Interactive Behaviours of Bottlenose Dolphins (<I>Tursiops aduncus</I>) During Encounters with Vessels

Abstract

Bottlenose dolphins (Tursiops spp.) are one of the most frequently encountered cetaceans in coastal regions and form the focus of a growing commercial dolphin-watching industry. Bottlenose dolphins are renowned for approaching and interacting with vessels. By obtaining information on the occurrence of interactive behaviours, further insight into the influence of vessel encounters on dolphins can be gained. This research examined the interactive behaviours (defined as bow-riding, wake-riding, and sustained approaches) displayed by Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the presence of different vessel types (motor vessel or sailing yacht) in a region with relatively low levels of commercial dolphin-based tourism activities. The patterns of acoustic emissions produced during these interactions were also recorded. Results indicated that a relatively small proportion of the population displayed interactive behaviours (22% of groups observed). Of the groups that displayed interactive behaviours, 59% contained at least one calf, and most were engaged in the behavioural state of milling (36%). The vessel type (p < 0.05) and vessel activity (p < 0.05) both significantly influenced the occurrence of interactive behaviour of the dolphins. More interactions per hour occurred with the motor vessel (0.32) compared to the yacht (0.26). The mean duration of interactions was 3 min (SD = 9.07). During interactions with vessels, dolphins emitted a diverse repertoire of whistles with a high repetition rate suggesting that either the group cohesion was affected or that there were higher levels of excitation. It is recommended that monitoring the levels and types of interactive behaviours of dolphins during vessel encounters may be useful to ensure that dolphin-watching activities do not negatively impact social cohesion and long-term survival of dolphin populations.