Manta Rays Are Homebodies – Forbes

Life & Non-Humans

There are numerous scientists who are working on the conservation of environment and wildlife with a mission to stop the degradation of our natural environment. But in order to properly manage an animal, one needs to understand their habitat use- where they move, why they are there, and for how long. Understanding their movements is key to identifying the threats they face, allowing scientists to better protect them.

Lauren Peel, a Save our Seas Foundation (SOSF) project leader and PhD graduate from the University of Western Australia, is one of these scientists. Her work at SOSF is part of the Seychelles Manta Ray Project, a global movement to better understand the biology and ecology of manta and devil rays.  Together with her co-authors, including Dr. Guy Stevens (Manta Trust), Dr. Ryan Daly and Clare Keating Daly (formerly from the D’Arros Research Centre), Peel deployed acoustic transmitters on 42 reef mantas at D’Arros Island and together they have tracked reef manta rays (Mobula alfredi) movement patterns across the Republic of Seychelles to understand how and where they move in this area. An archipelagic comprising about 115 islands in the Indian Ocean at the eastern edge of the Somali Sea, this area is renowned for their diverse marine life.

Peel and fellow researchers primarily focused on the D’Arros Island and the neighbouring St. Joseph Atoll – the only privately owned outer islands – which form part of a small chain of islands that comprise the Amirantes Group. “When we started the Seychelles Manta Ray Project, very little was known about the size of the local manta population, where individuals were aggregating, how far they were moving, and if they were moving between Island Groups of the archipelago,” explained Peel. “That’s why we really focussed our efforts on the aggregation at D’Arros Island: it was one of the few places in the country where we had reliable reports of mantas aggregating frequently. We wanted to establish how important D’Arros was to the population, how long the mantas were staying in the area, their habitat-use patterns around the island, and make use of as many research techniques as possible to get a better picture of what D’Arros Island means for the manta rays of Seychelles.”

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The team combined data from different tags and photos that identified each individual manta, and together they published the results from this latest study in the journal Frontiers in Marine Science. The data shows that the rays from D’Arros Island and St. Joseph Atoll are homebodies, staying mostly in the Amirantes Island Group region. “It turns out that while reef mantas wing their way through the Amirantes year-round, a startling 89% of acoustic detections recorded during this four-year study occurred within 2.5 km of the shoreline at D’Arros and St Joseph Atoll,” wrote Peel in a Save our Seas Foundation post. “We had suspected that D’Arros Island was an important site to reef manta rays because we routinely recognised individuals that returned to the island. We could identify them from photographs, and people were notifying us of repeat visits by individuals they had come to recognise. However, we had no idea of the sheer significance of the site, and certainly not of how their movements related to the broader Seychelles Archipelago”. It wasn’t just one age bracket (juveniles or adults) mantas of one sex in the area- the team saw both juveniles and adults, males and females, all spending a large amount of time at D’Arros Island.

Little published information exists about how reef mantas move in the Western Indian Ocean, and the work Peel and her team have carried out will form the basis of how researchers will study these animals here but also help scientists elsewhere in the world tracking marine animals like mantas.  These findings are especially ground-breaking since reef mantas are listed as Vulnerable by the International Union for the Conservation of Nature (IUCN), and the species also appear on Appendix II of the Convention for International Trade in Endangered Species. Like other mantas, reef mantas are targeted worldwide for their highly valued gill plates (which are used by manta’s to filter food) or are caught as bycatch (incidental catch) in other fisheries. Unfortunately, due to their tendency to hang at the water’s surface, they do suffer severe injuries from boat strikes that can lead to death.

“There is no formal protection for the species in Seychelles,” explained Peel. “It’s something that we are slowly working towards, but in the interim, the species is still under potential threat from fisheries and boat strikes. We would expect the recently designated zone 1 marine protected area (MPA) around D’Arros Island and larger zone 2 that includes St. Joseph Atoll to be beneficial to the reef manta ray population”. The high site fidelity (preference for a site) does indeed help support the need for an MPA to be established here to protect the local populations of reef mantas in Seychelles.

So, what does the future hold for these majestic underwater rays? Says Peel: “Moving forward, I hope that this research stimulates interest in the manta rays in Seychelles at a community level so that we can get even more citizen scientists involved in our research and promoting manta conservation in the region.”