Environmental Drivers of Immature Whale Shark Surface Sightings in the Gulf of Tadjoura, Djibouti
2025
Francesca Romana Reinero | Andrea Marsella | Gaetano Vitale | Antonio Pacifico | Makenna Mahrer | Primo Micarelli
Whale sharks seasonally aggregate in Djibouti (East Africa), supporting ecotourism activities which benefit the local community. However, the environmental factors influencing whale shark relative abundance at this site are still not well understood. Environmental drivers of immature whale shark surface sightings have been analyzed across a five-year period (2017, 2020, 2022, 2024 and 2025) in the Gulf of Tadjoura (Djibouti) using a Generalized Additive Model (GAM) and Hurdle model. Across 111 surface sightings and 83 photo-identified whale sharks, both sea surface chlorophyll-a (SSC) concentrations and sea surface temperature (SST) have significantly affected their relative abundance (p <: 0.001), while wind strength appeared to have a weaker and more complex effect (p <: 0.05). Whale shark surface sightings in the Gulf of Tadjoura increased when SSC and SST exceeded thresholds of 0.5 mg/m&minus:3 and 26 °:C, respectively. In contrast, the positive effect of wind strength &ge: 7 knots was limited, indicating that wind-driven influences on whale shark surface detections are localized and transient. Since prey abundance and distribution are the main drivers of whale shark seasonal aggregations, understanding the environmental effects on food availability at coastal locations and, consequently, on whale shark surface sightings is crucial. The present study highlights temporal and seasonal trends in whale shark sighting data, contributing to broader initiatives aimed at improving conservation and management strategies for this endangered species.
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