Original subtitles

(intense ringing music)

(gentle peaceful music)

- [Peter] Every year, a secluded bay

in Japan becomes a hive of shark activity.

Little is known about the elusive species movements outside

of these tranquil waters,

but here they thrive.

Their time in the bay is brief, but crucial.

The warm waters are the sharks only known breeding grounds.

To successfully bring in the next generation,

the mother sharks must use ingenious egg-laying methods.

The bay offers the perfect incubation conditions,

but these waters also harbor egg hunters

and are prone to extreme weather conditions.

For the developing sharks, survival is no guarantee.

(bright upbeat music)

(hyena laughing)

(lion roars)

(words whooshing)

(gentle peaceful music)

To the southeast of Japan's Shikoku Island

rests Cape Muroto.

Here, a warm current flows in from the Pacific Ocean

and attracts a wealth of marine wildlife.

(water splashing)

To the northeast of the jagged cape,

there is a tranquil bay.

Every year, the calm waters become a home

to a huge congregation of an elusive species of shark.

(gentle peaceful music continues)

For over 50 years, Dr. Nakaya

has been studying the annual visitors.

The sharks first began converging on the bay in May.

Coinciding with their arrival,

strange objects begin to litter the seabed.

They are the eggs of the shark visitors.

Made up of the same keratin protein as human nails and hair,

they reach around 10 centimeters in length.

Attached to each egg are string-like fibers.

(gentle peaceful music continues)

The mysterious sharks have been recorded

inhabiting warm waters between the Pacific

and Indian Oceans, but they are only known

to annually congregate in this secluded bay.

At five meters deep, the seabed is adorned with seaweed.

The aquatic garden is also full

of many different species of coral.

They come in an array of peculiar shapes,

and in some areas, reach up to three meters in size.

The bountiful seabed provides the perfect home

for many underwater residents.

Schooling fish thrive in the warm 20 degrees Celsius waters.

(gentle calm music)

The coral-rich seabed is now also the realm

of the bay's mysterious annual visitors,

the whitespotted bamboo shark.

Their slim and flat bodies

are perfect for life on the sea floor.

Many of the black striped and whitespotted sharks

are jostling for position amongst the bay's plentiful coral.

(bright lively music)

At ease in each other's company,

they peacefully congregate between rocks.

As sea floor specialists, the strange sharks can pull off

a maneuver that is difficult for most other sharks species,

reverse.

As bottom dwellers, they are able

to achieve backward movement by using their pectoral

and abdominal fins to propel themselves along the sea floor.

The highly adapted sharks are also armed

with sensitive whiskers to smell for food in the current.

(gentle peaceful music)

Equipped with small teeth, they swallow prey whole.

Behind their eyes, the sharks

have specialized holes called spiracles.

This unique feature is a necessity

for bottom dwelling sharks.

Located above the mouth,

spiracles allow the sharks to breathe in clean water

from above rather than potentially damaging sandy water

from the sea floor.

Both males and females have made the journey to the bay.

(gentle peaceful music continues)

Males can be identified by their telltale claspers

located under their abdominal fin.

During the day, both genders are relatively inactive.

Many of the bay's residents

wait until the night to come alive.

(bright lively music)

Under the cover of darkness,

Japanese spiny lobsters patrol the seabed.

The elusive Starry Night octopus also emerges

from the shadowy waters.

(bright lively music continues)

Nocturnal specialists rule the darkness.

(water splashing)

(bright lively music)

In contrast to the day, a male bamboo shark

actively patrols its surroundings.

The restless shark is on the hunt for a female.

After an extensive search,

the male has finally tracked down a potential mate.

Shadowing the female, the besotted shark is ready

to make his move, but unfortunately,

his advances are rejected.

However, elsewhere in the bay, a pair

of bamboo sharks are getting better acquainted.

(bright lively music)

Latching onto the female,

it appears this male is rather rough,

but this aggressive behavior is in fact all part

and parcel of the shark's mating ritual.

For almost half an hour, the pair remain entangled.

(bright lively music continues)

The rough biting is the male bamboo shark's bizarre method

of enticing his mate.

After a prolonged struggle,

the two sharks finally sink to the bay's floor.

With the male's clasper successfully attached,

he can now pass on his sperm.

It seems brutal, but the aggressive behavior

is all part of creating the next generation.

(gentle peaceful music)

Bamboo sharks are usually found

in much deeper parts of the ocean.

However, each year they congregate in the bay.

The reason for their annual visit can be found

in the bay's unusual terrain.

Just off the shore,

steep cliffs drop hundreds of meters below.

These expansive waters are

in stark contrast to the shallows of the bay.

(gentle peaceful music continues)

Nutrients from the deep ocean

are carried here by the current,

and when plankton blooms,

huge schools of anchovy are attracted.

Larger predatory fish,

like the meter-long dogtooth tuna,

are in turn lured by the small fish.

(gentle peaceful music continues)

This deep ocean is prevalent across much of the coast

of northeast Cape Muroto.

The quiet bay is one of the few spots that offer

the bamboo sharks a shallow and calm habitat

to mate and lay their precious eggs.

(calm uplifting music)

As June arrives, it brings with it the rainy season.

At this time of year, the number of bamboo sharks

entering the bay is at its highest.

Females are busy maneuvering around the seabed.

(gentle uplifting music)

Close to one resting shark, eggs hang firmly from a rock.

Many of the bay's females are now laying.

The 10-centimeter eggs

are almost perfectly camouflaged against seaweed.

(gentle uplifting music continues)

Located in its center is the yolk.

Within is a single embryo.

The string-like fibers stemming from the shell twine

around rocks, acting like anchors against the current.

(gentle uplifting music continues)

These eggs do not end up perfectly secured by chance.

Female bamboo sharks are ingenious egg layers.

(gentle peaceful music)

When close to laying, the expectant shark will start

an extensive search for a spawning ground.

(gentle peaceful music continues)

Protruding string-like fibers indicate

this female is on the verge of laying.

She must find a spawning ground immediately.

After a frantic search, the female settles

on a rock with a 50-centimeter gap.

(gentle calm music)

Finally, the tireless shark is ready to spawn.

With remarkable flexibility,

the pregnant shark begins the laying process.

By looping around the rock,

she secures her egg with its string-like fibers.

In total, she makes nine rotations.

The tireless female's work is not over yet.

(gentle calm music continues)

Bamboo sharks lay two eggs at a time.

The entire process must be repeated.

Throughout the bay, females are busy attaching their eggs

to the best locations they can find.

(gentle calm music continues)

For over three months, the bamboo sharks will continue

to breed in the shallow waters.

Once an egg has been laid, the mother will have

no time to guard the embryo within,

and there are many potential egg thieves in the bay.

Well camouflaged against the seaweed, most fish

pay little attention to the developing bamboo sharks.

(upbeat lively music)

A wandering crab, on the other hand,

has noticed one of the hanging eggs.

(bright upbeat music)

It's not the only crustacean to have registered

an interest in the developing sharks.

This larger crab is testing the eggs

for any signs of weakness,

but with the string-like fibers holding strong,

the would-be egg thief must accept defeat.

The anchoring fibers are so robust,

they can even become a hazard to passing fish.

Once entangled in the fibers, they are hard to shake off.

As spawning intensifies,

certain areas become particularly popular.

Another shark has chosen the same rock column

as the previous female.

While the spawning season lasts,

egg laying in the bay will be frantic.

(gentle uplifting music)

In July, the water temperature rises to 25 degrees Celsius.

Two months have passed since the bamboo sharks

first arrived in the bay.

Beneath the surface, much has changed.

(gentle peaceful music)

Seaweed from the Sargassum fulvellum family has grown up

to a meter in height, creating an underwater forest.

Warmer temperatures also trigger a change

in a pair of Spotnape cardinalfish.

Bizarrely, a male swallows eggs from its spawning mate.

The father fish has not turned cannibalistic.

He will keep the egg sheltered in his mouth

until they are ready to hatch in a week's time.

(gentle peaceful music continues)

As for the bamboo sharks, their numbers

in the bay are declining with each passing day.

Flattened, wrinkly bellies are an indication

that egg laying has already taken place.

Most of the sharks will have completed spawning

by the end of July.

Back at the popular rock column,

there are now six eggs clinging on against the current.

(upbeat cheerful music)

Within the shells, tiny sharks are developing.

At just four centimeters in length,

the embryo remains attached to the yolk

via its umbilical cord,

providing it with vital nutrients.

The warm waters of the bay provide the perfect conditions

for the developing bamboo sharks.

And after just two weeks,

the embryo has doubled in size.

(bright lively music)

Its eyes and fins are rapidly developing.

The tiny tufts on the side of its head

will soon grow into fully-developed gills.

Many shark species eggs take between six months

to an entire year to hatch.

It is not known exactly how long bamboo shark eggs

take to hatch, but the warm waters of the bay

seem to be rapidly aiding their growth.

By August, temperatures can rise to 30 degrees.

The warm weather should be having a positive effect

on the developing sharks.

However, back at the spawning site,

there is a nasty surprise.

The eggs have all been damaged.

(gentle calm music)

Inside the holes, the embryos are nowhere to be seen.

Something has predated the eggs.

Most predators are unable to penetrate

the tough outer shells,

but something has managed to riddle the eggs

with multiple puncture wounds.

There are many creatures passing through the bay,

including the meter-long painted sweetlips.

(upbeat lively music)

It specializes in vacuuming the seabed

for tasty treats like shrimp.

However, the painted sweetlips' mouth is far too big

to have caused the damage to the bamboo shark eggs.

The Japanese parrotfish is another potential suspect.

They are equipped with powerful jaws

for tearing off seaweed.

But none of these carnivorous fish

seem to seek out the anchored eggs.

(gentle upbeat music)

To discover the culprit, Dr. Nakaya examines

the only piece of evidence available,

the puncture wounds.

All of the predated eggs have clean cut,

diamond-shaped holes bored into their outer shells.

Using the jaws of a parrotfish,

Dr. Nakaya compares bite patterns.

The mark left has a zigzag shape.

It's not a perfect match.

(gentle upbeat music continues)

The search for the egg hunter must go on.

After further investigations,

Dr. Nakaya believes a puffer fish is the main suspect.

(upbeat lively music)

Plenty of the distinctive creatures inhabit the bay.

Puffer fish have particularly unique mouths.

They are armed with beak-like jaws.

A white-spotted puffer fish's jaws leave

a strikingly similar pattern.

(upbeat lively music continues)

To add weight to the theory,

a test in an aquarium is performed.

A bamboo shank egg stuffed with bait is placed

in a tank with a white-spotted puffer.

(teeth crunching)

With ease, the carnivorous fish punctures

the egg's tough outer shell.

(teeth crunching)

The repeated strikes leave behind

the incriminating diamond holes.

It's almost an identical match.

The potential discovery of puffer fish predating

bamboo shark eggs has never been encountered before.

(gentle poignant music)

Bamboo shark eggs may be well-camouflaged,

but they do have one fatal flaw.

Immediately after spawning,

the egg is completely sealed.

However, after two months, the developing shark forms

a mouth and must start to breathe in fresh seawater.

To allow a constant flow, the egg develops

tiny holes in each corner.

The gaps are vital for the embryo's development,

but the various scents the egg produces

leak out into the ocean and attract predators.

It's been three months since the bamboo sharks spawned.

(gentle peaceful music)

The best placed eggs have survived

and are now thriving in the bay's warm waters.

After months of development, the growing sharks are starting

to resemble fully formed adults.

The rounded yolk is also getting smaller by the day.

Most shark species take around a year to hatch,

but the bamboo shark eggs seem close

to hatching after just three months.

They may be growing fast, but Mother Nature

has one final challenge for the anchored eggs.

(waves crashing)

The typhoon season is commencing.

(gentle uplifting music)

For days, huge waves batter the usually calm bay.

(wind whistling)

(waster splashes)

(gentle poignant music)

In the wake of the storm,

coral reaching a meter in width has been destroyed.

The typhoon has caused havoc across the seabed.

Destruction may be widespread, but many

of the bamboo shark eggs have stayed in place

thanks to their strong anchoring.

(gentle hopeful music)

In some eggs, there is almost no space left

for the developing sharks.

After just 95 days, this shell is now completely empty.

(gentle hopeful music continues)

The warm and sheltered bay provides the bamboo sharks

with the best possible environment to develop.

(bright upbeat music)

There are still some eggs left in the tranquil waters.

An infrared camera gives an insight

into this shark's final moments

of development during the night.

The yolk has now completely vanished,

which means the tiny shark is ready

to leave its protective shell.

(bright hopeful music)

To free itself, it must use all its strength.

After swimming to the surface,

the juvenile soon settles on the seabed.

Like its parents, it uses its pectoral fins

to propel it across the bay's rocks and coral.

It is not the only recently-hatched bamboo shark in the bay.

(bright lively music)

There are many taking their first swim

into their aquatic realm.

It is not known where these tiny sharks will go

and how they will develop,

but those that do make it to adulthood

will one day return to the bay of their conception,

and like their parents before them,

give birth to the most remarkable of eggs.

(lively energetic music)

Life for the bamboo sharks revolves around one location.

Every year, the tranquil bay in southern Japan

becomes their home from home.

In the sheltered warm waters,

they mate and begin the process

of ushering in the next generation.

It is down to the mother sharks to lay

and secure their precious payloads.

After the eggs have been laid, the developing sharks within

have nothing for protection

other than their ingenious anchoring and camouflage.

And the bay is not without its dangers.

Threats come from would-be egg hunters and Mother Nature,

but the best-placed do survive

and thanks to the warm waters, thrive.

Unlike any other place on earth,

this bay has become the birthing ground

of the remarkable whitespotted bamboo shark.

(bright uplifting music)

(intense ringing music)