AUTHOR=Araujo Gonzalo , Agustines Ariana , Bach Steffen S. , Cochran Jesse E. M. , Parra-Galván Emilio de la , Parra-Venegas Rafael de la , Diamant Stella , Dove Alistair , Fox Steve , Graham Rachel T. , Green Sofia M. , Green Jonathan R. , Hardenstine Royale S. , Hearn Alex , Himawan Mahardika R. , Hobbs Rhys , Holmberg Jason , Shameel Ibrahim , Jaidah Mohammed Y. , Labaja Jessica , Leblond Savi , Legaspi Christine G. , Maguiño Rossana , Magson Kirsty , Marcoux Stacia D. , Marcoux Travis M. , Marley Sarah Anne , Matalobos Meynard , Mendoza Alejandra , Miranda Joni A. , Norman Brad M. , Perry Cameron T. , Pierce Simon J. , Ponzo Alessandro , Prebble Clare E. M. , Ramírez-Macías Dení , Rees Richard , Reeve-Arnold Katie E. , Reynolds Samantha D. , Robinson David P. , Rohner Christoph A. , Rowat David , Snow Sally , Vázquez-Haikin Abraham , Watts Alex M. TITLE=Improving sightings-derived residency estimation for whale shark aggregations: A novel metric applied to a global data set JOURNAL=Frontiers in Marine Science VOLUME=9 YEAR=2022 URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.775691 DOI=10.3389/fmars.2022.775691 ISSN=2296-7745 ABSTRACT=

The world’s largest extant fish, the whale shark Rhincodon typus, is one of the most-studied species of sharks globally. The discovery of predictable aggregation sites where these animals gather seasonally or are sighted year-round – most of which are coastal and juvenile-dominated – has allowed for a rapid expansion of research on this species. The most common method for studying whale sharks at these sites is photographic identification (photo-ID). This technique allows for long-term individual-based data to be collected which can, in turn, be used to evaluate population structure, build population models, identify long-distance movements, and assess philopatry and other population dynamics. Lagged identification rate (LIR) models have fewer underlying assumptions than more traditional capture mark recapture approaches, making them more broadly applicable to marine taxa, especially far-ranging megafauna species like whale sharks. However, the increased flexibility comes at a cost. Parameter estimations based on LIR can be difficult to interpret and may not be comparable between areas with different sampling regimes. Using a unique data-set from the Philippines with ~8 years of nearly continuous survey effort, we were able to derive a metric for converting LIR residency estimates into more intuitive days-per-year units. We applied this metric to 25 different sites allowing for the first quantitatively-meaningful comparison of sightings-derived residence among the world’s whale shark aggregations. We validated these results against the only three published acoustic residence metrics (falling within the ranges established by these earlier works in all cases). The results were then used to understand residency behaviours exhibited by the sharks at each site. The adjusted residency metric is an improvement to LIR-based population modelling, already one of the most widely used tools for describing whale shark aggregations. The standardised methods presented here can serve as a valuable tool for assessing residency patterns of whale sharks, which is crucial for tailored conservation action, and can cautiously be tested in other taxa.