THE “GROUPER MYSTERY”

It’s the story of a scientific adventure and diving record in a remote Polynesian paradise. A place where thousands of camouflage groupers, followed by hundreds of sharks, congregate in secret once a year. Laurent Ballesta’s team wanted to gain a better understanding of what pushes these fish to wait for the exact day of the full moon to reproduce simultaneously! With the help of researchers from the CNRS in Moorea, they made numerous dives and conducted many experiments to study and testify to this unique phenomenon. Taking advantage of this incredibly rich period, Laurent Ballesta made a record 24-hour dive.

It is 3 p.m. and the sun is shining over the turquoise water. I’m sitting on the pontoon of a semirigid boat and I am preparing to dive for 24 hours. For the first time in my life, before getting in the water, I can call out “Cheers and see you tomorrow” to my mates.

And it is when actually saying it that I evaluate the extent of my folly: I am really going to dive for 24 hours, and I will not emerge from the water until the same time tomorrow. I am completely determined. I have been dreaming of this for so long. But I am also disconcerted. I am afraid. Afraid of not succeeding, of being cold, of being hungry, of wearing myself out too quickly and wanting to get out before the end. I have been doing “committed” dives (meaning deep ones) for years, but today is different. It is no longer a vertical exercise, but a horizontal test. It is no longer just adive, it’s a marathon! I reassure myself by thinking that my doubts will only last for a while. In a few hours’ time, the question will no longer be relevant, since by then it will be impossible ascend at will: the mixture that I am breathing will have saturated my blood with helium. Even at a depth of 20 m, it would take me six hours to reach the surface if I had the misfortune to give up. A final glance at the members of my team and I roll backwards. The twice-round-the-clock epic has begun.

Nothing is more essential than time when it comes to solving the “grouper mystery”. It’s a mystery that is both subtle and complex. What I am hoping to witness is the rendezvous of all camouflage groupers (Epinephelus polyphekadion) around the Fakarava atoll, 490 km northeast of Tahiti. Their gathering takes place in this unique location that links the lagoon to the ocean: a pass that forms a break in the coral barrier reef, a tiny gate between the vast lagoon and the largest ocean in the world. In this indentation, the currents are violent but predictable: they follow the tide and the lagoon, alternately filling and emptying every six hours. The animals live according to this rhythm.

The resupply operation went perfectly, at least from my perspective. Later, I will learn that they’d had a pretty frantic time of it on the surface when it came to recovering the equipment, what with the current and the already well ensconced pitch-dark night.

It’s nighttime and I have 12 hours of night ahead of me. My buddies will come one after the other, Cédric, then Manu, Antonin and finally Cédric again. In turn, they will each spend three hours keeping me company by hovering 10 m above me with a powerful light. They light up my path and I see it as a great token of friendship. I owe them this magical vision, this indiscreet skylight on the little secrets of nocturnal life.

The fish have changed color. They have truly donned their pajamas, given the incredible difference in their livery from day to nighttime. Hour after hour, I add to my personal bestiary of nocturnal creatures. Nighttime is the kingdom of crustaceans and mollusks. In Polynesia, there are more than 5,000 species. Invisible by day, they wait for dusk to emerge from the bowels of the coral. Cautious, they remain on the threshold.

At the slightest glimmer, they plunge back into this overpopulated “crypt” of the coral reef. I have but a brief moment to capture a picture of them as they flee from the light.

The night continues, and I have already roamed 7 km along the reef, a long loop that brings me back to the refueling meeting place for a second time. It is midnight and I await the relief. It’s all going well and I’m not cold, but I am impatient. I learned that a diver recently set a record in Egypt by remaining under water for 55 hours, at a depth of 5m, sitting on the sand near a beach, without moving and connected to bottles on the surface by a long umbilical cable. I actually suspect that he took sleeping pills to make the time pass faster. For my part, I’m trying to extend the time!

Yanick has joined me for a few hours with his special slow-motion Phantom camera that is capable of taking 1,000 images a second. A violent and chaotic frenzy explodes before him. But the same scene, when watched in slow motion, will later show us all the efficiency and precision of the sharks’ attack. They devour the groupers in hundreds, perhaps in thousands: another factor that further deepens our “grouper mystery”. It would appear that the gathering nonetheless works, that this breeding ground is worth it despite the risks, and that the groupers have managed to solve the equation between sacrifice and benefit to their advantage. We are keenly aware that these hunting scenes filmed in slow motion, as well as these photographs that freeze the dazzling speed of the attacks, are all unprecedented images. Like me, my companions are exhilarated. As if we had transgressed a taboo: diving in the pass by night when the sharks are hunting.

During the night, the sharks make contact incessantly. My slightest movement and the slightest ray of light attract them. Initially just one excited representative, then two, then ten, and then they vanish as quickly as they appeared and the carrousel begins all over again. I even recognize individuals, because it is often the same ones that react. All make a beeline for me but although some make contact without ever opening their mouths, most turn around without touching me. In the end, when I get out of the water the next day, I barely notice two or three bruises on my thighs.

It is 6 o’clock in the morning. On earth, we say the day is breaking when, far away on the horizon, the light gradually ascends. Here, the light descends. In the small hours, it filters gently in from above. A dim glow pours blue-tinged water into the inky black depths. It is 6 o’clock and the bells are ringing. At least that is what comes to my mind all of a sudden, at the very moment when the light reappears and I hear whales singing! I unfortunately do not get to see them and maybe they are hundreds of kilometers away, but they sing for us. Who else would it be for after all? I have no idea if one can have goosebumps under a 7-mm-thick wetsuit but that’s still what it feels like.

It’s time for the final resupply. Sané, the Polynesian who has lived here for twenty years, has come for a little morning visit. With a naughty smile, he proffers the toothpaste tube and a toothbrush. I share his game happily and do the necessary without swallowing a mouthful of water. The night is over, along with much of the stress and I only have nine hours left in which to enjoy the surprises of the southern pass seabed. But it is nevertheless a critical moment: watched by Jean-Marc, I replace 87% of the helium with air. I am not at all dizzy, everything’s fine. This operation marks the beginning of my decompression but not the beginning of the ascent. I can remain at 20 m the entire morning.

The sharks have calmed down and the groupers are beginning to stir. Some resume their lethargic swimming, others their hysterical struggles. This morning, after spending a whole night in their presence, they look like survivors to me. Twenty-four hours down here is an opportunity to bear witness to a touching sight and to put together a tragic gallery of portraits,

I have never seen this many since our arrival. They too know that something is going to happen. The groupers’ excitement is also unusual, but after weeks of confrontations, a certain spatial organization has set in. This natural work of art is no longer abstract: the canvas now begins to make perfect sense. Firstly, the females in camouflage dress and with their bellies dilated with eggs, either near the seabed or sometimes even resting on it, and just above them the pale gray males, watching over them from above. A male regularly goes down to a female, and begins a parade consisting of delicate tremors and then very fast, he jostles her, always in the same way, by biting her stomach, undoubtedly to induce spawning, a phenomenon that appears to be imminent!

And suddenly, it’s all happening! Bands of groupers shoot upwards and the reproduction has well and truly begun, although unfortunately too far away and too fast for us to be able to get a good view of the intimate details. The fusiliers, of which there are more and more, block out the horizon so effectively that it is hard to make out the groupers. The cloud of eggs and semen barely has a chance to appear before the fusiliers rush to swallow the fertile milt.

Pandemonium reigns at the bottom of the pass. The groupers leap here and there, taking off all around us like live fireworks, while the fusiliers are everywhere and the sharks plunge into the fray but re-emerge empty-handed most of the time. The act lasts less than a second and we don’t even have time to understand what is happening. Two things however appear certain: it is always a band of a dozen or so groupers that leap from the seabed, never a single couple; and it is anarchy, the laws of survival of the fittest or fastest, that appears to prevail.

And it is precisely that which surprises me. What is the use of fighting for four weeks if the winner is not then entitled to a female all to himself? It’s a complete waste of energy! What is the use of coming so early in the season with the risk of being eaten every night if it doesn’t offer any form of privilege on breeding day? I don’t understand. The “grouper mystery” remains intact. Weeks of fighting, but when it comes to breeding, no rules appear to apply: all the males, winners and vanquished alike, leap towards the female laying her ova and all appear to have the same chance of fecundating her. Only the ocean currents, which blend this fertile soup, will decide who will be paired with whom. Will the happy sire be chosen by fate? I can’t believe it. This truly is the crux of the “grouper mystery” and something has definitely escaped us. But how can we possibly have any idea? The mating is so quick, although one can definitely understand the speed factor: to avoid the sharks when they ascend to the open water and also to be the first to fertilize the female’s eggs. But perhaps this speed hides another truth from us.