Population structure and site fidelity of photographically identified reef manta rays (Mobula alfredi) in Raja Ampat, Indonesia

The reef manta ray (Mobula alfredi) aggregates at numerous sites in Raja Ampat–one of the top manta tourism destinations globally. The population structure and site fidelity of reef mantas were examined using photographic... [ view full abstract ]

The reef manta ray (Mobula alfredi) aggregates at numerous sites in Raja Ampat–one of the top manta tourism destinations globally. The population structure and site fidelity of reef mantas were examined using photographic identification. A total of 525 different individuals were identified between Dec 2007 and Feb 2018 from 19 locations in 7 regions within the Raja Ampat Marine Protected Area (MPA) network. The first sightings of these individuals mainly occurred in the Dampier Strait (DS) (46%) and Misool (31%), located in central and southern Raja Ampat, respectively. The sex ratio was biased towards females, with a female to male ratio of 1.8:1. Manta coloration was predominantly chevron, though fully one third of the individuals showed melanistic coloration. The females were slightly larger than males, with an average estimated disc width of 3.1 m (±0.03) vs. 2.9 m (±0.04), respectively. One third of all individuals were re-sighted at least once during the study period. The longest period between re-sighting events was 3,708 days (10.2 years). Of 479 re-sighting events, 70% of these occurred at Manta Sandy – a cleaning station in DS that is a very popular dive site. One individual manta was sighted 24 times at Manta Sandy over the 10-year monitoring period. Re-sightings occurring over multiple years strongly suggest high site fidelity of many individuals to particular feeding and cleaning aggregation sites, which requires urgent efforts to better manage and ensure the long-term sustainability of manta tourism in the region.