Since 2020, the Mokarran Protection Society has been organizing Mokarran Weeks in Rangiroa. These are weeks of intensive dives dedicated to scientific research on the great hammerhead shark. They take place during the so-called high intensity observation period of this species from December to March. For the volunteer members of the association, these Mokarran Weeks are the opportunity to converge towards the Tiputa channel.
The year 2021 is marked by two new features.
On the one hand, the Mokarran Protection Society is conducting its first Mokarran Explorer mission in Tikehau. This Mokarran Explorer follows the reconnaissance dives carried out in July 2020 in this neighbouring island of the Tuamotu and the follow-up of the observations made since then, thanks to the generous contribution of our local diving instructors and friends: Loïc, Robert and Sébastien, whom we would like to sincerely thank. This first Mokarran Explorer mission aims at evaluating the possible return trips of the S. mokarran between the two atolls.
On the other hand, and unfortunately, the Mokarran Weeks 2021 coincide with the second wave of the Covid-19 pandemic worldwide. The second lockdown in Metropolitan France is thus severely impacting, not only the tourist economy of French Polynesia, but also the scientific research planned to be carried out at this period of the year. The team of the Mokarran Protection Society is mobilized to maintain its ecological and economic commitment in favour of our Fenua and in compliance with the legal and sanitary requirements. In spite of the logistic difficulties that this situation entails, we have decided to maintain as best as we can the Mokarran Weeks 2021 because we believe that the planet of tomorrow needs to be saved today.
The sex of S.mokarran individuals observed during the first Mokarran Weeks 2020 could be established 83 times out of a total of 135 observations, i.e. in 61% of cases.
The statistics are clear: 100% of the individuals that could be identified during the 2020 campaign were females. The presence of the great hammerhead shark in Rangiroa during this time of the year would therefore appear to be based on an inherent need for the species’ life cycle.
Data collected by the Polynesian Shark Observatory (Observatoire des Requins de Polynésie - ORP) since 2013, which include sex information since 2016, corroborate these results, since very few males were observed during the previous years between December and March.
Sex segregation by geographic location is a common characteristic of a number of shark species. This behaviour may result from specific intra-species competition, seasonal habitat and food resource needs, or pre- or post-breeding strategies.
A similar pattern could therefore explain the sex-segregation behaviour observed on the hammerhead shark population in Rangiroa. Our work in this area will continue during the 2021 season to confirm this trend and identify its potential causes.
Our goal is to unravel this mystery!
The second field mission of the Mokarran Protection Society has been launched early December. About 20 scientists and volunteer divers coming from France, Tahiti and New Caledonia, are expected to stay in Rangiroa for the occasion. We are planning to carry out about 200 OC dives and 40 days of CCR diving between December 2020 and February 2021.
The good distribution of the volunteers throughout three complete lunar cycles could, hopefully, allow up to 55% more observations than during the first mission Mokarran I.
This mission Mokarran II will be the opportunity to enlarge our research area and to carry out a reconnaissance expedition in Tikehau. This other atoll of the Tuamotu archipelago, which is located only 15 km from Rangiroa, builp up a first-rate reputation for the observation of the great hammerhead shark in its unique Tuheiava channel. Many local fishermen have also reported sightings of S. mokarran around their fish parks inside the lagoon. Juveniles were even observed from the village jetty, without the species being formally identified.
The simultaneous presence of divers in Rangiroa and Tikehau will allow to identify specimens in both atolls and highlight possible connections between the two channels.
The mission Mokarran II will also be an opportunity to deepen the areas of presence of S. mokarran in Rangiroa and its lagoon. This vast inland sea remains a mystery since no sightings of great hammerhead sharks have been reported, although observations in the channel have proven that individuals head there and return daily.
In addition to this expansion of our research areas, the identification effort in the Tiputa channel will be intensified to establish a possible seasonal sedentariness for some individuals that will be identified again this season. To this end, five new laser decks have been designed and made by Christian LUMBRERAS. While these new decks, made lighter thanks to the use of aluminium and polyacetal, are easy to handle, their major innovation is the greatly simplified system for laser fixation and calibration. More accurate than the old decks, the perfect symmetry of the two lasers is easily obtained and lockable, thus limiting measurement bias over time. In addition, the superior definition of the new GoPro© 8 acquired by the MPS, will allow a significantly improved image quality to facilitate laser photogrammetry measurements and photo-identification, in order to increase the identification rate of the measured sharks, which was 75% during the mission Mokarran I.
New generation of laser decks used for measurement by laser photogrammetry
The association warmly thanks Christian LUMBRERAS for the design of these new laser decks. A former fisherman, engineer and self-taught builder, he works on a voluntary basis to design tools applied to marine ecology.
The Mokarran Protection Society will soon launch a citizen survey for the inhabitants of Rangiroa and then on the other islands and atolls of French Polynesia. Each participant will be able to share their knowledge on and observations of the great hammerhead shark.
Such a survey is part of a participatory science approach with a double objective.
On the one hand, it is an opportunity to involve the inhabitants of the Tuamotu in the protection of the Polynesian environment, while presenting the association, its members and actions.
It is also a chance to learn about observations and behavioural data on S.mokarran from local populations, in order to improve our understanding and thus establish an effective strategy for studying the species and its associated ecosystems in French Polynesia.
The MPS thus hopes to collect new information on the behaviour observed individuals and on potential strategic sites: nurseries, fish parks, fishing docks etc.
This data is valuable for directing and focusing future scientific research towards the most relevant areas at the right times. This optimization of resources will hopefully lead to the acquisition of new data that will allow us to optimize our scientific study of the great hammerhead shark and the biological equilibrium of our Polynesian lagoons.
The questionnaire will be available in hard copy as well as online on the mokarran.org website. After three weeks of survey, two meetings will be planned in order to present the results to the inhabitants of Rangiroa, then online for the whole French Polynesia.
It is with a particular emotion that I take up the pen at the end of the year 2020, which will probably have tested us all very hard.
Because it is first of all the occasion for me to wish you with all my heart a happy holiday season, wherever you are, I hope that this month of December will allow you to recharge your batteries and to share pleasant and comforting moments with your loved ones and those who are dear to you.
It is also an opportunity to ensure you of our continued and growing commitment to the study and protection of the great hammerhead shark. This beautiful mission has only just begun. The Mokarran Protection Society was officially created on July 5, 2019, and here we are, a year and a half later, conducting our second mission Mokarran II, the first Mokarran Explorer in Tikehau, with the support of two partners, Blancpain and the Bank of Tahiti.
Jack London, an American writer and naturalist, is said to have brought back a Polynesian proverb according to which the coral grows, the coconut tree grows, and the man leaves. On the contrary, our ambition is to stay and to inscribe our scientific, ecological and participative action in the long term.
Thanks to you and your support, whoever you are and wherever you read us, divers or instructors, boaters, tourists, residents, scientists or simple lovers of the sea and nature, we are trying as best as we can to better understand and protect the S.mokarran. I wish you all a long life and a beautiful year 2021. Thank you!