Nature

In the middle of the Pacific Ocean,

the world's most isolated island chain

is shark paradise.

Some hunt in gangs,

others ride the tides to find food.

The biggest are loners.

But no matter what their size...

...or what they eat...

...Hawaii has everything sharks need.

Shallow reefs here are packed with fish.

The deeper blue offers different fare.

The warm water calls to many.

If it seems too perfect, it just might be...

for now.

The biggest sharks with the biggest needs

may be moving here, too.

These humpback whales are finally home.

After feeding all summer in the Gulf of Alaska,

they've traveled over 3,000 miles

to return to Hawaii, where they were born.

Some females have journeyed to these warm, clear waters

to entertain a mate or two.

And soon, those that are pregnant

will give birth to their own calves here.

The new mothers will be extremely protective

of their newborns.

They have to be.

Because while this place looks idyllic,

the whales have come back to an age-old battleground.

Tiger sharks are the apex predators in Hawaiian waters,

15 feet of clever camouflage

constantly patrolling the channels between islands.

They prey on whale calves,

a feast they've been anticipating all year.

Then, these mighty opponents will come face-to-face,

2,400 miles from the nearest continent.

Hawaii's archipelago is the most remote on Earth.

The eight main islands are merely the summits

of a vast, submarine mountain chain

stretching 1,500 miles across the Pacific.

They're all the result of a deep-sea volcanic hot spot

that builds new islands when the tectonic plates above it move.

Kilauea, on the Big Island,

is the most active volcano on Earth.

It's been continuously erupting for the past 40 years.

Lava meanders down the slopes in molten paths to the sea.

These islands are primeval,

but in Earth's geologic timeline,

Hawaii is a newcomer.

The first island rose above the sea

a mere 5 million years ago.

And, in the middle of nowhere,

it became an anchor for coral spawn

drifting in from open water.

Hawaii became a magnet for life,

sheltering thousands of unique species

found nowhere else in the world.

Hawaiian monk seals and Hawaiian octopuses

are natives here.

But Tiger sharks are much older than Hawaii.

They somehow discovered these islands

in the course of their migrations.

These days, Hawaii's bays and inlets

offer year-round opportunities for every palate.

Both the massive and the miniature

enjoy the islands' embarrassment of undersea riches...

...including at least 40 species of sharks...

...and their cousins, the rays.

The volcanoes created stark basaltic plains underwater,

which were first colonized by algae

and then by tiny coral polyps.

Over time, life moved in,

creating a stationary buffet for carnivorous sharks,

eels, tangs, and angelfishes, just to name a few.

At least 25% of Hawaii's coral reef fishes are native

and only live here.

It seems impossible that this delicate fairyland

could spring from such violent brimstone and fire.

Hawaii's two active volcanoes are the modern agents

of a process that is still unfolding.

Kilauea and Mauna Loa are both on the Big Island...

also called Hawaii...

which is the youngest island in the chain.

When super-heated magma meets the cool ocean,

a cauldron is born.

As the lava cools,

trapped air forms an undersea labyrinth of tunnels and tubes,

creating superb miniature bunkers

for those that need sanctuary.

They draw travelers in from the open ocean.

And even sharks need to find a safe haven.

The lava tubes are a perfect retreat

for nocturnal whitetip reef sharks.

Slender whitetips often escape into the narrow passageways,

thwarting more massive pursuers.

These reef dwellers sometimes become tiger shark prey

because they're so much smaller.

At five feet long, they're right in the middle

of a tiger shark's menu.

This tiger cruises just outside the maze,

perhaps hoping to surprise a whitetip away from home.

Deep in their lairs, whitetips can relax.

They use specialized muscles

to draw in oxygen-rich water over their gills,

making them one of the few shark species

that doesn't need to swim in order to breathe.

They cruise through the murky lava jungle,

always searching for a better place to rest.

Though they're able to suspend activity

in parts of their brain,

they never actually sleep.

They spend hours like this, simply resting,

sometimes alone, sometimes together.

Light doesn't reach into most of the lava maze,

but nocturnal whitetips still wait for the dark of night

to venture out.

Carefully, cautiously,

they'll morph from the hunted into the hunters...

searching their small territories

for prey that's also active at night.

The reef during the day is a different world,

whether you're predator or prey.

Beyond the coral heads, in open water,

there's no place to hide.

This silver flash is actually a school of small mackerel

called akule.

As juveniles, they lived on the reef,

but as adults, they've moved into deeper water.

They gather in the tens of thousands,

seeking safety in numbers.

When they sense danger, the small fish react

by crowding close together in what's known as a bait ball.

Instead of seeing individuals,

predators confront a much larger, confusing "creature."

But sometimes increasing their profile

only attracts more lethal attention.

Bluefin trevallies, 3 feet in length,

are some of Hawaii's most efficient carnivores.

Aggressive and sleek, they can carve up a bait ball

with exquisite precision.

Akule caught in the rift are the first to be devoured.

The others try to flee.

The sounds of plunder draw gray reef sharks to the scene.

Then, an elegant silky comes in from the blue.

They have the ability to hear prey through open water.

Now, the Akule have drawn multiple sharks

to the nearshore reef.

Sharks may hunt cooperatively,

but it's every individual for itself when it comes to food.

The hunters try to corral the baitfish

into more manageable masses.

After enduring attack after attack...

the Akule are tiring...

...but it won't be over until the sharks are satiated.

In the end, bottom dwellers reap the last spoils of war.

A blue pincher crab is camouflaged

by algae covering its claws...

...allowing it to steal a prize,

almost.

Like a furtive ribbon,

this undulated moray eel has followed the scent of flesh.

Needle-like teeth shred the meal.

Surviving Akule disperse

with their casualty count unknown.

Back on the reef, there is a constant kaleidoscope of color

and danger.

Every creature here has evolved a strategy to meet its needs.

The sharks are no exception.

Blacktip reef sharks are Hawaii's homebodies.

They prefer shallow water,

which suits their docile, social nature.

They often convene in groups.

Around the Big Island, these small sharks use the tides

in order to hunt ever closer to shore,

the best place to find tasty crustacean prey.

And the tides always deliver.

The Big Island is also known for its black sand beaches,

formed by volcanic glass that's rich in iron.

But, it's not the color of the sand

that attracts green sea turtles to Hawaii.

This is the natal home

of the largest hard-shelled sea turtles in the world.

Adults sport shells more than four feet across

and can weigh over 300 pounds.

As juveniles, their diet is quite eclectic,

but adults graze on algae and sea grass,

which tints their internal fat a pale shade of green.

Female sea turtles of all species

come ashore in order to lay their eggs.

But, this is the only place in the world

where males haul out alongside females.

No one knows why.

The males don't guard the eggs and the turtles don't mate here.

This exceptional behavior is a complete mystery.

Oceanic nomads,

green sea turtles swim endlessly until they reach maturity,

somewhere between 20 and 50 years.

Scientists don't know

how long these prodigious seafarers live,

but they suspect it's more than a century.