Effect of dolphin-watching boats on indo-pacific bottlenose dolphins' (Tursiops aduncus) behaviour

The Indo-Pacific bottlenose dolphin (Tursiops aduncus) is a coastal cetacean exhibiting complex social behavior and notable cognitive and ecological plasticity. Increasing anthropogenic pressures, particularly from unregulated dolphin-watching tourism, raise concerns about the species' welfare and conservation status. This study aimed to assess the behavioral response of a resident dolphin population off the northeast coast of Unguja Island (Zanzibar), in relation to the proximity of tourist boats. Behavioral data were collected between May 2024 and March 2025, as part of a long-term monitoring program conducted by the NGO Under the Wave. Observations were carried out twice weekly, using a standardized ethogram to classify behaviors as either natural or stress-related. The number of boats within 10 m and 50 m of dolphin pods was recorded for each sighting. Logistic regression models were applied to evaluate the association between boat proximity and the likelihood of stress-related behaviors. Results revealed a significant increase in stress-related behaviors, such as abrupt directional changes, increased speed, and avoidance maneuvers, with rising boat density, particularly at distances under 10 m. The presence of a moderate number of boats elicited the highest probability of stress behaviors, suggesting a non-linear relationship. These findings emphasize the behavioral sensitivity of T. aduncus to close-range human disturbance. This research underscores the necessity of implementing evidence-based regulations for wildlife tourism in Zanzibar and similar regions. Promoting responsible ecotourism practices is crucial to mitigate anthropogenic impact and support conservation efforts, in alignment with the One Welfare framework linking animal welfare, human well-being, and ecosystem health.