Ecologia acústica do boto-cinza (Sotalia guianensis) nas baías de Sepetiba e Ilha Grande

Abstract

Acoustic repertoires may change in temporal and spatial scales, which are influenced by social alliances, changes in soundscape or in geography. Thus, the goal of this study is to evaluate the spatial and temporal changes in the acoustic repertoire of the Guiana dolphin (Sotalia guianensis). This study is based on a dataset of acoustic recordings in Sepetiba Bay from 1998 to 2002, new recordings from 2015 to 2018 in Sepetiba Bay and 2017 and 2018 in Ilha Grande Bay. Temporal changes in the acoustic parameters of whistles, frequency contours and signature whistles were compared. Frequency contours were compared between populations of Sepetiba and Ilha Grande bays. Still in spatial scale, the influence of anthropogenic noise and environmental variables on the acoustic parameters and occurrence was modeled. Guiana dolphin's acoustic repertoire was stable for about 20 years. However, over time, there was a reduction in the diversity of whistles, a reduction in the duration of emissions, a reduction of over 90% in whistle rate, and an increase in the maximum and minimum frequencies. In the comparison between bays we identified 180 frequency contours in the population of Ilha Grande Bay and 53 in the population of Sepetiba Bay. The geographical variation observed is not only in the types of whistles emitted, but also in the diversity of sounds we found low sharing. Modeling indicated that Guiana dolphins vocalize more, with longer and more complex whistles in less noisy habitats. However, there is no change in the pattern of occurrence regarding noise levels, but due to environmental variables. It is still unclear the factors that promote differences in acoustic diversity between bays. However, both the temporal variation and the predicted by the spatial scale models indicate that the Guiana dolphin presents an acoustic response similar to the anthropogenic noise level. However, environmental variables were more important than noise levels for occurrence of Guiana dolphins