oa Understanding constellations: The use of ‘citizen science’ to elucidate the global biology of a threatened marine mega-vertebrate

Background Gathering data on the life of enigmatic animals remains a challenge, despite its important role in biodiversity conservation and management. For many species, biogeographic investigations are largely the result of information that is generated from multiple sources, often over long time-scales, because measuring biogeographic and biological data over large geographic areas is simply not feasible by a single team of researchers. But in the current age of a well-educated public and accessible and mobile digital technology, scientists are now able to harness the observations of many, thus infinitely increasing their power of observation. Despite its status as the world's largest fish, there remains a paucity of information on the biology and ecology of whale sharks (Rhincodon typus). This species is however a prime target for ‘citizen science’ monitoring because of its charismatic nature, presence at many coastal aggregation sites and the growth of ecotourism around this species. Approach Information on whale shark sightings worldwide can be gathered by various stakeholders and stored in the Wildbook for Whale Sharks (www.whaleshark.org) database. Whale shark identification images are collected when a swimmer photographs the individual's unique spot pattern immediately behind the gill slits, which is distinct and long-lasting, and this image (with associated sighting data and information on shark size and sex) is then submitted to the online database. Computer-assisted scanning technology is then employed to determine whether the individual whale shark in question is a ‘new’ shark or a ‘resight’ of a previously reported whale shark within the database. Wildbook can then be queried to gain insights on various aspects of whale shark biology and ecology from data available at the various global hotspots. Results Members of the public and researchers alike contributed in this collaborative citizen science project enabling (as of 31 December 2014) almost 30000 whale shark encounter reports, comprising 6300+ individuals from 54 countries, to be identified. The number of recognized global aggregation sites (constellations) has increased from 13 to 20. The majority of these (14 out of 20) show a marked sex-ratio bias towards males (>66%). Site fidelity is relatively high, with an overall mean percentage of sharks returning to the 20 hotspots in two or more years of 35.7% (to a maximum of 21 years). Despite photo-identification revealing movements of sharks between a number of neighbouring countries/regions, there are no records confirming large, ocean basin-scale migrations. Strong seasonality in sightings is evident at many locations, suggesting that in general, that these aggregations are frequently exploiting known coastal feeding opportunities. Conclusions This study demonstrates the utility of citizen science in amassing large datasets and their utility in elucidating key aspects of whale shark life-history and demographics.