Natural World (1983) s27e16 Episode Script

The Moon, the Earth, and the Earth's largest feature - the Pacific Ocean.
It's vast - a third of the whole planet, larger than all the land put together For us, this ocean is unknown, alien.
Imagine what it must be like to call it home.
A sea turtle.
She's an ancient traveller.
She will cross this whole vast ocean to lay her eggs.
On the way are lightening-fast fish and leviathans.
She'll encounter the ocean's most intelligent predators and terrified prey.
There are mountain summits over dark depths.
And beyond, sparkling coral reefs.
Most of life on Earth is here but it is changing, shifting like the ocean currents themselves.
In telling her story, we'll see some of the dramas she'll face along the way.
A little backwater off the west coast of Mexico.
The loggerhead turtle has made her home here It's a quiet, safe spot, with plenty of shellfish to eat.
Enough even to share.
35 years ago, she hatched on a beach on the other side of the Pacific.
She drifted, all the way across.
Now suddenly, she has an urge to lay her eggs where she was born.
Scientists satellite-tracked a loggerhead from Mexico.
They discovered details of a 9,000-mile route, longer than any other migration on land or in the sea.
A perilous journey.
Spanish explorers named this ocean Pacifica - peaceful.
They must have been lucky with the weather.
She's faced typhoons before.
She knows what to do.
She holds her breath, and keeps below for about six hours at a time.
The only ones in trouble are us.
Time to leave.
For the animals, a storm is wonderful.
It stirs up the water.
It will bring life.
Blown a little off course, she reaches the Doldrums, off Central America.
She's re-orientating herself.
She has pads on her flippers for walking the way her ancestors once did on land, before dinosaurs.
Turtles have been part of the Pacific since the ocean was young.
They are the oldest sea creatures that still have to breathe air.
Winds and currents sweep up the chaos of the storm into long lines of debris.
Not just flotsam - everything is gathered up, including turtles.
This is a green turtle.
The loggerhead will encounter many of them on her journey.
They all go along the lines of debris, and edges of currents.
They're busy highways.
Here in the Doldrums, famous for its becalmed sailors, the ocean's sweepings stretch visibly for hundreds of miles.
Nutrients churned up by the storm feed clouds of microscopic plants, phytoplankton, minuscule green worlds.
A teaspoon of ocean contains thousands of eggs and larvae, like seeds, waiting for spring.
Tiny animals magically appear - jellies, mysids, krill.
Clouds of plankton make up, worldwide, half of life on Earth.
It feeds the ocean.
Fish appear as if from nowhere.
The schools gather around anything for protection, even this disconcerted turtle.
The only other place for fish to hide is behind each other.
Looking for them are the most intelligent predators in the ocean.
These are spinners in hundreds-strong superpods, calling to each other, coordinating the hunt and spinning.
Are they getting their bearings? Communicating? Shedding parasites? Or is it just exuberance? We don't know.
The dolphins have allies - those most mammal-like of big fish, tuna.
Tuna are warm-blooded, powerful and intelligent, with a good sense of smell and good eyesight.
When they team up with dolphins to hunt, no other predators can compete.
Turtles, much slower, are just passers-by here.
The fish hear the dolphins and tuna coming and become a whirling tornado.
Fishermen call it a bait ball.
In less than an hour, the bait ball is devoured.
Too bad for the slower silky sharks.
On land, packs or prides are never on this scale But when one land predator comes to hunt here, it is on an industrial scale.
This yellowfin tuna alone justifies the expanse Better still is to catch the fish in their thousands, and sell them for millions.
The nets around the tuna and dolphin are slowly closed, trapping everything big.
So that the tuna can be called, "dolphin friendly", The dolphins are helped out of the nets.
Everything else is hauled up including huge manta rays and marlin, which are thrown back to die.
There are only a quarter of the turtles there were 50 years ago, when efforts to protect them began.
90% of the fish are gone from here, too.
Our loggerhead turtle is swimming through a poorer world.
Making a big comeback are the most primitive large sea creatures of all, 20 foot long open-ocean jellyfish.
They're filling in for the missing fish.
Lion's mane, common and moon jellies are increasing worldwide too.
For a loggerhead, good news.
Jellies, she can eat.
Jellies and other simple animals don't just drift.
Their daily trip to the depths is the largest mass migration on Earth.
Turtles can't follow the jellies down But they sense the dark landscape miles beneath them.
Their brains contain cells that can detect magnetic fields, and map the iron-rich ancient volcanoes below them.
Fish follow the same landmarks.
They mass above the foothills that surround the huge mountain ranges.
These foot-long trevally jacks are drawn here by food Plankton are fed by rich currents forced upwards from below.
It is the first sign that volcanoes are rising up ahead.
She follows the seamounts and valleys that stretch to the west.
Turtles need to sleep, and they can't afford to doze, just drifting on the currents Whenever she can, she finds a peak for the night.
They are like fish cities along the highway.
Other turtles are here.
Predators and prey live side by side A moray eel guards a nursery of young fish.
It would eat them if it could.
Instead, these teeth keep other predators at bay.
Anything dangerous hides baby fish.
Another defence is, just don't look like a fish.
You need to keep a step ahead of anything that might eat you White-tipped reef sharks, for instance.
They lounge around and let tiny wrasse clean them.
There are turtles on this seamount, some resident, and some passing through, and sharks do attack turtles.
By day, there's no problem.
As the sea starts to darken, the sharks get restless.
A sea turtle's shell offers some protections, but she can't pull in her head or flippers.
They can easily be bitten off.
She can't just hide all night.
She'll need a breath of fresh air at least once.
That means a careful dance around the sharks The sharks' main interest is fish, most of which sleep or hide motionless in crevices.
Any movement sends outs an electrical signal.
Refreshed by a breath of night air, the turtle looks for a place where she can sleep unmolested.
A cave is good usually.
Sometimes turtles, hiding from sharks, get lost in cave systems.
They can't get to the surface and they drawn.
Dawn.
The turtle can breathe in peace.
If it has been a really hard night, a turtle might briefly rest, seeing in another gang of night hunters - hammerhead sharks.
Hammerheads are no threat to turtles.
They're just here to be looked after.
The black and yellow barber fish and angelfish clean the shark's teeth from the night's hunt The hammerheads are up from the depths, chasing squid, sweeping through the dark with the electrical sensors in their heads Now they relax, roll over, and let the barber fish do their job.
Hammerheads in their thousands rest together.
Many will soon head for Hawaii, 2,000 miles away, to give birth.
The Pacific has few really long-haul travellers.
Turtles aren't normally considered in the same league as albatrosses, or humpback whales except for loggerheads.
She beats them all.
Leaving the seamounts behind, she crosses into deep open water - next stop, Hawaii.
All across the Pacific, she'll pass green turtles on the way to feed or nest, having their own difficulties along the way This green's shell is badly cracked.
Whatever attacked her, her shell saved her life.
It's easy to think of a turtle's shell as some prehistoric relic, a defence against monsters long gone.
In fact, the ocean is still dangerous.
The largest predator ever is alive today It is the sperm whale, with teeth twice and size of Tyrannosaurus Rex fangs.
A sperm whale could crush a turtle's shell.
But what it wants is a mile down squid.
The deeper you go, the larger squid get.
These are Humboldt squid.
Six feet long, they are aggressive and very dangerous.
Sperm whales can go further down and get the giant squid, 50 feet long and with eyes like dinner plates.
They're mainly known to science by the great scars they leave on sperm whales.
There's good reason to be built like a quarter-tonne tank.
Her armour comes at a price - she's slow.
All the other long-distance travellers are sleek and fast.
In a weightless world, some of the fastest are also the biggest.
Most of what's said about a blue whale refers to its size a tongue heavier than an elephant, veins wide enough for a human to swim down.
But they are very fast.
Few boats can keep up - they mainly have to be studied from the air.
The turtle seems from a slower, bygone age.
A blue whale burns up energy, over 1,000 calories a minute So do its relatives, fin and sei whales They zip around the Pacific.
The record is 2,500 miles in 10 days.
A loggerhead is slow and cold-blooded.
She can travel 9, 000 miles.
She just chugs on.
But like a tractor on a motorway, this isn't always safe The ocean's buccaneers are looking for bait balls.
Slow-moving objects are a magnet for frightened fish.
Better to keep out of the way.
All that's left is a shower of scales.
They ought to be top of the food chain, but they're not.
This is.
This is long-lining and the main targets are marlin, swordfish and tuna.
80 miles of lines, with baited hooks every few yards are reeled out one day and reeled in the next.
Lots of wildlife is caught.
Only swordfish and tuna are kept.
Turtles go for fish if they're just hanging in the water.
Turtles are legally protected, so sometimes, if they're lucky, they're unhooked and thrown back alive.
After six months, she is approaching the Hawaiian islands.
The loggerhead finds land beneath her again.
Most Pacific islands have a definite lifecycle.
They start as volcanoes.
Then the volcano dies and the island is, inch by inch, eroded down.
Humpback whales follow the loggerhead in.
They come 4,000 miles from the Arctic to breed here Mothers with last year's calves arrive first.
Then come the males, splashing and singing.
The mothers will wean their calves and mate.
Finally, the pregnant females.
They've been feeding in the Arctic until the very last minute.
Now their new calves will suckle and grow in Hawaii's warm bays.
The bays are also important for green turtles Which come here to breed.
Lovemaking in the surf can be exhausting for animals that weigh a quarter of a tonne.
The females haul out from time to time just to rest.
Scientists take the opportunity to paint numbers on them and albatross chicks come down to see what kind of improbable things live under a shell This is home for these green turtles and albatrosses, for a loggerhead it's just a rest stop.
It's seven months since she left Mexico and she's barely halfway.
Ahead is an ocean peppered with islands.
Below the equator, constellations of reefs reach down over an area the size of Europe.
It is like swimming into some exotic kingdom.
Suddenly everything's delicate, fragile, and beautiful Purple queen anthias.
Royal dottybacks.
Seahorses in disguises.
Flashing cuttlefish.
Green turtles go beyond the reef, heading for the white beaches of fine coral sand to lay their eggs.
They may not be the only reptile with their eye on the beach.
The largest reptile in the world is the saltwater crocodile, or saltie Salties swim between the islands and have even been seen miles out to sea.
We don't normally think of crocodile as seaworthy but they are.
A fully grown croc can easily catch a turtle and is strong enough to break the shell When man came to these islands he hunted both, and crocs nearly to extinction.
At least turtles are safer now from crocodiles.
The loggerhead stays north, swimming past Wake Island and the fringes of the Marshall chain.
All the beaches she passes would be fine, but no loggerheads nest here Maybe they were wiped out somehow.
This loggerhead has lost half a flipper She'll grow old here.
Turtles may live to 100 or more.
She's accumulated passengers over the years, especially barnacles.
Healthy turtles deal with hangers-on by paying a visit to the local coral reef, to a cleaning station.
Green turtles are regular customers here.
A turtle shell is fused from its ribcage and covered in living skin.
She can feel the tickling on her shell.
To encourage the service, a turtle adopts a special posture.
On a reef, as anywhere, there are those who'll abuse the hospitality.
Manta rays come to be cleaned by wrasse and surgeonfish Surgeonfish are spawning and the milky blue clouds are their eggs Surgeonfish breed with the cycles of the moon.
The mantas can schedule their cleaning appointments to make sure there's a meal afterwards.
The oceans have rhythms like the land The most influential rhythm is something the land doesn't have, tides.
When the Moon is over the Pacific, it pulls the whole, huge ocean towards it.
Tides govern the timing of our journey And the nesting at the end of it.
Many sea animals can detect rising tides with perfect accuracy.
A coral polyp has created miniature moons, each a bag of eggs.
Once a year on the same night, corals of a single species spawn.
The seawater is so thick with plankton and larvae that with just a pint of it, you could start a new reef, colonise a new seamount or seed a new bait ball.
If you look for hope, you can find it here The sea has an almost infinite ability to regenerate.
But it's also extremely fragile.
The white slabs along this reef are coral, dead coral.
Some of the richest places on Earth are dying because of a degree or two rise in temperature The seas are also absorbing more carbon dioxide, making the water more acidic.
It's harder to grow your skeleton in acidic seas.
Life in the whole Pacific is changing Some of the effects reach out like tentacles around the whole world.
The currents that flow between the Pacific and the other oceans are like huge conveyer belts.
As the warmth spreads, weather changes.
More water evaporates, it changes from ocean to cloud, becomes storms and floods or makes droughts.
No-one knows how bad it will get.
If turtles have any ancestral memory, they know.
55 million years ago turtles could visit coral reefs off Alaska or swim to the North Pole.
Now they're swimming over the evidence that it can happen again.
The cold deep Pacific can cool the ocean as it mixes with warm water, but there's a problem.
Miles down, in the dark is where the bodies are.
Decomposition produces methane.
Under-sea volcanoes do too and there are huge seas of it.
Cold water keeps the methane where it is, but if it warms, even a tiny bit, the methane bubbles up.
It is greenhouse gas 10 times worse than carbon dioxide The last time this happened, half of life was wiped out What happens here affects the whole planet.
Turtles have survived because they can travel.
The best food and currents have always been changing.
She's heading for the only beach she knows is safe The beach that produced her.
She's come a third of the way around the world and still has 1, 000 miles to go.
To find a dot of land not seen for decades, turtles need to map magnetic fields, chart currents and tides and use the angle of the sun to navigate.
Recent research also suggests that she uses the unique smell of the shore to guide her home.
Green turtles don't travel as far as loggerheads but 1,000 miles isn't unusual.
All female turtles mate a few weeks before they start nesting.
The males are smaller than the females and have long tails It's not only male turtles waiting offshore.
Tiger sharks know about turtle beaches, too.
Not many sharks specialise in eating turtles, but sometimes sharks seem to get a taste for it.
The loggerhead has been travelling for a year now and like the loggerhead that scientists satellite-tracked from Mexico, she's zigzagging her way home.
Her beach, it turns out, is in Japan She's travelled 9,100 miles in 370 days An average of one mile an hour.
Nobody saw her arrive, but it's the same for all turtles.
Thousands of loggerheads used to haul themselves up this beach.
Now there's only a handful of turtles.
She digs a hole a few feet deep and lays about 100 eggs.
Then she covers them up and struggles back towards the Pacific.
She won't return to Mexico, but spend her long adult life around here, Japan and China.
There are more and bigger storms now.
A typhoon in the Pacific last year was the most intensive and longest lasting on record.
Storms and rising sea levels wash turtle eggs away The scientists following the first loggerhead they tracked saw it had arrived safely.
But then saw it caught in a trawl net and drowned.
It was an accident.
It's also a sort of accident that the Pacific is changing.
No-one thought that our lives could have such an effect.
Now, we must plot a new course.
Luck has been kinder to our loggerhead's babies and two months after being laid most of them hatch.
In 35 years time, some of the females among them will be off Mexico and wanting to come back here.
Maybe a few will swim past clouds of plankton and huge whales, mantas and dolphins.
Maybe one of them will make it back safely, across this massive ocean.
The Pacific.