TAMATAROA

They saw it up close, very close indeed, and on several occasions. It came to them naturally, driven by instinct and curiosity. It showed itself to remind them that it existed, then left as dis­creetly as it had come, into the ocean depths. 

It was a furtive encounter, a powerful interaction that brought both happiness and concern and which, like their previous ones, will remain engraved in the two divers’ memories. They have reached their objective, their work is now done and every minute counts at this great depth. It’s time for them to go back up. 

They allow themselves to be carried back by the current to a small underwater cave, a convenient refuge where they will spend their long hours of essential decompression before returning to the surface. A parachute buoy is sent out by one of the divers to inform the boat’s crew that they have finished their dive safely. It is also the signal for the second pair of divers, who had remained on board, to get into the water to take over operations. But first, the boat’s pilot, who is well-versed in the procedure, carefully retrieves the underwater speargun and the small bottle attached to the buoy by the divers. The gesture is quick but meticulous, because he knows that the bottle contains a very precious sample. 

In their small cave, a few metres below the surface and sheltered from the current, the two divers now have time on their hands. Sitting on a small slab of dead coral, they observe the landscape before them. The cave overlooks a narrow coral canyon through which an array of multicoloured fish with evocative names parade: rainbow runners, parrotfish, butterflyfish, lionfish, blue­­­­s­ potted groupers, spotted eagle rays and blacktip reef sharks. The beauty of the scenery is breathtaking, all the more so as everyone in this small gathering seems oblivious to the presence, albeit discreet, of the two divers. Before their eyes, underwater life is in full swing. Silent witnesses to a natural symphony in perpetual motion, the divers admire the delicate balance of this wilderness, where every element, from the tiniest marine creature to the vast coral reefs, occupies a vital place in this ecosystem and contributes to maintaining its health and resilience. 

But the divers are not fooled: they know that a shadow hangs over the harmony of this underwater composition. A cloud that continues to darken, a global ecological crisis that threatens this fragile equilibrium a little more each day and of which one of the most alarming signs is the continuing decline in biodiversity. They have ringside seats to this situation. Not there, sitting in the cave in front of this teeming crowd, but just before, when, in the depths of the ocean, they were lucky enough to encounter one of its ­ sadly emblematic ambassadors: the great hammerhead shark. 

The two divers, dressed all in red, are scientists and members of Gombessa Expeditions led by marine biologist and photographer Laurent Ballesta. When they emerge from the water in a few hours’ time, they will join the other members of the team at their research base facing the immense lagoon of the Rangiroa atoll, in French Polynesia’s Tuamotu archipelago. It is here, in this remote corner of the Pacific Ocean, that they and members of the local Mokarran Protection Society – with Blancpain’s unfailing support through its Blancpain Ocean Commitment initiative – are ­ conducting one of the most ambitious research programmes ever dedicated to the preservation of this shark on the brink of extinction: the TAMATAROA project, named after the great hammerhead shark in the local dialect. 

Designed to take place over four years, the programme has ambitious yet necessary objectives: to provide scientific knowledge, identify pressures, define conservation issues and foster citizen involvement to support the implementation of sustainable manage­ment measures adapted to the conservation of the great hammerhead shark and its habitats in French Polynesia. 

The story of this animal, the mysteries surrounding it and the genesis of this project are expertly outlined by Tatiana Boube in her article published in the previous edition of Lettres du Brassus in 2023. Tatiana, a marine biologist based in French Polynesia, received a grant from Blancpain to support her doctoral studies and research on the great hammerhead shark at the University of French Polynesia. A year and a half after its launch, the considerable efforts deployed as part of this programme are beginning to bear fruit and are now a veritable source of hope for the preservation of this species and its environment. 

Over the last year and a half, scientific divers from Gombessa Expeditions and volunteer members of the Mokarran Protection Society have worked tirelessly to implement the programme’s numerous scientific protocols. In order to introduce effective conservation measures designed to halt the decline of this magnifi­cent shark, the first step involves answering questions about its ecology, the needs associated with its survival and the threats to its equilibrium: 

· What are the characteristics of the great hammerhead shark population in this region of the Pacific? Is it different from other known populations?

· Where, when and how does it feed? What species does it target in its diet?

· Where, when and how is it evolving? What is its range?

· Where, when and how does it reproduce? What are its preferred locations for giving birth and raising its young?

· What human and/or natural pressures and threats affect each phase of its life cycle?

The tracking tags that experienced divers are able to attach to sharks should make it possible to define their migratory routes and correlate them with their primary survival needs. Two types of tag are being deployed under the SMART system: ‘acoustic’ tags and ‘data archiving’ tags. Both are designed to track the movements of pelagic species that have little or no surface presence. The first kind of tag is the size of a pen and emits a regular acoustic signal specific to each tagged individual. This signal can be picked up by acoustic receivers fixed in advance at strategic points in the lagoon and its passes, so as to create invisible listening fields. The acoustic signals they pick up when a tagged shark passes close by can be used to identify the individual as well as the time and date of its passage. To obtain a precise idea of the movements of sharks within the Rangiroa lagoon, the team has deployed the largest underwater acoustic network in the central Pacific. 

‘Data archiving’ tags, meanwhile, are used to track major migrations in offshore areas. These are small, highly sophisticated satellite transmitters that continuously record data on depth, temperature and luminosity. Attached to the sharks for a pre-programmed period, they are eventually released automatically and return to the surface to transmit all the data they have stored via the Argos satellite system. By combining the data they record, mathematical models can be used to trace the movements of the individuals being tracked on a very large scale and in three dimensions. 

Throughout their migratory journey, great hammerhead sharks pass through a variety of underwater habitats. While some are merely travel corridors, others can play crucial roles for the species as feeding, reproduction, calving or nursery sites. It is these habitats that scientists are seeking to identify using dedicated protocols: counting potential prey, searching for juveniles, studying behaviour, etc. To do this, they conduct diving campaigns wherever sharks tend to linger. Each time an area of interest is identified, the scientists look at its ecological health and the various pressures that humans are likely to exert on it through their activities. This is where management measures will eventually be focused, to encourage those who use marine environments to adopt eco-responsible stances and contribute to the ecological transition of their activities by implementing more sustainable approaches. 

The design of this novel arrowhead – on which the success of a large part of the monitoring protocols depends – was a real technical challenge. To make their concept a reality, the Gombessa team naturally turned to Blancpain, its long-standing expedition partner. Passionate and always keen to support research and environmental conservation initiatives, the Blancpain teams drew on their excellent expertise in high-precision engineering to create this multifunctional, surgically precise instrument. 

This system enables divers to conduct all the monitoring proto- cols in the very short time available to them during their natural, close interactions with the sharks. It offers an alternative to conventional baiting and capture methods while paving the way for study protocols that are less invasive and more respectful of these large predators. 

USING THE SMART SYSTEM

At every encounter, the divers are filled with excitement, albeit barely palpable given how focused they are on their scientific objectives. For they know that the success of their scientific programme depends largely on the success of their mission, conducted ­ 60 metres below the surface in the face of this majestic animal. Positioned on the seabed, the diver equipped with his SMART system films the animal, which is curious and approaches him calmly. Later on, these images will reveal the small physical details that are unique to this individual’s body and that will be used to identify it. Coming within just a few metres of the diver, the shark – whose curiosity appears to be whetted by the encounter – turns slowly to avoid him. The two green dots projected by the lasers are clearly visible on its flank. Exactly 30 cm apart, they will be used to determine its size when the images are processed. But the diver isn’t looking at them. He is concentrating on his shot, which must be extremely accurate. The arrow shoots out, penetrates a few centimetres under the fin, then falls back to the ground. Inside its fine hollow point, a small sample of skin has just been taken. The action only lasted a tenth of a second. Barely affected by the sting, the shark continues on its way into the darkness of the deep. From a distance, the divers can see a small black spot on its back. This is the tag now attached to the shark that will enable them to track its long migration.