[pensive music] [mystical music] - [David] For generations men have lusted after them, the biggest, fastest, most dangerous game fish in the sea.

[majestic music] Dorsal fins rise like a warning.

Colors flash in excitement.

And like creatures out of myth, they wield formidable weapons, gigantic, slashing spears.

[dramatic music] For the chance to pit their skill against a billfish, anglers pay thousands of dollars [dramatic suspenseful music] But one man seeks something more, to encounter sword-wielding giants face to face, to meet these superfish in their world, in the freedom of the open sea.

[gentle music] [dramatic music] [majestic music] [majestic music continues] [mystical music] The billfish roams the open ocean, vast plains of water in places, thousands of feet deep.

It is a highway for seekers on an endless journey, an empty road connecting distant feeding grounds.

[gentle music] Suddenly, out of the barren blue, an oasis appears.

[gentle music] [water gurgling] [dolphin calling] [gentle music] [water gurgling] [gentle music] Driven by ever shifting winds and currents, it's a moveable feast, never lasting very long.

Few people can find it, let alone capture it on film.

So for two decades, marine biologist and cameraman Rick Rosenthal has set out to do the impossible.

- When we go looking for big fish, we try to go out in a wild area, on the banks, where there's a gathering place for food, and there's strong currents and lots of life.

If you're gonna find anything, you've got to go out in that big blue out there to those secret hiding places, those refuges that hold a great deal of pelagic life.

- [David] Pelagic life, the ocean wanderers that inhabit an environment so alien to our own, it's easy to forget we share a planet.

[mysterious music] Yet these creatures are ancient and amazing, honed through the eons to a perfect balance of predator and prey.

[gentle music] [water gurgling] At the top of the pyramid are the billfish.

They include the graceful sailfish, the menacing swordfish and queen of all, the marlin.

Few bony fish grow bigger or swim faster.

Propelled by a hyper-flexible backbone and a mammoth tail, she literally flies through the water, topping speeds of 60 miles an hour on migrations that can span 9,000 miles.

[water gurgling] Though their bills look like weapons, many scientists believe that the long overbite is primarily defensive.

It could be a vestige from prehistoric times when the ocean teemed with armed, predatory fish.

Just as a human face reveals emotion, the skin of a billfish telegraphs mood.

When excited, the tail and pectoral fins of a striped marlin flush vibrant blue.

[water splashing] The belly of an agitated white marlin shimmers in rainbow hues.

The master of its environment, a marlin hunts both far and deep.

In cold, dark waters, a remarkable muscle generates heat for its eyes and brain.

It keeps the billfish alert when other fish are sluggish, an important edge in its incessant search for fuel.

This blue marlin weighs in at 600 pounds, but some tip the scale at a thousand pounds and more.

Those are the prize fish, the ones known as granders.

We covet them as trophies, but a real superfish alive in the wild remains a mystery.

[gentle music] - The billfish seems to capture our imagination more than any other fish.

Their life history is such a mystery because we can't go with them.

We can't follow them.

We don't see them along the shoreline very often.

And that makes it very difficult for scientists and biologists to study them.

You read the books, you pick up the magazines, you talk to the scientists, they're still scratching their heads.

They know very little.

[gentle music] - [David] Though he is a biologist, Rick is not immune to the romance of the grander.

After all, his first glimpse of giant marlin came by way of a novel, Ernest Hemingway's classic, "The Old Man and the Sea."

Like the title character, Rick was hooked by the challenge of the great fish.

- [Rick] As a boy, I read Hemingway, and I read everything I could about the ocean and the outdoors and I thought, what would it be like to see a fish the size that Hemingway described in that book, or, you know, even better, what would it be like to swim with one of those?

[dramatic music] [gentle music] - [David] Rick begins his journey off Mexico's Baja Peninsula with the goal of bringing back a different trophy, a vibrant portrait of the living, breathing fish.

[dramatic music] - [Rick] To be here, and see these dolphins on the run, chasing fish, and the tuna exploding out of the water, sometimes eight, 10 feet in the air, catching flying fish and sardines, you're right in the marlin food patch.

You've found the show.

[dramatic music] - [David] Bright blue fins herald the arrival of striped marlin.

[upbeat music] - [Rick] Striped marlin aren't really schooling fish, but they're tuned to the same things, so they stay in close proximity to each other.

When they come upon a scene like this, they close ranks and force the bait fish together.

Is this cooperative feeding?

I don't know, but it's one heck of a food fight.

- [David] For Rick, it's a dangerously fine line between getting close to the action and becoming part of it.

- [Rick] Those small bait fish see you and they swarm around you for protection, to get away from the predators.

And it's pretty unnerving.

I can't see anymore.

It's dark in there, it's lights out.

[dramatic music] [water gurgling] [mysterious music] - [David] Alerted by the commotion, a small herd of sea lions shows up to gorge themselves.

It's a rare scene.

Sea lions seldom mix with marlin.

They only meet in the California current today because both animals will travel extraordinary distances to follow the food.

- [Rick] I'm holding my breath.

I'm not using scuba gear because the bubbles frighten the animals.

I have no where to go but up, and when things really get crazy I don't want to surface in a feeding frenzy.

[dramatic music] [water splashing] [dramatic suspenseful music] [water splashing] [dramatic suspenseful music] [suspenseful music] [water whooshing] [mysterious music] [mysterious music] [water gurgling] - [David] Within minutes, the predators leave nothing but a glittering rain of fish scales.

They take off in search of new hunting grounds, with Rick close behind.

[dramatic music] But right in the middle of their aquatic superhighway, they run into a wall, a massive net.

[dramatic music] - [Rick] Inside that big tuna net, it was just panic.

The tuna, the dolphins, and, to my surprise, there were big marlin and sailfish trapped inside there as well.

And that's the first time I felt like an oceanic animal that was totally panicked, nowhere to run, nowhere to hide.

[dramatic suspenseful music] - [David] The experience gives his mission a new sense of urgency.

[dramatic music] [people chattering] He's not the only one hunting billfish.

Ironically, his competitors are also the best source for locating his prey.

[gentle music] Rumors lead him east where the pincers of the western tip of Cuba and the jutting Yucatan peninsula create the Caribbean basin.

Here, sportsmen whisper about a fantastic, but elusive, annual event, a huge host of migrating sailfish.

No one knows why it has only recently come to light.

Perhaps oceanic conditions have changed, or it could be a measure of how well the sea keeps its secrets.

[gentle music] [water gurgling] On Mexico's Contoy Island, Rick waits for the sailfish display to surface.

[birds squawking] - I just hope I've timed this right.

The moon, the currents, the fish, and the food, they all have to come together here to get this big sailfish extravaganza.

[birds squawking] I'm glad to see all those birds.

They're like thousands of spotter planes helping me to find the fish.

There's far more frigate birds here than most places we'll ever see in the world.

In fact, this is the largest gathering of frigate birds in the whole Caribbean, right now, during the nesting season.

And they eat a lot of fish.

They require a lot of protein.

And for them to be here and roost and nest and feed their young, day after day after day, there has to be a lot of food out there.

And that food, the sardines, is the same food that the sailfish, the marlin, the tuna are eating, as well.

[gentle music] - [David] For the next several weeks, when the birds take off at first light, they have company.

There are no better guides for a billfish-chasing filmmaker.

- [Rick] Even though we have all this modern technology, radar and GPS and depth sounders, we still rely on some of those old tell-tale signs like seabirds hovering overhead, a distant dolphin blow, a splash, to take us to the action.

At other times, we look for converging currents, and we see those from coloration changes in the water, or maybe you almost see waves on one side of a current line and on the other it'll be smooth water.

You can almost hear what we call the sea wind.

And when we find those convergent lines, those are highways that take us to activity.

And that's just learned through years of working in the open ocean.

And having a lot of patience as well.

- [David] Rick's faith in the birds finally pays off.

They hover over another seafarer's signpost, sargasso weed trapped between converging currents.

He dives into a world bisected by color, blue on one side, green on the other.

He picks up new guides to point his way, a fleet of mobula rays.

[gentle music] - [Rick] I can feel the temperature difference.

One side of my body is warm and the other side is cold.

This must be what a fish feels.

The rays, they swim in and out of that current line.

They seem to know exactly where that temperature difference is.

[gentle music] [water gurgling] [gentle music] - [David] Rick spies a school of sardines on the run.

Hot on their tail, a sailfish.

Rick pursues it into the warm blue water.

It could be his ticket to one of nature's most dramatic events, if the stories are true.

[dramatic music] [dramatic music continues] For once, reality exceeds rumor.

In a 20-mile radius, several thousand sailfish flash and swirl through the water.

[gentle music] [water splashing] - [Rick] Because you go so long in the open ocean without seeing anything, you're on edge, you're ready for something.

So, when you first get in the water and you start swimming, and you get closer and closer, your heart's beating strong.

I mean you're pumped up.

It's the great rush.

- [David] The sailfish is the dancer of billfish, its turns are quick and elegant, all grace and control.

The birdlike pelvic fins allow it to tread water so it can stay in one place as it feeds.

It dazzles most when on the attack.

Unfurling its magnificent sail, it flushes from silver to black.

[gentle music] [water gurgling] - [Rick] When sailfish get excited, their skin shows it.

I think it's just an emotional response.

But the sail is what really distinguishes them.

It makes them look twice their size, very intimidating.

They seem to use it like a matador's cape to confuse and herd their prey.

[gentle music] This is a real special moment.

There's more sailfish in a group than I've ever seen anywhere in the world.

- [David] They come for the sudden concentration of prey, corralled by moon and tides.

Now that their secret is out, Rick fears for their future.

Fishermen are bound to exploit the event, as they have elsewhere.

One tragic example, the fertile waters where the biggest billfish ever were caught.

Along the coast of Peru, the Antarctic waters of the Humboldt Current meet warm equatorial currents.

Their collision creates a biological hotspot.

The harsh desert landscape stands in stark contrast to the rich diversity of life just offshore.

[waves crashing] Here, a steady wind stirs up a phenomenal crop of plankton.

Tons of bait fish course after them, and in their wake, even big fish, like sailfish, marlin, and swordfish, rise to the surface and into the waiting nets and harpoons of an army of fishermen.

The heart of the fishery is Cabo Blanco, a small village that looms large in angling lore.

Once, the fishing grounds just off its shore were known as Marlin Boulevard.

In the 1950s, Cabo Blanco's reputation as a grander goldmine attracted sportsmen and celebrities alike.

Hemingway stayed for a month.

But no one landed more of the thousand pound fish known as granders than Texas oilman, Alfred Glassell.

[dramatic music] He brought his boat, the Miss Texas, all the way down from Nova Scotia, where she was custom-built.

[sailor speaking in foreign language] [dramatic music] - [Narrator] Good Lord, there's no end to him.

[dramatic suspenseful music] A big, mean, magnificent fish, bent on tearing up the ocean.

[dramatic suspenseful music] - [David] At 1,560 pounds, it was the biggest game fish ever taken by rod and reel.

Macho swagger dictated that Glassell refer to the record-winner as a male.

But all marlin topping 400 pounds are actually female, nature's way of assuring only the largest individuals bear the next generation.

It could be argued that the human record holder is female as well.

By some accounts, Kimberly Wiss caught the biggest fish.

Unfortunately, when it was tipped upside down on the scale, 150 pounds of squid slid out of its mouth and the record slipped through Kimberly's fingers.

Glassell and his friends reeled in so many granders that they lined the path to their exclusive club with marlin tails.

60 years later, the sport fishing has dried up.

Only memories of the glory days remain.

[birds squawking] - [Rick] I have mixed emotions when I walk to the old clubhouse.

I would have loved to have been there, at that time when there was real excitement, knowing that there were big fish out there swimming, even close to the beach, that the ocean was probably boundless, that there was lots of food.

On the other hand, what we know today is that those giants may be just ghosts.

[waves splashing] - [David] Rick thinks one of the reasons the granders are gone from Cabo Blanco is the ever-increasing pressure on the squid fishery.

[dramatic music] [engine puttering] Squid fishing's a dirty job.

Out all night in every kind of weather, the fishermen endure conditions as brutal as their lures.

[mysterious music] [people chattering] Alien, even fearsome, they glide through the current, the creatures locals call Red Devils.

[mysterious music] [dramatic music] [people chattering] The reason becomes clear once they're caught.

It's a man-sized cannibal with a vicious beak.

[mysterious music] - This is really a wild fishery out here.

Here comes a squid.

It's holding onto a lure, a jig.

Look at him jet, like a big fire hose.

What impressive animals.

But everything is eating these squids, the whales, the big fish, the big black marlin.

The world-record marlin they caught here years ago, they were eating these squids.

Really an important resource, maybe one reason that the marlin are disappearing.

- [David] Rick's desire to swim with squid shocks the fishermen.

They place bets on whether he'll make it back out in one piece.

[mysterious music] He keeps a sharp eye out for nocturnal hunters which gravitate to the fisherman's lights.

[dramatic suspenseful music] [mysterious music] The hooked squid make easy pickings, especially for other squid.

[mysterious music] Frantic, the victim spews a jet of ink, poor protection against a deadly stranglehold.

[dramatic music] Even half-eaten squid get tossed in the hold.

The fishermen will take every ounce to reach their goal, six tons of Red Devils before morning.

[dramatic music] [people chattering] [birds squawking] Dawn on the docks reveals how much devastation just one night can bring.

There are hundreds of small craft, each carrying tons of squid.

The fishermen make pennies on the pound, a pitiful return, and yet the lifeblood of the local economy.

As the night shift comes in, the day shift goes out.

The clock never stops in the world's most productive fishery.

[birds squawking] [people chattering] The Humboldt Current yields nearly 1/5 of the ocean's total catch.

That includes the daily mountain of anchovies, the anchor fish that supports the entire ecosystem.

It's sold to make fishmeal for livestock feed and fertilizer.

Cheap protein for our pigs and gardens comes at a terrible price to the ocean community.

[gentle music] What is left for the billfish?

[thoughtful music] The story is the same up and down the coast, in all the seaports that line the Humboldt Current A relentless harvest driven by poverty and greed.

[gentle music] [people chattering] [gentle music] [people chattering] - Unbelievable.

Billfish after billfish, marlin, sailfish, swordfish, dorado, mahi-mahi, wahoo, sharks, the whole pelagic system.

Boat after boat unloading on this beach, to be taken away by truck and put on a plane, and most of it going to the United States.

- [David] Buyer beware.

A century of industrial pollution has contaminated the entire marine food chain.

Mercury concentrates in toxic levels in top predators like marlin, tuna and swordfish.

Except in small quantities, this fish is unsafe.

Yet we keep eating more of it, to the detriment of all.

- [Rick] When you see a scene like this, you really get the idea of how this can't continue, why there's such a shortage of fish in the ocean.

The demand is just so insatiable.

This is why we're in trouble.

We can't keep harvesting the sea this way.

- [David] They bring in a rare grander, the last way Rick wants to see one.

[pensive music] [waves splashing] - [Rick] These marlin populations won't recover if we keep taking the big, egg-bearing females.

We've lost more than 90% of billfish in just the last 50 years.

- [David] Fortunately, a new consciousness is rising elsewhere.

[gentle music] In South Florida, the culture of the sportsman runs deep.

But in recent years, it's been easier to find big fish on the walls than in the water.

[gentle music] Commercially valuable broadbill swordfish have been hit especially hard.

Now, a moratorium on long lines in South Florida is bringing this most aggressive of billfish back.

- So, this bill came off of a 400-pound swordfish.

Swimming at 50 miles an hour, that's one powerful animal.

If you have to attack something, this is what you want to have on the end of your nose, your upper jaw, one big bill that can cut through the water, or run another predator through.

But these fish will take on anything and they're really unpredictable.

They've been known to skewer big sea turtles, and even Mako sharks that attack them.

They've found bills broken off in their spine.

And even the research submarine, Alvin, was attacked by a swordfish at depth.

It penetrated the hull of the boat.

The sub had to surface, in real danger.

And when it came up, the swordfish was still attached, and the crew ate the swordfish later.

So I'm gonna try to swim with one of these critters at night, and it's sporting one of these bills, this weapon.

It's gonna be an exciting evening.

We better go then, huh.

- All right, let's go.

- All right, let's get going.

- [David] Rick joins researchers who are gathering data for the National Marine Fisheries Service.

The team's captain and guide is commercial sword fisherman, Tim Palmer.

He has a unique gift of finding these deep dwelling, secretive fish, and keeping hooked ones healthy.

Tonight the research team will fit swordfish with satellite tags, part of the effort to restore their populations.

The tools of their trade, the holding device known as a snooter, baited lines, and the pop-off satellite tags.

Over three months, these tags will record temperatures, light levels and diving depths every 10 seconds, then pop off for collection.

- [Tim] I can't believe after all this time, still taking off like that.

[dramatic suspenseful music] - [David] After three hours, the team pulls in the lines.

It's exhausting work, because whatever's on the other end resists with all its might - Gonna try for 10 more minutes [indistinct] only.

[dramatic suspenseful music] - [Sailor] There's a 400 pound fish right under us right now.

- Okay.

It's moving ahead, that's the nice thing.

- Is it a big one?

- Yeah.

- [Sailor] No, it's a [indistinct] turn him over.

- [David] Nearly 12 feet long and more than 450 pounds, it's the largest swordfish ever brought in for tagging.

[dramatic music] [people chattering] Tag's in.

Now if only Rick can be as successful getting his shot.

- [Rick] I'm in the dark water with just the camera, and you wonder if the guys on the surface that are trying to tag the fish really have a hold of it.

Can they hold onto this fish if it gains strength and energy?

That's really a tricky situation.

- [David] The crew runs water over the fish's gills, building up its oxygen so it will be in good shape for release.

[water gurgling] [sailors groaning] - Ow!

- You all right?

[people chattering] - [Sailor] Wow!

- [Rick] These fish are so unpredictable.

You let your guard down and you get slammed.

If I had been swimming and filming between the fish and the boat, as I often do, it would have busted me up.

[water gurgling] [people chattering] - [Tim] All right, see you later, fish!

[mysterious music] - [David] The swordfish heads back down into the Gulf Stream, while Rick travels 1,000 miles west to Costa Rica's Pacific coast.

[dramatic music] Years ago, in the deep water close to shore, he spotted something in these strong currents and sheltering reefs that few have ever seen.

Now he's come back, to capture it with his camera.

[engine puttering] He waits for night, when the plankton rises.

[people chattering] - [Rick] What do you think?

Depth?

Depth is looking food for what we want to do tonight?

- [Captain] Yeah, I think so.

Got bait slowly rising up.

Hopefully, they'll come up and give us a show.

- [Rick] Look at that water temperature, 87 degrees.

- [Captain] Yeah, you think you need a little thicker wetsuit.

- [Rick] I don't think I need any, but I don't like to be stung.

[captain laughing] - [David] The boat drifts in the current till it melts into the darkness.

Its light cheats the moon, drawing countless tiny animals into its sphere.

[engine rumbling] But will he find the extraordinary creature he seeks?

The odds weigh heavily against it, and yet.

- [Rick] We have squid now.

Squid are in the lights right now.

So just let that light work, and see who comes up.

[dramatic music] [people chattering] [gentle music] - [David] Marine snow, the larvae of other fish, and baby squid abound.

But still no billfish.

[mysterious music] [mysterious music] [water gurgling] [gentle mysterious music] Rick swims through a shadowland thousands of feet deep.

Out of the dark, animals can materialize not just from in front or behind, but above or below as well.

[mysterious music] - [Rick] We're down swimming around in that dark sea, looking in the miniature world, and suddenly I feel a whoosh underneath my armpit, and I think it's my dive partner.

And I look towards him and he points towards the surface and there's an adult sailfish swimming right over our head, feeding.

That's the last thing I was expecting!

- [David] Unlike swordfish and marlin, sailfish don't see well in the dark.

Until this image, the first of its kind, few suspected an adult sailfish would ever feed at night.

- [Rick] They're far more versatile than we ever thought.

This fish is taking advantage of the underwater light.

It's the kind of behavior we can only learn by getting into the water and spending a great deal of time in their world.

[gentle music] [water gurgling] - [David] Then, drawn by the light, it appears a miracle in miniature.

[sweet gentle music] A baby sailfish.

It's tiny, but not defenseless.

Though not all billfish are born with a bill, a sailfish baby comes into the world already armed.

It has razor-sharp teeth which it loses only as it grows larger.

Its sleek body makes it a formidable hunter even at only a few months old.

[sweet gentle music] This baby is but one among dozens.

Rick has found a nursery.

[dramatic music] Launched on a life of perpetual motion, the tiny sailfish must swim constantly just to breathe.

When it matures, it will travel 20 to 40 miles a day.

[water gurgling] [gentle music] In a potential lifespan of 16 years, a sailfish will log some 200,000 miles, it's a superfish in the making.

[dramatic music] [mysterious music] Certainly, Rick's travels have yielded wonders.

But like "The Old Man and the Sea," he's still after his big fish, a living grander in the wild.

[dramatic music] There's still one more place to look, halfway round the globe, off of Australia's Cape York peninsula, in the wildest part of the Great Barrier Reef.

The key is to locate a spawning ground where the big egg-bearing females gravitate.

Out of hundreds of miles of reef, there are only a few areas where tides, winds, and currents combine with abundant food.

The Endeavour River creates such a system.

A persistent wind stirs up these tropical waters and keeps them cool.

Good for fish, but tough on filmmakers.

Turbulent seas make shaky pictures, and they're dangerous for swimmers.

It's too easy to get separated from the boat.

Time is ticking for Rick.

If he is to find his giant marlin this year, he'll need to enlist the aid of the best big game fish captain in these parts Tim Dean.

- What about this wind?

- It's been with us now for three weeks.

- Wow.

- Late season wind, it's unseasonal for us, but it protects the fish.

That's part of the deal here, you know.

It's rough weather, it's hard.

Nothing easy about chasing 1,000-pound black marlin.

- [Rick] That's why I brought the biggest camera I could find.

- You're gonna need it.

- Okay.

- And a big lens.

- [Rick] So how's your season been, Tim.

- [David] And still the wind blows, as much as 40 miles per hour.

Captain Dean promises it will be worth the wait, to see one of his granders feed.

- The big blacks, they eat just about anything that swims past them.

Rick, when these fish are coming into your pattern of baits or lures and you watch these things actively feed, it's frightening.

A lot of people say if they roared you wouldn't catch them.

You'd be too scared.

- [David] And then, finally, the weather breaks.

It's Rick's last opening to get offshore.

He heads east with Dean to the ribbon reefs.

They form a narrow but treacherous ridge about 30 miles off the coast.

There, Tim feels confident he'll find marlin.

- Get ready there, Rick!

- [David] The crew prep large bonito and mackerel as bait.

They don't use hooks.

They're not trying to catch her, just bring her close to the boat.

Preparation is critical, because when the moment comes, it comes quickly and it won't last long.

Tim tells Rick he'll be lucky to get 30 seconds in the water with his marlin.

From his vantage point on the flying bridge, Tim scans the surrounding waters looking for shadows.

Any dark shape could be a big game fish.

But it could also be a shark.

Mistaking one for the other could prove fatal for Rick.

[reel whirring] - [Tim] There he is, Dave, on you.

Wind it up.

Get ready there, Rick.

Get ready.

Nice big fish.

Clear yours, Andy.

Clear yours.

Get ready with that camera.

Hold 'em there, Dave.

Hold 'em there.

Okay, there he is.

Wind it up.

Wind it up.

Oh, it's a nice fish.

- [Andy] Right on.

- You're in!

- Go, Rick, go!

Go!

You're in, you're in.

Camera!

Wind it up there, wind it up.

Oh, nice work.

[dramatic music] [dramatic music] - [Rick] The big fish is on me so fast, I just have enough time to switch on the camera.

All I can think about is, don't blow it, get the shot.

[dramatic music] - [David] The marlin is a giant, five times Rick's size and far more powerful.

- [Rick] I'm fighting a strong current, pushing this heavy camera.

And the fish moves so quickly, with just a flick of her tail she's out of sight.

[mysterious music] - [David] She could charge him, flee him, ignore him all together.

[mysterious music] [water gurgling] But surprisingly, she seems to find him interesting.

She keeps coming back to check him out.

What does a fish make of a man?

[gentle music] - [Rick] I'm wondering what she's seeing.

Is she looking in the dome of my underwater housing?

Does she see her own reflection, or does it look like one big eye?

I have this feeling that she's looking me over and that I'm something different in her world.

But she doesn't appear to be frightened.

[gentle music] - [David] For an extraordinary 20 minutes, Rick swims with the great marlin, the one that Hemingway hunted but never caught, a grander.

[gentle music] - [Rick] This big marlin seems so confident, and why wouldn't she be?

She's in command of the situation.

It's all up to her.

She's letting me into her world.

[gentle music] Just when I'm finally keeping up with her, I realize I've come upon a mating scene.

There are a couple of little males, maybe a quarter of her size, in there too.

- [David] Flushing bright blue, they look for their chance to fertilize some of her millions of eggs.

[gentle music] The grander is more than just a big fish.

She's the hope of the next generation.

But her life in these blue waters is never simple or safe.

[gentle music] Though deep and wide, it's a world where just a few hundred feet are all that separate birth and death.

[sinister music] - [Rick] The entire time I was filming that big marlin, there were three bull sharks circling below.

And if you're gonna go in the water off Australia, on the Great Barrier Reef, and film marlin, you better be prepared for sharks.

- [David] They've been known to devour an exhausted marlin in 17 seconds.

Rick has pressed his luck long enough.

[dramatic music] - Tim, what a big fish!

- Unbelievable, Rick.

- I don't know what a grander looks like underwater, but this fish was this big around.

- She was a fish, well over 900 pounds.

All the way up there, you were right in the center of them all.

It was great to watch you.

- Spectacular.

- [Tim] In all my years, I've never seen a big fish just follow us along like that for such a long time.

- She came back.

She kept coming back.

Weaving, coming in.

Eating the bait.

Three bull sharks just underneath there, looking at the scene.

- Nice work, mate.

[gentle music] [people chattering] - [Rick] Thank you, again.

- [David] Rick Rosenthal has ventured into uncharted waters and found that the heart of the ocean is still beating.

With his camera, he has faced the mighty fish, not as worthy opponent but as fellow creature.

[gentle thoughtful music] He has taken the trophies down from the wall and brought them to life, capturing instead both the power, and the plight, of sword-wielding giants.

[gentle thoughtful music] [dramatic music] [dramatic music continues] [bright music]