Propagation of the Guiana dolphin sounds in their habitat: measured transmission loss and influence of environmental factors

This study aims to determine the influence of distance and environmental parameters of water on Sotalia guianensis sounds. We used recordings of three distinct vocalisations for testing their propagation in places with different environmental characteristics in the Northeast and Southeast of Brazil. We observed that the propagation of all the sounds tested depended on the distance, turbidity, and concentration of oxygen dissolved in the water. Relative amplitude data for each sampled distance were smaller than the values predicted by the cylindrical spreading law. This result indicates that there are probably other factors that can influence sound propagation besides the distance in the sampled areas. The relative amplitude was also proportionally higher when there were lower levels of turbidity and higher concentration of dissolved oxygen in the water. From the data presented here, a model was generated that can be used as a tool to predict acoustic alterations of the environment against natural or anthropic changes in salinity, dissolved oxygen, and water turbidity. In addition, the methodology of this study is an important tool for conservation studies, for it can be replicated in other areas and with other species.