Original subtitles

We live on an ever-moving planet.

(dramatic music)

It's the driver that brings seasonal change.

And as landscapes are altered,

wildlife must march to its rhythm,

performing endless journeys.

As if by magic, they follow a map, built into their DNA,

driven by instinct,

and the wisdom of the thousands of generations

who have gone before.

Migration is a phenomenon that wows us

as animals show incredible feats of endurance.

Some run, some fly,

but most swim,

performing some of the longest journeys on earth,

facing endless hurdles.

But for marine migrators, nothing can turn the tide.

These creatures were born ready for the big swim.

(gentle music)

Giants are on the move.

Gray whales chose the warm waters

off the Pacific coast of Mexico to breed.

In the clear shallows, it's easier to keep their calves safe

from predators like sharks.

But migration is built into the ancient DNA

of these animals.

They're driven to keep on the move.

But as they leave coastal lagoons and enter open ocean

to travel north, they face danger head-on,

killer whales.

Giant members of the dolphin family,

the sleek predators are sometimes known

as the wolves of the sea.

(whales crashing)

Because like wolves, they hunt in packs

and perform coordinated attacks.

They're capable of killing even the biggest of whales,

but the adult grays are known to put up quite a fight.

(dramatic music)

The killers are after the baby.

They must drive a wedge between the frightened calf

and its defensive mother.

The female will do all she can to stand her ground.

But she's outnumbered.

The killer whales chase until the calf is tired.

They nip and push it under water,

preventing it from catching its breath.

Despite the mother's efforts, it's too late.

Undertaking migration is a huge risk.

There are many calves that won't make it.

But by hugging the coastline, sticking to shallow waters,

some mothers will successfully escort their calves

across an ocean.

Gray whales perform some of the biggest journeys of all,

a round trip of 20,000 kilometers.

This is why.

During summer, the northern extremes of the planet

get much longer hours of sunlight than the tropics.

More light means more plant growth,

or in the sea, algae.

It feeds the base of the food chain,

making the cold waters of the North Pacific

some of the most productive on the planet.

(soaring music) (waves crashing)

Gray whales can gain several tons

in just a few short months,

thanks to the shellfish they can sift from the seabed.

But as the autumn creeps in,

the days get shorter and the water colder.

This is no place to raise young.

So the whales quit binging and head south again.

During its lifetime, a gray whale covers enough ground

to get to the moon, come home,

and go back to the moon again.

These are typical drivers

to move from one habitat to another,

to find favorable conditions to raise young

or to exploit a major food source.

(dramatic music)

All across the ocean, giants are on the move.

Marine life undertake some of the biggest migrations

on earth.

Driven by currents, changing with the seasons,

bringing in or washing out great riches,

motivated by the need to be in the right place

at the right time.

The biggest animal mass on the move isn't the giants.

It's the little guys by sheer number.

Herring move between feeding and spawning grounds.

Some populations also make a winter stop off.

In the deep fields of Norway,

the fish gather in unimaginable numbers

to sit out the worst of winter,

but as they pour into the submarine valleys,

predators follow,

humpback whales.

These giants undertake the longest known migrations

of any mammal, 8,000 kilometers each way.

Some reroute to cash in on the herring,

and they are being tailed.

Killer whales,

but these ones are different.

Unlike the whale eaters of the Pacific,

the whales here prefer fish.

They are joining the humpbacks for a feast.

The orcas work together to concentrate the fish,

scaring them with squeals.

(whales squealing) (dramatic music)

And then release their weapons,

powerful blows from their tails.

The shock waves from the strikes are so forceful

that they literally stun the fish.

The killer whales can hoover them up one-by-one.

(seagulls squawking)

The humpbacks are less delicate.

When they get to a tightly packed ball of fish,

they simply open their mouths to engulf the lot.

Pleats in their throats expand

allowing them to take in more than 20,000 liters of water,

the amount of a fair-sized backyard swimming pool.

Then the throat contracts forcing the water out,

but trapping the fish behind their baleen.

One whale can eat more than two tons of herring a day.

The humpbacks and the surviving herring

will resume their migration once the weather improves,

moving to rich feeding grounds to the north.

Food is one of the primary motivators of migration.

Seasonal abundance is worth the epic struggle.

For big bodies, it takes hard work to gather enough food,

especially if you eat the smallest creatures in the sea.

Basking sharks are the second biggest fish on earth.

Longer and heavier than a minibus, they need plenty of food.

The sharks spend winter 1,000 meters or more

in the depths of the ocean.

But in summertime when strong light fuels algal growth,

they migrate to the shallows,

for feeding on the algae are plankton, lots of plankton.

And that's what the giant fish sieve from the seas

simply swimming open mouthed through the shoals

and sieving the tiny creatures

with net-like structures in their gills.

But not all migrations are driven by food.

The waters around the Galapagos

undergo dramatic changes through the year.

They have two key seasons.

For half the year, they're bathed by the warm waters

of the Panama current and trade winds

that create the wet season on land.

But this is a hard time for marine life.

The tropical seas are not very productive.

But the dry season is brought on by a shift in currents.

The Humboldt Current swarms the Galapagos with cold water

brought up from the Antarctic.

Because the Antarctic gets long sunlight hours,

it's highly productive.

The water flowing from it is packed with nutrients.

Now there is a time of abundance for the fish.

Many oceanic species visit.

(gentle music)

But not all of them are after food.

Hammerhead sharks are ocean wanderers,

but during their travels, they accumulate parasites

and other blemishes on their skin.

To fix the problem, they hire cleaners.

A little head nod over the reef

(playful music)

is a signal that it's here for spa treatment, not dining.

And the fish willingly oblige.

The pests and dead skin are a feast for the fish.

And after their stop at the health spa,

the spruced-up sharks can continue their journeys.

Hammerheads travel for food, cleaning services,

and to find a mate.

The Galapagos is one of the few places

where huge aggregations occur.

They like to be discreet when it comes to sex.

No one has ever seen it,

but it's likely the coupling happens

during their big social events.

Many of the females have bite wounds on their fins,

the love bites of males holding on during mating,

testimony to their nuptial encounters.

The Galapagos, like many other archipelagos

and tropical coasts, attract lots of animals

looking to enrich their sex lives.

Green sea turtles, just one of seven species

that undertake similar journeys.

Turtles have long, slow lives,

but they don't shy away from some serious swimming.

(upbeat music)

Because they're reptiles,

they hatch from eggs laid on beaches.

For five to seven years, they make long migrations

around the Eastern tropical Pacific

living an oceanic lifestyle.

Then they head to coastal waters.

But the journey's don't stop as they move

between feeding grounds.

Only once around 30 years old do they think about sex.

After hatching, male turtles never return to land,

but they will make their way to breeding sites

where they hang out looking for females on the reef.

The hopeful males turn up every year,

(gentle playful music)

but the females only come to breed every two to five years.

So scrums are common as males try to lay claim

to the receptive females.

During coupling, the male does his best to hold on.

(gentle music)

Other males will try to muscle in.

But one-by-one, they give up

and head back to the reef to continue their search.

Once mated, the female will set off on yet another journey

back towards the beach where her own life began.

Not all swimming marathons are marine.

Across the world, streams and rivers

host epic fish Olympics.

(upbeat music)

More than half of all fresh water fish species migrate

between feeding, breeding, or wintering grounds.

(slow gentle music)

In temperate regions, winters can be cruel.

Ice-locked rivers and lakes can make it hard to move around.

But as soon as winter's power starts to ebb,

fish get busy.

Pike are one of the first.

It's the perfect time for their high-energy journey.

(upbeat music)

Snow is melting all over the landscape,

gushing into waterways, churning oxygen into them.

The powerful fish exploit the oxygen

in their battle against the currents.

The epic struggle, just so that they can deposit their eggs

in the perfect spot.

The meltwater is a valuable resource, but it's shallow.

(dramatic music) (fish splashing)

Like all migrations, their struggle is an essay

in determination and endurance.

The pike run the risk of grounding themselves on the rocks.

And that's not the only danger.

(bird squawking)

Migrating cranes and other birds drop in

to take advantage of any casualties.

(birds squawking)

Eventually, most will make it

and spawn before wriggling back

to their summer feeding grounds.

The eggs develop,

and in only a few weeks, hatch,

and the tiny larvae begin to patrol,

already feeling their predatory instincts.

These baby pike have never migrated,

but they are born with the instinct.

And when they mature in a few years,

they too will join the epic struggle upstream.

For most fish, the process of baby-making

is simply to squirt out eggs and sperm

and let nature do the rest.

For other swimmers, it's more of an uphill struggle.

An ocean giant is nearing the end of a great journey.

Leatherback turtles are the biggest of their kind,

little changed since the time of the dinosaurs,

but their vast size doesn't hold them back.

Over the year, this female has traveled

more than 6,000 kilometers

from feeding grounds along the coast of Canada.

And this is why,

the long sandy beaches of an island of Western Africa

where her own life began many decades ago.

Her streamlined body is the perfect hydrofoil.

Powered by huge flippers, she can fly through the ocean

at more than 30 kilometers per hour.

But now on the beach, every stride is a monumental struggle.

She must drag her one-ton bulk above the tide line,

searching for the perfect spot,

not so high up the beach that it dries out,

but not low enough for it to get waterlogged by a high tide,

and with just enough sun exposure

to create the perfect temperature.

She's aiming for a nest that holds at 27.5 degrees.

If she gets it right,

she'll produce equal numbers of boys and girls.

If the nest is warmer, more will be female,

and cooler will result in more males.

She will make this gargantuan journey up the beach

several times during the season,

and each time deposit around 100 rubbery,

ping pong ball-sized eggs.

(inspirational music)

She gently covers the nest site

and begins a hard exit back to the sea.

This is the end of her motherhood.

In two months time, the eggs will be ready to hatch,

but they will do so alone, again driven by instinct

to take up their lifetime of journeys.

(waves lapping)

Migrations have long captured the human imagination,

but few more so than the journey of salmon.

These mighty fish don't just move themselves

from one area to another,

but from fresh water to the sea and then back again,

forcing transformations that literally destroy their bodies.

It's the unstoppable instinct of migration.

(birds chirping)

Salmon begin life hatching from eggs

in small freshwater streams far inland.

Several very different life phases lie ahead.

Newly-hatched salmon are known as alevin.

Tiny tails push along the big yolk sacs

that nourish them while their bodies grow.

Gradually, the delicate translucent forms

start to look more fish-like.

These are par, small, stripey, freshwater fish

that can forage for little organisms

in the streams where they hatched.

For six months or more, sometimes even a few years,

their lives will remain constant.

But then a cue from deep within

(upbeat music)

tells the fish to move downstream.

Their bodies are changing inside as well as out

to cope with the transition from clean, fresh water,

to the high salt content

and lower temperatures of the open ocean.

After a few years, up to five depending on the species,

adult salmon feel an unignorable urge to breed,

and they begin their titanic journeys

to the place of their birth.

The fish follow the earth's magnetic fields

to aim for the coast,

then recognize the chemical smell

of the river they were born in,

using that path to guide them inland.

(birds chirping) (water flowing)

As they enter the shallows,

predators gather to greet them.

These bears have been waiting for several days,

knowing that any moment the flood gates will open

with fleets of salmon charging into the rivers.

For bears, the salmon run is a vital resource.

It's no surprise that they camp out waiting for the fish.

(dramatic music)

Bears only have a narrow window before winter

when they can bulk up.

They need huge amounts of fat stored in their bodies

if they are to survive their long winter sleep.

Some populations are totally dependent

on the salmon migration.

It comes at just the right time for them to top off.

It literally makes the difference between life and death,

something worth fighting for.

But as the rivers fill with fish,

the normally solitary bears develop a temporary tolerance.

There's enough fish for everyone.

(playful music)

Gulls, crows, and eagles gather.

There are so many salmon

that the bears simply nibble off the best bits

and move on to the next.

There are plenty of scraps for watchful birds.

A big bear might consume

2 or 3,000 kilos of fish per season.

For the fish that dodge bear claws,

the struggles have barely begun.

(water gurgling) (foreboding music)

Many species spawn at elevation,

so not only must they battle against the current,

but also scale mountains.

Athletes of the fish world, salmon can climb waterfalls.

Triggered by the change in chemistry

and lower salt level of the rivers,

they change the way they use their bodies.

Instead of the muscle groups

that normally power fast, straight swimming,

they switch to ones that power bursts of speed.

Bending in a tight S-shape, flipping from side to side,

they create thrust against the water

and launch themselves into the air.

Skyrocketing, they can clear three meters.

Some battle hundreds of kilometers inland,

through strong currents and rapids.

A few populations swim 1,400 kilometers

into mountain ranges,

climbing more than 2,000 meters in elevation,

and all the while their bodies

are undergoing massive changes.

Some species radically alter their appearance

ready for the breeding season.

None more so than the sockeye.

Normally sleek and silver,

they now display fiery red breeding colors.

The males grow massively enlarged shoulder humps,

so they look pumped up to impress the girls

and intimidate rivals.

Exhausted, the fish that have dodged death

finally reached the spawning streams.

While they've been traveling,

the females have been developing eggs inside them,

and they are now ready to deliver their precious cargo,

known as roe.

(gentle music)

They select only fast-flowing streams

where the current will flow over the eggs,

keeping them clean and well oxygenated.

With a few sweeps of the tail,

a female can scoop out a gravelly nest

into which she deposits the roe.

As she's laying, eager males gather.

There's stiff competition,

but the males have also been developing weapons.

Their jaws have become elongated and arched,

and packed full of canine-like teeth.

Like nightmarish crocodiles, they can nip at rivals

They try to fight their way to the top of the line

to be alongside the spawning female.

The victim will mark his triumph

by squirting sperm over the roe-filled nest.

With fertilization complete,

the female gives another few sweeps of her tail,

stirring up gravel to gently cover the eggs.

Then finally, their unimaginably demanding mission

is complete.

The energy required to fight inland,

the massive impact of remodeling their bodies

to cope with fresh water and to arm them to breed,

and the art of spawning have all taken their toll.

They also haven't eaten for months.

Their withered bodies have given all they have to give

and literally fall apart.

After one of the most epic journeys on earth,

they find peace back in the rivers of their birth.

But the salmon's death

is perhaps their greatest gift of all.

In their struggles, the fish have carried nutrients

from the sea in their bodies.

As they rot, the nutrients are released into the water,

providing essential minerals to the surrounding landscape.

This ensures that their offspring

will grow up in rich waters full of food,

but way beyond that,

they're literally fertilizing an entire forest

and everything that lives in it.

Without salmon, the forest would be a poorer place,

all thanks to the driving force of migration.

Of course, bears and birds are not the only predators

the migrating salmon face.

Fishermen also descend on the rivers

for the sport of luring salmon to their bait

and fighting the powerful fish.

Fortunately in most places,

the harvest doesn't have a massive impact

on the salmon stocks.

But many human activities do.

By its very nature, migration puts animals in danger.

In some places, fishing, development,

and other human activities may be controlled

to help protect wildlife,

but migrators don't recognize international boundaries.

They might be protected in one area,

but then exploited in the next.

Their wanderings make it very hard

to strategize their protection,

and it's especially tough for marine migrators.

The swimming animals spend most of their lives

underwater and out of sight.

It's hard to see what's going on in their lives.

Data is lacking, but already clearly shows

that the majority of species are in decline.

These international travelers really do belong to everybody

and need everyone's help to survive.

(whales squealing)

And there is another more recent challenge

that humans have caused.

Our activities have altered the gases in the atmosphere

and change the chemistries of the seas.

Climate change affects the seasons all over the world.

Migrating animals might arrive too early or too late

to find the conditions they need.

Research reveals that 80% of marine migrators

have already changed the routes and timings

that they have been following for eons.

Some have altered their course

by as much as 1,000 kilometers.

Warmer seas are less productive.

Some species seem able to adapt quickly to the changes,

but are showing massive die-offs

due to starvation and breeding failures.

More than ever, we need to manage

and minimize our footprint on the planet,

for the sake of migrators as well as ourselves.

But there is hope.

Despite the odds, life shows tremendous resilience.

On that quiet beach of Western Africa,

the sand seems to spring to life.

Both green and leatherback hatchlings

are digging their way from the ground.

It's already been an arduous task.

They've had to tunnel through the weight

of more than 50 centimeters of sand that covered their nest.

But the challenge has barely begun.

Though you could fit a handful

of these tiny turtle hatchlings in your pocket,

they're destined to become

among the largest reptiles on earth,

if they can make it down the beach.

The tiny flappers looking more like bath toys

than ocean travelers must somehow make it to the sea.

Instinct drives them in the right direction.

They paddle along making little angels

in the sand as they go.

But even little ridges in the sand

are like mountain ranges for creatures born to swim.

Not all will make it.

Some are imprisoned by debris washed up on the beach.

Small and vulnerable out in the open,

even tiny crustaceans can become lethal predators.

Any dawdling, and the red ghost crabs strike.

Much bigger shadows fall across their path.

The keen eyes of a pied crow guide it

to what it expects to be an easy meal,

(dramatic music)

though a Palm-nut vulture has other ideas.

The onslaught is relentless.

But turtles are born to a life of migration.

The urge to begin their journeys

compels them to tackle the challenges head-on.

Only one in 1,000 will survive,

but turtles, like many migrants, make it work,

and they have for millions of years.

Their instincts run deep to keep on the move.

They're undistractible, answering to a call

written in their DNA.

They just keep swimming.

Animals that migrate are some of the toughest on earth.

They have learned to face hardship head-on

to get the best out of their environment,

and in doing so enrich the environment for others,

including us.

(victorious music)

(fish splashing)