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The ecological connectivity of whale shark aggregations in the Indian Ocean: A photo-identification approach

Sammy Andrzejaczek, Jessica Meeuwig | Nov 16, 2016

Sammy Andrzejaczek, Jessica Meeuwig

Nov 16, 2016

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Photographs of the sharks’ flanks taken by researchers, tourism operators and tourists can be used to identify individual animals.

Photo: Dr. Mark Erdmann

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CITATION

Andrzejaczek S, Meeuwig J, Rowat D, Pierce S, Davies T, Fisher R, Meekan M. 2016. The ecological connectivity of whale shark aggregations in the Indian Ocean: A photo-identification approach. Royal Society Open Science, 3: 160455.

ABSTRACT

Genetic and modelling studies suggest that seasonal aggregations of whale sharks (Rhincodon typus) at coastal sites in the tropics may be linked by migration. Here, we used photo-identification (photo-ID) data collected by both citizen scientists and researchers to assess the connectedness of five whale shark aggregation sites across the entire Indian Ocean at timescales of up to a decade. We used the semi-automated program I3S (Individual Interactive Identification System) to compare photographs of the unique natural marking patterns of individual whale sharks collected from aggregations at Mozambique, the Seychelles, the Maldives, Christmas Island (Australia) and Ningaloo Reef (Australia). From a total of 6519 photos, we found no evidence of connectivity of whale shark aggregations at ocean-basin scales within the time frame of the study and evidence for only limited connectivity at regional (hundreds to thousands of kilometres) scales. A male whale shark photographed in January 2010 at Mozambique was resighted eight months later in the Seychelles and was the only one of 1724 individuals in the database to be photographed at more than one site. On average, 35% of individuals were resighted at the same site in more than one year. A Monte Carlo simulation study showed that the power of this photo-ID approach to document patterns of emigration and immigration was strongly dependent on both the number of individuals identified in aggregations and the size of resident populations.

FUNDING & ACKNOWLEDGEMENTS

We thank all those who contributed photographs for this study, in particular the Australian Institute of Marine Science, the Western Australia Department of Parks and Wildlife, the Marine Conservation Society Seychelles, the Marine Megafauna Foundation in Mozambique, the Maldives Whale Shark Research Programme and ecotourism operators including those based in Exmouth and Coral Bay, Western Australia. We are also grateful for the critical comments from Jesse Cochran and two anonymous reviewers that improved the draft manuscript.