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Population estimates of Alfred mantas (Manta alfredi) in central Maldives atolls: North Male, Ari and Baa

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Abstract

The Alfred manta, Manta alfredi, is economically important in the Maldives due to the large number of tourists attracted to SCUBA dive and snorkel with them. It is important to understand the size of populations around main diving points and throughout the Maldives so that manta based tourism activities can be developed more successfully and the impact of tourism can be monitored. Using natural markings to identify individual manta rays, Petersen and Jolly-Seber probabilistic estimators were used to assess population size for main dive sites and the central atolls of North Male, Ari and Baa. Between 2000 and 2009, 1835 individual mantas were identified from 3373 sightings. There was a significant gender bias with a male: female ratio of 1:1.8. Only 24.7% of manta rays were re-sighted between 1 and 34 times with a maximum gap of 7 years and 11 months between sightings. Estimates for populations around main dive sites were 181–562. The estimated population of M. alfredi for North Male atoll is 537 (SE ± 53.2). Estimated atoll populations were extrapolated to obtain an estimate of Manta alfredi population for the entire Maldives of 9,677 individuals.

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Acknowledgements

This research was conducted as part of a research program at Newcastle University, UK. We thank Douglas David Seifert who sponsored the research at Hanifaru in 2009, Rob Bryning of Maldives Scuba Tours who has been fully supportive of our manta ray research, Matt Kitchen, Nick and Demelza Masters, Lisa Allison, Shaff Naeem, Guy Stevens and the many volunteer divers who assisted with data collection and donated photographs from 2006 to 2008. We would like to express our thanks to the reviewers of this paper for their thoughtful comments.

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Correspondence to Anne-Marie Kitchen-Wheeler.

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Kitchen-Wheeler, AM., Ari, C. & Edwards, A.J. Population estimates of Alfred mantas (Manta alfredi) in central Maldives atolls: North Male, Ari and Baa. Environ Biol Fish 93, 557–575 (2012). https://doi.org/10.1007/s10641-011-9950-8

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