Original subtitles

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The eternal underwater dance of predator and prey

is as hypnotic as it is horrific,

but one thing's for certain,

in the water,

you don't have to be big to be an effective predator.

That said, being big certainly doesn't hurt.

These are water warriors.

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Sharks.

They are some of the most notorious hunters

in the history of the planet.

They are predatory works of art,

400 million years in the making.

Their lethal reputation strikes fear

deep into the hearts of beachgoers.

Even though the odds of getting attacked by one

are extraordinarily low.

Statistically,

you're more likely to be killed by a vending machine

than a shark.

But humans are the exception.

For prey in the sea, the nightmare is real.

Sharks are actually the perfect predator

in the marine ecosystem.

Sharks have a lot of things going for them,

they've got speed, they've got perfect senses.

So, most sharks have excellent vision,

we think that most sharks can see in color,

they certainly see in high contrast,

they've excellent sense of smell.

The first thing that they're gonna probably key-in on

is sound and vibration

that travels farther, it travels faster.

Once they get into the immediate area

they're then looking for the smell, they pick that up.

The cool thing with sharks is they've got two nostrils.

If they smell blood over here, they go that way,

if they smell blood over here, they go that way.

Razor-sharp senses are a huge part of their arsenal,

but sharks have a sixth sense,

and it pushes their hunting prowess

into the realm of the supernatural.

All living things give off a very faint electric charge,

and sharks use their gel-filled pores

called Ampullae of Lorenzini to pick up electric current.

These are pores on every

snout of every single shark species.

When hunting, at the moment of attack,

great white sharks roll their eyes

back into their sockets to protect them.

They're blind in that moment,

they're using that network of pores

to then determine what to bite,

because they're getting that electric cue.

And that whole network of senses

makes them truly the perfect predator.

After the shark locks onto its target,

speed and brute strength take over.

Some species can strike at speeds of up to

55 miles per hour.

Six or seven rows of serrated teeth

tear flesh and break bones,

leaving their prey either dead or disabled.

And the wide diversity of sharks

means that there are plenty of different things on the menu.

They filled all niches of the marine ecosystem,

some eat small little shrimp crawling around the bottom,

some eat large marine mammals by zipping through the water

at extreme speeds,

being able to takedown animals with serrated teeth.

The two biggest species of sharks,

the basking shark and the whale shark

are actually filter feeders.

So rather than just kinda spending

all this time and energy

hunting and looking for that sole meal

they're constantly feeding.

They flare their gills open,

they have gill rakers on their gills

that actually trap that krill

and then they're able to get that off of their gills

and use it for nutrition.

No matter what the size of prey,

a shark's instinct to find food and thrive is undeniable.

For sand tiger sharks,

the killer instinct kicks in before they're even born.

They have intrauterine cannibalism,

the pups develop inside the mom's uterus,

they have eggs that hatch out.

And kind of the first shark to really hatch out,

they start feeding on all their brothers and sisters,

and then, one shark is born from each uterus.

By the time they've been born,

they've eaten 50 to 100 of its siblings.

Mastering your craft before birth

is yet another survival advantage

of this ancient lineage

and another reason sharks have been on the planet

for hundreds of millions of years.

They kill from the day they're born

until the day they die.

They're immaculate specimens of predatory power.

Apex predators in every way imaginable.

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The ocean, it makes up about 71% of the Earth's surface,

and contains 97% of the water on the planet,

but 95% of it is still unexplored.

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Below the surface

are some of nature's most stunning works of art,

fish shoals.

Millions of fish harmonized and moving in unison

are a beautiful and mysterious sight.

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If you come upon a fish shoal,

what you'll find is a group of fishes

that are typically moving in the same direction,

and so in that way,

the shoal looks like a co-ordinated whole organism,

as opposed to many individuals that behave differently.

So there's synchrony

amongst individuals moving in the group.

It's a mesmerizing display and that's exactly the point.

The ocean is a dangerous place,

to defend themselves and survive,

fish find strength in numbers.

Among all fish,

about 80% of families have members that join shoals,

and they group together for many different reasons.

The main selective pressure in nature

for grouping or shoaling is from predators.

So, individuals then will form a group

to reduce their individual risk of being caught by predators.

A predator can easily home in on a single lonely fish,

so as a group,

fish increase their rate of survival

by diluting the possibility of being the chosen one.

Shoals can be two fish or they can be millions,

but the bigger the shoal the better.

A shoal also experiences an increased ability

to problem solve.

We now know that animals that live in groups

including fish,

can have increased or enhanced accuracy and precisions

of decision making.

In other words, which area to explore

and which orientation when you're migrating

are all improved when you join a group,

and also, improvements increase with group size.

And shoals not only look like a single organism,

they act like one too.

Split second decisions made by the vanguard

shoot through the shoal like lightning

in a phenomenon called "swarm intelligence".

Swarm intelligence is where the movement of a group

in one direction or speed

is dictated by first the movement of a few individuals

the predictive directions that is so called leaders.

And then, once you have a sufficient numbers of followers

reaching a certain threshold number

then the entire group will move in that direction.

It doesn't mean that the move is intelligent per se,

but that there is collective decision making.

Grouping together also increases a fish's success

in finding a mate.

With plenty of fish around them,

they don't need to search the sea for a partner.

Another reason fish gather is to find food.

Food sources in nature are not evenly distributed,

and so, individuals and--

that form members of shoals can find food faster,

because there have many eyes looking for food.

But when fish find food together,

they have to share that food

and this increases competition for resources.

Some species have been known to form smaller shoals

when food is near,

and larger ones in the presence of predators.

Shoals come in all shapes, sizes, and colors.

The colors have been known to contribute

to a phenomenon called the confusion effect.

When all members of one shoal look similar

predators can experience perceptual confusion,

slowing down their attack

and giving fish the time to get away.

Yet, fish are constantly changing shoals.

Joining the right shoal is critical,

a fish must blend in with the rest of their shoal mates,

joining the wrong shoal

could have unfortunate consequences.

But studies show

that they're excellent at choosing shoal mates

with similar traits to themselves.

What I found most fascinating about fish shoal

is the range or diversity of group sizes that you find

and the types of species that do shoals,

ranging from very small fishes to very large fishes.

And they're not only found in the deep blue sea.

You can find fish shoals in all kinds of aquatic habitats

ranging from small ponds that you might find in your backyard

to small rivers and lakes,

and up to, of course, the open ocean.

So there's a huge diversity of ecological functions

of fish shoals that we know about.

Ocean predators are highly evolved

and shoals offer a creative defense,

because whatever your size, shape or color,

there is strength in numbers.

Fish shoals are a truly captivating example

of survival in the sea.

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They look like something from outer space;

they're born with three hearts, two for their gills

and one for the rest of their bodies.

Cuttlefish,

unlike humans and all vertebrates on Earth,

have no hemoglobin in their blood cells.

Instead, they're filled with copper-based protein,

meaning their blood is green like a movie alien.

As strange as they look,

cuttlefish are also the oceans' sneakiest predator,

a truly gifted and sometimes a deadly imposter.

Their very name is a decoy.

Cuttlefish are not really fish at all,

they're molluscs like the octopus and the squid.

They belong to a family of cephalopods

that's been around

for hundreds of millions of years.

And at that time, they've learned a thing or two

about avoiding been eaten by arch enemies,

mainly dolphins, sharks, and seals.

For one thing, their eyes are highly developed

among the most developed within the invertebrates.

But, when trouble comes a knockin',

it's not just their eyes that can save their skin,

it's also their built-in jet packs.

They have jet propulsion.

So, they can suck in water in their mantle cavity--

This is a cavity inside their body

and they can push this water out the back.

Like squeezing a bubble, it moves forward

with the water squirting backwards.

Their jet engine escape comes with a neat trick

they share with their cousins, the octopus.

Black ink.

So they burst forward through jet propulsion,

and they leave this sort of cloud of black ink behind them

to confuse the predator that might be chasing them.

Their greatest trick of all however,

is their incredible ability to seemingly vanish like a ghost.

Cuttlefish are the chameleons of the sea,

their highly-developed nervous system

allows them to change color in almost the blink of an eye.

The speed of change is so spectacular,

no other animal in the ocean can be equal to cuttlefish.

What allows them to change color

is what happens to millions of little cells below their skin

called chromatophores.

And these chromatophores are rapidly reacting

to tiny, tiny muscle contractions around them

and these contractions or extension

will change the density of the color.

Their light-reflecting pigment cells can combine

to create hundreds of colors.

So, as it goes from one micro habitat to the next

it can change subtleties of its pattern.

So, in some circumstances it can accurately background match.

Cuttlefish can also match textures

and even patterns from its background

to create what is known as disruptive coloration.

Disruptive coloration is the ability to trick

the eye of the predator.

So, it's where you can have high contrast, edge colorations

that intersect the boundary.

And this breaks up the shape and edges of an animal.

Using their flexible arms

along with shifting colors and patterns,

the cuttlefish can pose as a plant,

a sandy rock or a scary fish, but that's not all.

Not only can cuttlefish adapt to conceal themselves

from their predators,

they also use their rapid-changing of skin color

to communicate between one and another.

Because cuttlefish aren't tricked

by one another's camouflage.

This visual communication allows them

to pass on secret warnings amongst themselves

without the predator having a clue.

But cuttlefish aren't always in defense mode...

...like all cephalopods they are predators.

Always on the lookout for crabs, fish, and small shrimp,

cuttlefish have perfect camouflage

and sneak up on their prey using their powerful arms,

and pair of tentacles tipped with suckers,

and mashing teeth to kill.

These arms are powerful, thanks to strong muscles,

also with the suckers,

which are very powerful to hold on to a clam

or a prey of some sort.

And then, they bring it to the mouth,

and they will inject the poison.

The poison they inject is neurotoxic

and comes from their saliva.

The mouth of a cuttlefish isn't technically a mouth;

it's a hard crushing beak like that of a parrot.

Whatever you wanna call it, the result isn't very pretty.

Among all invertebrates,

cuttlefish are considered some of the most intelligent

with a strong ability to learn and adapt.

It's that intelligence and that knowledge

that has kept this fascinating lineage alive on this planet

for hundreds of millions of years.

Crocodiles.

With that sly smile they lurk with patience,

waiting for some unfortunate prey to wander by.

And then,

a set of powerful traits of these creatures

skillfully capture their dinner.

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Crocodiles are amphibious,

which means they live both in water and on land.

They're frighteningly quick swimmers.

On land, however, crocodiles are generally pretty slow.

They sort of bumble about with these limbs

that are not very articulateable

and so, they really wouldn't do very well

in the long distance chases in the terrestrial environment,

which is where most of their preferred prey are found.

So, their better strategy is really just to hang back

on the edge of water,

wait for that prey to get close enough,

and to pounce on them.

And the water is where the crocodile truly shines.

This is where the deadly predator hunts for fish,

molluscs, birds

or anything else that unwisely happens to step into

its watery lair.

Crocodiles vary in size

from less than 5 feet to almost 22 feet

and weigh more than 2,000 pounds.

Regardless of size,

all crocodiles have one common advantage as hunters,

they are amazing swimmers.

The power and thrust for their swimming

comes mostly from that undulating tail,

which is very long and very muscular,

giving them the ability to sprint at great distances

and speeds underwater.

Using their powerful tail for propulsion,

some species can reach speeds of more than 15 miles an hour.

To help it underwater,

the crocodile has developed a nostril opening

with a membranous flap that shuts tight when it dives,

keeping the water out.

Another flap closes off the mouth cavity,

so it can breathe even when the mouth is open.

What makes the crocodile such a skillful hunter

is its innate ability to sneak up on its prey.

Their eyes are on the top of their head,

the ears are on the top of their head,

the nose on the top of their head,

in a perfectly straight line.

So no matter how big they are,

when they're laying in the water,

that's all you see sticking out.

But not all crocs are content with just eating fish

and molluscs.

For those, like the Nile crocodile,

their large bellies require much bigger game,

like wildebeest, deer, and even lions.

To be successful with these enormous animals,

crocodiles rely in their special sense organs.

A crocodile's sixth sense.

Around the nose of the crocodile,

they have little nerve endings

that tell them when something's touching or breaking

the surface tension of the water.

And as soon as that happens,

they'll then explode out of the water,

lunging out to try and grab whatever they can.

And there would be an unsuspected prey item,

like a zebra or wildebeest

or whatever it is,

they'll grab it and pull it straight into the water.

Whether sneaking up in ambush, or chasing down its prey,

the crocodile's weapon of choice are its jaws.

They can apply as much as 5,000 pounds of pressure.

That's six times stronger

than the bite of the notorious great white shark.

Because their jaws are not very articulateable,

meaning that they can open and close,

but they don't really move around in any other plane.

The only way for them to able

to get pieces off of a larger animal

are to tear it off by thrashing their body about.

To protect their eyes during these violent maneuvers,

the croc has a third eyelid known as a nictitating membrane.

In addition, the skull itself offers protection.

When they close their eyes,

the bony plates of the eyes will not only protect the eye,

but the eyes will even drop down into a socket,

which will protect them even further from damaging the eyes.

A lesser known aspect of crocodiles

is that they are very smart and cunning.

A croc will sometimes work with others

in what is known as co-operative hunting.

One co-ordinated strategy

is for several crocs to wait in line

as prey like the wildebeest cross the river

waiting to ambush the small or injured,

whoever happens to cross their path.

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Crocodiles have roamed the Earth for roughly 200 million years,

their specialized hunting skills have allowed them to outlive

even the mightiest dinosaur.

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From powerful sharks,

to mysterious and beautiful fish shoals,

the underwater dynamic between predator and prey continues.

Evolution is on display in these clever creatures

that are using all their skills to survive.

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