title: The ecological connectivity of whale shark aggregations in the Indian Ocean: a photo-identification approach.
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.
authors.affiliation: The UWA Oceans Institute, School of Environmental Systems Engineering, University of Western Australia, Crawley, Western Australia, Australia; Australian Institute of Marine Science, Crawley, Western Australia, Australia.
authors.forename: Samantha
authors.identifier: 0000-0002-9929-7312
authors.initials: S
authors.lastname: Andrzejaczek
authors.affiliation: Centre for Marine Futures, Oceans Institute , University of Western Australia , Crawley, Western Australia , Australia.
authors.forename: Jessica
authors.initials: J
authors.lastname: Meeuwig
authors.affiliation: Marine Conservation Society Seychelles , Victoria, Mahe , Seychelles.
authors.forename: David
authors.initials: D
authors.lastname: Rowat
authors.affiliation: Marine Megafauna Foundation , Truckee, CA 96161 , USA.
authors.forename: Simon
authors.initials: S
authors.lastname: Pierce
authors.affiliation: MRAG Ltd , 18 Queen Street, London W1 J 5PN , UK.
authors.forename: Tim
authors.initials: T
authors.lastname: Davies
authors.affiliation: Australian Institute of Marine Science , Crawley, Western Australia , Australia.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Fisher
authors.affiliation: Australian Institute of Marine Science , Crawley, Western Australia , Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Meekan
keywords: I3S; Rhincodon typus; citizen science; matching; migration; photo-ID