Social preferences and network structure in a population of reef manta rays
Understanding how individual behavior shapes the structure and ecology of populations is key to species conservation and management. Like many elasmobranchs, manta rays are highly mobile and wide-ranging species threatened by anthropogenic impacts. In shallow water environments, these pelagic rays often form groups and perform several apparently socially mediated behaviors. Group structures may result from active choices of individual rays to interact or passive processes. Social behavior is known to affect spatial ecology in other elasmobranchs, but this is the first study providing quantitative evidence for structured social relationships in manta rays. To construct social networks, we collected data from more than 500 groups of reef manta rays (Mobula alfredi) over 5 years in the Raja Ampat Regency of West Papua. We used generalized affiliation indices to isolate social preferences from non-social associations, the first study on elasmobranchs to use this method. Longer lasting social preferences were detected mostly between female rays. We detected assortment of social relations by phenotype and variation in social strategies, with the overall social network divided into two main communities. Overall network structure was characteristic of a dynamic fission-fusion society, with differentiated relationships linked to strong fidelity to cleaning station sites. Our results suggest that fine-scale conservation measures will be useful in protecting social groups of M. alfredi in their natural habitats and that a more complete understanding of the social nature of manta rays will help predict population responses to anthropogenic pressures, such as increasing disturbance from dive tourism.
In social animals, relationships between individuals have important implications for species conservation. Like many other sharks and rays, manta rays are threatened species, and little is known about their natural behavior or how their populations are structured. This study provides evidence of social structure in a wild, free-ranging population of reef manta rays. We show for the first time that individual manta rays have preferred relationships with others that are maintained over time, and structured societies. This study extends our knowledge of elasmobranch ecology and population structuring. Results suggest that understanding social relationships in manta rays will be important in protecting populations from human impacts and developing sustainable, localized conservation and management initiatives.
KeywordsReef manta ray Mobula alfredi Social network analysis Social preferences Generalized affiliation indices
We would like to thank Papua Explorers Dive Resort, Raja Ampat SEA Centre, University of Papua, Barefoot Conservation, and KemenRisTek-Dikti for their invaluable support in enabling our fieldwork in Raja Ampat. We are grateful to all citizen scientists, recreational divers, and photographers who have submitted photographs and videos to MantaMatcher.org. Thanks to E. Germanov, E. Sinderson, G. Winstanley, and J. Holmberg for support with MantaUtil and MantaMatcher and E. Germanov for help with illustrations. We would also like to thank D. Jacoby and one anonymous reviewer for their helpful comments.
RJYP was the primary author of the manuscript. RJYP and DWF conceived the central idea of the manuscript. RJYP, SKV, ADM, and RFT collected and input data. RJYP conducted all statistical analyses with input from DWF and CB, ADM, and SKV contributed to editing and manuscript revisions.
No external funding was received for this research. Research was funded by the authors with some funds sourced via donations to Marine Megafauna Foundation and through RJYP student research budget at Macquarie University (during 2017–2018).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and institutional guidelines for conducting research on animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution at which the corresponding author is based.
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