Nutrient availability drives local seasonal movements of an endangered marine megafauna species

Abstract

Abstract Understanding drivers of animal movement is key to predicting species distributions and guiding conservation. Whale sharks ( Rhincodon typus ) are an endangered species known for broad seasonal migrations across oceans influenced by factors like temperature and prey availability. However, finer-scale local movements within aggregations are less studied. We analysed four years (2016–2019) of sightings data from a year-round aggregation in South Ari Marine Protected Area (SAMPA), the Maldives. Using MODIS-Aqua remote sensing data, we examined seasonal patterns in chlorophyll-a (Chl-a) and sea surface temperature (SST). Generalised additive mixed models (GAMMs) revealed significant seasonal rhythms in SST across SAMPA, and significant seasonal Chl-a variation in the south but not the east of the MPA. In a separate GAMM, we found that seasonal rhythms in shark sightings were significant throughout the MPA but more pronounced in the south than in the east. Chl-a was significantly associated with sightings, with both peaking in the south during the Northeast Monsoon (January–March). SST was not significantly associated with sightings. As Chl-a is tightly linked to the abundance of zooplankton, these findings suggest that whale shark movement within the year-round aggregation is driven by prey availability. The results could be used to inform dynamic management or predict aggregations elsewhere and responses to environmental change.