Behavioral observations on the common bottlenose dolphin (Tursiops truncatus) at fixed points in the open waters of Italy's Northern-Central Adriatic Sea

This study is based on sightings collected over a 3-year monitoring period, at fixed points in the open waters of Italy’s Northern-Central Adriatic Sea. Marine mammals were monitored during the construction of four offshore gas platforms to manage the construction work if any cetaceans approached the vicinity of the sites. A total of 340 common bottlenose dolphin groups were sighted and relative behavioral data were collected and analyzed. Group size (mean ± SD = 4.4 ± 2.67, range = 1–15) varied significantly based on seasonality, behavioral state, and presence of calves, but no synergistic interaction effects were detected. Traveling was the most frequently observed behavior, in 42.3% of sightings. A Multinomial Logistic Regression was used to analyze the probability of occurrence of behavioral states, with season and the presence of calves serving as explanatory variables for behavioral state. Notably, both the analysis performed does not include the human activities as a statistically significant factor in the determination of the group size dynamics and the behavioral choice and, in addition, we identified two pelagic feeding seasons, in the spring and autumn. The data gathered allowed us to provide valuable information on the Italian Adriatic bottlenose dolphin population behavioral traits in the open sea.