Can citizen science monitor whale-shark aggregations? Investigating bias in mark–recapture modelling using identification photographs sourced from the public
Tim K. Davies A F , Guy Stevens B , Mark G. Meekan C , Juliane Struve D and J. Marcus Rowcliffe EA Imperial College London, Silwood Park Campus, Ascot, Berkshire, SL5 7PY, UK.
B Maldivian Manta Ray Project, Catemwood House, Corscombe, Dorchester, Dorset, DT2 0NT, UK.
C Australian Institute of Marine Science, UWA Oceans Institute (MO96), 35 Stirling Highway, Crawley, WA 6009, Australia.
D University of Florida, Fisheries and Aquatic Sciences, 7922 NW 71st Street, Gainesville, FL 32653, USA.
E Institute of Zoology, Zoological Society of London, London, NW1 4RY, UK.
F Corresponding author. Email: timothy.davies08@imperial.ac.uk
Wildlife Research 39(8) 696-704 https://doi.org/10.1071/WR12092
Submitted: 10 May 2012 Accepted: 30 September 2012 Published: 24 October 2012
Abstract
Context: The conservation status of the whale shark, Rhincodon typus, remains uncertain. Throughout their range, whale sharks are a focus for wildlife tourism and many identification photographs taken by tourists have become available online, presenting a potentially valuable source of data for monitoring populations using mark–recapture techniques. However, the suitability of these photographs for mark–recapture models has yet to be investigated.
Aims: We explore the suitability of identification-photographs available from online databases to produce assessments of life-history parameters and conservation status of whale sharks in the Maldives.
Methods: To test the validity of using publically sourced images, we used photo-identification images collected from both experienced researchers and tourists between 2003 and 2008 to construct two databases. Images taken by tourists were compiled from online databases. Researcher and public databases were analysed separately and the results of mark–recapture models then compared.
Key results: The dataset constructed from online public databases did not violate the assumptions of mark–recapture modelling. Estimates of parameters and abundance obtained from models using these data were similar to those produced using data provided by experienced researchers.
Conclusions: Publically sourced data allowed for the accurate estimation of abundance of whale sharks. These estimates were not confounded by the suitability of photographs, probably because of the high encounter rate in the aggregation, the high residency rate of sharks and the retrospective nature of photo-identification, which limited heterogeneity in capture probability between marked and unmarked sharks.
Implications: Our findings support the use of publically sourced data for use in mark–recapture studies of whale sharks, at least in situations where sharks are resident to the location. This approach will be useful in regions where data collected by tourists are available online, and research funding is limited.
Additional keywords: abundance, flickr, photo-identification, online database, resight, survival, threatened species, YouTube.
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