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[David Attenborough] Just 50 years ago,
we finally ventured to the moon.
For the very first time, we looked back at our own planet.
Since then, the human population has more than doubled.
This series will celebrate the natural wonders that remain
and reveal what we must preserve
to ensure people and nature thrive.
Immense shoals of fish throng our shallow seas.
These are anchovies.
Small fish, in turn, sustain bigger ones.
Hunters, such as giant trevally...
and mobula rays.
When hunters such as these work together, they become extremely efficient.
The rich coastal seas are the fishing grounds of our planet
and can provide an abundance of food for wildlife and humanity.
The seas fringing land make up less than a tenth of the world's oceans,
yet, astonishingly, 90 percent of all marine creatures
live in these coastal waters.
This superabundance is due to the fact that the seafloor here
is within reach of sunlight.
Everglades National Park in southern Florida.
Fields of seagrass carpet the shallow tropical waters.
Like savannas on land,
these lush marine meadows support a great variety of animal life.
Stingrays search for prey hiding in the seagrass.
The Everglades are also the hunting grounds of the coasts' most ingenious fishermen.
[dolphins clicking]
Bottlenose dolphins.
They search for food using echolocation, a type of sonar.
[dolphins clicking]
Ahead of them, a shoal of mullet.
These particular dolphins
have developed their own special way of catching their prey.
They carefully herd the fish into just the right place.
Then one dolphin stirs up a ring of mud that encircles the shoal.
The fish panic and take to the air.
Most escape.
Catching flying fish isn't easy.
But the dolphins move on and take another helping.
People aren't allowed to fish commercially within the national park,
so there's plenty for the dolphins.
Only from the air can we really appreciate the industry of these master fishermen.
The shallow seas are vitally important in the fight against climate change.
Seagrass absorb 35 times as much carbon dioxide
as the same area of rainforest,
and that reduces the damage caused by the recent warming of our seas.
Mangroves often border the seagrass meadows.
These remarkable trees are the only ones that can cope
with the varying saltiness of coastal waters.
They not only protect our coasts from the destructive forces of hurricanes
but also, like seagrass, capture carbon dioxide.
Their tangled roots create safe nurseries for young fish,
which will eventually leave the mangroves
and make their homes in the tropical seas' most magical wonderlands,
coral reefs.
These reefs cover less than one percent of the seafloor,
yet they are home to a quarter of all marine species.
None of these creatures would be here were it not for the coral.
Corals create the structures that provide food and shelter,
on which the entire community depends.
Every resident has a role to play in maintaining the health of the reef.
Unfortunately, few reefs are as pristine as they once were,
and most are now missing
one extremely important member of the community.
Sharks.
Relentless overfishing has reduced shark populations around the world
by over 90 percent.
Today they only thrive in anything like their former numbers
on the very remotest of reefs.
French Polynesia, in the middle of the Pacific Ocean.
Here, at least, sharks are fully protected.
By day, gray reef sharks hang in the current.
They let little wrasse pick their teeth clean
in readiness for the night's hunt ahead.
These sharks prefer to hunt in darkness,
when their acute senses give them an advantage over their prey.
Nightfall.
Time for small fish to take refuge within the nooks and crannies of the reef,
beyond the reach of the gray reef sharks.
The sharks can detect the slightest movement.
Breaking cover is dangerous.
Stay motionless and the sharks may not detect you.
A little fish may outmaneuver a single shark,
but with so many hunters there is little chance of escape.
Sheltering within the coral branches is usually the safest option,
but the arrival of a second hunter changes everything.
Whitetip reef sharks.
Slender and more agile,
the whitetips can get into hiding places other hunters can't reach.
Those that are not caught by the whitetips
are flushed out to the waiting gray reef sharks.
With both kinds of sharks hunting in partnership,
there is little respite, even within the reef.
More and more sharks arrive, attracted by the commotion.
Such numbers of sharks were once common on reefs around the world.
And while so many predators may seem damaging,
sharks, in fact, assist in maintaining the health of the reef.
They help to keep a balance in the fish community
by hunting the predators that feed on small grazing fish.
The grazers, in their turn,
keep the corals free of seaweeds and parasites
that would otherwise overgrow the reef.
A balanced community, with sharks as top predators,
gives a coral reef much greater resilience in the face of damage and disaster.
But today, even healthy coral reefs are facing a greater threat.
With climate change, our seas are warming.
Microscopic plants that live within the tissues of the corals
give them both their color and most of their nourishment.
But if seas temperatures rise by just a degree or two,
the corals expel their plant partners. So they lose their main source of food...
and turn white.
Here, on Australia's Great Barrier Reef, unusually warm seas
have caused many of the reefs to bleach in this way.
It may look hauntingly beautiful,
but if temperatures remain high for a few weeks,
the corals will starve and eventually die.
The carbon dioxide that causes global warming
is also making the seas more acidic.
No reefs can survive both changes.
And without living corals,
many of the reef's residents will also perish.
During 2016 and 2017,
over a thousand kilometers of the Great Barrier Reef bleached.
Six months later,
and many of the corals are dead.
The community destroyed.
Worldwide, half of all shallow coral reefs have already died.
The rest could be gone over the next few decades.
Away from the tropics, in higher latitudes,
the seas are much cooler.
Storm-lashed waters bring essential nutrients to the surface.
The enriched water, combined with long summer days,
make these the most productive seas on the planet.
Fur seals thrive and even have time to ride the waves.
Spring off the coast of California
and fronds of golden kelp floating on the surface
hint at the riches hidden beneath.
A magnificent submarine forest.
These stands of giant kelp are as important to the oceans
as trees are to the land.
Like a rainforest,
the dense canopy provides food and shelter for an abundant community.
In the cool, rich seas, giant kelp can grow 50 meters high.
Air-filled floats lift the fronds towards the sunlit surface.
Nestling in this canopy,
a sea otter.
His thick fur keeps him warm in the chilly water.
Blowing air into it gives him extra insulation.
Sea otters have the densest fur of any animal,
and such a luxuriant coat requires a great deal of attention.
They need to eat a lot to keep warm
and consume up to a quarter of their body weight every day.
Sea urchins are a favorite food.
There's one.
And a second.
And then the otter is out of breath and must return to the surface.
An urchin looks like a rather prickly meal,
but if you can break the shell, there's a feast inside.
Sea otters are crucial to the health of the kelp forest
because they keep down the number of sea urchins.
The urchins graze on kelp,
munching through their tough stems.
Left unchecked, they spread across the seafloor like a plague.
Fortunately, the otters have a helper in the fight against these spiny grazers.
Sheephead wrasse.
They have powerful teeth
and can make short work of the smaller purple urchins.
The larger black urchins are more of a challenge,
especially for smaller wrasse.
Only the very largest sheephead can tackle them.
But it still has to get past those long spines.
The urchin has to be flipped over to expose its vulnerable underside.
Not easy when you have no hands.
Success at last.
And everybody benefits.
These fish and otters, living within marine protected areas,
keep the kelp grazers under control.
But just outside these sanctuaries, the urchins graze unchecked...
and fell the kelp forest.
All those that depend on the kelp have disappeared.
In California, kelp forests grow abundantly in protected areas
where the whole marine community can live without pressure from people.
Here, at least, sea otters can chill out Californian style.
[bird caws]
Three thousand kilometers further north, in Alaska,
spring arrives much later in the year.
After a cold, hard winter,
the first rays of the sun trigger a great annual event.
Immense shoals of herring rise up from the depths
and move into shallower waters.
They're gathering to breed.
But predators are waiting for them.
Steller's sea lions.
So intent on their mission, the herring make easy prey.
Sea lions drive the fish to the surface, within range of aerial hunters.
Bald eagles, normally solitary birds, have assembled in numbers for the feast.
In places, the herrings reach shore,
and there the eagles don't even need to take to the air.
Humpback whales.
[whale lows]
They have come all the way from the tropics,
hoping to get their first meal in months.
These whales have a remarkable way of collecting this seasonal bounty.
They work as a team.
The lead whale dives first...
and blows a curtain of bubbles to concentrate the fish.
[whale calling out]
A call synchronizes the attack.
[whale song increases in volume]
By cooperating in this way, each whale can eat a ton of fish a day.
Yet the herring are so abundant
that, in spite of the whales, most managed to reach the shallows.
And here they spawn.
The females lay their eggs on the seagrass.
The males follow, fertilizing the eggs with clouds of sperm.
Once, herring thrived here in an abundance we can barely imagine today.
They used to turn shorelines white with spawn,
right across the North Pacific from Japan to California.
With industrialized fishing techniques
it's all too easy to overexploit these breeding stocks.
This is one of the few places where a fishery still survives.
Pacific herring populations are greatly reduced.
A mere fraction of what they once were.
This sorry tale of unsustainable fishing
has been repeated time and again around the world.
Many of the world's fish stocks are now in serious decline.
A third of them have collapsed altogether.
In coastal seas,
jellyfish are taking over waters that were once dominated by fish.
Compass jellyfish have an ethereal beauty,
but they provide very little sustenance for other wildlife or us.
These immense swarms are becoming increasingly common.
A worrying sign of a serious imbalance in our shallow seas.
Unless we start to fish sustainably, our seas, once so bountiful,
will be filled with little more than vast swarms... of jellyfish.
But the future does not have to be like this.
On the Pacific coast of South America, we can see how the oceans can recover.
The Atacama, the world's driest desert.
Inland it's barely able to sustain life of any kind,
and yet the coast could not be more different.
For centuries, seabirds have gathered in millions on these desert shores.
But 50 years ago the great colonies disappeared
because we overfished the local waters.
Controls were introduced , and now the fish stocks are recovering.
So today, three million guanay cormorants assemble each year to raise their young.
[cawing]
Each morning the birds head out to sea.
The colonies are so vast they take over an hour to empty.
Joining the procession, Inca terns.
Peruvian boobies.
A great caravan of hunters, all searching for the same thing.
Anchovies.
These little fish are so abundant
that they support the greatest fishery on our planet.
Astonishingly, they can account for a tenth of all the fish
we harvest from our oceans every year.
Sea lions are first to find the shoals.
As fish are driven to the surface, they come within range of pelicans.
Cormorants dive to grab their share.
Boobies strike from heights of 20 meters.
They hit the water at a hundred kilometers an hour.
Today, the lives of five million cormorants and boobies
depend on the great shoals.
Yet, if we allow the anchovies to fully recover,
they could sustain the 25 million seabirds they once did.
It is a vivid reminder
of the astonishing riches our coastal seas can support.
And, when given the chance, they can recover surprisingly quickly.
The islands of Raja Ampat in Southeast Asia.
These seas were largely stripped of sharks and other large fish
by years of unregulated fishing.
This lagoon was once occupied by a shark fishing camp.
Now it's a nursery for baby sharks.
The seas around Misool were fully protected in 2007,
and the recovery has been miraculous.
Today there are 25 times more sharks than a decade ago.
Turtles that used to be hunted now peacefully graze on the seagrass.
Sharks are returning to local reefs,
helping to restore the balanced community,
giving them a greater resilience against the effects of coral bleaching.
Ocean-going manta rays.
Seven meters from wing tip to wing tip.
These endangered giants
spend most of their lives roaming the high seas.
But now they are returning to this sanctuary
to seek the attention of cleaner wrasse.
Misool is one of the few places on Earth where biodiversity is actually increasing.
Since protection, there are three times more fish
than just ten years ago.
Fishermen working nearby waters profit from the overspill.
They now catch more fish for less effort.
We have far too few marine sanctuaries,
and in many commercial fishing is still allowed.
We need to turn a third of all our coastal seas
into properly protected areas.
If we do that, our planet's fishing grounds would recover
and help sustain both humanity and the rest of the natural world.
Please visit ourplanet.com
to discover what we need to do now to restore our coastal seas.
♪ I can hear the whole world Singing together ♪ ♪ I can hear the whole world Say it's now or never ♪
♪ 'Cause it's not too late If we change our ways ♪
♪ And connect the dots to our problems ♪
♪ I can hear the whole world Say we're in this together ♪