The great hammerhead shark, Sphyrna mokarran or Tamataroa in Tahitian, has been a protected species in Polynesian waters since 2006, along with 20 other shark species that inhabit the area. According to a study published in Nature in 2020, French Polynesia is among the few places in the world where sharks populations are thriving thanks to a total ban on shark fishing. The great hammerhead shark population is "critically endangered" worldwide, meaning that the next step in the status would be "extinct in the wild", according to IUCN (International Union for Conservation of Nature). Yet, the species still faces major threats by targeted fisheries and by-catches, which accelerate its decline.
The S. mokarran is a highly migratory species, able to travel more than 3000 km in the Atlantic Ocean, but its movements in the Central Pacific Ocean remain a mystery. Its migrations could very likely lead it to unprotected waters where the fleets of foreign fisheriesawait. To date, discovery of key habitats, i.e. reproduction or breeding grounds in Polynesia, or even in the world has yielded nothing – meaning human activities could easily be affecting these key habitats without our knowledge. Consequently, the protection of the species in French Polynesia does not guarantee its conservation in the area. Understanding the ecology of the animal, its movements and its key habitats, can enable suggested management tools to be put forward to Polynesian public authorities in order to set up appropriate measures for the conservation of the great hammerhead shark in French Polynesia and more widely in the Central Pacific.
For the past two years, the Mokarran Protection Society has carried out descriptive and identification work of the great hammerhead shark population in Rangiroa and Tikehau, without the use of baits, and with non-invasive measuring techniques. At least 50 different individuals have been identified, in Rangiroa atoll alone, which demonstrates the high value of the area for the study of this species. In order to give a major scientific and technical boost to the knowledge of the great hammerhead shark population and to provide local decision makers with management tools, an ambitious project called Tamataroa is underway. This innovative study has set up the first acoustic monitoring network for the great hammerhead shark in the Central Pacific. The mission was possible thanks to the collaboration of two entities: Gombessa Expeditions, which are internationally recognized for technical, diving and scientific skills, and which operates on a one-off basis on its missions, and the Mokarran Protection Society, which boasts extensive experience on the local field and a deep-rooted presence in the territory.
In addition to the characterization of the population, the study of the sharks' movements will be a priority, using acoustic techniques. Firstly, by scaling the atoll itself, to locate potential key habitats, before then conducting the monitoring at the Tuamotu Archipelago level. What are the migratory patterns? Do all sharks follow the same trajectory or does each one evolves regardless of the others? An acoustic network set in all passes of the west Tuamotu atolls should provide major answers to these questions. These acoustic receptors will also connect to the world's other networks and will enable researchers to follow international great hammerhead sharks migrations. This network is also adequate for the monitoring of other species, namely sharks, marine mammals or reptiles, and the intention is for this to remain for many years in Polynesian territory. Identification of key habitats and migrations occurring only in the protected waters of French Polynesia, means that a true sanctuary would have been located for this species on the verge of extinction elsewhere in the world. The completion of this migration study will then focus on protocols on population genetics and diet.
In line with the work already carried out, there is no intention to capture the creatures, as this method is too stressful for this sensitive animal. This large-scale study on a cryptic and poorly known species requires long hours underwater in deep and challenging conditions to conduct all operations in-situ, with an approach that only a closed circuit rebreather can allow. Hence, the Gombessa team alone has the necessary expertise to undertake this magnificent project.