Population structure, residency patterns and movements of whale sharks in Southern Leyte, Philippines: results from dedicated photo‐ID and citizen science

Abstract

Abstract The whale shark, Rhincodon typus, is a charismatic umbrella species whose highly mobile nature is not yet fully understood. Whale sharks roam the Philippine archipelago with two major aggregations known to occur at Donsol and at a provisioning site in Cebu. This is the first description of a previously identified aggregation occurring off Panaon Island, Southern Leyte through the use of photographic identification. In total, 93 individual whale sharks were identified, with significant male bias (58%). The mean estimated total length of individuals was 5.72 ± 1.02 m S.D., indicating a juvenile aggregation. Partial or complete fin amputations, potentially resulting from fishing lines, boat propellers or net entanglement, were observed on 27% of animals, highlighting some of the risks human activities can have on this threatened species. Multiple parallel scars, identified as propeller impact, were observed on 45% of animals. Dedicated research seasons in 2013 and 2014 yielded very different whale shark encounters with 366 in 2013 and 12 in 2014, yet highlighted the recurrence of individuals at the study site. Complemented by data collected through citizen science, maximum likelihood methods were used to model mean residency of whale sharks at Panaon Island of 27.04 days. The modelled lagged identification rate showed that many whale sharks return to the study site over time. Whale sharks from Panaon Island were identified through photo‐ID and citizen science at other sites in the Philippines, as well as a match to Taiwan, representing the first international match through photo‐ID in South‐east Asia with a minimum distance covered of 1600 km. Given the highly mobile nature and recent exploitation of this species, management is recommended as a single unit regionally in South‐east Asia. Additional research is needed to focus on the drivers of variation in encounters at whale shark aggregation sites. Copyright © 2016 John Wiley & Sons, Ltd.