Spatial distribution and habitat selection of common bottlenose dolphins (Tursiops truncatus) within two estuaries in southern coastal USA.

Coastal waters are increasingly exposed to anthropogenic pressures, resulting in the degradation of critical habitats that shape the distribution of marine predators. This study used photo-identification data to define drivers of common bottlenose dolphin habitat selection in Mobile Bay and Perdido Bay, two urbanized estuaries in southern USA. Dolphins exhibited distinct seasonal habitat selection between estuaries. In Mobile Bay, dolphin occurrence decreased with water temperature and increase with dissolved oxygen during winter, and dolphins were more frequently observed closer to shore, near a key confluence point (Mobile Bay Pass) and in deeper water near ship channels in summer. In Perdido Bay, dolphin occurrence increased with pH and dissolved oxygen in winter, while in summer, dolphin occurrence increased in deeper waters, near ship channels and closer to gillnet exclusion zones. Across both systems, dolphins occurred in moderate-to-high salinity waters but also used very low salinity areas. Our results indicate a seasonal transition from physiochemical drivers in winter to structural and habitat-related factors in summer and suggest that ship channels may function as salinity refuges and prey hotspots, due to water stratification and higher prey availability. This work highlights dolphins' adjustment to local conditions within dynamic estuarine environments under natural and anthropogenic influences.