Le mystérieux sanctuaire de requins du Pacifique | Documentaire Monde

La pleine lune révèle un monde sous-marin où chaque espèce joue sa survie.
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00:00 Introduction aux Tuamotu et à Fakarava
01:08 La passe de Tetamanu et ses cycles lunaires
02:26 Les requins gris et la chorégraphie des prédateurs
05:05 Stratégies de survie : poissons clowns, coraux et anémones
07:26 Le lagon : refuge et poumon de biodiversité
12:14 Mérous marbrés : migrations et reproduction
21:06 Les chirurgiens bagnards et la ponte massive
27:09 Cycles jour/nuit et dynamiques prédateurs-proies
36:15 Stratégies nocturnes : coraux, murènes et poissons
45:03 Ponte des mérous et équilibre de l’écosystème
49:43 Conclusion : un cycle éternel de vie et de fin

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Au sud de l’atoll de Fakarava, dans l’archipel des Tuamotu, la passe de Tetamanu devient chaque nuit le théâtre d’une vie intense. Gouverné par la lune et les marées, ce sanctuaire sous-marin accueille migrations, chasses, accouplements et pontes, où requins, mérous, poissons chirurgiens et une multitude d’espèces s’entrecroisent dans un fragile équilibre.
Entre le crépuscule et l’aube, la survie de chacun dépend de l’autre. Ce documentaire en 4K nous plonge dans l’un des derniers territoires vierges de la planète, une fenêtre fascinante sur la magie et la brutalité des océans.

Titre : DU CREPUSCULE A L’AUBE
Réalisé par Yann Hubert
© AMP

#documentairenature #ocean #mer #conservation #requin #shark

At the end of the world lies a constellation
of coral islands lost in the heart of the great ocean. Isolated and preserved ecosystems where
the light of the early days still shines. A lost world, free and wild.
Home to exuberant underwater life , each island is an oasis of
fertility lost in an oceanic desert. Rich in hundreds of species and teeming
with life, these coral constructions are among the most complex biotopes in the ocean.
There is a secret and mysterious nature in what is one of the last
wild territories on the planet. We are six thousand kilometers from the
nearest continental coast, in French Polynesia, which has
five archipelagos including the Tuamotu. This constellation of 76 atolls, which
stretch over two thousand kilometers long and six hundred kilometers wide, constitutes the
largest chain of coral atolls in the world. A marine area of ​​twenty thousand
square kilometers, of which only five percent is land.
South of the Fakarava atoll, the Tetamanu pass is at the height
of its underwater activity. It is the southern winter and
tonight the moon will be full. The night star is the mistress of the tides and
therefore the perpetual engine of the current. Underwater, the moon also governs biological cycles.
The pass is then the scene of decisive events which preside over
the future of many species. It welcomes gatherings of those who
need a route to the ocean to reproduce. Between the twilight of evening and the dawn of a new
day, many play their destinies in a fragile balance between life and death.
An armada of several hundred sharks faces the current.
The flow created by the tide is a considerable comfort for them because, like all
fish, the sandbar shark must circulate water through its gills to breathe.
But like all pelagic sharks, its gills, insufficiently muscular,
are unable to do this alone.  An eternal marauder, he is condemned
to swim endlessly to get oxygen. The current becomes a real boon
because it provides him with beneficial respiratory assistance which allows him to limit his
efforts and conserve his energy. Carried by a steady current, the animal
can remain practically motionless. An opportunity for the cleaner wrasse to
attempt an operation in the predator’s mouth. An acrobatic and
risky operation for the little fish. Body wounds are also inspected.
The southern winter is a period of high activity for the predator colony.
It has new arrivals every day. We come across females
marked by recent mating… …as well as future mothers close to term.
Grey sharks do not exhibit ostracism. Other species fit easily
into the group’s choreography. These young silvertip sharks, which
usually prefer great depths, are perfectly tolerated.
As is the sharpnose shark, which is a permanent resident.
Sometimes the coral shark joins the circle of swimmers, although it has
no need to move to breathe. Lying on the bottom, it spends most
of the day in deep inactivity. It is a more docile client
for cleaner wrasses. It is rare to come across mutilated sharks because
the slightest handicap is generally fatal to them. This one, although disfigured, seems to have
recovered well from a bad encounter. Surprisingly, the presence of all these large predators does not generate
any particular tension in the ecosystem. It is in a serene atmosphere that
everyone goes about their business. Places with good
power are highly sought after. A pair of clownfish sit
nearby in their protective stinging anemone. To ensure peaceful cohabitation and avoid
being mistaken for prey, they often rub themselves on it to coat themselves with its mucus.
They only move away from their tentacle citadel to gobble up
plankton drifting in the current. Suddenly, the passage of a school of
fusilier fish disrupts the calm of the pass. Stimulated by the arrival of this providential meal,
a group of sharks emerges from its lethargy. The hunters are nervously moving around
trying to surround the fish. In such a large gathering of sharks,
there are inevitably a few individuals with empty stomachs who seek by
all means to appease their hunger. They try their luck… without success. Exhausted by hunger, a despondent shark
even worries the clownfish. With the fusiliers gone, the tension
drops as quickly as it rose. But all this commotion has attracted
the attention of a larger predator. The great hammerhead shark
regularly puts the grey shark on its menu. The animal, with its characteristic head, can reach 5 meters in length and
weigh several hundred kilos. He is always looking
for his next meal. Today, its large
dorsal fin will only pass through. The pass is an umbilical cord
between the ocean and the lagoon. An open road to the open sea or a
gateway to the lagoon universe. Trapped in its coral crown,
the lagoon is a small inland sea. A refuge from storms
and a place of abundance. A protective environment but sufficiently open
to the outside world to avoid the risk of asphyxiation. Oxygenated and cleansed by the
tidal currents that circulate in the passes, the clear and rich waters promote
the development of an entire ecosystem. The lagoon thrives in a delicate balance
regulated by the exchange of waters with the ocean, and genetically, by allowing
species to disperse.  A huge nursery, it is an essential nursery for
the development of many young fish. From algae-eating fish to large predators, all find in the lagoon a
suitable environment to live, grow and reproduce.  On the deep blue side, the pass ends
in dizzying vertical walls which plunge towards the abyss.
These formidable drop-offs form a barrier around the island where the
waves of the Pacific break and mark a border between the island and the pelagic environment.
We come across great travelers, like the manta ray…
… a few sharks posted as sentinels…
… or barracudas, victims of a very unjustified bad reputation. They wait peacefully in a school for the moment
to separate to go hunting alone.  A bulwark against the assaults of the swell, the reef flat
is made up of very resistant massive corals. The waters, agitated and oxygenated by
the ocean swell, are frequented by a lush fauna of fish.
Facing the blue desert of the deep ocean, life opposes emptiness, multitude opposes absence, in an
exuberant kaleidoscope of shapes and colors. This large female gray stingray
recently gave birth. The cavities that hollow out its back were, until
recently, swollen with embryos. The male who follows her relentlessly is
already offering to mate. The female neither dissuades nor
encourages the suitor. She cleverly organizes the chase to
test her motivation and physical abilities. If he is up to the task, the seduced female
will allow him to pass on her genes. At the entrance to the channel, the paddle perch
are also in the middle of their mating season. At the end of this afternoon, there are
only a few dozen of them, but they only represent the vanguard of a gathering
of several thousand individuals. For several weeks, another species has been
gathering in the center of the pass for the same purpose. Predatory and misanthropic, the
marbled grouper is a loner. But a slave to biology, once a year
he must respond to a sovereign call which forces him to join his fellow creatures.
He then undertakes a long and perilous migration which must reach its goal
at the full moon of the winter solstice. The Tetamanu Pass hosts one of these
unique and spectacular gatherings. Every day for the past four weeks, it has
welcomed new arrivals from all corners of the immense atoll.
They are now complete. This overpopulation of groupers
is under close surveillance. Gentlemen groupers are by
nature irascible and aggressive. The prevailing promiscuity and
the proximity of pregnant females are sources of many conflicts.
A sideways glance, a female to seduce, a place to defend and it’s a confrontation.
A brief but particularly violent face-to-face. The bites are not simulated and
each opponent loses scales. An exasperated and much
larger neighbor ends the altercation. It is usually difficult to distinguish
the sex of a grouper because it changes sex several times during its life, and its color
varies easily depending on its mood. But here the females are easy to
distinguish thanks to their swollen bellies. They are full term and ready for the big moment. They are also highly coveted targets.
For a shark, a female with a belly full of fatty, protein-rich eggs is a
substantial energy resource. A few leopard rays pass by,
carried by the current, indifferent to the groupers’ concerns.
It is also called the eagle ray because of the elongated shape of its head
and its majestic gliding flight. Although pelagic, it is on the seabed that this distant cousin of the
shark finds its sustenance. Her infallible sense of smell guides her
to her future victims. With its snout-like mouth, it
searches the ground for crabs, shellfish or other large invertebrates. Sand accidentally ingested is
excreted through the respiratory tract. This green turtle emerges from a
sleep episode spent in the shelter of a small cave.  A cold-blooded animal, its reptilian organism
allows it to perform feats of apnea. During her recovery periods, she
falls into a state of deep lethargy, close to a coma, where her
energy consumption is insignificant. His metabolism is reduced to
the essentials, which allows him to remain in apnea for several hours.
A few swimming strokes and she’s fully operational again.
The afternoon is coming to an end. The rugged terrain of the ocean slopes of the pass
comes to life thanks to those who prefer shade to light or who need refuge.
Like the squirrel fish whose large, dark-adapted eyes
cannot tolerate strong light. The nurse shark
is also a reef night owl.  A placid giant during the day, it transforms at night into a
very efficient active hunter. Cerberus of the reef, the Javanese moray eel
stands guard over its domain. Due to its territorial instinct,
it rarely leaves its coral lair during the day. This pair of cleaner shrimp, currently
idle, are waiting for their next customer. For 15 days the female’s
belly has been distended by her eggs. They are full term and hatching is near.
The larvae will join the plankton for a series of moults which will
metamorphose them into full-fledged adults. Varied in shape, but always
adorned with sublime colors, the nudibranch is a sea slug.
Carnivorous, it feeds on the walls rich in sponges, polyps or bryozoans.
Its sensitive antennae allow it to smell, hear and taste.
The feather duster that stirs the water with its tentacles is its respiratory system.
Like the snail, the nudibranch is hermaphrodite, meaning that it possesses
both eggs and sperm. To be viable, its eggs must
be fertilized by a conspecific. For this slow and slow-moving animal,
crossing paths with a similar one is an event. The encounter inevitably causes
an exchange of their male gametes. Each person will thus be able to inseminate their eggs.
This brightly colored Chromodoris lays a long adhesive ribbon of thousands
of fertile eggs on the seabed, which will ensure its offspring. The sun slides gently towards the horizon.
The day is coming to an end. The legions of convict surgeonfish
graze on a last mouthful of seaweed. Full and full of energy,
they will now have to take all risks to
ensure the future of the species. More prolific than groupers,
it is with each new lunar cycle that they must, during a
frenetic ritual, succeed in giving life. A real challenge as the pass is
not short of hungry predators. Arriving from all sides, they form a
moving tide which invades the overhangs of the pass. On the surface the half-beaks seem
indifferent to this commotion. Patient, they wait for the laying because
these are the eggs they love. For their part, sharks,
blue trevallies and napoleons are looking for victims. These opportunists intend to have a feast. As with feeding, the
defensive strategy of convict surgeons lies in multitude.
By the hundreds, in a compact, fast and moving school, they destabilize the attackers.
Their identical shapes and colors, crossed with black lines, help to
create a form of optical illusion that confuses the senses of predators.
The individual is lost in the crowd. Unable to focus on a
specific fish, the attackers are ineffective. While many easily dodge attacks…
…inevitably the less skillful succumb. By dispersing in columns
towards the centre of the pass, the convict surgeons avoid
being cornered on the reef. Suddenly, in a sudden
upward movement, a few small groups begin to lay eggs.
This is the signal. In an incredible burst of energy,
the thousands of fish break free. A tide of rampaging spawners
disperses their gametes in a tremendous underwater firework display, close to
the surface, where the current is strongest. It’s a deadly game of dodging where only
the fastest emerge victorious. The released eggs are instantly
fertilized by a handful of males. The wedding is quick but
the energy expended is substantial. Most species of
fish lay eggs. Many practice group fertilization. It allows for a beneficial genetic mixing
of the entire population. The mixing of cells is such that there
is almost no chance that genes from two parent individuals can meet.
But whatever the laying method chosen, one constraint applies to all.
The eggs or larvae must join the zooplankton in the
open sea for a period of ocean drift. This wandering of a few weeks, far from the
lagoons, is a founding stage of life. Expelled from the lagoon and scattered by the current,
the next generation begins its odyssey. This large white cloud is the promise of life for an
entire population of convict surgeons. At the end of its course, the sun reaches the horizon. The dying light of
evening twilight floods the pass. In this brief moment between dog and wolf,
some leave the ocean to spend the night sheltered in the lagoon, while
others make the opposite journey. For them, it is the beginning of a night during which
they will sail the ocean. With the arrival of darkness, the
daytime actors are looking for shelter in which to hide.
Others, never satisfied, swallow their last mouthfuls of plankton on the surface in the last rays
of light. The triggerfish finishes flushing out its
dinner buried under a blanket of coral. The paddle perch will huddle
against the drop-off for the night. This chiaroscuro is a
particularly favorable moment for predators. Concealed in the halo of
this ambiguous light, they can more easily exploit
the weak points of their prey. A small team of dogtooth tuna
goes on the hunt. Every day, at this same time and in this same
place, a multitude of fish leave the lagoon to join the ocean.
Like a gigantic organism, the column advances in dazzling pulsations.
The passage is done at high speed and under high tension because the fish must
use the gray shark canyon. But there are so many of them and they pass so
quickly that the sharks are caught off guard. Although this migration occurs
daily at the same time, predators do not seem to have anticipated it.
The more knowledgeable passing tuna manage to catch a few fish, while the
disconcerted sharks seem completely inhibited. Restless and disjointed, they fail to
create opportunities. The passengers had time to take shelter in the ocean
before they could react effectively. Again, being in large numbers
is an effective survival strategy. The sharks reform the group.
The coming darkness is full of promise. A day of light ends and the darkness of night begins.
The night star is at its peak. Like a night sun, its pale light
reveals a little of the underwater gloom. These latecomer banana fish have not
yet returned to their quarters for the night. After a day of listlessness, this
coral shark begins its long night of stalking.  A veritable bouquet of poisonous thorns, the
scorpionfish leaves its collective shelter during the day to go on a solitary hunt.
It sucks in small fish, which it flushes out by stretching the
veil of its long fins. Wedged into a crevice, this
turtle has found its nest. During the night, the coral unfolds
its polyps which remained closed during the day. It is more vulnerable to attacks
from the spiny starfish. Protected by its crown of spikes, the animal
devours relentlessly, leaving behind only a limestone skeleton.
Imperceptible during the day, a universe populated by fantastical
and improbable creatures emerges from the darkness.  A waving ribbon, the
licking sea cucumber has a long digestive tract. It moves by alternately contracting
the rings of its soft, supple body. Its mouth is surrounded by
adhesive tentacles that capture microscopic organic particles that pass within its reach.
It is one of the cleaning organisms essential for maintaining
the good health of the lagoon. At the slightest alert, it
instantly retracts its rings. During the day, grazing fish
mow the lawn of algae growing on the seabed. At night, they give
way to the sea urchins which remained totally invisible during the day.
Together, they regulate the overabundance of plants, thus preserving
the balance between organisms. Crustaceans are to the marine environment what
insects are to the terrestrial environment. The hermit crab is a
strong supporter of recycling.  Since nature offered him no protection
for his soft body, he collected various empty shells which he used as a “mobile home”.
A temporary residence that it must renew with each of its growth molts.
Each new shell must be adapted to its new size and have a reasonable footprint.
The tank type is very popular… …the sport model, more colorful and
faster, also has its fans. A few rare fish are
active both day and night. Almost invisible with its camouflage,
the tropical turbot likes sandy bottoms as a hunting ground.
Nyctalope, its stalked eyes allow it to spot small
fish that it surprises while they are asleep. On the prowl, the lizardfish with its
oversized jaw is a patient hunter always ready to pounce on a victim.
Even during the night, the sergeant major does not abandon his post.
Loyal to the extreme, he mounts a protective guard around his spawn.
While a few fish remain active, most spend the night in a
lethargic, sleep-like state. There are many reasons for
this nighttime torpor. In particular, and as with the majority
of living organisms, the metabolism of fish needs a period of
rest to maintain its efficiency. This moment of
reduced responsiveness makes him vulnerable. Since there are fewer predators,
night is the best time to release. An individual capable of effective survival strategies
under sunlight will have every interest in using darkness, the
period when he is least efficient, to save energy and replenish his reserves.
You have to be as discreet as possible.  With the body deployed, sheltered by an
overhang or hollow in the coral, activity is reduced to a minimum.
But total stillness is often impossible. Even when asleep, you still have to breathe
by stirring the water with your fins. Among fish, there are as many
pajamas as there are ways of sleeping. Strangely, despite the deep darkness, a
change of attire for the night is common. Sometimes for garish colors
more vivid than during the day… …or for clever camouflage.
The parrot fish is comfortably installed. However, being placed on the bottom makes it vulnerable
to attacks from parasites of all kinds. To protect themselves from this inconvenience,
some individuals cover themselves completely at night with a protective slime
that they secrete from their mouths. Enclosed in their mucus “mosquito nets
“, they are safe from unwanted pests such as stinging worms.
For the clownfish, the night is peaceful. By stimulating his anemone,
he encourages it to retract. It thus offers him a perfect protective cocoon. The shark belongs to the night as
the dolphin belongs to the sun. It is in darkness that he
takes on his true dimension. Its hydrodynamic elegance has reigned over the
underwater darkness for 100 million years. Moonlight attracts a large number of
fish larvae and fry close to the surface. The gray shark does not disdain any prey.
Despite their small size, he spots them perfectly.
To be an effective predator, it is essential to understand your environment precisely.
The shark’s senses are particularly efficient, but
it has an astonishing ability to tell the difference. It has sensory organs that detect
from a distance the smallest variation in the electric field surrounding it.
This high-performance system allows it to detect very weak
electrical impulses, such as fin strokes or the heartbeat of fleeing prey.
Located on its head and along its body, these receptors, combined with its other senses,
make it a veritable underwater radar. Like a magnet attracting iron, the
movements of a fish guide the shark’s search head towards it.
Equipment is one thing, strategy is another.
The energy gain from such small prey is paltry compared
to the expense of capturing it. The shark’s predatory instinct
sometimes seems to play tricks on it. The reef, however, provides
larger catches. A lone grey shark patrols, looking for
the slightest sign of movement that might indicate a meal. A restless sleeper is spotted.
The duel is a strange dance between life and death.
The little fish knows that if he tries to escape, he is doomed.
Full of composure, he lets the predator approach so as to better dodge
the outbursts at the last moment. This high-risk strategy neutralizes
the shark’s advantage in seeing poorly at night. Although he is good at spotting fish that are moving and at a
distance, he is particularly clumsy when the fish is motionless and very close to him.
Discovered, this zancle uses the same strategy. But less experienced, he loses his control.
The reaction is instantaneous. All the sharks nearby target him and
his fate is sealed a little further on. It is the spark that starts
a chain reaction. A shark flushes out a fish which attracts other
sharks which flush out other fish which attract more sharks, and so on.
The scenario is always the same. Although there is no
premeditated and coherent desire to form a pack, the many sharks present in the
area do, in fact, find themselves in groups. There is no common tactic, but being
numerous gives them more opportunities. This proves to be very beneficial
and they multiply the catches. For fish it’s a nightmare. Their survival depends on their ability to remain
inert and unresponsive to the passing sharks. No mercy for those who crack.
But how can you not panic in the middle of a horde of hungry mouths?
The hunters are ruthless and the competition between them is fierce. Whoever manages to grab a
meal must swallow it as quickly as possible or be
attacked by his fellow creatures. You don’t always emerge unscathed from such a melee. The night is coming to an end.
Slowly the darkness fades. The faint glow of dawn shines through.
The curtain of night rises on a new day. With the new tide, the
lagoon flows into the ocean. The outer threshold of the pass
is already in full activity. After several weeks of waiting, it’s
finally the big moment for the marbled groupers. With one impulse, females and males rush
to the surface to release their seeds. Each female selected the males to
make them her small circle of genitors. More vulnerable than
surgeonfish because they are larger, groupers spawn at intervals in small,
scattered groups to confuse sharks. The uncertain light offers
precarious protection from the greed of sharks. This one was a close call. Sharks aren’t the only threats.
Arriving from the blue by the hundreds, a rain of fusiliers falls on the bridges.
The food chain would not be complete without the arrival of
dogtooth tuna, which are great fans of fusiliers. The egg clouds are stormed and
many are swallowed up before they have time to disperse in the current.
But the price paid by the groupers and their spawning remains bearable and does
not endanger the future of the species. This sacrifice is an essential cog in
the balance of the pass ecosystem. Many resident species depend on this
occasional protein boost to survive. The prosperity of the grey shark colony
is fundamentally dependent on these large, regular gatherings.
The first moments of an egg’s life are the most perilous. Fortunately,
most of it will soon be safe offshore. They will join the
surgeonfish spawned before nightfall in the ocean. A new generation of
these species will emerge. After this time of drifting, the
survivors, having become autonomous, will return to colonize the lagoon
and perpetuate the cycle of life. The empty bellies of females
signal the end of spawning. For their part, with full stomachs,
the guests disperse. The groupers, exhausted by
the effort, leave the pass. They will return to their territories and their
solitary lives, until next year. In water, as on land, actors and
behaviors differ between day and night. Metronome of the ecosystem and primordial link,
the cycle of currents is a cycle of life. From one twilight to the next, each day is
a mysterious alchemy of life and death where the future and survival of each depend on
the other in a miraculous balance. Lost in the Pacific, the Tuamotus, and
more particularly the Tetamanu pass, are a unique window onto the
wonders of the underwater world.