales have also been trapped." "These are belugas." "Their tiny hole in the ice has been kept open not by currents, but by the belugas' continuous movements as they rise to breathe." "Open water is now some 20 miles away." "It will be two months yet before the ice melts." "The belugas are extremely thin and most of them are horribly scarred." "But their wounds were not inflicted by the ice." "A whale would be a huge prize for any meat-eating hunter, and these belugas, trapped by the ice, are within reach of polar bears." "Well aware of the danger, the belugas stay submerged as long as they can, but they can only hold their breath for about 20 minutes." "Catching a four-metre-long whale that weighs one tonne is no easy task, even if that whale is weakened by starvation." "But a beluga is well worth waiting for." "Day by day, as the hole gets bigger, it becomes increasingly difficult for the bear to land a whale." "Keeping its fur in good condition and free from salt is important for warmth, and the bear uses snow like blotting paper." "These belugas have been attacked by many bears over the last six months, and some have been caught." "It may have taken a long time and a lot of patience, but a catch when it's made brings abundant rewards of energy-rich blubber." "Gulls rely on bear kills at this time of the year, and the colour of blood staining the ice attracts them from a long way away." "The remaining belugas still have a long wait before they're released from their prison and the threat of slaughter." "Arctic foxes also rely on the polar bears to hunt on their behalf." "They're the jackals of the north, and scavenge from bear kills whenever they can." "In winter and early spring, they're wholly dependent on bears." "Only in the summer, when the sea ice melts, will they regularly catch prey for themselves." "They're not strong enough to tackle adult seals, but can certainly take new-born pups or birds." "This canny individual is going to bury its prize." "It may need it during the uncertain times ahead." "The presence of bears affects the behaviour of almost all the animals here, big and small." "The bears tend to avoid the fringe of fragmented ice bordering open water where travelling can be very laborious, but that very fact makes this area - the pack ice - a particularly good place for seals to pup." "Harp seals breed here." "Their pups are born with white coats which camouflage them very effectively against the snow." "Harp seals have a very short nursing period - a necessity on this unstable pack ice - but suckling is intensive." "The pup feeds for just 12 days on milk that is 45 per cent fat." "Then it's abandoned and has to fend for itself." "A male hooded seal." "This impressive nasal display is used to warn away other males... and to win a mate." "Hooded seals also breed on pack ice." "Their pups suckle for only four days, the shortest nursing period known for any mammal, and all because the threat of polar bears caused them to breed on the unstable ice." "Another Arctic seal opts for the solid ice further north." "Because it's easy for bears to hunt here, these ringed seals must be particularly vigilant and have to hide their pups." "Ringed seals are comparatively small, so they can give birth to their pups in little caves or lairs under the snow." "Here, a pup is out of sight and protected from bad weather." "In late March and into April, female bears emerge from winter dens with their new cubs." "The mother has not eaten for at least five months and she's hungry - very hungry." "If she doesn't succeed in catching a regular supply of seals, her milk will fail and her cub will die." "Bears have an extraordinarily sensitive sense of smell and can detect seal pups hidden in the snow from two kilometres away." "But a female ringed seal uses several lairs and a bear will have to break into a number before it finds one that is occupied." "This is a crucial time for the cub." "By watching its mother hunt and by copying her actions, it's beginning to acquire the rudiments of its own hunting skills." "Play is also important for developing muscles and improving co-ordination." "As the days go by, the sun rises higher and remains above the horizon even at night." "The female bear continues to hunt until her cub is too tired and can't keep up." "She's smelt something." "The pup escapes through a hole in its lair that leads to the sea below." "Only one in 20 hunts is successful, but this mother must find a seal pup soon if her cub is not to starve to death." "As spring turns into summer, the sun's heat begins to melt the sea ice." "Now, the ocean is accessible and the Arctic's summer visitors return." "Migrating birds arrive from the south to nest and feed on the seafood now within their reach." "Brunnich's guillemots are the northern equivalent of penguins, but they have retained the power of flight for they need to reach cliff ledges where their nests will be safe from predatory bears and foxes." "Nonetheless, they are as at home in the water as in the air." "They dive down to a depth of 50 metres or more to catch fish." "In June, the ice begins to fracture." "The cracks - or leads - form useful corridors of open water for air-breathing animals." "Belugas, migrating to their feeding grounds, use these leads to penetrate the ice-covered seas and reach areas where their preferred food, Arctic cod, has spent the winter." "The males regularly dive to about 500 metres to find fish." "The females and young, which have smaller lungs, only go to about 350." "In late June and July, narwhals arrive." "The females, who usually lack tusks, come first with their new calves." "The males follow a little later." "They also move up the leads in search of fresh feeding grounds." "Bowheads." "Up to 18 metres long and weighing 100 tonnes." "These are the only large whales that stay in the Arctic all year round." "They are not after fish." "They're seeking smaller prey." "Despite having the largest mouths in the animal kingdom - the size of a small garage - they eat tiny crustaceans - copepods - straining them from the water with the four-metre-long strips of baleen that hang from their upper jaws." "In the summer, they store enough energy to last them through the following winter when food will be less abundant." "As the ice melts away, the polar bears are forced to head for land." "They are excellent swimmers, and can cover 100 miles of continuous open water if need be." "Off east Greenland, there is little ice left by August, so walruses haul out to rest on land." "At this time of year, they are moulting, getting rid of their old, scarred, parasite-ridden skin." "A bathe in cold water brings some relief from the itching... but even there, the odd scratch is irresistible." "They make daily excursions out to deeper water." "Down at 20 metres, they root around in the sediment, using their sensitive bristles to search out soft-shelled clams." "Once they find a clam, they suck its flesh from the shell with their powerful, muscular mouths." "Walruses can feed for about five minutes at this depth before they have to return to the surface to breathe." "Elsewhere in the Arctic, belugas are gathering in their thousands." "They congregate in just a few large estuaries." "Belugas of all ages and sizes come here." "There are even young calves." "Some are so young - born only a week or so ago - that they need help." "They swim on their mothers' backs so that they can breathe more easily." "As the tide moves up the estuary, the belugas follow, swimming into surprisingly shallow water." "Like walruses, they also need to moult." "A combination of warm fresh water and vigorous rubbing against the gravel does the trick." "They remain here for days or even weeks, so it's likely that socialising is also important to them." "After moulting, they head back out to sea to feed." "It's now autumn, and the sea begins to freeze over once again." "Thin sheets of ice form at the surface and pile up, layer upon layer, gradually creating an impenetrable barrier." "By late November, the Arctic ocean is sealed once again by ice." "The lights of the aurora play in the winter sky." "And at the other end of the planet - in the Antarctic - there is the southern aurora." "Antarctica is now emerging from winter." "This is the coldest, windiest place in the world." "Temperatures are still hovering at a numbing minus 50, and the returning sun has virtually no warmth." "Very few animals can survive such extreme conditions... but Emperor penguins can." "(HOWLING, ROARING WIND)" "Standing on the frozen sea, they endure the full force of the Antarctic storms." "Only by huddling together can they survive the appalling winter months." "They take it in turns to bear the brunt of the gales." "They can only live here at all because Antarctica is surrounded by the great Southern Ocean and no land predators have been able to reach it, so, unlike Arctic animals, they're not threatened by polar bears." "The sea is still frozen, but one seal, nonetheless, manages to stay here, even throughout the winter " "the Weddell seal." "Underwater, it's protected from the storms above, but it must have access to the air all year in order to breathe." "And they keep their breathing holes open with their teeth." "Only by continually scraping away at the ice can they maintain access to the air, but that means that their teeth get badly worn down." "Then, they can no longer hunt and eat effectively." "Weddell seals die young." "The continent of Antarctica is so isolated and so high - almost 5,000 metres in places - that it's considerably colder than the Arctic." "Ice slides slowly down from its centre towards its rim in immense glaciers." "During winter, the continent effectively doubles in size as the sea freezes over." "Ice forms around its shores and extends outwards for hundreds of miles around the entire land mass." "Under the sea ice live small shrimp-like creatures - krill." "They have been here all winter." "During these dark months, they feed by scraping algae from the ice." "Remarkably, they also shrink in size and revert to their juvenile form to save energy." "As the temperature rises in spring, the ice begins to melt, and little air bubbles trapped within it are released." "Microscopic algae grow around these bubbles and the krill now graze on them, gathering them up with their beating legs." "As the sun's rays grow stronger and penetrate deeper into the water, floating algae begin to flourish," "and krill leave the dwindling ice and gather in swarms as they harvest this new crop." "Far to the north, beyond the blanket of sea ice, chinstrap penguins have been overwintering in the open ocean." "The occasional iceberg gives them the chance of a rest - if they can get onto it." "But at this time of year, where they really want to be is on land." "It's just getting there that's tricky." "It's spring, and the penguins are returning to breed." "Their need to get ashore is now urgent and imperative." "Doing so is all a matter of timing, and picking the right wave." "But their journey has only just begun." "Most of them will have to walk many miles before they can find a nest site." "(TREMENDOUS DIN)" "This is Zavodovski Island, which has the largest penguin colony in the world." "About two million chinstraps breed here, and they come to THIS island for a good reason." "It's an active volcano." "The heat from the crater and the fumeroles keeps the slopes free from the ice and snow, allowing these chinstraps to start breeding earlier than those further south." "But then again, living on an active volcano is not without its risks." "Unlike the Emperors, these penguins are able to lay their eggs on the bare ground." "Little wonder so many choose to brave the mountainous waves in order to get here." "Further south, near the continent, the blanket of sea ice is beginning to break up." "Icebergs are gigantic fragments of ice that have broken away into the sea from the front of glaciers." "During the winter, they were frozen into the sea ice, but now they're set adrift once more." "As the bergs break up, they form brash ice." "It litters the backwaters of the Antarctic peninsula." "Minke whales make their way into these placid waters in summer." "This is the most abundant whale in the Southern Ocean." "Minkes are one of the smallest of all the baleen whales, and like all others, they come here to feed." "The majestic humpback whales are also summer visitors." "They have travelled thousands of miles from their winter breeding grounds in the tropics to gather the food that becomes available here in summer." "In just four months, they accumulate enough fat to provide them with energy for the whole of the rest of the year." "All these animals have come here in search of one thing - the krill." "Krill is the mainstay of the Antarctic food web." "It occurs in phenomenal quantity - billions of individuals in a single swarm, and swarms can stretch for miles." "Fur seals also collect this rich, super-abundant food." "Krill swarms are very patchy, but once found, feeding is easy." "Humpbacks engulf hundreds of thousands of them in a single gargantuan mouthful." "When the going is good, the whales feed continuously, each eating up to two tonnes of krill in 24 hours." "Further south, near the continent, the sea ice is still sound." "Here, where the ice remains for most of the summer," "Emperor penguins make their home." "These have been feeding out at sea, and are now ready to make their way back to the colony to feed their chicks." "Instead of heading straight for the ice edge, the penguins hesitate some distance from it." "They're nervous." "They dive down and investigate the ice edge..." "And for good reason." "Leopard seals patrol this border." "Leopard seals are the Antarctic's equivalent of polar bears." "They're the top predators, but they hunt most successfully in the water, so by and large, the animals they prey on are safer out on the ice." "They have a lazy grace that belies their ferocious nature." "Confident that the coast is clear, the Emperor penguins head for the ice... but they certainly don't linger." "Now they have a long walk back to the colony." "Emperor penguin colonies are some way back from the ice edge." "In winter, they may be as much as 100 miles from it, but as the summer progresses and the ice melts, the edge comes ever closer to the colony." "So by the time the chicks are fledged and ready to take their first swim, the water is close by." "This colony is in the lee of a headland, and that prevents the ice from being broken up by ocean currents." "The returning adults are so full of food that they can barely walk, but with no predator to threaten them now, they can take their time." "Somehow, in this mêlée of 60,000 or so penguins, a parent has to find its chick." "It returns to the place where it last left its chick in the hope that it might still be close by... but chicks tend to wander, so the adult has to call to it." "(ADULT MAKES LOW TRILLING CALL)" "(CHICK MAKES HIGH-PITCHED PEEP)" "The chick responds, and they slowly home in on one another." "The plaintive entreaties of the chick stimulates the adult to regurgitate a mouthful of fish." "With the return of one parent, the other is free to go to sea to feed for itself." "Aware of the leopard seal's presence, the penguins press together at the ice edge unwilling to be the first to risk diving in." "Occasionally, the seal comes out onto the ice and attempts to grab one..." "But its most successful strategy by far is to lie in wait." "It hides behind a corner of ice." "The Emperors gain confidence and make a dash for it." "The first wave of penguins escape." "Once in open water, they will be safe." "But the seal is alerted by the noise, and through the mass of bubbles, it makes its attack." "Almost invariably, it makes a kill." "Encouraged by the absence of the seal, the remaining penguins make a break for the open sea." "In time, their chicks will fledge, and when the Antarctic autumn is near its end, these adults will walk across the newly-formed ice to endure yet another winter on the frozen sea."