Investigating the behavioral patterns of Risso's Dolphin (Grampus griseus) in the Gulf of Taranto: Ecological and Conservation Perspectives

Understanding the behavior of a species is fundamental to assess its responses to environmental pressures and anthropogenic impacts, as behavioral patterns reflect both ecological requirements and adaptive strategies. In this context, behavioral studies provide crucial insights into habitat use, social structure, foraging strategies, and responses to disturbances, all of which are essential for effective conservation planning. Risso’s dolphin (Grampus griseus) knowledge in the Mediterranean Sea remains limited compared to the other regularly occurring cetacean species. The classification of the Mediterranean subpopulation, as Endangered by the IUCN, further highlights the need for improving our understanding of its ecology and behavior. Therefore, this research aims to provide detailed information on behavioral patterns of G. griseus inhabiting the Gulf of Taranto (Northern Ionian Sea, Central Mediterranean), an area of growing ecological significance for the species. Data were collected between January 2019 and December 2024 through vessel-based surveys conducted by the Jonian Dolphin Conservation. During this period, 180 sightings of Risso’s dolphins were recorded. Behavioral information was obtained using the focal-group protocol with instantaneous scan sampling, with each observation session lasting at least 15 minutes. Predominant activity states (traveling, resting, feeding, and socializing) were compared with group size, depth and other group composition variables, including group size, group formation, swimming speed, dive duration, and interaction among individuals. Results revealed that traveling was the most frequent activity, followed by resting, feeding, and socializing. Statistical analyses highlight significant associations between behavioral states and different variables. For instance, feeding was typically observed in smaller and more dispersed groups, while resting and socializing involved larger and tighter formations. No significant differences in water depth among behavioral states were detected. Moreover, a list of behavioral events which occurred, as well as their relative frequency of distribution among activity states, is reported. This study provides the first long-term insights into the behavioral ecology of Grampus griseus in the Gulf of Taranto, enhancing the understanding of its current status in the Mediterranean Sea and offering a solid scientific basis for targeted conservation measures. The results indicate that the Gulf of Taranto represents a habitat of high ecological importance for this species, potentially serving both as a feeding and resting area. Observed patterns of behavioral plasticity and spatial use suggest that G. griseus is adapting to local environmental and anthropogenic pressures, including intense vessel traffic and underwater noise. Such insights into behavioral responses are essential for guiding effective conservation planning and the management of this vulnerable population.