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

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.