The Hunt

The open ocean.

It covers more than half the surface of our planet.

Yet, for the most part

it's a watery desert, empty of life.

Hunters here spend their lives in a constant search

for scarce and elusive prey.

Remarkably, this seemingly barren wilderness

is home to the largest hunter of them all.

The blue whale.

Weighing 200 tonnes and 30 metres long,

these are the biggest animals ever to have lived.

Despite their immense size

blue whales are one of the most streamlined

and energy-efficient of all swimmers.

Their food is so scarce and widely spread

that blue whales must journey across whole oceans

just to find a single meal.

They can travel over a hundred miles a day, for weeks at a time.

The ocean's largest animal feeds on one of its smallest.

Krill, small shrimp-like crustaceans.

Opening its gigantic mouth takes so much effort

that they only do so when the swarms of krill are rich and concentrated.

The krill here is too scattered,

not even worth slowing down for.

This blue whale's lonely search for food must go on.

Out here feeding opportunities are always few and far between.

And they never last long.

Prey is devoured within minutes.

When it's all over the hunters must resume their endless search.

Frigatebirds, the pirates of the high seas.

Soaring effortlessly on the gentle trade winds,

they can scan vast tracts of ocean for food.

Frigates must be so lightweight that they can't afford the heavy oils

that waterproof the plumage of other sea birds.

So getting wet would be lethal.

This may seem an impossible limitation for a seafaring hunter.

But frigatebirds overcome this handicap with help from others.

Dora do.

One of the fastest and most voracious of ocean predators.

They patrol close to the surface, searching for prey.

Little fish try to hide amidst the undulating swell of the ocean,

the only cover there is.

It's a game of hide and seek

played out amongst the waves.

Their cover blown,

escape seems impossible.

But these particular fish have a unique ability.

They're flying fish.

With an extra thrust from their tails,

the flying fish get airborne once more.

With a good wind, they can glide for hundreds of metres.

But this is just what the frigatebirds have been waiting for.

When frigates join the hunt,

the flying fish are literally caught between the devil

and the deep blue sea.

If the flying fish get too much lift

they become easy prey for the frigates.

If they dive to evade attack from above,

they could fall into the mouths of the dorado.

With the help of the dorado

the wily frigatebird has become a flying fish specialist,

and without getting a single feather wet.

Not all open ocean hunters are able to travel in search of their food...

Some have no choice, but wait fora meal to come to them.

A mat of sargassum weed

drifts in the middle of the Atlantic.

Sargassum is the only seaweed to live entirely at the surface,

it never attaches to the sea floor.

This floating tangle of fronds

is home to a surprising open ocean predator.

The sargassum fish.

Every part of his body mimics the weed.

His fins are more suited to walking than swimming.

In fact, he can barely swim at all.

He will spend his entire life marooned on this weedy raft.

This sargassum fish must lie in wait

for those seeking shelter amongst the weed.

Unfortunately, his mat is empty for now,

but at least he's not wasting valuable energy searching for food.

In the featureless ocean,

these mats are much sought after sanctuary for juvenile fish.

At last...

...his first opportunity for weeks.

He must get closer.

He can only strike when he's within a few centimetres of his prey.

Trusting his perfect camouflage, he hides in the weed.

Patience.

Still not close enough.

Hunger is clearly getting the better of him.

Surely this time.

Blown it.

It may be weeks before he gets another chance.

The open ocean is so vast

that some hunters can only find enough prey

by searching as a team.

Dolphins live in highly sophisticated social groups.

Working together they can cover a huge area of ocean.

These are spinner dolphins.

Why they make these twisting leaps is still debatable.

Perhaps it's a form of communication.

Or perhaps it's just fun.

Small groups sometimes come together,

forming super-pods five thousand strong.

And these are on the hunt.

Spinners are the most vocal of all the dolphins.

They use echolocation, a kind of sonar,

to find their prey.

Each hunter sends out a series of clicks

and then listens for returning echoes.

Allowing them to scan for distant prey, hundreds of metres away.

The super-pad spreads out into a wide hunting line

up to a mile across,

producing a wall of sound.

They're searching for their favourite prey.

Lanternfish.

They are the most numerous fish on the planet.

But these small fish spend most of their time down in the deep ocean,

way beyond the reach of dolphins.

It's only when they come up to the surface to feed

that they become prey.

Once they've found a shoal

the dolphins use their sonar in a different way.

They stun the fish with loud blasts,

then simply gather them up.

As they feed, the dolphins work the underside of the shoal

to stop their prey from escaping back into the safety of the deep.

Within a few minutes, all that's left is a shower of scales

drifting downwards to the ocean depths.

The deep ocean is by far the largest habitat for life on earth.

And home to some of the most bizarre hunters of all.

Down here, food is much scarcer than at the surface,

so deep-sea predators must do all they can

to save precious energy.

Waiting patiently, a viperfish,

special light-producing organs on its head

entice prey towards fearsome teeth.

Strange, yet deadly, jelly hunters also live here.

Most simply drift,

trailing tentacles loaded with lethal stings.

Others, propelled by lines of beating hairs,

glide gently through the darkness.

Beroe, the top deep-sea jelly predator.

They actively hunt other jellies.

Like this ctenophore.

To grasp its gelatinous prey,

beroe has special teeth-like spikes in its mouth.

Many deep-sea hunters just hang in the abyss,

saving their energy,

luring their prey to come to them.

Chiroteuthis.

This deep-sea squid fishes for prey using long sticky tentacles.

Each has a glowing lure

pulsing to attract passing prey.

A gentle twitch adds to the temptation.

Down here in the darkness this meal is a rare bonanza.

The open ocean may be a vast blue desert,

but like all deserts it has oases.

Scattered widely across this endless space

are thousands of small islands.

These are the summits of underwater mountains,

which rise up from the sea floor many miles below.

The seamounts deflect deep ocean currents upwards,

forcing nutrient laden water to the surface.

A busy oasis in the emptiness of the big blue.

For potential prey there's plenty of shelter

amongst the coral.

And in the caves that are hidden beneath the reef itself.

Small fish take refuge here,

out of the reach of most of their predators.

But not all.

Lionfish.

They're not built for speed...

Success here depends on delicate maneuvering.

Their strategy is to hide in plain sight,

lulling their prey into a false sense of security.

The lionfish's stripes are visually confusing,

making it difficult for their prey to judge how close it is.

Using its extravagant fins

to hide slow and deliberate tail movements,

it edges ever closer.

It must get to within a few centimetres,

close enough for a sudden strike.

Got one.

The deep-water currents that sustain so many residents

also attract visitors to these oases.

Silky sharks.

They journey hundreds of miles between seamounts,

using them as gathering places in the featureless ocean.

They're joined by hammerheads.

Both these sharks constantly travel between the Galépagos

and other isolated seamounts in the Eastern Pacific.

No one knows for sure why they gather in such numbers,

but some certainly come to these oases in search of food.

A school of resident silversides cloaks the seamount.

If these little fish stay close to the coral

the sharks won't be able to get at them.

Other more agile visitors are attracted by the potential feast.

Striped bonito.

And golden trevally.

To get a meal they'll need to drive their prey up and away from the reef