Great Blue Wild

This is the sardine run.

The world's largest marine migration.

It's like the greatest showon earth.

It's madness.

It's absolute chaos.

There's so much energy and so much life.

Whooo, look at that ball!

This mass of fish on the coast of South Africa,

draws the ocean's most feared predators.

It also draws one of its mostdocile, the manta ray,

an unlikely guest.

As I'm jumping into thesewaters that are full of sharks,

my mind's racing because I don't understand why mantas

would be in this hostile environment to begin with.

What is it that they're comingdown here to do?

Manta researcher Andrea Marshall and her team of specialists dive

into the sardine run to unlock this mystery

on a first ever manta ray expedition

to South Africa's wild coast.

The wild coast of South Africa, stretches for 170 miles.

Here, the waters of the Indianand the Atlantic converge,

forcing powerful waves towardsthe shoreline.

Its savage winds and heavy seashave claimed many ships.

There's a reason why they call this the wild coast'.

It's incredibly hostile: really cold waters,

incredibly turbulent.

I've been put into all kinds ofdifferent environments but

this is by far the hardest conditions

that I've ever worked in.

Andrea Marshall is one of the world's leading experts

on manta rays.

Oceanic Mantas are among the world's largest fish.

Andrea's research isprimarily based in Mozambique

but today she's embarking onher first manta ray expedition

across the border to South Africa.

And it's one of her own mantarays that's brought her here.

The very first manta that I tagged made a beeline

down the coast from Mozambique to South Africa

and it begged the question

where is this manta going?'

And for the first time Irealized that they may not live

in Mozambique

where I've been studying them for the past 15 years.

Mantas inhabit tropical waters in every ocean

and are heavily fished for their gill rakers,

which are used in Chinese medicine.

Despite their size, little isknown about their movements,

which makes them hard to protect,

especially in international waters.

Andrea is hoping to prove thatthe mantas she studies

in Mozambique are migrating toSouth Africa.

She believes mantas may be attending the sardine run,

a mass fish spawning event onSouth Africa's wild coast.

But mantas eat plankton, notfish, so the question is: why?

I couldn't wait to make this sort of migration

of my own, to find out what ishappening down at the sardinerun.

Are there mantas there?

What are they doing along this coastline?

Andrea and her team travelnearly 900 miles south

from Tofo in Mozambique to Port St. Johns.

Known to divers as the heart ofthe sardine run.

Though the forces that drive theannual journey of the sardines

aren't completely understood, it's believed that the fish

abandon colder waters off the southern tip of Africa

and travel north in pursuit of more favorable conditions.

For much of the year, the warmAgulhas current sweeps

southwest, keeping temperaturestoo high for the sardines.

But in winter, a corridor of cooler water allows

the fish to comfortably move up the coast.

As the sardines move north, Andrea believes the mantas

in Mozambique are migrating south.

It's June, the start of winterin South Africa.

The cold water is beginning tomove up the coast,

bringing with it, the sardines.

Millions of them, in rippling masses,

that can stretch for more than nine miles.

It's a migration that rivals thejourney of the wildebeest

across the plains of the African savannah.

Along the way, strong currentspush plankton to the surface,

providing a steady source offood for the migrating sardines.

As the fish converge on thesurface, they make ideal targets

for hungry predators.

Super pods of dolphins, sharks, birds and whales.

So essentially all of thesepredators from all over SouthAfrica

descend upon this really narrowstretch of coastline.

Swimming through this swirlof sharp teeth

are giant oceanic manta rays.

With a wingspan of 22 feet,

they're as wide as a pickup truck is long.

But these passive filter feeders are easy targets

in an area teeming with top predators.

The giants are defenseless against sharks.

Manta rays rely solely on their speed,

and their flattened bodies for protection.

A bite to the manta's flat, large wings generally won't be fatal.

To kill a ray, a shark must through the central body

that contains its vital organs.

Manta rays are incredibly fastthrough the water.

And can hit top speeds of 20 miles an hour,

to escape predators.

Manta rays have no sharp teeth, no venom,

no defensive weapon to speak of.

Unlike their relatives, the stingrays,

which have a protective spine atthe base of their tail.

Mantas don't have a stinger to fend off attackers.

They're really quite vulnerable.

Why they would come all this wayand hang out in this area

when there's so many predators, we have no idea.

And that's the question that's driving us:

what are these manta rays doing off this coastline?

I've assembled a team of international scientists.

We've brought in Dr. FabriceJane all the way from Australia

who's a telemetry specialist on manta rays

and we're going to try and deploy the first tags

in South African history.

Andrea hopes her satellitetags and Fabrice's new cameratags

will provide some much needed answers.

If they can fit a manta ray with both tags,

they'll learn where the ray is going,

And get a first-ever look at what it's doing

when nobody's watching.

But first, they need to analyze the manta track

that's brought them here to the sardine run,

in the first place.

They hope that retracing the steps of this manta ray

will help them find others.

So for the first part of the track,

it spent quite a bit of time in front of Tofo

where you were based.

Wow it really did.

Eventually it decided totravel south and it went south

all along the coastline, fairlyclose to the shelf edge again

and it ended up

in South Africa and it ended up near Port St. Johns.

What are these animals doing down here?

It's freezing and there's a lot of sharks.

Yeah, I mean look, thecontinental shelf seems to be

right up close to the coastline.

That's quite interesting; theremay be some upwelling happening.

A lot of productivity being brought up to the shelf

near the coastline.

It may be food-related, but it may be related

to the sardine run as well.

You know a lot of food scrapsin the water and so on.

I mean dolphins and whalesand sharks all descending upon

this coastline, every year.

And so to have mantas here inthe mix is just so exciting.

I can't wait to get in the water.

I know, I can't wait to getin the water.

Tomorrow will be the first ofmany grueling days

of field work, to uncover why this manta ray migrated

to the sharkiest coastline on earth.

t's going to be a really challenging few weeks

because this is a really wild part of the world,

in fact it's probably the mostchallenging place

I've ever had to do research.

I've prepped my team.

I've told them that this is notgoing to be a walk in the park

but I'm actually excited to come out and do research

in places like this because it is a challenge.

Day one of the expedition,

and the team faces its first obstacle,

before they even make it out to sea.

The pounding waves of the wild coast limit

the launch of the boat to just one spot.

Andrea and her team must leavethrough Port St. John's

river mouth, and tackle incoming waves head on.

We're waking up at 4 or 5 o'clock in the morning,

and it's bitterly cold.

The launches are extreme.

We're launching through thesemassive waves.

So you get soaking wet.

I mean it is such an excitinglocation but obviously

it's not a very easy locationto do any research.

The team eventually clearsthe breakers.

But the hardest part, is yet to come.

You're freezing cold on theboat in this wind looking formantas.

You have to get in this freezing cold water

and you have to find it in visibility that sometimes

is less than a meter

and you know there are sharkseverywhere.

I knew from the outset that it was going to be

really difficult in-water conditions.

So I really wanted to give myself the best leg up

that we could possibly have.

And one of the most importanttools in our arsenal

is having aerial support.

The fact that my husband's apilot and we can fly the coast

and find the mantas from the airis a huge blessing for us.

My role at the sardine runis to fly in a plane

and to spot the animals from the air.

It's very difficult: harsh conditions, bad visibility,

big swell, everything.

So you can see way better from the air

than in the water itself.

Plankton blooms cloud the water,

creating the poor underwater visibility.

An aerial perspective allowsJanneman to spot disturbances

on the surface caused by swarming sardines,

and guide the divers to the action.