A Study of the Behaviour and Conservation of Manta Rays in the Maldives

This study of the world’s largest recorded population of Reef Manta Rays (Mobula alfredi) uses seven years of photo-ID data and three years of video observations of foraging in the Maldives to investigate social structures at both the large (aggregation) and fine-scale (foraging group), individual foraging flexibility and the impacts of ecotourism management strategies on foraging behaviour.
M. alfredi can be observed aggregating in large numbers, yet little is understood about their social interactions. Using social network analysis, I found no evidence of structure within either the large or fine-scale. Individuals showed no preference in either aggregating or foraging with associates. There was no difference among individuals in gregariousness and dyads exhibited low temporal stability. Aggregations and foraging groupings did not appear to be driven by sociality, but by the dispersal of their ephemeral zooplankton prey, with strong fission-fusion dynamics and loose relationships.
Within aggregations, manta rays have been seen to forage in both groups and solo. I examined whether M. alfredi adopted specific roles within groups and the drivers of group feeding. Using mixed models, I found that individuals were more likely to forage in groups than solo when food availability was high and smaller general aggregations resulted in larger individual foraging groups. Females were more likely to lead foraging aggregations than males. Variance partitioning models showed low among-individual variance in group size, positioning and leadership, showing that individuals were highly flexible in their foraging behaviour.
Although multitudes of tourists interact with M. alfredi annually, few studies have assessed potential disturbance to their natural behaviour. I found significant changes to foraging behaviour resulting from intrusive human behaviours and interactions within 3m. My findings provide a clear evidence-base for the development of a binding code of conduct. This shows that manta rays are behaviourally flexible, with a tolerance to fluctuations in environmental conditions, yet are specifically vulnerable to disruptions to their prey.