Stay here, but keep quiet: the effects of anthropogenic noise on Guiana dolphins (Sotalia guianensis) in southeastern Brazil

Shipping is the principal source of anthropogenic noise in the aquatic soundscape of many coastal areas. Noise can affect temporally or permanently the physiology, behavior, and ecology of marine mammals. As noise pollution is considered to be an important threat to Guiana dolphins (Sotalia guianensis), we focused the present study in the effects of noise on occurrence and acoustic behavior in Sepetiba Bay, southeastern Brazil. We modeled the impacts of anthropogenic noise on the acoustic behavior and distribution of these dolphins in an estuarine area. We considered the acoustic parameters (maximum frequency, minimum frequency, delta frequency, duration of whistles, and whistle rates) and occurrence of Guiana dolphins as the response variables and sound exposure levels (SEL) and environmental factors (sea surface temperature, depth, bottom heterogeneity, and bottom type) as the explanatory variables. While dolphin occurrence was explained by environmental variables, mainly SST, the whistle rate was explained by SEL (contribution = 52.4%). The dolphins used noisier areas but communicated mainly in less noisy areas. Although the dolphins did not appear to avoid the noisiest areas, noise levels were the most important variable to explain the reduction in whistle rates. Our results are particularly important since they indicate the effects of noise on an endangered species living in a region with high cumulative impacts.