Original subtitles

(gentle music)

- [Narrator] It covers a third of the world's surface,

(sweeping music)

rimmed by fire,

constantly reshaped by the almighty clash

of Earth's tectonic plates.

Creating life forms that, in turn,

become the architects of underwater empires.

Here, the world's most primitive life forms

have outlived dinosaurs

and found astonishing ways to adapt and survive

in one of the most competitive environments on the planet.

This is the Wildest Pacific.

(gentle music)

The Pacific Ocean spans 15,500 kilometers of latitude

from north to south,

across vastly varying temperatures and topography.

With such far-reaching, unseen boundaries,

it's little wonder that 25,000 islands

within the Pacific Ocean

look so vastly different from each one to the next.

From New Guinea, the world's largest island

in the heart of the coral triangle,

to sand quays, barely meters across,

sitting atop reef crests.

Across the Pacific, long chains of atolls support life

on the remnants of ancient volcanoes.

In its eastern fringes lie islands

that are little more than rocky, exposed peaks,

the tips of underwater mountains so enormous

they rival the world's tallest mountains on land.

These summits of sand and stone

scarcely hint at the incredible living networks

that exist below the water line,

a food chain that constantly feeds upward

and nourishes the land, and the air-breathing life above.

This ocean's scale is difficult to comprehend.

The Pacific's basin is greater than the land mass

of all the world's continents combined.

It spans more than 155,000,000 square kilometers.

The long stretches of open water between land form

appear to offer scant opportunity to feed, rest, and survive

and yet, still, they do.

Many organisms, like jellyfish,

live out their entire existence

without ever coming into contact with land,

the sea floor, or the surface.

Large sea birds with great wingspans,

such as albatross and frigates,

can spend days, even months at sea before returning to land.

Oceanic fish species, like the four-meter-long sunfish,

include some of the biggest and fastest beings in the water.

These are pelagic species.

Pelagics usually have a darker-colored upper body

to avoid being spotted from air,

and a lighter underbelly that blends with the sunlit surface

when seen from below.

Many are migrators, undertaking trans-Pacific journeys

in constant search of places to feed, mate,

and birth new generations.

(sweeping music)

Dwarfing their reef counterparts,

giant oceanic manta rays reach astounding disc spans

nearly nine meters across.

They can dive to 1,000 meters,

but tend to feed on surface plankton,

and that's what compels them

to travel exceptionally long distances.

Giant manta rays will migrate some 12,000 kilometers

across the Pacific, to stopover points.

They follow the oceanic currents to coasts and islands

with seasonal conditions ripe for planktonic blooms.

So, too, do whale sharks.

This is the planet's largest living fish.

They can grow as large as 18 meters long

and weigh in at 20 to 30 tons.

Whale sharks have an intimidating mouth size,

but it's one that is purely designed

for a mass ingestion of plankton.

With its cartilage skeleton, it is a shark,

but this is a filter feeder,

and they need enormous amounts of tiny plankton

to fuel their large bodies.

Little is known about whale shark migration paths,

except they are incredibly long.

One such path stretches from the Central Americas

deep into the Pacific.

One female whale shark has been reported

logging more than 20,000 kilometers in under a year.

Extraordinarily, considering it's the world's largest fish

and can live for a hundred years,

where they go for several months at a time

remains a mystery.

(gentle music)

Indo-Pacific sailfish roam the ocean across latitudes,

heading south for summers

and toward the equator each autumn.

On the south of the Central American west coats,

they're chasing these, sardines.

The sardines, too, are following a feeding route.

Plankton flourishes in the colder currents.

When sardines school tightly in a ball like this,

it's not for feeding.

(intense music)

It's because they're under attack.

Sailfish hunt in groups.

Much like dolphins and some whales,

they have learned to herd sardines

toward the water's surface,

into tight schools called bait balls.

The sailfish separate out a group and surround it.

In strong hunting grounds,

scores of sailfish can work a few tiny bait balls at a time.

They plunge into the sardine's school from all directions

until they're forced to pack together densely.

With nowhere to go either side,

the sardines head further up into the water column.

Sailfish rely on speed sprints.

They have large hearts and gill surface areas

for their body size,

so they can extract more oxygen from the water.

These are nature's machines, built for racing,

but sardines are also fast, and their smaller size

means they have better maneuverability.

For the sailfish,

their secret weapon in this hunt isn't speed.

It's their bills.

They're dagger sharp and 30 centimeters long.

The sailfish thrust the bill

into the center of the bail ball,

and with a quick head shake,

strikes a sardine out of the school

and swallows the fish whole.

The sails work the bait ball

closer and closer to the surface.

Over hours, they hit the small fish.

The sardines are tired,

and most are wounded from bill strikes.

When they reach the surface, there's nowhere else to go,

and that's when a second attack launches,

this time from above.

(birds crying)

The sailfish now have competition.

Great frigate birds

are incredible oceanic endurance hunters.

They can stay at sea for two months at a time

without touching land.

However, frigates don't have great waterproofing

on their feathers.

Rather than spending time

sitting on the surface and fishing,

they wait until other predators herd the fish upward,

and then.

(splashing)

Frigates will spend hours tracking bait schools,

simply waiting for the sardines

to reach striking distance from the air.

Under attack from above and below,

the bait balls scatter and regroup,

circling tighter and tighter,

looking for any path for escape.

Finally, it opens up.

A small hole in the wall of bills,

and a slim chance for the school to charge through.

They take the risk,

and it works.

(soft music)

They plunge as deeply and as quickly as they can,

but more than a dozen sailfish sprint behind them

in relentless pursuit to the depths below.

(waves crashing)

Where open ocean nears coastlines,

species diversity increases.

(soft music)

Mouth mackerel are found out wide in warmer waters,

but close to shores with planktonic blooms.

These fish have found a way

to maximize their plankton intake.

They swim with their wide mouths

and large gill rakers open,

effectively straining the small larvine eggs

from the salt water.

(lively music)

Loggerhead turtles return to Pacific feeding grounds

after heading east and north for the nesting season.

They undertake long journeys of up to 12,000 kilometers.

As loggerheads near land,

clashes over rights to feeding territories can be fierce.

These ancient reptiles eat jellyfish, crustaceans, and algae

and can weigh around 150 kilograms.

(soft music)

For most open ocean travelers,

the chance to rest and feed comes at small points of refuge

in this vast oceanic desert,

Pacific atolls.

A classic atoll is a ring-shaped reef

that encircles a shallow lagoon,

often with a small island in the center.

An atoll begins its formation

as an underwater volcano, called a sea mount.

As the volcano erupts, lava builds, hardens,

and increases the underwater mountain in height.

It eventually breaks the ocean's surface, forming an island.

Coral polyps colonize the walls below sea level

and fan out to form a fringing reef system from the island.

Over millions of years, the dormant volcano erodes and sinks

leaving an atoll reef behind.

Within many of these rings of reef,

sand accumulates and forms an island once more,

which is then propagated by sea birds.

The atoll is complete.

Atolls litter the Pacific,

providing a safe haven for both oceanic nomads

and resident coral reef communities.

(waves crashing) The surf zone is where waves,

created by winds traveling long oceanic distances,

finally collide into the atoll outer walls.

Hardy surgeonfish are unfazed by the buffeting energy.

They're aided by thin, streamlined bodies

engineered to navigate a perpetually dynamic environment.

A common reef fish,

there are more than 70 species of surgeons worldwide.

They vary dramatically in color,

but all have these distinctive tails.

Tipped with a set of razor-sharp spines each side,

these scalpels earn them their surgeonfish qualification.

However, their most important role

is that of resident gardener.

The sunlit oxygenated lagoons around atolls

create prime conditions for growing algae.

It's resilient, fast-growing,

and competes with coral for space.

Keeping it in check is essential for the health of a reef.

The surgeonfish is a herbivore that prefers algae.

Large schools of these grazers,

like striped convicts and white-spotted surgeons,

are a healthy indication

the lagoon ecosystem is well balanced.

Parrot fish are also designed to negotiate surf zones,

with strong pectoral fins that beat much like

the wings of the birds they're named for.

These are one of the many reef species

that change gender throughout their lives.

To keep a male-female ratio balance,

the parrot fish can completely change their physiology

to create male or female gametes.

They then reproduce communally via broadcast spawning.

Small groups of males and females

rise up to the mid-water column,

above the reef but below the waves,

out of reach of surface and seabed predators.

The parrotfish twist and turn in a tight ball,

releasing eggs and sperm.

For the best chance of the gametes meeting

and being carried away from feeding areas,

they carefully time the broadcast release

on the outgoing tide.

It pays to be careful.

In a vast ocean sparsely littered with structure,

these atoll walls are thick with predators.

(intense music)

Bluefin trevally solo or in small packs.

It gives them enough confidence

to tailgate an apex predator, the gray reef shark.

In this way, they can take advantage of any stray scraps

in the event of a shark strike.

The trevally may even risk using the reef shark

for a quick clean,

by rubbing up against the shark's rough skin

to slough away parasites.

These reef sharks favor deep grottoes and canyons

on the seaward side of an atoll.

Although most active at night,

even by the day, the gray reef shark is on high alert.

It constantly scans its surrounds

via a highly-advanced sensory system.

It hears by picking up vibrations,

using sensory pits called the lateral line.

It smells minute traces of blood in the water

by sweeping its head side to side to engage both nostrils,

and its vision is so specialized, it can hunt by starlight.

(soft music)

Sharks with poor eyesight, like this lemon shark,

rely more heavily on an additional sense, electroreception.

Jelly-filled tubes open to tiny pores on their snout.

These allow them to detect electrical currents.

Salt water carries these currents

from other animals' muscle twitches and movement

in a way air does not.

The lemon shark slowly cruises an inner atoll channel,

waiting to pick up the faintest pulse of prey in hiding.

(gentle music) Inside the lagoon walls,

weaker swimmers are protected from the rolling surf.

Schools of fish congregate to feed on the small crustaceans

and larvae that flourish in the calmer waters.

Sea snakes are strong oceanic swimmers

that come into lagoons to hunt.

They have small, flattened heads

to minimize water resistance,

and paddle-like tails.

True members of this family, like the olive sea snake,

live out their entire lives in the water.

Sea crates are also marine reptiles,

but spend some of their time on land,

returning to digest prey, drink fresh water, and reproduce.

The banded sea crate has enormous lungs,

large enough to allow them to stay underwater

for more than 30 minutes.

Like many land snakes, it's also armed with a deadly venom.

A sea crate's venom is 10 times stronger

than that of a cobra or rattlesnake.

Often hunting in pairs or even a pack,

these reptiles investigate every lagoon crevice.

It's one of the few animals

that can send a much larger moray eel deep into hiding.

Sea crates will stalk and eat eels

more than twice their own size.

The crate's venom is powerful enough to paralyze it

and swallow it whole.

This eel remains undetected today.

The sea crates move on.

(cheerful music)

Emperors, snappers, and trumpetfish

forage in the fading light,

eager to boost energy stores before nightfall.

Remote lagoons foster their own set of social norms

amongst the schooling fish.

With such high and varied populations

all competing for space, a feeding hierarchy is created

to allow a number of species to co-exist.

However, they'll all make way for the top-tier residents.

Sundown cues the arrival

of gray and blacktip reef sharks.

(ominous music)

Blacktips are smaller sharks of about two and a half meters,

but like most reef sharks, they tend to hunt in packs.

In outer Pacific lagoons, they rarely travel beyond a range

of a couple of square kilometers.

The sharks find crevices in currents to rest in by day,

and come out to feed at night.

The resident pack builds in numbers

as gray reef sharks join them to hunt alongside.

The sharks re-establish their territory

and make it clear they are the dominant species.

A fusilier school is scattered in different directions

as they sprint to give way to the night visitors.

But there is one lagoon predator

approaching from the distance

that trumps them all.

It's a tiger shark.

(intense music)

Tiger sharks are consummate predators.

In open ocean, tiger sharks can reach the size

and weight of a large car, one and a half tons in all.

Lagoons are usually stalked by juvenile tigers,

where they're safer from cannibalistic adults,

but here, even a small tiger

is still the largest predator in the water.

Named for the distinctive stripes across its massive girth,

this tiger won't hesitate to take on a blacktip reef shark.

It doesn't feel the need to eat yet,

but still exerts its dominance

at the top of the lagoon food chain.

The blacktip pack thins out around the tiger's path.

Near the atoll wall,

one courting pair is oblivious to the nearby danger.

(gentle piano music)

Titan trigger fish are a large reef fish.

They can grow to three-quarters of a meter long.

Titans have strong mouths and sharp teeth

for grinding into coral to forage

for small worms and mollusks.

Normally solitary, in the mating season,

males move to traditional nesting grounds.

They set up in the same area year after year,

generation after generation.

Here, they'll be visited by a female.

The trigger fish pair decide if they'll be parents together,

based on how well they dance.

The fish circle one another in a matin ritual.

Their focus is solely on each other

for the duration of the courtship.

For an hour or two, the enclosing sharks are ignored,

relegated from the role of predators

to that of audience members.

The dance will come to a close

when the sun is well below the horizon,

before the lagoon night hunters begin to feed.

The Pacific is so vast, as one day ends in a western atoll,

another dawns on an eastern island.

(uplifting music)

Although atolls can exist for centuries,

their shallow caves and lagoons yield easily

to the rise and fall of the sea.

Islands, in contrast, stick around much longer.

Oceanic islands are formed in the same way as atolls,

but remain stable rather than collapsing.

Sea mounts rise hundreds

or even thousands of feet from the floor,

but are yet to reach the water's surface.

Islands have breached the surface

to a point where land exists beyond the reach of high tide.

Oceanic islands have never had connections to continents.

One such island is Malpelo.

From the air, it presents as little more than

a barren, rocky outcrop populated by a seabird colony.

But below the water line, this massive volcanic mountain

is the epicenter of a vast, very complex,

and extremely busy underwater metropolis.

Malpelo island is a part of Columbia.

It sits about 500 kilometers from its coast.

It's the corner of a triangle that includes

the Cocos and Galapagos islands,

where major ocean currents and counter-currents converge.

(soft piano music)

Here, in the far eastern fringes of the Pacific,

unique biological behaviors have evolved.

Inter-species relationships occur,

rarely seen elsewhere in the Pacific.

Like far-flung villages with little contact,

the rules and laws of nature are very different

on these isolated oceanic islands.

Beyond the immediate reach of continental land pollution,

garden beds of lush and vivid soft corals flourish.

The very cold Humboldt current comes in from the south

and collides with equatorial counter-current,

both bringing bounties of nutrient-rich water.

Thermoclines occur where the warm surface water

mixes with the cooler deep water from below.

In this layer, vision is distorted.

Animals like butterflyfish appear to shimmer and buckle

where the pockets of mixed temperatures collide.

The Malpelo residents aren't impervious

to the temperature changes.

While this leather bass forages alongside a moray eel,

a thermocline passes by.

Most fish are ectotherms, which means they are cold-blooded.

Their body temperature changes

with the environment around them,

and here, it's in a constant state of fluctuation.

(soft music)

The base of Malpelo is some 300 meters below sea level

and plunges to more than four kilometers below

at a nearby drop-off.

However, there are many vast steps along the island flanks.

Sunlight can still reach the upper ledges

at 30 to 40 meters.

Here, large volcanic boulders

are thick with algae and sponges.

Hawksbill turtles are voracious consumers of both,

eating 500 kilograms of sponge alone each year.

Their big mouths are designed to mow into algae,

which helps keep it from reaching levels

that would smother the coral.

More often residents than passers-by,

this hawksbill becomes a mobile serving plate

for a school of angelfish.

Angelfish are herbivores,

today, grazing on the algae on offer

straight from the hawksbill's shell.

These turtles can live for 50 years.

Though it continuously grows out new layers of shell,

this one is likely to have built up

a substantial algal coat over many years.

(lively music)

Along the boulders, large schools of these angelfish

forage side-by-side with leather bass.

Leather bass are notorious for capitalizing on the hard work

of other species.

They prefer small mollusks and crustaceans,

but keep up with the grazing herbivores

to scavenge any morsels they may stir up.

They'll also hunt alongside another

more predatory partner, the moray eel.

Morays usually take up residence in a reef bommie or crevice

and simply wait for prey to pass by their entrance.

They have poor eyesight,

so this is a reliable method for them,

but they do have an excellent sense of smell.

(suspenseful music)

At Malpelo island,

they come far out of their protective holes

and actively stalk the boulders,

and they do so in large numbers.

Not content to wait for a meal to come to them,

the eels work together to probe for shrimp,

crabs, fish, and smaller eels.

Their bodies are perfectly designed

for winding between the boulders.

As the eel numbers increase

and small creatures begin to flee,

shoals of leather bass descend to join the hunt.

The eels and the large fish begin

a rare, co-operative hunting technique,

a feeding behavior

unique to these far-flung oceanic islands.

The leather bass pounce on escapees,

and begin to flush out crevices themselves.

Soon, huge schools of leather bass

hover above the hunting area.

Like seagulls over a bait school,

they are a dead giveaway as to where

the fleeing prey is trapped.

It encourages more eels to move in.

It's thought perhaps, in this way,

the leather bass may help the poorly-sighted eels

pinpoint where the food is.

There are only a handful of animals across the world

known to hunt together this way.

With strong currents swirling

along the undersea mountian edges,

it pays to have a good set of brakes.

(upbeat music)

Pufferfish have undulating pectoral fins

to propel them along, or fan out to stop.

These large, bloated-looking fish are built for hovering.

There are more than 120 species worldwide.

At Malpelo, guinea fowl, spotted,

and yellow pufferfish forage together.

They suspend head-down over rocks

to pick at mussels, clams, and shellfish,

aided by their unusual teeth.

Pufferfish only have four teeth,

but they're fused together into long, sharp plates.

They occasionally squabble with each other,

but are rarely bothered by other fish.

That's because nearly every pufferfish is highly poisonous.

It's believed they synthesize their deadly toxins

from the bacteria in the animals they eat,

converting it to poison stored in their own liver and skin.

Some also have spikes embedded in their scaly skin.

It's a combination that usually affords these pufferfish

safe passage through boulder terrain.

(soft music)

Along the island's walls, blacknose butterflyfish

soar out of the thermocline.

As the light grows darker, these fish will fade in color

to blend better with the dark crevices

they'll hide in for the evening.

They make way for a barrage of bluefin trevally

coming up from the deep,

heading to the surface to look for small fish to feed on.

Rival predators already await.

(suspenseful music)

Streamlined and sharp-toothed,

barracuda are relentless hunters.

When they determine it's time to attack,

they can surge after prey

at sprints of 40 kilometers an hour,

but until then, energy conservation is key.

By schooling closely together, they draft on the fish ahead.

There's less drag on the barracuda's body,

and so, less energy is needed to swim.

(soft music)

In the cavernous areas of the island,

big-eye trevally aggregate in huge numbers.

Schools of more than 1500 fish move in circles,

right up and down the water column.

Forming dense clouds that span 30 meters across,

it's difficult for any other species

to penetrate the trevally group.

When night falls, their large eyes will help them

to hunt crab, octopus, and smaller fish.

But now, with dusk approaching,

they come together to keep watch.

Malpelo island is renowned for its shark aggregations.

(suspenseful music)

The silky shark is a cornerstone species here.

In such a large expanse of open ocean,

the opportunity to converge on a food chain

as dense and rich as this one is simply too good to refuse.

These sharks are named for their silky-smooth skin,

or at least, for a shark's standard.

The silky has such densely-packed scales

that its smooth skin creates

a distinctive sheen in the light.

They close in on a massive school of snapper.

Stragglers speed up to join their group.

There's safety in numbers,

but these silkies simply join the school.

At a relaxed pace,

they can sway their snouts from side to side

to sniff out any signs of sickness or weakness in the group.

With thousands of silkies patrolling Malpelo,

prey fish like these juvenile red snapper have been forced

to adapt with highly sophisticated schooling techniques.

Like all sharks, silkies are armed with electroreceptors

to detect even the faintest of electrical signals

emitted by living beings in the water.

Around Malpelo, the young Jordan snapper

bunch together extremely tightly.

It's less conducive to free swimming,

but it's thought the densely-packed bodies

produce an electrical force field

so large, it confuses the shark.

(gentle music)

Shape-making is another technique,

and near this island, schooling fish take it to new levels.

They effectively take on the shape and mass

of a much larger creature.

They get the detail extraordinarily accurate,

even taking on the characteristics

of a larger head and narrower tail.

Moving between schools is a high-risk activity.

The fish create thin, fast-moving highways,

then quickly regroup again.

If a predator isn't deterred by the time

they come close enough to investigate,

a wall of closely-packed eyes is extremely off-putting.

In the world's largest ocean, space may not be an issue,

but grouping together in this extremely close-knit way

allows the best chance of survival.

(gentle music)

Other species simply try to stay out of sight.

Blue and gold snapper hug the walls of Heaven's Gate,

the name of a large sea cave

at the bottom of a 30-meter drop to a ledge floor.

These brightly-colored fish are particularly abundant

in the Pacific's far east,

and a target species for most predators here.

They stay deep and close to sea caves in peak feeding times.

Sea caves within the island flanks

begin as a small crack or weakness in the rock walls.

Tremendous force from waves and currents

puts pressure on the weakness

and cracks the rock from within.

The areas erode over time,

gouging out overhanging ledges, grottoes, and deep caves,

dark areas for hiding, hunting, and resting.

Whitetip reef sharks spend their days

holed up under ledges and in caves,

saving their energy for night hunts.

Technically, sharks don't sleep.

They oscillate between periods of wake and rest.

Some sharks are able to do this

while slowly cruising the sea floor.

They have to, to keep oxygenated water

flowing through their gills.

Whitetips are equipped with speracles

or small holes to pump water through their gills

while they lay immobile.

(soft music)

Deep within Heaven's Gate,

large figures emerge from the dark.

With wing spans of nearly three meters,

distinctive white spots, and long, trailing tails,

spotted eagle rays are difficult to miss.

These rays are extremely social.

They can journey long distances of thousands of kilometers

across the open ocean, in small groups,

traveling in formation at the same speed.

However, it's recently been discovered

eagle rays do tend to have home bases,

and Malpelo island appears to be one.

Deep within the caves, they can corner squid and small fish.

Hunting in the dark is not an issue.

Like their close relatives, sharks,

they have electroreceptors to detect electrical pulses.

The rays also pursue each other.

A male will follow a female at a safe distance

until her interest is assured.

At the top of their long tails are up to six venomous spines

which deliver a nasty sting if used defensively.

Emerging from the sea cave, the spotted eagle ray

is immediately attended to by yellow butterfly fish.

These butterflies offer cleaning services at Malpelo.

They groom the oceanic travelers,

picking parasites built up over long journeys.

The eagle ray eats at the same time,

straight from the volcano flanks.

It has a large, duck-like bill

designed to shovel for invertebrates.

Inside their mouths, specialized jaws with plates

grind the shells of mollusks and crabs.

The ray then swallows the fleshy parts of the animal,

and spits out the shell.

(mellow music)

The spotted eagle ray's disc-like body shape

makes them incredibly adept at steering

and negotiating all conditions,

from open ocean to narrow cave beds,

and along the relentless surf zone of the island peak.

(waves crashing) (sweeping music)

The summit is similar to that of a land-based mountain.

This one stretches 4000 meters from base to the tip.

It just happens to largely be underwater.

If it peaks below the water line,

it will be classified as a sea mount.

It's the jagged, exposed rocks,

jutting almost 400 meters above sea level

that define Malpelo as an island.

Pacific island life in the warm climes

offers a stunning range of biodiversity.

But on this rocky outcrop, miles from any other land,

conditions are harsh.

(ominous music)

Trade winds from the northeast and southeast

converge here, stripping the rock

of anything but the hardiest moss, lichen, and algae.

(birds crying)

Even this sparse vegetation is kept to minimal levels

by the island's terrestrial crab, the Johngarthia lagostoma.

(gentle music)

However, this tiny outpost,

little more than a square kilometer of land mass,

supports the world's largest colony of Nazca boobies.

This distinctive orange-gold species

(birds crying) is endemic to the Pacific.

As many as 50,000 live on Malpelo's summit.

From the rocky peaks, the Nazcas watch for bait balls

and schooling action at the water's surface.

These are fishing birds, and they must hunt

and return to feed their young.

The perilous cliffs are not a kind terrain

for such a vital rookery.

Each of these chicks (chick crying)

is already a survivor.

Every breeding season, two eggs are laid,

but only one chick lives beyond the first days.

The hatchling to emerge first will push the second chick

out of the nest when it's born.

The late arrival starves (chick chirping)

or perishes on the cliffs below.

(birds crying)

Resources are scant here.

The parents can only afford to tend to the older sibling.

Only one Nazca booby chick ever survives.

(lively music)

Though schooling fish are commonly

in deep and mid-water around islands,

here, the first few meters of depth

are unusually thick with huge numbers.

They're drawn to this top layer by cold upwellings.

Upwellings occur when strong winds

consistently move the top layer of water.

Colder water, rich with plankton, is drawn to the surface.

The cold currents bring another, much larger fish.

(ominous music)

A hammerhead shark.

Eyes at either side of the shark's anvil-shaped head

offer a near-360-degree view.

It swings its head from side to side like a metal detector,

allowing its electroreceptors

to constantly scan its surroundings.

Hammerheads roam the entire Pacific Ocean,

but they're drawn to the waters around Malpelo island

by the thermoclines, the layers of water

where hot and cold currents collide.

The cold upwellings around the island

bring the sharks particularly close to the surface.

Meters below, many hammerheads begin to come together

in organized, evenly-spaced hierarchies,

and they do so in astonishing numbers.

(intense music)

The waters from Malpelo, east to Cocos islands,

and south to Galapagos

are known as the hammerhead triangle.

It's one of the world's extraordinary natural sights.

Schools of hundreds, sometimes thousands of

hammerhead sharks gather and slowly circle the island.

At Malpelo, they are predominantly scalloped hammerheads,

named for the markings on the ridge between the eyes.

The schools are almost entirely female.

They outnumber the male sharks by six to one.

The largest, most aggressive females are in the center.

The reason, it's thought,

is to make them easy for males to locate.

A large shark is a strong one, and the biggest females,

reaching over four meters in length,

are the most highly sought for mating.

Apart from the odd food grab at the surface,

these huge aggregations are mostly social.

The hammerheads are only here by day.

Their night-hunting grounds are in deeper waters nearby.

Their birthing grounds are even further afield,

close to the coastline, some 500 kilometers away.

It will take many years for the juveniles

to grow large enough to travel the distance

and avoid being eaten themselves

before they, too, can join the astounding aggregations

around this remote, rocky outcrop.

(waves crashing)

(gentle music)

Malpelo defies all tropes of the typical Pacific island,

but is a testament to the astonishing variety of terrain

in this enormous sea.

The variability of plants and animals existing in one area,

known as marine biodiversity, appears to thin out

across the Pacific, from west to east.

It spurred recent scientific theory

that the coral triangle, the western region,

with the densest marine biodiversity on earth,

may have seeded the greater Pacific.

Oceanic currents carry tiny larvae and great migrators alike

across staggering distances.

Settlers in new corners survive, adapt, and evolve

in astonishing ways,

and with the Pacific Ocean's depth,

less mapped than the surface of Mars,

we are yet to uncover so many more of these life forms

that we share this planet with.

(sweeping music)