Short-term Impacts of Marine Traffic on the Behaviour of Dolphins in the Aegean Sea

With an expected further increase in marine traffic comes progressive negative environmental impacts on cetaceans. This study investigates the impact of motorised vessel presence on Delphinus delphis and Tursiops truncatus behaviour in the eastern Aegean Sea using a time budget analysis of their behaviour in the presence and absence of motorised marine traffic. Behaviour was categorised using an ethogram and BORIS software was used to obtain the total duration of each state and category for the time budget analysis (Elias et al., 2021; Friard and Gamba, 2016). When comparing the percentage frequency of time per sighting that D. delphis and T. truncatus were visually observed from the research vessel exhibiting each behaviour in the presence and absence of marine traffic, the results showed that feeding, socialising, and travelling were more prevalent in vessel presence, whilst energy intensive behaviours such as, diving, porpoising and sharking were the opposite. A key finding of this study was that there was no significant difference in the percentage time either species spent resting in the presence or absence of vessels. Additionally, the results found that both species exhibited different changes in behaviour during vessel presence and absence. This study concludes that increased travelling and stress behaviours can have biologically significant consequences on the physical fitness, energetic budget, health, and reproductive output of D. delphis and T. truncatus populations. Improving our understanding of how marine traffic intensity can impact the short and long-term behaviour of these populations is essential to aid in their preservation.