Bottlenose dolphin (Tursiops truncatus) habitat partitioning in relation to age classes in the northwest Mediterranean Sea

Understanding the impact of environmental and biological factors on species’ habitat use is crucial for conservation. A regular presence of common bottlenose dolphins (Tursiops truncatus) has recently been observed in the Western Ligurian Sea, but their distribution, habitat preferences, and social dynamics remain poorly understood. This study aims to investigate these aspects, focusing on spatial distribution and habitat partitioning by age classes. Data were collected during 273 boat-based surveys from April 2018 to December 2021, resulting in 146 dolphin sightings. Group size and composition were analysed based on three group-types: N-groups including at least one newborn (n = 35), C-groups with at least one calf but no newborns (n = 62) and A-groups comprising only independent juveniles, subadults and/or adults (n = 49). Using an ensemble modelling approach (BIOMOD), each group’s distribution was separately modelled incorporating seven environmental variables. Bathymetry, distance to the shelf break, bottom type and sea surface temperature emerged as the most significant predictors influencing groups’ distribution. Results showed N-groups predominantly occupying areas further from the shore, C-groups distributed across both coastal waters and areas near the shelf break and A-groups principally found very close to shore. The study suggests habitat selection and group size vary based on the unique needs and threats faced by the different age classes. These insights are highly valuable for managing bottlenose dolphins in the Ligurian Sea, considering the area’s particular morphology that leads to an important overlap between their presence and local anthropogenic activities.