The Mokarran Protection Society (MPS) was born from the passion of three Rangiroa diving instructors and a meeting with Marc Hayek from the Blancpain Manufacture.
It is a non-profit association under the French law of 1901, created in 2019 to study and protect the great hammerhead shark (Sphyrna mokarran) population of French Polynesia. It aims to gather the human and material resources necessary for a better knowledge and the preservation of this species seriously threatened with extinction.
The association is based in Rangiroa, in the Tuamotus archipelago, in the center of the known territory of the great hammerhead shark in Polynesia, also called the "tamataroa" in Paumotu language. Rangiroa is one of the few places in the world where it is possible to observe this shark without feeding (1).
The paradigm of the Mokarran Protection Society is participatory science, which allows the association to collect observation data and images throughout the year from a network of instructors, visiting divers and the population of the archipelago.
Its team is composed of marine biologists, photographers, underwater and terrestrial videographers, lawyers, communication officers, computer specialists, and school teachers. All of them are experienced divers (in open or closed circuit) and familiar with the Tiputa channel.
In order to carry out its missions, 4 areas of expertise work together on a daily basis:
An initial three-year research campaign (from 2019 to 2022) has yielded groundbreaking results that show that the Western Tuamotus, host a large population of great hammerhead sharks. Today, Rangiroa atoll can be considered as the most important observation site in the world for this species. Even better, several clues suggest that these atolls concentrate key areas of its life cycle (mating, gestation, calving, nurseries, and growth). Based on these results, a new three-year scientific campaign has been set up in close collaboration with the Department of the Environment of Polynesia, the municipality of Rangiroa, the inhabitants of the Tuamotus and the expertise of Andromeda Oceanology. It started in December 2022. This mission is named "TAMATAROA" in honor of the shark that protects and guards the passes, as described by the fishermen. This program is fully in line with the dynamics of the Fenua to protect its natural heritage.
The association leads a network of partners that grows year after year: municipalities, sea professionals and schools. Since 2019, observation and census missions have been carried out with the support of territorial and scientific institutions, and in partnership with leading players: the Blancpain Watch Manufacture through the Blancpain Ocean Commitment, the Bank of Tahiti, the Environment Department of Polynesia, the French Office of Biodiversity and Air Tahiti.
Our objectives are threefold and tend to understand the movements of great hammerhead sharks in the "pass system" according to lagoon-ocean exchanges:
Although a protected species in French Polynesia, the great hammerhead shark remains vulnerable in international and foreign waters. Determining the origin of these individuals and their migratory routes is essential in order to protect this species throughout its range.
Photo-identification consists in establishing, by means of identification sheets, a database for each individual observed. They include information on the size and sex of the individual, a description of any details likely to facilitate identification (scar, stain, etc.), as well as a photo of the dorsal fin to identify a notch code. This is a three-digit ID number assigned to a dorsal fin. The photo of the dorsal fin is first trimmed so that the top end and base of the fin are positioned, and then cut into three horizontal stripes. Every detail (shearing, blistering and deformation) of the posterior edge of the fin is raised and located. They can be the result of injuries, mating bites, disease, old age and provide a unique profile for each shark. The number of details is reported per band to form the notch code formula. This formula is one of the identification keys.
Photo-identification meets our objective of evaluating the sedentary lifestyle of individuals and is established over several seasons to obtain inter-annual conclusions. Indeed, we still do not know if the individuals observed remain present on Rangiroa all season long, or even if they return to the following seasons.
Underwater, observers fill out a form for each shark, noting characteristics and identification marks, as presented below :
The laser photogrammetry technique provides more accurate information on the size of the individual than by simple observation, avoiding approximation errors. Two lasers mounted in parallel are fixed on a plate with known dimensions. A Gopro is fixed equidistant from the lasers and allows the capture of an image with projection of this distance on the animal, thus giving a scale to make different measurements of the individual (Fork Length, Pre-caudal Length, Width of the Cephalofoil, Height of the 1st Dorsal Fin, Total Length). It is then possible to determine the stage of sexual maturity of the individual: 225 to 270 cm for males against 210 to 300 cm for females (Stevens et al., 1989).
The use of this photogrammetry technique, combined with photo-identification, is in line with the work carried out at Bimini, Bahamas on the S. mokarran. In accordance with their material and method we use a 30 cm wide plate and a second of 50 cm width in order to check the most suitable to our need depending on the challenging diving conditions in Tiputa.
Rangiroa currently has six dive centers, some of which have been established since 1985. Their experience on the field and their continuous year-round observations are a major asset in data collection. Beyond the high intensity Mokarrans Weeks, the association collects observations of S.mokarran and of Leopard Eagle ray (A.ocellatus). Indeed, A.ocellatus is a targeted prey of this predator and gathers in flight several individuals at this season. The main hypothesis put forward for the moment is therefore a presence for food purposes.
After each dive in the Pass, the instructors can enter their observations on a form as presented below:
1] Feeding: The activity of feeding the shark for bait and providing close observation to the client.
2] Cephalofoil: Sensory organ located at the head (T-shaped in the hammer) that performs sensory functions (detection), manoeuvring in the water and handling prey.