Emissões sonoras de Sotalia guianensis (Cetartiodactyla: Delphinidae) na Baía de Guanabara, sudeste do Brasil

Abstract

Acoustic communication plays an important role in the social interactions of delphinid species. However, information about the relationship between whistle and burst-pulsed sound emissions and behavioral states is still restricted to a few delphinid species. This dissertation provides a summary of existing knowledge on this topic, and presents new findings for Guiana dolphin (Sotalia guianensis) emission sound communication. Chapter 1 is a review of studies on the relationship between the acoustic communication and social behavior in different delphinid species. Chapter 2 reports on the variation of the S. guianensis whistles in Guanabara Bay, Rio de Janeiro State, between 2010 and 2014. Recordings of Guiana dolphin whistles were made with a Fostex FR-2 digital recorder, with sampling rate of 192 kHz and an omnidirectional C54XRS hydrophone. Whistle rates and sixteen acoustic parameters of the Guiana dolphin whistles were compared between behavioral states and group composition. A total of 664 whistles were analyzed and eleven acoustic parameters differ between behavioral states. The whistle duration was short (280 ± 121.8 ms). Guiana dolphin produces whistles with a high frequency, up to 66.7 kHz, the maximum value reported to this species. Guiana dolphins emitted whistles more frequently while socializing than while foraging or traveling (Tukey test, p<0.05). Three acoustic parameters contribute to the difference between behaviors: frequency at ½ of duration, delta frequency and inflection point. Whistle rate was high in groups with calves and comparisons between groups with and without calves were different in maximum frequency and number of step (Mann-Whitney Test (p<0.05)). Chapter 3 characterizes Guiana dolphin burst-pulsed sounds recorded in Guanabara Bay between 2013 and 2014. Burst-pulsed sound analysis was performed using custom routines in MATLAB and the Triton software package. Burst-pulse analyses involved three steps: recordings per day in a single file (Long-Term Spectral Average), burst-pulsed sound detections, and acoustic parameter analysis. Eight variables were analyzed for each burst pulse: duration, number of pulses, pulse duration, interclick interval, peak frequency, center frequency and frequency bandwidth of -3dB and frequency bandwidth of -10 dB. Burst pulses were emitted by groups with calves of Guiana dolphin during socializing and feeding. Burst-pulse emission rate was as high as 8 burst pulses per minute per individual. A total of 197 burst-pulse sounds were analyzed, with an average number of pulses of 168 and an average pulse duration of 0.3 ms. The interclick interval was short (0.2 to 2 ms). Burst pulses exhibited a broad frequency range, from 3 kHz to 96 kHz. Mean values for center frequency and peak frequency were 29.3 kHz and 28.0 kHz respectively. The ranges of -3dB bandwidth and -10dB bandwidth frequency values were 2.8 kHz to 39.2 kHz (15 ± 7.5 kHz) and 6.1 kHz to 78.7 kHz (14.3 ± 41 kHz) respectively