Whistle emissions were recorded from small groups of marine tucuxi dolphins (Sotalia fluviatilis) in two beaches located in an important biological reserve in the Cananéia estuary (25°03′S, 47°58′W), southeastern Brazil. A total of 17h of acoustic data was collected when dolphins were engaged in a specific feeding foraging activity. The amount of 3235 whistles was recorded and 40% (n=1294) were analyzed. Seven acoustic whistle parameters were determined: duration (ms), number of inflection points, start and end frequency (kHz), minimum and maximum frequency (kHz), and frequency range (kHz). Whistles with up to four inflection points were found. Whistles with no inflection points and rising frequency corresponded to 85% (n=1104) of all analyzed whistles. Whistle duration varied from 38to627ms (mean=229.6±109.9ms), with the start frequency varying between 1 and 16kHz(mean=8.16±3.0kHz) and the end frequency between 2 and 18kHz(mean=14.35±3.0kHz). The importance of this study requires an accurate measurement of the whistles’ emissions in an unusual foraging feeding behavior situation on two beaches where several tucuxis, mostly mother–calf pairs, are frequently present. These two beaches are located in a federal and state environment Environmental Protected Area threatened by the progressive increase of tourism.