♪♪ NARRATOR: The oceans are full of wonder... an alien world, waiting to be explored... ...a place of extraordinary life-forms... with intriguing social lives... and incredible intelligence.

To reveal their secrets, a hidden team goes undercover.

Spy Creatures.

♪♪ The most innovative undersea robots in the world.

♪♪ They not only look like the animals they film, they interact with them as no human can.

♪♪ Equipped with hidden cameras... ♪♪ ...they reveal their astonishing lives.

As our Spies join their undersea world... they shed light on some of the mysteries of the deep.

♪♪ NARRATOR: The ocean is a beautiful and mysterious place, but as our Spies discover, trouble can lie just below the surface.

For a humpback calf, the first few months of life are the most dangerous.

And in the seas of French Polynesia, a mother with young has a lot to worry about.

Spy Humpback and Spy Dolphin are discovering what she fears the most.

♪♪ To avoid drawing attention, they communicate only in whispers.

[ Whale song ] Conversations picked up by hydrophones in our spies.

♪♪ Above, Spy Frigate is also on duty.

It's soon clear a calf has other ways to make a noise!

Below, his splashes travel far.

Our spies' hydrophones pick up another sound... a call not far away.

[ Whale song ] Spy Dolphin investigates.

A male humpback.

[ Whale song ] He's what's known as a singer -- a male looking for a mate.

With the singer so close, the calf should stay silent.

But like any youngster, he can't keep still, and certainly can't keep quiet.

Spy Dolphin is still with the singer.

The whale heard the leaps and sets course to find where they came from.

♪♪ Aware of the danger, the mother guides her calf away.

But it's already too late.

♪♪ The singer circles the pair.

♪♪ All the calf can do is stay close to his mother.

But even this won't keep him from harm.

The male wants to mate, and that's where the danger lies.

[ Whale song ] She slaps him away... and keeps herself between him and her calf.

He wouldn't knowingly harm her baby, but courtship can be a rough affair.

As things escalate, the calf stays even closer.

It's about to get worse.

Other males are arriving.

They heard the singer's song, now they've heard the commotion.

The calf is in grave danger and there's little his mother can do.

♪♪ As the whales circle, there's no escape.

But the newcomers are now the singer's rivals.

His warning -- a bubble blast.

But they aren't scared off easily.

A second warning from the singer.

A dangerous moment.

Things could spiral out of control.

♪♪ The mother pushes her calf to the surface, protecting him as best she can.

The singer issues his third and final warning.

He's bigger than any of them, and ready to fight.

♪♪ The threat's enough to drive the males away.

♪♪ The calf is now safe to swim on his own.

♪♪ The singer's behavior seems to have changed.

With his rivals gone, he now keeps a respectful distance.

Accepted by the mother, he'll stay by their side and protect them from danger.

[ Whale song ] In return, one day, he should win the mother's affections.

♪♪ Until then, he'll be their escort.

♪♪ [ Birds squawking ] On this remote island in the South Atlantic, there's trouble on the beaches.

Each year, South Georgia is invaded by elephant seals.

They are the heavyweights of the seal world.

For a pup, it's a tough place to be born.

Fighting is all around.

The pup is blissfully unaware of the risks he's facing.

It takes a battle-hardened spy to survive here.

BoulderCam -- a souped-up version of the first spycam ever made.

[ Grunting ] Its rock-hard exterior offers some protection from these mountains of blubber.

The pup's only defense is his mother.

But despite the current calm, she can't stop danger coming to them.

The beachmaster.

The largest seal in the colony and the father of the pups.

Weighing nearly four tons, he's 10 times heavier than the females... [ Pup squeaks ] ...and doesn't know his own weight!

He has plenty else to worry about.

Such as a male cavorting with one of his females.

Not the wisest move.

An outrage for the beachmaster.

A danger for the pup.

[ Pup shrieking ] He has nowhere to hide.

♪♪ ♪♪ When eight tons collide, the risk is for those who are in the way.

This time, it's an easy win for the beachmaster.

But this clash of the titans separated the pup from his mother.

If he doesn't find her soon, he won't survive.

Approach the wrong mother, and you'll learn the hard way.

[ Pup shrieks ] But he still tries each in turn.

♪♪ Just when it seems things couldn't get any worse, a skua arrives.

♪♪ But this pup is a fighter... and won't give up.

♪♪ Then, a familiar figure.

The beachmaster, fresh from battle.

Approaching him could be a big mistake.

♪♪ ♪♪ But the beachmaster has a more sensitive side.

♪♪ A father and son moment.

♪♪ He may be welcoming, but beachmasters have other priorities.

Like snoozing.

[ Squeaking ] But where is his mother?

She's been close by all along.

[ Mother grunting ] [ Squeaking ] They're together again.

♪♪ A tender moment in an inhospitable land.

In a colony, harmony is briefly restored.

Wherever serenity seems to reign, trouble is rarely far away.

And finding food is often at the heart of it To find a creature with a killer solution, Spy Crab embarks on a dangerous mission.

It's after a creature with a fearsome reputation.

♪♪ Plumes of sand are the giveaway.

Spy Crab risks all by taking a closer look.

♪♪ ♪♪ It's wise to be cautious.

For this creature in hiding has deadly powers.

It's a peacock mantis shrimp.

Despite its size, it packs a killer punch.

This was just a warning.

Better stay back.

Fortunately, the mantis has a job to do.

A bit of housekeeping.

His next task is to find food.

While he's away, his lifelong partner guards the nest.

She's carrying their eggs.

So it's up to her mate to bring home a meal.

♪♪ Spy Crab will join him to find out how he catches it.

The mantis hunts with cunning and initiative.

He uses the coral as cover to stage an ambush.

♪♪ He's helped by the most complex eyes of any creature.

They see colors invisible to most other life.

They even move independently, useful for targeting prey.

He aims to take it by surprise.

Our spy moves in for a closer angle.

♪♪ This is the moment.

He strikes!

The most powerful punch in the world.

Faster than a bullet from a gun.

A force 1,700 times his weight.

Even the locals seem impressed.

With his victim out cold, he carries it home.

♪♪ ♪♪ Spy Crab dares to move closer.

It's a meal that will last the couple for days.

♪♪ After a bit of dismantling, shell fragments are discarded.

♪♪ It's tempting to move closer still.

But is this wise?

♪♪ Our Spy is a crab after all.

♪♪ [ Glass shatters ] You can't say it wasn't warned.

For ingenious ways of catching prey, few can beat a mantis shrimp.

But even the greatest hunters can find themselves in trouble.

This Galapagos sea lion has the odds stacked against him.

The rest of his hunting team had been killed by a pod of orcas.

Not only that, in the fighting, he lost an eye.

But every day, he still needs to eat.

To see the challenges he faces, Spy Frigate is deployed once more.

Spy Sea Lion captures the view from below.

Despite his problems, the sea lion is fit and healthy.

But he's after one of the most challenging fish of all.

A tuna.

To hunt it alone is almost impossible.

Our spies will see how he fares.

Without his team behind him, it's all up to him, with our spy just an observer.

His best hope is to trap it against the rocks.

But as soon as it's cornered, it finds a way out.

The chase goes on.

Again he has it trapped.

♪♪ The sea lion cuts off the tuna's escape.

Spy Sea Lion picks up the chase.

♪♪ Once more, it's cornered.

♪♪ Once more, it escapes.

♪♪ It's now a test of endurance, and the sea lion is tiring.

But it's not his only problem.

A Galapagos shark.

And not just one.

They aim to steal his catch.

He drives them away and is back in pursuit.

♪♪ ♪♪ ♪♪ Close, but not close enough.

♪♪ Then he has it!

♪♪ And drags it to the shallows.

But it's not over.

It's what the sharks were waiting for.

♪♪ The sea lion is outnumbered.

They steal his tuna away.

But the sea lion won't give up.

He steals it back.

And takes what's left to the rocks.

[ Barking ] With the tuna out of reach, the sharks retreat.

His sheer tenacity made the impossible possible.

Tomorrow he'll have to do it all over again.

If you're looking for trouble, the coast of California is the place to be.

Here lives the sarcastic fringehead.

Better known for its aggression, rather than it's sarcastic nature.

♪♪ But he does use his mouth as a weapon.

A way to guard his home.

♪♪ ♪♪ A new spy is up for the challenge.

It's subject of interest is close by.

As our spy approaches, it films his threat display.

This is what a rival sees.

Our spy's no match for the real thing.

Another fringehead is seeking a new home.

But this one is considerably smaller than our spy.

He soon has second thoughts.

♪♪ He tries the neighbor instead.

♪♪ Again, they use their mouths as a threat.

The neighbor's gape is far bigger than his rival.

And he's ready to fight for his home.

♪♪ ♪♪ ♪♪ He chases off the competition.

And returns to his burrow.

Safe once more.

The loser is still searching.

He finds a vacant home.

♪♪ Or so he thought.

An octopus was already in residence.

Eviction over, he finally moves in.

Returning to the neighbor, our spy discovers why he's so defensive.

He's guarding eggs his mate has laid.

Fanning them keeps them well oxygenated.

Spy Fringehead will leave him to it.

Life on the beach isn't always the paradise it's cracked up to be.

When hermit crabs gather to swap their shells, things can go very wrong very quickly.

Spy Hermit Crab is back to find out the trouble they sometimes get into.

When things go to plan, they line up in order of size and the swap begins.

But leaving one shell and entering the next is tricky.

This crab has missed the new shell completely.

And someone's taken the one he was after.

She won't be giving it back!

Left naked and exposed, he's in serious danger.

At the worst possible time, a ruddy turnstone arrives.

An unfortunate name, and no fun for the hermit crabs either.

Their best defense is to hide in their shells.

♪♪ An option not available to the naked crab.

For the rest, it's everyone for themselves.

♪♪ ♪♪ Fortunately for the naked crab, the turnstones are still focused on the gathering.

♪♪ But these crabs have all the protection they need.

It's those that don't who are in trouble.

♪♪ The naked crab must think on his feet.

♪♪ His solution is certainly innovative.

He's found the cap of a sunscreen bottle.

It's not the perfect solution.

It isn't a good fit and will act like a greenhouse in the sun.

♪♪ What he really needs is in short supply.

♪♪ Could he be in luck?

He's happened on another shell exchange... and takes his place in line.

Or, rather, tries to jump it!

And comes away with nothing.

But what's this?

A shell far from the crowd, with just Spy Hermit Crab on guard?

Has he found himself a home?

♪♪ It's an easy fit.

Now he has the protection he needs.

The ruddy turnstones must look elsewhere.

While hermit crabs must fend for themselves, others face trouble together.

Swathes of kelp and sea grass draw visitors to the Pacific Northwest.

Pacific herring come here to spawn.

They arrive in astonishing numbers.

Spy Bald Eagle captures the true scale of the spectacle.

They are here in the millions.

♪♪ Joining them is another spy creature.

With its fishlike movement and onboard camera, it homes in on the shoals.

♪♪ As Spy Herring nears, it detects a strange sound... [ Clicking ] ...and slips into the shoal unnoticed.

♪♪ The clicking is made by the herring.

♪♪ As the shoals build, so do the clicks.

♪♪ They're from bubbles squeezed from their swim bladders.

The bubbles are thought to guide others following in their wake.

The most experienced herring lead the way.

The commotion soon attracts predators.

♪♪ Sea lions herd the herring towards the shore.

Spy Bald Eagle shows their technique in action.

♪♪ They trap them in the shallows, where they're easier to pick off.

The survivors head for the kelp.

Here, they'll lay their eggs.

Soon, the kelp is completely covered.

They race to finish laying before the sea lions take them.

♪♪ ♪♪ There's more trouble ahead.

[ Birds squawking ] ♪♪ Surf scoters time their arrival to feed on the eggs.

The ducks can dive 60 feet, as they take what they can.

♪♪ One million eggs smother every square foot.

Enough for billions upon billions to survive the onslaught.

♪♪ Having also run the gauntlet of the sea lions, the males take over.

As they fertilize the eggs, their milt clouds the bay.

Spy Herring is vanishing from view.

♪♪ ♪♪ Above, a clear and beautiful scene.

The sea turned turquoise by the spawning males.

♪♪ While herring confront danger with sheer numbers, cuttlefish rely on subterfuge.

They need to -- they spend their lives under fire.

But they are experts at disguise.

For Spy Cuttlefish, a new investigation.

♪♪ As well as creating patterns to communicate, they use them for camouflage, too.

Just as well... New Zealand fur seals are an ever-present danger.

As they go on the hunt, Spy Seal is among them.

♪♪ But cuttlefish have some tricks to play.

♪♪ Under the skin, muscles contract and cause it to rise.

These papillae break up their outline.

Add some color affects, and he soon blends in.

Enough to fool the fur seal.

It's a truly life-saving transformation.

All our spy can do is hide... ...while cuttlefish vanish before its camera eyes.

But it only works for those who see the seal coming.

♪♪ He spots it too late.

The seal doesn't hesitate.

All the cuttlefish can do is release an inky smokescreen.

The seal tries to stun him.

But he has another secret weapon.

Jet propulsion.

Then hide among the inky clouds.

♪♪ But it's not over.

He's grabbed again.

More ink clouds.

More battering.

♪♪ This time, the ink cloud worked.

Then, amazingly, he morphs into the surrounding seaweed.

♪♪ To the seal, he's totally vanished.

Today, on the shores of Mexico, there's no refuge from predators.

To find out more, there's a spy that fits in with the locals.

The crabs are a pugnacious bunch.

Despite the size difference, they stand up to our spy.

It's the highest tide of the month, and the tide is turning.

Our spy is about to witness an extraordinary event.

The first arrivals are already here.

♪♪ They're the front-runners of what will become an invasion.

Our crab is not filming alone.

Spy Pelican is already capturing what's happening.

These are grunion, fish with an extraordinary way of spawning.

♪♪ It's a race against the tide, for grunion lay their eggs on the high tide line.

Just once a month does it reach this far.

By laying in the sand, their eggs are safe from predators in the sea.

♪♪ The females use their tails to drill deep.

The males coil around them, fertilizing the eggs as they're laid.

By spawning all together, each reduces its chances of being eaten.

Spy Pelican has already been joined by a hungry flock.

It's now part of a fishing party... ...one that's growing in size... ...just as spawning reaches its peak.

The grunion must lay their eggs before the tide turns.

But time is running out, and they've nowhere to hide.

♪♪ For the pelicans, it's an all-you-can-eat buffet.

At least it should be.

But despite the feast laid out before them, their bills are now their handicap.

It wasn't designed for this.

What scoops up shoals in the sea is useless on the sand.

But as the tide retreats, so do the grunion.

This is what the pelicans were waiting for.

♪♪ In deeper water, the fish are easy game.

The onslaught begins.

♪♪ ♪♪ Then, on its own accord, Spy Pelican takes a dive.

♪♪ A catastrophic malfunction.

Our crab is now the last spy standing.

It captures the last grunion returning to the sea, having left their legacy in the sand.

The eggs they leave will hatch on the next high tide.

As the tide retreats, it gives back what it's taken.

Our spies' mission is over.

It looks like it's Spy Pelican's last.

Of all the problems faced by ocean life, few are as unpredictable as the weather.

For marine iguanas, it's a test of survival.

Whatever the weather, they must face the waves to feed.

Spy Iguana will attempt to join them, despite the worsening conditions.

It won't be easy.

Even the fish are in trouble.

It's even harder for the iguanas.

They must somehow feed without being washed away.

Our spy also needs a foothold fast.

Secure for a moment, it can see how the iguanas are coping.

Their claws act like crampons, but they can only do so much.

They must eat as fast as they can, while they can.

♪♪ ♪♪ Even a turtle is struggling.

♪♪ One by one, the iguanas yield to the swell.

♪♪ ♪♪ ♪♪ Those that give up the fight head to the surface.

♪♪ Our spy hangs on with the still undaunted.

♪♪ In the end, it's not up to our spy.

The swell has the last word.

As with all our spies, it keeps filming to the end.

In Indonesia, others, too, will soon be weathering the storms.

Spy Octopus discovers what happens when things take a turn for the worse.

♪♪ In calm conditions, the reef is a place for relaxation, and green turtles certainly know how to chill out.

Even Spy Octopus hardly creates a stir.

But conditions are changing... and the swell is building.

♪♪ Our spy braves the growing storm to track down the coconut octopus again.

He's already in a spot of trouble.

Being small, he can easily be swept away.

He must find refuge fast.

The octopus finds cover of sorts.

He can't be choosy.

A discarded grain sack will have to do.

But was this the right decision?

♪♪ Perhaps not.

♪♪ ♪♪ He tries to hold it down... ♪♪ ...but it's a losing battle.

♪♪ Spy Octopus is faring even worse.

The octopus needs an alternative.

♪♪ What better than the shelter that gives him his name?

A coconut shell for a coconut octopus.

Something that will weigh him down.

But our spy is still in trouble.

What it needs is a helping hand.

♪♪ Or an arm, to be precise.

♪♪ ♪♪ A perfect way to end their partnership.

♪♪ On all their journeys, our spies found many ocean wonders.

They found emotions... [ Whale song ] [ Barks ] ...and intelligence, too.

There is friendship and danger... but there's still so much more to explore.

♪♪ ♪♪ ♪♪ ♪♪ ♪♪ ♪♪ To learn more about what you've seen on this "Nature" program, visit pbs.org.

♪♪ ♪♪