The identification of short-term behavioral reactions by marine tucuxi dolphins (Sotalia guianensis) in the Cananeia estuary, Brazil, to the presence of boats

Muller, Krista
Jon Atwood, PhD
Department of Environmental Studies
In recent years, widespread concern has arisen over the potential impact that anthropogenic noise created by boat traffic may be having on marine mammal populations. Previous research has shown that many cetacean species respond behaviorally to the presence of this type of disturbance. Typical reactions include avoidance, shortening bouts of feeding, and conducting longer dives. In Brazil, cetacean research has generally focused on site fidelity, photo identification and population sizes. Few studies address the effect that boats may be having on the region’s whale, dolphin and porpoise populations. From July – October 2006, research was conducted in the Cananeia estuary of southeastern Brazil to determine if interactions with boats caused the local marine tucuxi dolphin (Sotalia guianensis) population to exhibit short-term changes in their behavior. In particular, I provide basic descriptive information regarding dive times and respiration rates of tucuxi in the absence and presence of boats, and the use of tow beaches for foraging during low tides. Additionally, I hypothesized (1) that the amount of time dolphins spent diving would increase in the presence of boats, (2) respiration rates of dolphins would decrease in the presence of boats, and (3) that the number of surface-active behaviors would decrease in the presence of boats. Results suggest that beach-hunting tucuxi dolphins were present less frequently during the high tidal phase, at one of the two study beaches (Pereirinha), and more frequently in the afternoon hours. Beach attacks (“feeding behavior”) were performed more frequently by beach-hunting dolphins in the presence of boats. All boats in the research area caused a significant difference in the dive times and respiration rates of beach-hunting individuals and mother-calf pairs.

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