Abstract
Reef manta rays Mobula alfredi have fragmented populations across their range and show high site fidelity to certain aggregation sites. The species has been observed around Mayotte, an island in the northern Mozambique Channel with a surrounding barrier reef and a large 1500 km(2) lagoon. Here, we examined their distribution, movements and population demographics using a combination of citizen science observations and archival satellite tag data. Mayotte's lagoon and the passes that connect it with the open ocean were important for two life history functions: a bay in the northeast of the island appears to serve as a nursery habitat, and surface feeding is frequently recorded in several areas of the lagoon. All five tracked individuals remained in local waters within similar to 285 km of Mayotte, although estimated track lengths were up to 1579 km over the 4-month tracking duration, highlighting that other regional aggregation sites in Mozambique or the Seychelles are within their potential dispersal range. The four tracked mature individuals spent extensive time outside Mayotte's lagoon, often diving to mesopelagic depths. Their median swimming depth had a crepuscular signal, being particularly shallow at sunrise and in the early morning (similar to 5 m depth), potentially feeding in surface waters, while the median swimming depth was between 30 and 40 m at other times. Considering the small population size and isolation shown here and the low population growth rate of the species, it will be important to identify and minimise threats in the region around Mayotte to improve the conservation of this Vulnerable species.
