Recurrent seasonal habitat patterns of Mediterranean bottlenose dolphins revealed by long-term monitoring and validated SDMs

Seasonal environmental variability strongly shapes the spatial distribution of marine megafauna, particularly in semi-enclosed basins such as the Mediterranean Sea, where oceanographic conditions typically follow predictable seasonal patterns. However, resolving recurrent seasonal habitat patterns at basin scale remains challenging because long-term datasets with consistent multi-season coverage are rarely available in marine systems. Here, we analysed 15 years of standardized ferry-based surveys (2008–2024), comprising more than 635,000 km of observation effort and 1020 sightings, to characterize recurrent seasonal habitat configurations of the Mediterranean common bottlenose dolphin (Tursiops truncatus) across the western Mediterranean and Adriatic Seas. Using a seasonally structured climatological framework, occurrence records and environmental predictors were aggregated into multi-year climatologies. MaxEnt habitat suitability models were independently validated using external datasets and integrated with encounter rate analyses and environmental clustering to link predicted suitability, observed habitat use, and underlying oceanographic conditions. Across all analytical components, results revealed a coherent basin-scale seasonal reconfiguration of relative habitat suitability. Winter–spring patterns were dominated by productive coastal and shelf–slope systems, whereas Summer–Autumn showed a marked offshore expansion into pelagic environments and reduced coastal use. These transitions were consistently expressed across major Mediterranean subbasins, indicating a recurrent and structured seasonal habitat cycle. By combining independent validation with complementary distribution metrics and environmental characterization, this study provides the first four-season climatological baseline for Mediterranean bottlenose dolphin seasonal habitat patterns. The framework strengthens the robustness and ecological interpretability of SDMs in seasonally variable marine systems and supports seasonally informed spatial planning and conservation strategies.