The Mokarran Protection Society is a non-profit association under the 1901 law, created in 2019 to study and protect the Great Hammerhead Shark (Sphyrna mokarran) population of French Polynesia. It aims to bring together human and material resources necessary for a better knowledge and preservation of this species critically threatened by extinction.
The association is based in Rangiroa in the Tuamotus archipelago at the centre of the known territory of the Great Hammerhead Shark in French Polynesia. Rangiroa is one of the few places in the world where it is possible to observe it frequently without feeding.
The vision of the Mokarran Protection Society is participatory science that allows volunteer scientists to exploit the observations of contributing divers. It therefore seeks to establish and maintain a network of dive centers and diver partners to collect data and information throughout the year on the Great Hammerhead Shark.
Its team consists of marine biologists, experienced open circuit divers familiar with the Tiputa Pass, specialists in closed circuit rebreather diving with mixed gas and IT specialists in image processing.
The Mokarran Protection Society organizes both weeks of diving exclusively dedicated to research on the Great Hammerhead Shark during high intensity period called the Mokarran Weeks and cruise missions embarking a mixed team of divers, photographers and scientists to discover unexplored atolls likely to be frequented by S.mokarran, the Mokarran Explorers.
The Great Hammerhead Shark S. mokarran is present in Polynesian waters and particularly in the Tuamotu. In Rangiroa, the second largest atoll in the world with a lagoon surface area of 1,450 km², these observations are frequent while more occasional in other atolls of this archipelago. The Mokarran Protection Society was therefore founded in Rangiroa. It has two Passes which regulate the flows entering and exiting the lagoon under the influence of the tides: Tiputa to the east and Avatoru to the ouest. The Tiputa Pass presents characteristics particularly favourable for the observation of S. mokarran in the wild, rare and still poorly known, without feeding . During the four months of more intense observations of the Great Hammerhead Shark, from December to March, divers from all over the world come to this site to try to catch a glimpse of this fascinating shark, so original by the typical shape of its cephalofoil  and by its imposing size.
It is this privileged presence in the Tiputa site that led the Mokarran Protection Society to set up the Mokarran Weeks from its base in Rangiroa, Polynesia. This particular high intensity phase has been established empirically, thanks to the gathering of various observation databases since 2011. It is a first in Polynesia as the main study areas for this animal have only been Australia, South Africa and the American Caribbean so far.
Although being a protected species in French Polynesia, the Great Hammerhead Shark remains critically endangered in international and foreign waters. Determining the connectivity of these individuals and their migratory routes is essential in order to protect the species over its entire range.
The main South Pacific Current (the South Equatorial Current) flows from the north-western coast of South America to the east coast of Australia over part of its cycle. Polynesia could only be a stage for feeding, breeding and even giving birth, as it could be an area where the Great Hammerhead Shark has settled.
Here is the state of the questions that remain unanswered to date and to which the Mokarran Protection Society would like to contribute by using different methods: laser photogrammetry, photo-identification, or the set up of a citizen networks.
For this first season of the Mokarran Weeks, our objectives focus on three main areas and aims to understand the movements of the Great Hammerheads Sark in the "Pass system" according to the Lagoon-Ocean exchanges:
To set up an observation network with the different dive centers of Rangiroa which dive every day of the year, and which are therefore privileged partners to collect data and information on the long term.
Also, the collection of testimonials from local fishermen gives a rough idea of the distribution of Great Hammerhead Sharks in the lagoon. This is a way to discover new aggregation areas or even nurseries. This contact with fishing professionals, especially longliners, is also important to find out if the Great Hammerhead and juveniles of the species are part of the local bycatch.
As an environmental association, our role in educating and informing the general public is paramount. The state of the art of knowledge on the Great Hammerhead Shark and the results of the association are the subject of presentations within the Rangiroa community and more widely in Polynesia (schools, fishermen, diving clubs, tourists), in order to raise public awareness on the vulnerability of this species and its predominant role in the trophic chain.
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.