Movements of Reef Manta Rays in a Large Marine Protected Area at Multiple Spatio-Temporal Scales

Mobulid populations are declining on a global scale as a result of both targeted fisheries and indirect anthropogenic threats. In order to implement effective conservation strategies for species of this taxa, it is crucial that movement patterns at a range of spatio-temporal scales are defined. To gain insight into such patterns, we deployed a combination of acoustic (n=21) and satellite (n=8) tags on reef manta rays (Mobula alfredi) in the British Indian Ocean Territory MPA (BIOT MPA) between 2013 and 2017. An extensive array of acoustic receivers (n=52) were deployed at atolls, islands, banks and seamounts to record movements of acoustically tagged mantas throughout the MPA. Telemetry data revealed high individual variation in horizontal movement patterns, ranging from high local site fidelity for up to three years, to large scale regional movements (>200 km) around the entire MPA. Depth time-series data recorded vertical movement patterns consistent with other epipelagic elasmobranch species, including oscillatory diving and deep dives down to a maximum of 888 m. Both horizontal and vertical movement patterns were influenced by time of day and lunar phase. No individual was directly recorded to depart the MPA throughout the study. However, gaps in detections and travel speeds documented here, as well as existing knowledge of manta ray spatial ecology, indicate that long-distance movements to other manta aggregations outside of BIOT MPA, such as the Maldives, cannot be discounted. Collectively, our data suggests that, with effective enforcement, the BIOT MPA is likely to offer adequate protection to its reef manta ray population. Characterization of movement patterns across ontogenetic classes, however, is required to fully characterize the spatial ecology of this species and ensure protection across its life history.