French Polynesia
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December to March 2022

Mokarran III

In 2022, the Mokarran Protection Society puts its fins back in the water for a third season in the Western Tuamotu archipelago, during the austral summer period (December to March) to study the seasonal great hammerhead shark (S. mokarran) population. The first two campaigns brought to light new results on the species in French Polynesian and at the central Pacific scale, a data-deficient area. The study was a real success in view of the field constraints related to a high depth - ranging from 50 (open-circuit) to 70 m (Closed Circuit Rebreather) and strong drifting current, without any provisioning to attract the sharks. Based on the previous years’ results and pending issues, the association has continued and expanded its protocols, further focusing its effort on lagoon exploration, local community involvement and fundamental research on S. mokarran in Rangiroa and Tikehau atolls.

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Previously, the citizen survey conducted in connection with local fishermen, excursionists, and dive instructors, revealed through testimonies the potential presence of essential functional areas (such as pupping, nursery or feeding grounds) for the great hammerhead shark life cycle in Rangiroa and Tikehau lagoon, confirming the need to explore these inland seas. But the task is not simple when venturing further into remote areas. Reconnaissance and prospecting campaigns were carried out based on the areas identified during the citizen survey. A base camp was established in the "sector", an isolated and practically uninhabited area of Rangiroa atoll. Accompanied by local guides, members of the association, the objective was twofold: to identify the features of the area (currentology, temperature, type of habitat, species encountered) and to prospect for potential functional habitats using non-invasive methods. Attention was directed to the observation of behaviour of interest (passage, hunting or parturition scenes) and of presence of juveniles. In the case of juvenile sightings, the accuracy of species identification is a difficult task due to the known risk of confusion with other hammerhead shark species at this early stage. Further forays into the lagoon will be necessary in the future to unveil the secrets that these pristine areas hold in the ecology of the great hammerhead shark in the Central Pacific.

For the third time, a scientific campaign was conducted in Tiputa (Rangiroa) and Tuheiava (Tikehau) passes to refine descriptive features of the seasonal S. mokarran population in the western Tuamotu archipelago. Using non-invasive techniques (photo-identification and laser-photogrammetry), results have revealed an unprecedented recorded number of great hammerheads identified in a 3-year seasonal timeframe with at least 70 females, all likely mature. Other established highlights have been seasonal residency, with S. mokarran remaining for up to 6 months in the area, and sexual segregation, as only females are sighted during the austral summer months. Completing these sampled data with photos collected from dive instructors since 2006, analysis show that at least 30 individuals were newly identified (15 females and 15 males), revealing empirical sexual segregation, with males mainly sighted from August to October and females from November to May. These citizen data have provided a hindsight of more than 15 years on great hammerhead shark sightings in the Tiputa pass and 6 years in the Tuheiava pass, enabling to prove that 33 identified great hammerheads have showcased site fidelity behaviour, meaning they return to the study area year after year, sometimes over a 14-year timeframe. The austral summer occurrence of only adult females demonstrating fidelity and residency to the Tiputa and Tuheiava pass indicate that these two areas and their atolls play a major role in the life cycle of the species, likely related to different critical life-history needs such as breeding or feeding.

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These results highlight the importance of Rangiora atoll, and to a lesser extent Tikehau atoll, for S. mokarran conservation and enhance the relevance of rapid conservation measures. The forthcoming TAMATAROA project focusing on the species movements in the area (using biotelemetry techniques) will provide all year-round evidence on essential habitats, fine scale movements of S. mokarran inside the lagoon, and migration patterns within and outside the Tuamotu archipelago, to inform long-term species-specific conservation planning at local and regional scale.

In parallel to the lagoon exploration, the association has continued its efforts to further involve Polynesians of all ages in its initiatives. A Va'a (traditional Polynesian canoe) race was organized in partnership with the municipality to reunite the whole atoll community during a local sporting event. Themed on the migration of the great hammerhead shark in the lagoon, this race involved women, men and children on courses from 5 to 20 km. Supporters were interviewed about their sightings of the species in the Tuamotu and informed about its conservation, thus reaching a wider public but just as concerned. This popular event will be repeated next seasons focusing on the S. mokarran inter-atoll migration between Rangiroa and Tikehau. New interventions in primary and secondary schools allowed to educate a young audience of the Tuamotu and Society Islands to the preservation and the importance of this species for their marine ecosystem. An educational kit, designed entirely as a local and eco-friendly board game, was initiated for the first time among Polynesian schoolchildren with the objective of educating while having fun. With questions on the ecology of the great hammerhead shark, the marine ecosystem, and the legal protective mesaures of marine fauna in Polynesia, the game meets the educational requirements of school programs and is supplemented by a booklet to deepen all the knowledge addressed in the game.

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