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Much of our planet
still remains unexplored...

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..for most of it is covered
by water.

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Every journey below the surface
can reveal something extraordinary.

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More than a thousand new species
are discovered here every year.

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The ocean is home to 80%
of all animal life on Planet Earth.

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But today,
thriving in this varied world

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sometimes demands
the most surprising behaviour.

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The shallow seas of the tropics.

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This may look like a paradise...

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..but beneath the surface,
it is an arena

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for constant
life-and-death struggles,

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where not everything
is quite as it seems.

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A predatory lionfish...

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..on the hunt for shrimp
and small fish.

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With so many places
for its prey to hide,

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the lionfish has to be patient.

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This shrimp appears tempting.

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As the lion-fish closes in,

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it fans out its fins
to disorientate its prey.

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The hunter becomes the hunted.

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Tricked by one
of the shallow sea's

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most extraordinary predators...

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..a clown frogfish!

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On its head, it carries
a fishing rod –

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a modified dorsal fin,

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baited with a lure -
easily mistaken for a shrimp.

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But, when the fish stop biting,

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it's time to pack the rod away

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and move on.

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And, for a frogfish,
that takes time.

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Rather than swim, frogfish walk!

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Its fins have, in effect,
become feet.

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It may not look pretty,

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but what appears to be coral living
on its skin is actually camouflage.

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As every good angler knows,

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picking the right spot is important.

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Jigging the rod sends out
pressure waves

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to attract the attention
of possible prey.

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These dragonets
are certainly interested.

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Almost there.

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Hook, line, and sinker.

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Like all shallow seas,
the cold waters

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off the coast of North America,

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benefit from the intensity
of the sunshine.

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Here, that fuels

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one of the fastest-growing
organisms on the planet...

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..giant kelp.

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Towering forests
can eventually reach the height

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of a 12-storey building.

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These forests are nurseries
for young horn sharks.

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As the sun begins to set,

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they leave their daytime shelter

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and set off into the heart
of the kelp forest to find food.

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Barely half a metre long,

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this little shark
is extremely vulnerable.

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There are monsters here.

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A giant sea bass –

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weighing over 200kg...

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..and wolf-eels, with big teeth

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that can crush
little red sea urchins.

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But the biggest danger
comes from other sharks -

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houndsharks...

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..and huge broadnose sevengills.

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In this forest,
it pays to keep a low profile.

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An angel shark...

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..one of the most deadly sharks
in the kelp forest,

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and certainly
the best camouflaged.

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An angel shark
will lie in wait for days...

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..but this one has already attracted
too much attention.

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It's not welcome here.

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Now, the coast is clear.

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But angel sharks hunt
around the clock.

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Openings for breathing,
called spiracles,

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blow out sand
that helps cover its body.

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The trap is set.

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Staying close to the seabed is
a good way to avoid most predators.

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Faster than the blink of an eye.

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But it's not over yet.

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Horn sharks have a secret weapon.

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Sharp spikes keep them very much
off the menu for most.

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So, this young horn shark
can hunt in safety...

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..for now.

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Violent winter storms
batter these kelp forests.

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The plants can be ripped
from the seafloor...

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..and carried away far out to sea.

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The open ocean
is a vast, featureless desert.

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Even a small piece of drifting kelp
can become valuable.

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It's just what these fish
have been searching for.

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Here, shelter where eggs can be laid
unobtrusively is rare...

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..so they make the most of it.

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Each female produces
up to a thousand eggs,

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and the males rush in
to fertilise them.

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All this activity attracts
the attention of blue sharks.

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They can travel thousands of miles

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through the ocean
in search of food...

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..and they may not have eaten
for weeks.

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It seems that they're in luck.

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But these fish are no easy meal.

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They are flying fish!

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The blue shark, however,

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are not here for the fish...

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..they have come for the caviar.

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But flying fish lay so many eggs,

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that the sharks' feasts
hardly make an impact.

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And, in a few months' time, a new
generation will take to the skies.

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Floating islands of weed
are always attractive to creatures

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looking for shelter
out in the big blue.

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But, in today's ocean, they are
being replaced by something else...

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..plastic.

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12 million tons of it
end up in the ocean every year.

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The deadliest kind are discarded
fishing lines and nets.

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Each year, it's likely over
half a million animals are ensnared

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and killed by these "ghost nets."

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But some animals are learning

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how to take advantage
of the plastic rafts...

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..and use them for shelter,
or even as a home.

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This male Columbus crab – barely
bigger than your thumb nail –

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is a castaway.

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Clinging to his net,

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he may have been drifting
on ocean currents for months.

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Now, fully grown,
he needs to find a partner.

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But where?

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Certainly not here,

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alone on the net.

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Columbus crabs are not good
swimmers, so this male is marooned.

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Perhaps a passing loggerhead turtle
could be the chance

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to hitch a lift.

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Made it!

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But there's more than one
passenger here -

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a female Columbus crab!

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They waste no time
in getting acquainted...

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..and start to mate.

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This pair may well stay together
for the rest of their lives.

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A turtle, after all,
makes an excellent home.

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In return, the crabs provide
an onboard grooming service.

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Finding a partner in the vast ocean
is not easy.

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Dawn in the Sea of Cortez...

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..Mobula rays.

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They're gathering here,
most likely to breed.

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No-one is sure why they leap,

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but the loud splashes
certainly seem to attract more rays.

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Other creatures, however,
are also listening.

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Orca have heard the splashes.

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This female specialises
in hunting rays.

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But today, she is teaching
two youngsters

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the finer points
of Mobula ray hunting.

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The rays are fast
and can outmanoeuvre an orca.

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She knows she needs to herd
the prey into a tight group...

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..but she can't do that on her own.

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It will take teamwork,

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and that is today's lesson.

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The young orca
are quick to catch on.

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The rays are surrounded.

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They dive...

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..only to be forced back up again
by the experienced female.

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And now, with the exhausted rays
trapped against the surface,

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she attacks...

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..and the young ones
follow her lead.

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This family are the only orca
known to hunt rays like this...

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..and they are lethally efficient.

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But it appears that school
is over for today.

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For a few battle-scarred survivors,

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it's a lucky reprieve.

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With the orca gone, the rays
can resume their courtship...

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..and they do so
in astounding numbers.

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Tens of thousands of rays
in a single shoal.

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Vast areas of our ocean
are yet to be explored.

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The least known parts of it
are its great depths.

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Only highly-specialised vessels
can take you there.

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As you descend,
the sunlight rapidly fades.

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200m down,
you enter the twilight zone...

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..an alien world, inhabited
by creatures beyond imagination.

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A siphonophore – with a cloak
of lethal stinging tentacles.

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Siphonophores repeatedly
clone themselves

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and so grow to immense lengths.

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This one measures 45m and is
the longest animal ever recorded.

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With such deadly predators around,

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creatures here go
to great lengths to hide.

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A glass squid...

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..completely transparent,

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except for its eyes...

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..and stomach,

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so it is extremely difficult
to find in the gloom.

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Below 1,000m,

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all traces of sunlight
have disappeared.

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This is the midnight zone.

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Catching food in the perpetual
darkness is not easy.

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A gulper eel.

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Its giant, extendable mouth

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can engulf prey
larger than its own body.

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Two miles down,
you finally reach the ocean floor.

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We know more
about the surface of Mars.

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The pressure of the water is 300
times greater than at the surface...

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..and it's freezing cold.

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Yet, amazingly,
there are animals living here.

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00:33:55,770 --> 00:33:58,690
Muusoctopus robustus,

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nicknamed the pearl octopus.

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Breeding, in these
extreme conditions poses

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a particular problem
for these animals.

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00:34:14,730 --> 00:34:17,050
At these low temperatures,

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this female's eggs could take
over ten years to develop.

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00:34:30,810 --> 00:34:35,090
So she travels
to a very special place.

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This is the largest known
gathering of octopus in the world.

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00:35:04,530 --> 00:35:08,570
She joins 20,000 other females...

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00:35:10,490 --> 00:35:13,370
..all here to lay their eggs.

206
00:35:19,850 --> 00:35:23,450
Water, heated deep
in the Earth's crust,

207
00:35:23,450 --> 00:35:26,730
rises through cracks
in the seabed...

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00:35:28,610 --> 00:35:33,890
..raising the temperature
to as much as 10 degrees Celsius.

209
00:35:35,290 --> 00:35:38,130
A deep-sea thermal spa!

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00:35:43,130 --> 00:35:46,170
This warmth significantly speeds up

211
00:35:46,170 --> 00:35:49,330
the development of their eggs.

212
00:35:49,330 --> 00:35:53,450
Even so, they will still take
nearly two years to hatch.

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00:35:55,650 --> 00:35:58,090
Once a female is settled,

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00:35:58,090 --> 00:36:00,650
she won't move from her spot...

215
00:36:02,130 --> 00:36:04,650
..not even to feed.

216
00:36:16,170 --> 00:36:20,250
She will constantly tend
to her brood –

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00:36:20,250 --> 00:36:23,170
keeping them clean,

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00:36:23,170 --> 00:36:25,250
and oxygenating them

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00:36:25,250 --> 00:36:27,890
with jets of water.

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Pearl octopus mothers must surely be
amongst the most devoted.

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00:36:53,930 --> 00:36:59,410
After almost two years,
the ordeal take its toll.

222
00:37:06,410 --> 00:37:09,170
But the vigil is almost over.

223
00:38:07,970 --> 00:38:12,330
The last of the brood
are gently encouraged to leave.

224
00:38:20,330 --> 00:38:23,290
But this will be a final act.

225
00:38:25,130 --> 00:38:31,410
Like all the mothers here, this
octopus is starved and exhausted.

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00:38:34,570 --> 00:38:37,530
Her life will soon be over.

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00:38:55,570 --> 00:38:59,210
But this devotion means
that her offspring are among

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00:38:59,210 --> 00:39:04,090
the largest and most developed
of any octopus

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00:39:04,090 --> 00:39:06,770
and have the best chance of survival

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00:39:06,770 --> 00:39:09,610
in the demanding world of the deep.

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00:39:25,970 --> 00:39:30,330
We're finding more of these
strange hot springs every year.

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00:39:41,210 --> 00:39:45,170
In some places,
they can be astonishingly violent.

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00:39:46,610 --> 00:39:51,410
Super-heated water –
hot enough to melt lead -

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spouts from the seafloor.

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00:39:55,530 --> 00:39:58,010
Dissolved minerals
condense around them

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00:39:58,010 --> 00:40:03,090
to form towering chimneys,
known as hydrothermal vents.

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00:40:07,490 --> 00:40:11,290
They are home to unique
communities of animals

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00:40:11,290 --> 00:40:15,130
that all rely on the nutrients
in the scalding water.

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00:40:25,090 --> 00:40:28,930
Some suggest that vents
like these could be the places

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00:40:28,930 --> 00:40:33,130
where life on Earth first began
four billion years ago.

241
00:40:41,170 --> 00:40:44,250
And there is now evidence
of hydrothermal vents

242
00:40:44,250 --> 00:40:47,330
on the moons of Jupiter and Saturn.

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00:40:49,250 --> 00:40:52,010
Could they too be supporting life?

244
00:40:56,650 --> 00:41:00,970
Here on Earth,
the influence of these vents

245
00:41:00,970 --> 00:41:03,930
extends far beyond their chimneys.

246
00:41:05,610 --> 00:41:08,930
The essential nutrients
carried in these plumes

247
00:41:08,930 --> 00:41:13,850
can rise all the way to the surface
two miles above.

248
00:41:19,370 --> 00:41:24,210
Here, they stimulate the rapid
growth of tiny marine plants...

249
00:41:24,210 --> 00:41:26,930
..on an astronomic scale.

250
00:41:33,650 --> 00:41:37,090
This phytoplankton is so abundant

251
00:41:37,090 --> 00:41:41,370
that it produces half
of all the oxygen on Earth.

252
00:41:59,450 --> 00:42:04,050
It's also food for a host
of minute animals -

253
00:42:05,530 --> 00:42:07,850
zooplankton.

254
00:42:09,610 --> 00:42:13,330
Together, they are the basis
of the food chains

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that sustain
nearly all life in the ocean.

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In the Pacific waters
off South America,

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they feed anchovy
that gather here in billions.

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This is one of the world's
most productive ecosystems.

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00:42:59,850 --> 00:43:03,490
These South American
sea lions are on the hunt.

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00:43:23,810 --> 00:43:28,730
But the anchovy shoal
has already been located...

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00:43:33,330 --> 00:43:36,730
..by the planet's
most efficient hunters.

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A net, over half a mile long,

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00:43:42,850 --> 00:43:44,810
encircles the shoal.

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00:43:47,770 --> 00:43:50,850
It can trap over a million fish.

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00:44:02,810 --> 00:44:05,650
But the sea lions
aren't about to go hungry.

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00:44:07,970 --> 00:44:11,570
They have learnt
to look for holes in the net.

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00:44:22,090 --> 00:44:28,690
Why waste energy when food
comes to you as easily as this?!

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00:44:35,370 --> 00:44:38,650
As more and more sea lions arrive,

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some change their tactics.

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00:44:48,730 --> 00:44:51,770
They line up
on both sides of the net...

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..and wait.

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00:45:10,010 --> 00:45:14,890
As the net tightens, the anchovy
panic and rush for the surface.

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00:45:21,290 --> 00:45:25,410
This is the moment the sea lions
have been waiting for.

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00:45:39,690 --> 00:45:43,450
It's such an effective way
of hunting that the sea lions here

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are changing
their natural behaviour...

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..and are raiding the fishing nets

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00:45:53,250 --> 00:45:55,690
in their thousands.

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00:46:03,370 --> 00:46:05,610
With the net almost drawn in,

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00:46:05,610 --> 00:46:08,850
the fishermen beat out
a warning signal.

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00:46:12,330 --> 00:46:14,330
Time is up.

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00:46:43,730 --> 00:46:47,850
In the confusion,
not everyone manages to escape.

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00:46:56,450 --> 00:47:00,970
The trapped sea lions are in danger
of being drowned.

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00:47:22,650 --> 00:47:26,410
Pups are separated
from their mothers.

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00:48:30,170 --> 00:48:34,890
Then, at the last minute, the
fishermen briefly drop their net...

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00:48:42,290 --> 00:48:45,410
..and the trapped sea lions
can escape.

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00:48:53,690 --> 00:48:56,930
But many are not so lucky.

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00:48:58,810 --> 00:49:03,850
Around the world, millions
of animals are accidently caught

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00:49:03,850 --> 00:49:07,930
and die in fishing nets every day.

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00:49:10,330 --> 00:49:14,130
And this by-catch, as it's known,

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00:49:14,130 --> 00:49:17,530
is pushing many species
toward extinction.

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00:49:22,370 --> 00:49:25,770
Animals have evolved
in remarkable ways

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00:49:25,770 --> 00:49:28,410
to the demands of life in the ocean.

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00:49:33,090 --> 00:49:36,130
But can they now adapt
to the new challenge -

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00:49:37,370 --> 00:49:39,890
living alongside us?

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00:49:57,090 --> 00:50:00,210
The open ocean is home
to some of the largest

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00:50:00,210 --> 00:50:02,930
and most extraordinary animals
on Earth.

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00:50:05,370 --> 00:50:07,610
But here, off the Canary Islands,

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00:50:07,610 --> 00:50:11,210
the Planet Earth team are searching
for one of its smaller,

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00:50:11,210 --> 00:50:13,850
and less familiar residents.

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00:50:13,850 --> 00:50:16,410
We're looking for a tiny creature
called a Columbus crab,

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00:50:16,410 --> 00:50:18,570
which is only about the size
of your thumbnail,

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00:50:18,570 --> 00:50:22,250
which live on floating objects
in the open ocean.

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00:50:22,250 --> 00:50:25,570
Columbus crabs were once
only found on natural debris,

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00:50:25,570 --> 00:50:27,650
like driftwood or seaweed,

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00:50:27,650 --> 00:50:29,690
but the oceans are changing,

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00:50:29,690 --> 00:50:31,890
and they've been forced to adapt.

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00:50:46,290 --> 00:50:50,690
One of the most common items
they find is discarded fishing gear.

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00:50:53,010 --> 00:50:58,290
Over a million tons is left adrift
in the ocean each year.

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00:50:59,850 --> 00:51:02,650
And Columbus crabs are now
making their homes

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00:51:02,650 --> 00:51:05,170
on these unnatural materials.

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00:51:12,690 --> 00:51:15,970
Surprisingly, Columbus crabs
are thriving on this new habitat.

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00:51:21,250 --> 00:51:26,130
But, for larger ocean creatures,
these nets can be lethal.

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00:51:28,170 --> 00:51:31,810
Loggerhead sea turtles
are especially vulnerable.

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00:51:35,450 --> 00:51:38,850
Many times, they are very injured

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00:51:38,850 --> 00:51:42,730
and many times
they don't even survive.

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00:51:42,730 --> 00:51:45,250
It's a sad situation.

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00:51:46,690 --> 00:51:50,690
As a rule, wildlife film-makers
observe natural behaviour

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00:51:50,690 --> 00:51:52,770
and do not interfere.

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00:51:56,410 --> 00:51:59,730
But this is far from natural.

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00:51:59,730 --> 00:52:03,170
The team feel they must take action.

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00:52:12,770 --> 00:52:15,530
Sh...

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00:52:15,530 --> 00:52:17,890
It seems that the turtle
is quite OK.

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00:52:17,890 --> 00:52:22,530
We'll just finish to cut
the plastic and then we release it.

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00:52:38,970 --> 00:52:41,170
It's a bittersweet moment,

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00:52:41,170 --> 00:52:46,410
as this is one of eight turtles
they rescued whilst filming here.

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00:52:46,410 --> 00:52:49,730
This situation is not natural,

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00:52:49,730 --> 00:52:53,490
it's something that is
being caused by human beings.

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00:52:55,090 --> 00:52:58,530
Sadly, the crew now face
dilemmas like this

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00:52:58,530 --> 00:53:01,850
on many of their
filming expeditions...

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00:53:03,890 --> 00:53:08,010
..including, when they travelled
to the Pacific coast of Chile,

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00:53:08,010 --> 00:53:10,970
to show how sea lions
are competing for food

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00:53:10,970 --> 00:53:13,530
with one of the biggest fisheries
on Earth.

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00:53:18,610 --> 00:53:23,370
Expedition leader Fernando Olivares
takes the team to the fleet.

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00:53:30,570 --> 00:53:34,210
Diving near fishing nets
is extremely dangerous,

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00:53:34,210 --> 00:53:37,770
so the crew must ensure they have
the full cooperation

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00:53:37,770 --> 00:53:39,690
of the fishermen.

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00:54:04,090 --> 00:54:07,170
Pretty hazardous place to dive.

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00:54:07,170 --> 00:54:09,490
It's just a case of trying
to keep an eye on the divers,

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00:54:09,490 --> 00:54:12,050
but the sea lions also like
to go down and blow bubbles,

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00:54:12,050 --> 00:54:13,890
so you'll think
you're following the divers,

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00:54:13,890 --> 00:54:16,210
and then a sea lion will pop up.

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00:54:21,810 --> 00:54:23,930
Taking the utmost care,

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00:54:23,930 --> 00:54:26,010
the divers get a close-up view

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00:54:26,010 --> 00:54:28,570
of the sheer scale of the operation.

345
00:54:34,490 --> 00:54:38,050
This one net must have
about 15 tons of fish in it

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00:54:38,050 --> 00:54:41,170
and there's eight or nine boats
in this one little bay,

347
00:54:41,170 --> 00:54:42,850
and these are just the small boats.

348
00:54:42,850 --> 00:54:44,930
Out there, there are huge
factory ships that are taking

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00:54:44,930 --> 00:54:47,090
even bigger catches.

350
00:54:48,330 --> 00:54:50,690
How much fish a year from just here?

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00:54:50,690 --> 00:54:54,530
From a million tons a year
more or less.

352
00:55:02,570 --> 00:55:05,210
The catches are so vast,

353
00:55:05,210 --> 00:55:08,330
the sea lions have changed
their natural behaviour

354
00:55:08,330 --> 00:55:11,650
to collect anchovies
directly from the nets.

355
00:55:15,810 --> 00:55:17,850
But it's a risky strategy.

356
00:55:19,410 --> 00:55:23,370
The crew witnessed sea lions
caught in nets multiple times.

357
00:55:24,410 --> 00:55:27,570
Whoa, it's intense mate,
there are so many in there.

358
00:55:33,770 --> 00:55:36,370
There's a pup stuck in the net,
calling to its mother,

359
00:55:36,370 --> 00:55:39,410
and its mother's just on the outside
of the net calling back.

360
00:55:45,690 --> 00:55:48,290
That's really hard to watch.

361
00:55:53,810 --> 00:55:56,090
Oh, the pup's really panicking now.

362
00:55:58,570 --> 00:56:03,090
Sometimes, fishermen are able
to release trapped sea lions...

363
00:56:04,410 --> 00:56:06,570
..but not this time.

364
00:56:08,890 --> 00:56:11,210
The pup is in serious danger.

365
00:56:13,330 --> 00:56:17,010
Once again,
the crew decide to step in.

366
00:56:18,890 --> 00:56:22,130
Hey, he's going to go
inside of the net to save him.

367
00:56:45,850 --> 00:56:48,090
Wow.

368
00:56:51,930 --> 00:56:55,850
Nice, really nice.

369
00:56:55,850 --> 00:56:57,930
It's a relief this time...

370
00:57:00,450 --> 00:57:05,930
..but it highlights the new
realities of filming wildlife

371
00:57:05,930 --> 00:57:09,570
in today's changing ocean.

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00:57:18,610 --> 00:57:22,930
Next time, a journey to Earth's
greatest wilderness -

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00:57:26,650 --> 00:57:30,250
deserts and grasslands...

374
00:57:35,770 --> 00:57:39,210
..where nature puts on
its most dramatic show.

375
00:57:42,090 --> 00:57:46,210
Habitat Explorer brings animals
and their habitats to life.

376
00:57:46,210 --> 00:57:49,850
Explore this free interactive
and make origami animals.

377
00:57:49,850 --> 00:57:53,930
Go to...

378
00:57:53,930 --> 00:57:56,330
And follow the links
to the Open University.

379
00:57:56,330 --> 00:57:58,490
Or to order a free printed version,

380
00:57:58,490 --> 00:58:02,250
visit the website
or call the numbers on the screen.