The Elusive Mantas of the Chagos Archipelago

by ZSL on

By Niv Froman @MantaTrust

Manta rays are undoubtedly among the most charismatic marine species, so it’s no surprise they are always found on the top of every ocean lover’s wish list. It has been estimated that through tourism they generate a global revenue of more than 140 million US dollars annually and thus their beauty plays an important role in the economy of a number of island countries, such as Indonesia, Japan and the Maldives. As too often when it comes to natural wonders there is a dark side to the story. Manta rays are in fact targeted by fisheries globally to supply a growing demand for their gill plates which are used in Chinese medicine where they are believed to have healing properties. This targeted fishery, coupled with by-catch and the effects of climate change, are posing serious threats the survival of manta rays.

Manta ray in BIOT May 2018

An understudied population of reef mantas exists in the British Indian Ocean Territory (BIOT), but whether the Marine Protected Area (MPA) status of the archipelago and the lack of commercial fisheries and tourism are sufficient to guarantee the survival of this remote population is still unclear.

The Manta Trust team joined the recent Bertarelli Programme in Marine Science expedition with the aim of helping to answer this question using a suite of methodologies such as genetics and satellite telemetry. Thus armed with underwater cameras, satellite tags, and a biopsy pole we set sail to the heart of the Indian Ocean! Finding mantas is not an easy task, especially in such an unexplored region of the planet, and the task turns out to be even more challenging knowing that only two days will be spent at Egmont Atoll – the site with the highest currently known concentration of these animals in the archipelago.

Manta ray identity markings BIOT May 2018
Each Manta has a unique pattern on its underside to identify each individual

Although our expectations were relatively low, luck seemed to have smiled upon us. In only two days we recorded 55 sightings of 41 different individuals bringing the photo-ID database of the BIOT manta population to 107 individuals. We deployed three satellite tags which will record depth profile, location, and other important data for the next six months, and we also managed to collect tissue biopsy samples of half a dozen individuals - samples which will provide important information of the level of genetic and geographic isolation of the manta population here.

Being in the BIOT, the only ‘mega’ MPA in the Indian Ocean, with a rarely observed manta population, and being able to study these animals is not just a privilege, but a unique opportunity to contribute to their improved conservation status of this globally threatened species.  

For more updates from this and future expeditions, follow us on Twitter @BIOTscience.

This work was kindly funded by the Bertarelli Foundation as part of the Bertarelli Programme in Marine Science.

Previous blogs on this expedition can be found here:

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