By DIVE Staff
A recently published study investigating the manta ray populations of Seychelles has highlighted the importance of D’Arros Island and St. François Atoll for reef mantas. (Mobula alfredi)
Conducted using photo-identification and remote underwater camera systems between 2006 and 2018, a team led by researchers from the Save Our Seas Foundation and the UK’s Manta Trust identified a total of 236 individuals, 65 per cent of which were sighted around D’Arros Island and 22.5 per cent at St François Atoll, part of the Alphonse group of islands.
Identification of the mantas – by the unique spot patterns present on their ventral surfaces – was aided by photographs submitted to the Seychelles Manta Ray Project by citizen scientists, plus dives conducted by the researchers. A new ‘Manta Cam’ was also deployed over a two-month period at a manta cleaning station located at D’Arros Island, which not only helped to identify individual rays, but also captured a display of courtship behaviour, which had not been seen before at that location.
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‘Having access to this site motivates us to prioritise mantas as one of our long-term monitoring projects,’ said Dillys Pouponeau, research officer at the Save Our Seas Foundation. ‘We are now taking advantage of technology to monitor them more effectively than before – our MantaCam is scheduled and swapped in a way that ensures we always have a camera “on” at the cleaning stations. We are also starting to integrate drones into our surveys. These new methods enable us to monitor the mantas in a non-invasive manner and for longer than ever before, gathering data in their natural state.’
Although D’Arros island is home to one of the largest known aggregations of manta rays in Seychelles mantas, little is known about their population and its movements. D’Arros Island and St François Atoll are remote and not easily accessible – an undoubted benefit to the manta rays but not easy for the human study; vital to ensure ongoing protections are enforced and, if necessary, further conservation areas established.
‘The remoteness of D’Arros Island and St François Atoll keeps these manta aggregations rather isolated in nature,’ said Dr Peel. ‘This provides an important opportunity to both conserve manta rays in Seychelles and gather important baseline information about the biology and ecology of these animals in the absence of common human disturbances.’
The team found that equal numbers of male and female rays were identified across the population, and almost all of the identified rays were reef mantas, although a handful of oceanic manta rays (Mobula birostris) put in an appearance over the course of the study. The mantas tended to visit the cleaning stations at around midday, and were observed to have ‘crepuscular’ feeding habits – undertaken in the dimmer light at dawn and dusk – but there is much more research required to better understand the mantas’ behaviours.
‘This was an adventure that generated more questions than it answered!’ said the new study’s lead author, Dr Lauren Peel, Project Adviser for the Seychelles Manta Ray Project. ‘It sounds like an easy task, answering these seemingly simple questions. How many manta rays are there? Where are they going? But when you consider the scale of Seychelles and how remote these coral reefs are, the whole process becomes more challenging and exciting.’
The new study provides invaluable data for the conservation of a species in Seychelles which is otherwise in decline across the globe. The team is encouraging any divers who visit the islands to submit their own photographs to the database to aid future research.
‘Citizen scientists form a big part of our work, not only because they share data with us, but they help to raise awareness about manta rays throughout Seychelles,’ said Dr Peel. ‘Sparking an interest in and starting conversations about manta rays across Seychelles is an exciting part of the Seychelles Manta Ray Project and it’s something that we want to nurture.’
‘Remote hideaways: first insights into the population sizes, habitat use and residency of manta rays at aggregation areas in Seychelles’ by Lauren R Peel, et al, is published in the online journal Marine Biology.
To submit a Manta ID shot – taken anywhere in the world – head to www.mantatrust.org/idthemanta
