The ocean's depths
are home to mysterious animals. Amongst them,
a creature known mostly by its corpses. The sea serpent. Beachings have enabled scientists
to study the strange anatomy of this bony fish,
the longest in the world. Its head, crowned with a tuft of rays, has earned it the name
king of the herrings, or more commonly, the oarfish. Because it had rarely been observed alive, little or nothing
had been known about its biology. Until today. Off the coast of France, the world's first pioneering
scientific equipment, anchored in the very depths of the ocean, was to accidentally enable
some high-tech divers to observe, study, and reveal the extraordinary habits
of this singular creature. Until the turn of the 19th century, the sea serpent belonged
to the class of legendary sea monsters, mythical creatures which haunted the imagination of men
and the shadowy edges of marine charts. Its amazing appearance, size, rarity,
and colors gave rise to sailors' superstitions
and fishermen's tales. It had been seen attacking ships and was even reported
to spot fearsome teeth, which made it resemble a marine reptile. In the 19th century,
its teeth were to disappear, thanks to the descriptions
of the first naturalists. Nevertheless, their observations
were rare, unreliable, and scattered. Over the last two centuries,
less than 250 beachings of dying, dead, or atrophied oarfish have been reported
on temperate coasts all over the world. The longest ever found
measured an astonishing 23 feet. Recently, through an incredible
combination of circumstances, this giant fish had been observed
quite alive off the French coasts. In the south of France,
the Carefree Riviera with its yachts, citadels,
and fine sand beaches. Every year, more than 12 million tourists
delight in the pleasures of the warm waters
of its slim coastal fringe. Who would have thought
that the implementation of a strange scientific apparatus
off the coast of these beaches would make sea monsters reappear? It was nevertheless to be
the indirect consequence of an incredible experiment. In the heart of the summer
of the year 2000, the Oceanographic Observatory
of Villefranche-sur-Mer, in association with the top international
space research organizations, undertakes the deployment
40 miles off the coast of Nice of an oceanographic buoy
named La Boussole, the compass. Its goal seems more poetic
than scientific. It's intended to collect and transmit data
on the color of the water. This data will permit the calibration
of satellites that observe the oceans. The color of the water, which varies according
to the seasons and locations, is a good indicator
of the presence of plankton. Thus, in the spring, microscopic algae
and their predators abound. This is called a planktonic bloom. The algae's chlorophyll
gives the seawater a green color. Here starts the vast food chain
of the oceans. To study the evolution
of the Mediterranean Sea, the observations of La Boussole buoy
must be continuous over several years. The buoy must therefore
be solidly anchored and periodically checked. To carry out this maintenance,
a passionate biologist. My name is David Duke. I'm a scientific diver and work
at the marine lab of Villefranche-sur-Mer, where I am in charge
of all diving activities. With tools as efficient
as they are rudimentary, he intervenes only near the surface
on the submerged part of the buoy. Beyond this, he hands the work over
to other specialists of underwater projects. To be at the heart of plankton production, scientists decided to anchor the buoy
in the middle of a gyrating current. The problem is in the chosen location,
depths exceed 8000 feet. Therefore, a heavy mooring attached
to almost two miles of Kevlar cable must be laid down. Lost in the immensity of the ocean, the buoy's structure and chains
attract many ocean wanderers. Barrelfish. Amber jacks. Pilot fish. Finally, the Atlantic wreckfish. These fish live in the photic zone. That is to say,
the layers of water at low depth sufficiently exposed to light
so that photosynthesis is possible. By the buoy's shadow cone,
all find both food and shelter. Most swim by sight. Some come to feed on algae
which grows on the structure, and the smallest
are devoured by the largest. Others, such as pilot fish, are specialized
in one particular activity. Feeding on leftovers of meals or parasites of large predators that visit the buoy. Including the most feared. The great white shark. The shark has been observed only
in the spring near the surface, swimming in vast concentric circles
around La Boussole buoy. A small population estimated
at nearly 350 great whites survives in the Mediterranean. What have they come to look for here
40 miles from the Riviera coast? Most likely, other visitors to the buoy, such as tuna. No one has ever seen white sharks
feeding here and their visits are rare and brief. David can expect
such unforeseen encounters during his monthly maintenance visits
to the buoy. His mission is to clean
the underwater optical sensors. The equipment is still just as rudimentary
but efficient, solidly fastened to the diver
so as not to sink 8000 feet to the bottom. Risky dives, David is alone
in the open ocean without any protection. In less than a month,
colonies of algae and seashells render the buoy's 20 measuring instruments
totally inoperative. To every sensor, a specific brush. Cleaning creates vibrations
emitted in all directions. Sound waves which are perceived
by all the nomads of the ocean. They awaken their curiosity. These sounds propagate along the structure
all the way down to the depths. Fish do not know man. Therefore, do not fear him. Their curiosity is reciprocal. David, under the buoy,
is a man faced with the unknown. One day, in April, during the planktonic bloom, the water was really very cloudy. I had just finished my work,
and I went down to inspect the bottom of the buoy at
the level of the Kevlar cable. And there... I saw a very long silver ribbon
coming up from the depths. The king of the herrings. Curious but fearful. For the first time ever,
a diver swims with the mythical fish. An ambassador of the deep
comes to the borders of our world. David discovers that it swims vertically,
not horizontally, like the sea serpents in ancient prints. Curiously,
the tail of the animal is split. Could this be the result of an encounter
with the great white shark? To answer this,
David would need to get close and observe the bite marks. Unfortunately, his bubbles
seem to frighten the animal. This accidental encounter
is too brief to examine the wound. After a few minutes,
the crowned fish returns to the orthotic zone. Depths where so little light penetrate
that photosynthesis is no longer possible. To be able to anticipate other encounters,
David must first understand how the giant oarfish manages to detect
the buoy in the immensity and half-darkness
of the Mediterranean Sea. Luckily for him,
thousands of miles from the boy, a series of extraordinary events
was going to enable scientists to reveal unknown facets
of the biology of this mythical fish. In Japan, the giant oarfish goes by the strange name
of ryugu no tsukai, meaning messenger
of the palace of the gods. Over the several months of winter in 2014, more than a dozen
giant oarfish of all sizes were deposited by marine currents
on the shores of southern Japan. According to Japanese mythology, the beachings of the messenger
of the palace of the gods announce an imminent earthquake. These sudden appearances
have never been proven to be correlated to seismic activity in the region. They offered Dr. Tyson Roberts,
the worlds expert in giant oarfish, an unhoped for opportunity to carry out
a systematic study on fresh animals. Its anatomy would beat all records. This is an oarfish
that attains a total length of eight meters longer
than any other bony fish, with perhaps one of the smallest brains,
relatively speaking. To prove it, he's going to use
the latest technological advances in a veterinary clinic. The Japanese provided him with a magnetic
resonance imaging machine, or MRI, which produces images
in two or three dimensions of a living body
applied to a giant oarfish head. The veterinarian MRI,
designed for small animals, enables them to create images
finer than with a human MRI, indispensable to isolate the brain
of the giant oarfish with its ramifications. I'd like to know more about its brain
and its glandular system or fish anatomy. It basically has nearly all
of the organ systems and organs of human anatomy. This really is the first concerted attempt to learn as much
about oarfish anatomy as we can. The MRI images
confirm the initial hypothesis. The brain is only about an inch long,
and it's about half the size of the eye. A pea in the head. Here is the size
of the giant oarfish's brain, but however fine it might be, MRI resolution cannot discern the nervous
system associated with the brain. Fortunately, the x-rays
of the veterinarian scanner will enable Dr. Roberts
to resolve a tenacious enigma. How does the giant oarfish find its way
in the pitch darkness of the depths? Fish can use sight, sometimes sound,
but above all, smell. However, in the giant oarfish,
this sense seemed altogether absent. I've examined now around
35 specimens of oarfish, and I've never seen a nostril. The external opening
of the olfactory organ. Nobody's ever reported nostrils in oarfish
nor have they reported an olfactory organ. With these large oarfish,
I found the nostrils. The nostrils are not on the side
of the head, they're at the absolute front
of the snout, and they open anteriorly. The nostrils are thus situated
inside its mouth, so to catch
and locate odors in the twilight zone, the giant oarfish must keep its jaws
partially open and continually pump water. Now, it's quite possible
that both of those which are elongate slits
wider at the bottom and at the top could close. Opening and closing
could provide a possibility of directional sensation. The consequence is surprising. The giant oarfish is capable of working
its way back up the trail of odors in the vastness of the ocean. Simply by making pirouettes. If you're receiving
a strong olfactory signal in your nose
but you don't know where it's from, you face in the direction
you think it might be. If it's weak, then you close the nostrils and then you turn to another direction
where it might be and open the nostrils. If it's stronger, then you home in on it by successively moving your head
and opening and shutting the nostrils. It's a real underwater game
of blind man's bluff. When the eyes see
only an infinite expanse of blue, the giant oarfish
with its tiny brain can localize, go to, and remain around the La Boussole buoy, thanks to a particular smell. Could it be the smell of the buoy? That of a food source? Or another scent altogether emitted
by a creature of the depths. To make a clean breast of it, David must dive to the very limit
of the photic zone where all light stops. As this is beyond his capacities, David calls upon a specialist
of deep dives in the Mediterranean: italian cameraman Roberto Rinaldi. I really want to
meet the regalec. but as soon as we left,
I was starting to feel a little lost in the
immensity of the sea. We're going to be little
tiny dots in the blue, and it's going to be really
difficult to meet this fish. To approach it,
he plans on using a respiratory apparatus which combines performance
with discretion. The rebreather. Today, thanks to the rebreather,
we can dive deep and for a long time. We will recover the gas
mixture that we breathe. When we film, we don't
make bubbles with the recycler. Fish are used to
everything except bubbles. With the rebreather,
we have much more time and luck to approach the regalecs. On the way to La Boussole buoy, David suggests diving
under another nearby one, equally moored at a depth of 8000 feet. A meteorological buoy
simply named the Côte d'Azur. It's a sophisticated instrument
that measures temperatures, swells, and wind speed,
and supplies data to forecast centers. Under its metal skirts,
this groaning structure seems to attract more fish
in the open sea than La Boussole bouy. Its creaking carries over a great distance
in all directions. Nothing is left to chance. Gone are the short monthly dives
at La Boussole. Henceforth, David and Roberto
stay for several days at a time at the meteorological buoy,
diving at all hours starting at dawn. They've synchronized their visit
with the spring peak of plankton production,
and therefore of animal proteins. Thus, if the giant oarfish
is indeed attracted by a source of food that gives off a smell
or by the sounds of the buoy, they increase
their chances of an encounter. At the surface, velellas. These are not jellyfish, but polyp colonies
that drift with the winds and currents. For his first dive,
Roberto doesn't go down with a camera, but with a stick
topped with a scouring sponge. This is intended to take mucus samples
from the skin of the giant oarfish to conduct genetic analysis. David at shallow depths with his air tank and Roberto deep down with his rebreather, thus organize the methodical quest
for the giant oarfish. These serpent-shaped creatures
are neither giant oarfish nor jellyfish, but salps. Animals who filter bacteria
and phytoplankton and develop their chain
of fellow creatures by hermaphroditic reproduction. At a depth of 120 feet, where the warm and cold waters meet, where their food is abundant, they clone and proliferate. In this organic soup, Roberto made a record-breaking encounter. A 15-foot giant. The largest living oarfish
ever observed in its environment. The longest bony fish
ever recorded in the Mediterranean. Its tail isn't split unlike that
of the first animal observed by David. A unique opportunity
to become acquainted with it before it heads back to the depths. To be able to take a mucus sample, Roberto relies upon the discretion
of his rebreather and upon the fish's curiosity. About him and about the buoy. Curiously, the smooth, scaleless skin
of the oarfish seems insensitive to this rough contact, to any contact. Once its curiosity has been satisfied,
the giant heads back down into the depths. Covered with its precious mucus, the scraper is sent in alcohol
for analysis to the University of Western Brittany. Eleanor Muir tries to extract
the giant's DNA and compare it
with rare samples from beached animals. In fact, there is very little
genetic data available. We can learn a lot from a genetic study
with samples from live animals in their natural environment. After quite a few technical challenges,
we managed to extract DNA from the mucus samples and we analyzed it. We found a 10 percent variation
between different individuals from the same species. It's quite surprising
for a given DNA sequence. In fact, it looks
like there are two different populations, two different species of oarfish,
and our sample comes from one of them. This data seems in keeping
with the hypothesis of Dr. Tyson Roberts, who believes that there isn't one
but two species of giant oarfish. In the Mediterranean, the giant oarfish belongs to the species
Regalicus Glesne present in temperate waters
all over the world. In the warm waters of the Pacific Ocean, it's the species Regalicus Russelii
which dominates. The differences in the morphologies of the two kings of the herrings
are subtle. Glesne possesses
between four to seven more crests on its crown than Russelii. The University of Western Brittany focuses less
on these morphological debates than on a most puzzling enigma. What does the giant oarfish feed on
in the Mediterranean? We even initiated
some fatty tissue studies. We tried to reconstruct the food chain
with the available samples. Instead of getting some stomach content, we used the fat
which abounds in animal tissues, as a direct link between the composition
of the prey's fatty tissue and that of its predator. Unfortunately, the mucus did not provide
satisfactory results. Ideally, we need real tissues like fins. A mission that seems impossible,
taking samples from fin tips. Not from one,
but from several living giant oarfish. Another difficulty, even during the plankton bloom,
encounters remain uncertain. When the weather allows it, divers make several dives per day
at one or the other of the buoys. David's statistics are eloquent. Out of more than 120 dives
at La Boussole buoy, he saw a giant oarfish only twice. Luck does not exist. Only perseverance pays off. A giant oarfish
answers the call of the buoy, and it is not alone. How can these open ocean fish
meet up here at the same time? Probably, thanks to their sense of smell. Still, they need to emit a substance
which can travel over long distances with the currents. But what might this substance be? A pheromone that is a specific chemical
produced by an oarfish to attract another oarfish. Thus, the giant oarfish is capable
of sending out a coded message only detectable by other giant oarfish
over very long distances, and when they're close, the giant oarfish communicate
by using body language. What is the significance
of the dorsal fin crests and of the pelvic fin or oars,
which give the fish its name? They look obviously like intra-specific
signaling devices. The divers are going to confirm
this hypothesis. To be seen by its fellow creatures,
the fish with mirror-like skin adopts an astonishing posture. The cross. These static postures should allow David
to approach it and to take tissue samples. But he'll still need to be able
to swim at its pace and force it to remain near the surface. Easier said than done. And with its little fin that vibrates, it
doesn't move, it vibrates constantly. He is capable of
going very fast. You could call him a trap fish
because he actually has a mean attitude. but he does nothing, he
doesn't make any movements. And is that for a fish, Verticality, does it mean something, like for us? For the divers, descending is easy, but they risk the bends
by coming back up too quickly. One solution remains, passing gently
underneath the giant oarfish. Over the course of several months, David and Roberto carry out more
and more dives and fin samplings. Each time they return to port, they send the samples
to the university laboratory. Just like the giant oarfish
first encountered by David, most have mutilated bodies. The great white naturally appears
among the list of suspects. This time, divers were able to observe
in detail multiple scars. Dr. Tyson Roberts puts forth
another hypothesis based on the numerous animals
washed ashore in Japan. The oarfishes typically undergo
serial autonomy. Meaning, they undergo a consecutive series
of auto self amputation. It's like in a lizard
when it drops its tail, except the lizard
can only drop its tail at one place. The oarfish can drop
the body posterior to the vent repeatedly, starting from just in front
of the caudal fin, and then progressively
breaking off additional parts that are either short or long
or any length once at a time. It can do it all the way up to the vent,
which is right here. We can get oarfishes in which
only this much is left. Unlike the lizard,
the giant oarfish doesn't abandon its tail to escape a predator,
but for other astonishing reasons. Autonomy, the extent of autonomy,
and the number of times autonomy is totally a matter of individual history. It's energy conservation
to metamorphose into a body form where you're only conserving your gonads
and your vital organs. It's very rare in fish,
this is the only fish known to do that. To be able to prove
this revolutionary hypothesis, one must observe
this self-inflicted mutilation or find pieces of giant oarfish bodies
at the bottom of the oceans. One might as well try to find fish bones
in the muddy seafloor. Nearby to the village of Maserati
on the eastern coast of Italy, a geologist had a stroke of luck. Professor Patricia Bronzy
just excavated in a nearby quarry a curious fossil
dating back some 2.2 million years, which had surfaced
after a tectonic movement. This is the only known example
in the world of regal fossils. This is the rear
part of the body. She is withdrawn into
herself, but we can open it. The principle of autonomy
was thus engraved in ancient maritime sediments
for all eternity. Other clues, notably its feeding habits,
might be found by lipid studies. Thanks to the fins
collected by David and Roberto. Still, it's now necessary
to identify the preys of the giant oarfish
and thus their lipid signature. We're going to sink some special traps. One is going to be near the surface
to catch shallow drifters, and the other one deeper
to catch small fish and crustaceans. Like an underwater beacon,
the light from the trap arouses the curiosity
of the vagabonds of the open sea. They swim around the net
or try to find refuge in it. During the day, the catches are meager. When the trap is immersed
for a whole night, the morning collections
reserve many a surprise. These small shrimp
are none other than krill. This species, present in abundance
in the northern Atlantic, makes its bioluminescent organs
glow in the aphotic zone of the Mediterranean. Better; after sample analysis in the lab, the lipid signature of this krill is found in the flesh
of the giant oarfish. At night, krill make
their vertical migrations towards the surface to feed on plankton. Thus, they avoid diurnal hunters, like most of the fish
which swim around the buoys. In their wake, they lure all the predators
whose sight is adapted to very weak light. Among them is the giant oarfish. To observe their feeding habits, Roberto and David
will have to dare night dives in the open ocean, using rebreathers, without any bearings. You really have to be attentive.
We are in complete darkness. And we have no way
of orienting ourselves. Strange ghostlike visitors
make their appearance out of the infinite darkness. Like superorganisms,
these aliens of the deep ascend together each and every night
for an exceptional feast. It is the largest
biomass migration in the world. In the stinging traps, krill is a promising sign, but where have the fish gone? They seem to fear
great invisible predators and huddle together. Likewise, faced with ghostly threats,
David and Roberto regroup to keep a better watch in all directions. A sunfish, false alarm. Diving offshore at night is
like a child entering a toy store; with the beams of light, we
will reveal magnificent colors, we cannot see during the day. We
know there are lots of toys everywhere. We see very little, but it's enough
to be amazed by what we see. The king of herrings in all its splendor. The diver's underwater lights
reveal multicolored reflections. What use is this shiny skin
in total darkness? Maybe to mirror the dim lights
of the krill and blend in with its prey. It's a mystery. All the more so, as the oarfish
pays no attention to the krill. Nevertheless, it partially opens its mouth as if to catch invisible prey. The diver's light seems to disturb it. A closer look reveals tiny visitors which swim in and out of the mouth
of the oarfish of their own free will. Parasites. These are external parasites which do not remain permanently
in the body of the giant oarfish. Internal parasites, on the contrary,
pass from prey to predator. These give scientists a clue
as to the oarfish's predators. This is the opinion
of American doctoral students specialized in the study
of fish parasites. At the University of California
at Santa Barbara, the stomach contents of stranded oarfish
enabled Sarah Weinstein and Anna Garcia to make astonishing discoveries. Parasites offer a really great snapshot
of their life history. The information
that you wouldn't get any other way because most of these parasites
have complex life cycles, so they go through multiple hosts. For instance, we've found at least
three different species in the nematode. This is interesting
because one of them looks a lot like a species that uses marine mammals
as its final host. After further DNA analysis
of the parasites, scientists at the University of California
in Santa Barbara deduced that the oarfish
fall prey to deep sea predators such as sperm whales because they found
some juvenile nematodes in oarfish and some adult nematodes in sperm whales. These nematodes
actually end up in the oarfish. They're picking it up
from what they're eating like krill. The krill also provide oarfish
with bioluminescent bacteria. Until now, no bioluminescent organ
had been found on the oarfish for a good reason. No one had ever dived in the twilight zone
with a living oarfish. David and Roberto suggest
replacing the ordinary lamps with ultraviolet ones,
which revealed bioluminescence. Notably, the bioluminescent
lures of the krill eaters. Unfortunately,
the range of such UV lamps in water is far less than that of ordinary lamps,
which cancel out their effect. The task is both dangerous and difficult. David is going to have to spot the oarfish
with ordinary white lights, then turn them off and let Roberto
and his UV lights try to approach it. A daring challenge. A success. The UV lamps reveal
two bioluminescent organs on the oarfish's head. One on the forehead,
the other under its chin. Like luminescent miniature traps, these organs enable the oarfish
to be both seen and to lure its prey. Its beauty can also prove fatal
for divers. At one point I realized that
its crest was rising upwards. And I realized we were
going downhill at full speed. When I looked at the
watch, we were at 71 meters. It's a trap of this little fish. He
brought me to his house, to his abyss. The sea serpent is no longer
the mythical creature which devours ships. Its only menace
is its spellbinding beauty. David and Roberto looked deeper
to uncover the first secrets of the oarfish. The rare, eerie, yet harmless ghost of the open seas.
