Marine ecotourism has undergone worldwide expansion in recent years, leading to increased concern regarding the impact on the environment. Despite this, however, few studies into the potential effect of tourist boats on dolphin welfare, have been carried out. In order to evaluate the
impact of these activities on the presence and foraging behaviour of the threatened marine tucuxis (Sotalia fluviatilis), we observed them: 1) prior to the arrival of a boat in the bay; 2) for the duration of a vessel's stay in the bay and 3) after the boat's departure: ie pre-exposure,
exposure and post-exposure phases. Both the average number of dolphins and the foraging activity were significantly reduced while a vessel was in the bay. Marine tucuxis are exclusively coastal and show fidelity to the site where they choose to live which makes any environmental disturbance
of particular importance. Moreover, our findings are further evidence of the need for motorboat activity to be regulated and monitored to protect marine tucuxis as well as other coastal and estuarine dolphins.