Mexico 1 Deadly 60

'My name's Steve Backshall.'

Wo-o-oo!

'And this is my search for the Deadly 60.'

That's not just animals that are deadly to me...

but animals that are deadly in their own world.

'My crew and I are travelling the planet.'

Are you coming with me?!

'Every step of the way.'

'Deadly.'

'Deadly is in paradise.

'Mexico's Yucatan Peninsula.

'It's a miraculous place, lying between the Caribbean Sea

'and the Gulf of Mexico.

'Home to pristine jungles...

'seas alive with lethal fish you simply will not believe...

'and it's peppered with cave systems,

'some of which contain some spine-chilling predators.

'We're going to be going underwater,

'underground, and even doing both at once.

'But first up, it's a high-octane marine mission,

'and one of our toughest assignments yet.'

On Deadly 60, we do love a challenge, and the next animal

we're going looking for could be the most difficult,

the most challenging, we've ever tried.

Now, I know that might seem a little bit far-fetched

when I'm walking down a paradise beach just after dawn,

but this isn't where we're searching.

We're heading out there into the open ocean.

We're going in search of the fastest fish on Earth - the sailfish.

'Growing up to 3m long,

'with a distinctive spear-like upper jaw,

'these imposing undersea snipers are the speedsters of the deep.

'They feed on shoals of smaller fish,

'but gather in tight formation and move as one,

'in what's known as a baitball.

'The idea is to confuse predators and work together

'so that no single fish becomes an easy meal.

'The sailfish chase and herd the baitball,

'trying desperately to knock the fish off balance,

'whilst the small fish are doing everything they can to survive.

'So, to find the sailfish, first, we have to find a baitball.

'But as sailfish can obliterate a sardine shoal in minutes,

'we'll have to move fast.'

We have tried to film sailfish before,

in Mozambique in East Africa.

We spent three days out at sea and saw nothing at all.

This truly is one of the trickiest animals we could ever hope for,

and the reason for that is that they're what as known as pelagic.

It means that they're an open sea fish.

So, finding them at all is really, really hard.

All we've got to do is put in the hours.

We're just over an hour away from shore

and we're into prime sailfish-spotting habitat.

Now, really, it's just a question of spending as much time as we can,

just looking out and trying to spot these baitballs.

They could be anywhere, and we've got quite a swell,

making it really, really difficult to spot anything.

These baitballs don't last very long.

We're going to only have a few minutes to get into the water

and stand any chance of spotting this incredible fish

that we've come halfway round the world to find.

'But the baitball itself is going to be submerged. So, out of sight.

'Well, luckily, we're not the only ones in search of a sardine feast.

'There are airborne huntsmen scouring the skies.

'We just need to follow them.'

BIRDS SQUAWK

These classic, formidable silhouettes above me

are frigate birds. They're, themselves, fabulous predators

and really, really imposing animals,

but these are the sign that we're looking out for,

as they're going to be diving down, spotting the baitballs from above.

They have far, far better eyes

and a far broader range of vision than we could ever hope for.

So, we're going to be watching the skies, watching these birds,

and hopefully, they will find the baitballs and the sailfish for us.

'What we need to look for

'is a change in behaviour in the frigate birds,

'as they dive to the surface in a frenzy of activity.

'They'll be our early warning system.'

Oh-h-h!

'It wasn't long before we got our first glimpses,

'and encountered some other people on the hunt for sailfish.'

We're not the only people out here today looking for big fish.

There's lots of game fishing boats out.

There's one in front of us right now,

and it looks like they might have snagged something of a good size.

This is obviously a good sign for us.

It means that there are sailfish out there,

although personally I'd always rather hunt an animal with a camera

than with a hook.

'Sailfish can breach clear of the water when chasing prey,

'seeking to remove parasites from their bodies,

'or trying to evade a fisherman's hook.

'It's a tantalising glimpse of their acrobatic abilities.

'We'd been out on the choppy seas all day and about to head for home,

'when something on the horizon caught my eye.'

OK, we've just got exactly the sign that we've been looking out for.

There are frigate birds.

They're diving down, which looks like there could be a baitball.

So, time is now absolutely critical. Things are really going to kick off.

We've got to get over there and in the water as soon as possible.

OK, guys, let's hit it!

'The sardines are going to be frantically fleeing

'from the birds and the predators beneath.

'Keeping up with them is going to be near impossible.'

This really is a once-in-a-lifetime opportunity.

There's obviously an enormous shoal of fish there

to have all of these birds active here.

Just got to get in right, because they're so fast,

once they decide to take off, you have no chance of following them.

Right here. Right on the bottom.

-Camera, camera, camera!

-Go, go, go, right there!

Right here, right in front of you!

'I was hoping to see one sailfish, and at a distance.

'Instead, there's a menacing shoal of dark shapes.

'A pack of undersea wolves pursuing the sardines with murderous intent.

'Their hydrodynamic shape makes them look like dark torpedoes,

'and even casually cruising,

'they disappear into the distance in seconds.'

This is absolutely unbelievable.

There must be 40 sailfish, maybe more.

Just an enormous shoal of them with genuine intent.

I haven't even actually seen the baitfish yet, and it was just

the merest of glances before they disappeared off into the blue.

If we can just get close enough, this is going to be unbelievable.

-MUFFLED:

-Over there, look over there! Can you see them?

-Can you see them feeding?!

-Go, go, go, go, go!

'The sailfish have split the baitball,

'isolating a smaller group.

'This lot are as good as gone.'

'The sailfish glide past like shadows.

'They're deceptively big and can weigh more than me,

'but their acceleration

'would put any speedboat or sports car to shame.

'Their sickle-shaped tails power them through the water.

'They use their distinctive sail-like dorsal fins

'to herd the small fish.

'The sardines frantically flock together,

'but they're battling the fastest force in the seas.

'The sailfish lash around with their rapier upper mandible,

'separating and stunning the sardines.

'It's utterly remorseless.'

I don't believe it. I just don't believe it.

There was clouds of the fastest predator in the sea

just circling around us, circling around us,

coming up and hammering the small fish at the surface.

We've got to get back in as quickly as we can.

They're moving off in this direction.

There are so many sailfish, you can see the dorsal fins

actually cutting through the surface, almost like sharks.

Look! Thrashing through the water. Definitely time to get in.

There's the sardines! The sardines are here.

'Under ceaseless attack,

'the bait-ball is diminishing minute by minute.

'The relentless onslaught continues from above,

'with the swooping frigates.

'Everywhere the hapless fish turn, they're torn to shreds.

'The sardines may be more manoeuvrable,

'but in explosive bursts of straight speed, the sailfish has no equal.

'The bill slices side to side, disorientating the smaller fish,

'leaving them as isolated, easy targets.

'The sardines will take any shelter on offer - even me!

'I'm in serious danger of getting skewered.

'Once the bait-ball is diminished, the sailfish won't stop

'until every last fish is gone.'

'The sole memory of this dazzling display

'are snowflakes of shimmering scales.'

That was one of the most extraordinary things

I've ever seen, in a lifetime looking at wildlife.

I've just been absolutely surrounded by one of the most

extraordinary predators on earth that is in its way,

every bit as spectacular

as seeing lions tear apart a gazelle in Africa.

Within minutes, a huge shoal had been reduced to a few fish.

There's no doubt in my mind that this is one of the most

extraordinary animals that's ever been on the Deadly 60.

The fastest fish in the sea - the sailfish. Definitely deadly.

This swimming speedster can reach 68mph.

A flick of their scimitar-shaped tail brings top speed

in a millisecond. With their spear-like upper jaw,

they stun their prey before gulping them down.

It's a true Deadly icon.

Scintillating sailfish...

# Deadly! #

We're journeying even further from the Yucatan Peninsular mainland

to the island of Cozumel - not exactly Caribbean weather,

but it's not going to be raining underwater and that's where

we're heading, in search of some of the finest diving in Mexico.

So below us now is a pristine coral reef

at around about 20 metres of water.

One thing about scuba-diving is that really,

you have no idea what you'll find.

You cannot predict it, but there's so many things

that live on reefs that we could easily put onto our list.

My hopes are fairly high - fingers crossed.

So, after final preparations, with safety checks complete,

we entered the underwater wonderland,

in search of something deadly, but different, to add to the list.

Well, this is really impressive.

HE INHALES LOUDLY

Exactly what you'd hope for from a Caribbean reef.

The barrier reef that runs along the east coast of Mexico

and down through Belize is the second-longest in the world

after Australia's Great Barrier Reef.

And it is truly magnificent.

There is so much life here, so much biodiversity.

And the colours are just exquisite.

'And it wasn't long before we stumbled upon our first

'killer candidate.'

Just sleeping underneath this overhang here is a nurse shark.

They're very unusual sharks, really.

Quite often, people will say that a shark needs to be swimming,

it needs to be up in the water column

in order to drive water over its gills,

but that's not always the case.

These sharks have small holes behind their eyes called spiracles

that they can breathe through,

which enables them to lie like this, just chilling out in the daytime.

At night though, they go out on the reef to hunt.

Looking at the front of the nose,

there are two sensory barbels that hang down.

They use these to taste crustaceans

and other animals that are down in the sand on the seabed.

It uses those to sense its prey.

They're really rather wonderful.

I have a bit of a soft spot for nurse sharks.

'Definitely a good start, but we've had lots of sharks on the list.

'This time, I'd like to find something more unusual.'

Some of the largest fish on the reef are groupers.

This is a black grouper.

Although it's actually changed colour quite dramatically

from where it was originally - it's now gone much, much lighter.

It has a huge lips,

a big old mouth

and they are predatory.

This particular species feeds on smaller fish.

Nice.

'Another possible contender,

'but I think we can find something with a bit more bite.'

Oh, yes.

Lurking underneath this crevice is truly a worthy contender

for my Deadly 60 list.

It's a green Moray eel.

It's one of the largest species of Moray eel and this one here

looks like he's probably as fat around as one of my legs.

He's huge! Probably over two metres long

and it's an animal that has quite a nasty reputation

amongst divers and when you look inside their mouth, you can see why.

They've got really quite an impressive set of teeth on them.

During the daytime, they do tend to hide out in crevices like this.

Occasionally, they will go out on the reef to hunt, but normally,

they just sit here waiting in ambush for something to come by.

One of the things though that actually sets Morays apart

is their senses.

The eyes are quite milky, not tremendously useful,

but they have an incredible sense of smell.

There are four nostrils.

Two small, recessed ones just in front of the eyes

and then at the end of the nose are two nostrils on tubes,

and those are incredibly good

at just plucking the tiniest scents out of the water.

Then it will snap out and grab a hold of

usually things like fish, sometimes crabs and other crustaceans as well.

The green Moray - he's a menacing monster

and I think has to go on my list.

With huge, muscular bodies

that can grow up to 2.5 metres long

and gaping jaws that are rammed with rows of pointy teeth,

these stealthy ambush predators

sniff out their prey and snatch it as it passes.

Moray eel...

# Deadly! #

'For the final leg of our Mexican mission, we're heading underground.

'The Yucatan is peppered with caverns,

'some of which are filled with sinister predators.

'Others offer some of the most dramatic spectacles imaginable.

'Sunken wonderlands filled with water so clear,

'it feels like floating in air.

'These caves were formed when sea and water levels were much lower,

'but were later flooded with subterranean rivers.

'They're called cenotes

'and are one of the wonders of the natural world.'

This is just unbelievable.

All of these formations - they're like thrones and chandeliers.

It's just some curious subterranean sunken kingdom,

indescribably beautiful.

'And amongst all this splendour, there is some wildlife.'

Catfish are remarkably well adapted for living in these cave systems.

Those long whiskers tapping around.

They're called barbels and they're extremely sensitive.

They're covered with receptors for tastes and smells

and also thousands of very, very sensitive nerve endings.

This animal is sensing its whole environment through those whiskers,

so even in total darkness, it still knows what's going on.

'Deeper in the cave, in a world that hasn't seen sunlight

'in millions of years, it was as if we'd swum into a strange dream.'

The water here has taken on a very, very curious consistency.

It's because we've dropped from clear, freshwater into salty water.

It's called a halocline - an area where salty water, which is heavy,

sits underneath the lighter freshwater.

Look at how the whole water has gone...all weird!

Very, very curious.

'In the next chamber, we found another animal hanging out.'

Some of these caves are the perfect place

for bats to make their day roosts.

They're really safe from predators in here,

but there's one cave system on the Yucatan Peninsula

that I know of where the predators have learnt exactly

where the bats live and they're nothing like so safe.

That's where we're headed to next.

This is our cave.

Somewhere inside there is a massive colony of bats

and the predators that are hunting for them...

Well, for a clue, I've got my snake stick with me.

This cave is home to dazzling,

dangling hunters that have to be seen to be believed.

The local people call this cave "La Cueva de las Serpientes Colgantes",

or something like that - my Mexican isn't particularly good.

But what it means is, "the cave of the hanging serpents".

Which bodes well, I guess.

For lots of people, that should be their living nightmare,

but for me, it's a very exciting thought.

'The snakes are here because they eat the bats,

'but we're unlikely to see them hunting just yet.'

One thing about cave that makes them

really, really good for wildlife is that they're constant -

they have constant temperature, the environment inside here tends

to be very similar, day-in, day-out and the other thing is

the animals that live here tend to be constant in their behaviour, too.

Every single day, they'll be pouring out to the outside to feed.

The fact that they do that like clockwork means that

predators know exactly what they're going to do.

Where I'm expecting to find the snakes is at areas

that are natural bottlenecks, where the bats are going to have to

pass through as they're heading out to feed.

'The bats won't start properly emerging until nightfall,

'so in the meantime,

'I'd like to show you a snake before it's in full-on hunt mode.

'And here's one, lazing around before the deluge begins.'

So... This is the snake that we've come here to find.

Isn't it beautiful?

It's a Mexican night snake

and gorgeous, gorgeous colours

running down the length of its body.

And it's chosen to live in this cave

because of the amount of food that's around here.

Now, it might seem incredible that a snake of this size could

catch something as big as a bat.

I mean, it only has a very tiny head,

but it does have the ability to stretch its jaws

and take in prey that's many, many times larger than its own head.

Look at the size of the eyes.

They're huge in comparison to most snakes of this size.

So it's pretty good at seeing in near-total darkness.

But it's also exceptional at striking out at animals

and catching them on the wing.

The underside of the body is concave - acts almost like one big,

long suction cup and it also grips with these two portions

of the underside of the body,

plus those scales there give it extra grip.

It makes them absolutely fantastic climbers - let's see it at work.

'The first few bats are taking flight,

'but soon these caverns will be thronged with flapping wings.

'We need to find one of those bottlenecks

'where the snakes are waiting to feed.'

The main area that the bats are emerging from is a cave tunnel

just here, to the side of where I'm standing now.

If we go in there with all of our bright lights, then the snakes

will simply call back into their holes, so the best thing for me

to do is go in on my own,

using this infrared camera with this light.

Hopefully, the snakes won't pick that up

and they'll be able to go about their business of hunting and

I should stand at least a chance of seeing one catching a bat.

So you guys wait out here, yeah? All right.

See you soon!

'Infrared light has a different wavelength to visible light,

'which means that animals can't see it.

'But I can't see it, either, so I'm crawling around in the pitch

'darkness and my only view is through the camera.'

OK,

I've got a snake in front of me, in absolutely perfect position

and posture, so I'm just going to hang out now

and hope to catch it striking on camera.

It's pulled itself back up into the rocks.

It probably heard me and is feeling a bit intimidated.

I might just have to push on a little bit further into the cave.

'Every night, the bats have to run the gauntlet past these

'hanging huntsmen to get out into the forests and feed.

'There are tens of thousands of bats

'and these must be some of the best-fed snakes on earth.'

There's a snake. There's one right there.

'The night snakes can get over a metre and a half in length

'and this one doesn't look far off.'

This is incredible. He's just hanging down,

striking out into the air.

And it seems like it's the vibrations

that are caused by the bats as they fly past that he's centring on.

It's not so much other cues, as just the pure movement of the bats.

He's got one. It's got one right now.

I didn't quite get the strike on camera, but it's so fast.

It's wrapping coils of the body around the bat and now,

what it's going to do is squeeze.

Science shows that constricting snakes can actually sense

the heartbeat of their prey, so they can tell

if the animal is still alive, so as soon as this bat is completely dead,

it will start to swallow it and that's when I can think about

calling in the camera crew.

It's a phenomenal sight. These bats are leaving in enormous numbers.

There are tens of thousands of bats flying through here

and they're travelling so quickly,

but this snake, in total pitch darkness, still has

the wherewithal, the speed, to strike out at

and catch these bats in flight.

It's just a remarkable feeding strategy.

Johnny? Johnny!

'Now the night snake is swallowing the bat,

'it shouldn't be put off by our lights.'

You can see it's manoeuvred the bat so that it's headfirst

and it's starting to work it down its throat.

It's an extraordinary achievement,

just purely to get this bat down its throat.

Look at that - it's pretty grotesque, really.

It's eating a bat that's many times larger than its own head.

You can see it's quite a fat-bodied snake.

I mean, once it's got this one down into its stomach,

it might easily feed again,

possibly even twice more tonight.

They are absolutely extraordinary snakes.

I'm looking down into the tiny,

needle-sharp, backwards-pointing teeth

that are delivering that bat back into its gullet.

You can see, it's having quite a struggle getting the animal down.

You can see the exact shape of the bat running right down

the back of its throat.

The bat-munching Mexican night snake,

quick enough in strike to catch the fastest-flying mammals

on the wing. Definitely deadly!

With superb climbing skills,

they hang from the cave walls.

Hunting in total darkness,

they pick up tiny vibrations from their prey, catching bats

that are much bigger than their heads and swallowing them whole.

These splendid, stealthy serpents are going on my list.

# Deadly! #

'Join me next time as I continue my search for the Deadly 60.'

This is one of the greatest spectacles I have ever witnessed.

Subtitles by Red Bee Media Ltd

# Deadly! #