Manta ray (Manta birostris) is the largest ray species, but little information is available regarding its biology, distribution and migratory pattern. During an aerial survey conducted in French Guiana waters (South America) in 2006, the observation of several dozen individuals all swimming in the same direction prompted us to develop a research programme on this species as part of an environmental impact assessment for oil drilling. Overall, 117 aerial surveys were performed over 3 years in order to complete a database for this species. In 54 of these flights, a total of 138 individuals were observed. A phenological analysis of this species in French Guiana waters shows a peak presence between July and December, which correlates with sea surface temperature and net primary production in the ocean. The primary production in French Guiana waters is particularly active during this period and could explain the annual pattern for this filter-feeding animal.