During a recent oceanographic expedition Pakaihi i te Moana (Respect the Ocean) to Marquesas Islands in French Polynesia between October 2011 and February 2012, I recorded every sightings of manta rays among a hundred of dives. I reported the first sighting of Manta birostris in French Polynesia and reported the presence of its sister species, the reef manta ray Manta alfredi, at the most easterly location in the Pacific Ocean. Manta rays were sighted at seven of the 10 islands surveyed. No manta rays were sighted at seamounts nor around oceanic rocks. Individuals of M. alfredi were observed at seven islands and individuals of M. birostris were observed at four islands. Occurrence of both species was observed on four islands, but a mixed aggregation was observed on only one occasion in Nuku-Hiva. As described by Kashawagi et al. (2011), this suggests that the two species occur in microsympatry (record of co-occurrence at the same dive site) at least in Nuku-Hiva. The occurrence of the two species, however, generally appears to be spatially segregated.
Prior to this study, the most easterly known record of M. alfredi in the Pacific Ocean was at Keauhou, Hawaii (19◦ 33_ N; 155◦ 57_ W; Kashawagi et al., 2011). The observations in the Marquesas Islands, reported here, extend its eastern range in the Pacific Ocean to Fatu Hiva (10◦ 29_ S; 138◦ 37_ W). The present surveys also documented the first record of M. birostris in French Polynesia.
This study was published in Journal of Fish Biology:
Mourier J. (2012). Manta rays in the Marquesas Islands: first records of Manta birostris in French Polynesia and most easterly location of Manta alfredi in the Pacific, with notes on their distribution. Journal of Fish Biology. DOI: 10.1111/j.1095-8649.2012.03449.x