Fish chorus variation in a tropical estuarine environmenta).

Fish choruses are still understudied in the Southwestern Atlantic Ocean. Temporal and spatial variation of fish choruses at two sites inside Guanabara Bay were investigated between 2021 and 2022; one sampling site was in a Marine Protected Area (MPA), and the other was in a rocky environment closer to vessel trafficking areas. Acoustic recordings were performed on 17 sampling occasions of 24 h, coupled to a temperature data logger. Long-term spectral averages were employed to determine choruses' start, end, and peak times, and third-octave levels were used to characterize spectral characteristics. Fish sounds were also analyzed and investigated with a principal components analysis. Choruses in the MPA lasted, on average, 4.5 h and had a peak frequency of 547.2 ± 226.6 kHz with a peak level of 104.6 ± 8.7 dB re 1 µPa. In contrast, the rocky site choruses lasted 5.5 h on average and had a peak frequency of 371.7 ± 131.0 Hz with a peak level of 113.4 ± 4.0 dB re 1 µPa. Chorus peak frequency was positively correlated to temperature (r = 0.4). Different types of fish sounds were identified, with some acoustics parameters varying between sites. Results indicate more than one chorusing species that may react to different factors.

Whistles of Atlantic spotted dolphin from a coastal area in the southwestern Atlantic Ocean.

Atlantic spotted dolphins were recorded on the coastal area of Rio de Janeiro with equipment of 192 kHz sampling rate. The animals produced an average of 33 whistles/min. The repertoire was balanced among four contour categories, with the occurrence of a stereotyped whistle. Frequency parameters were measured between 1.3 and 29 kHz, which represents an increase in the frequency range previously reported for this species in the southwestern Atlantic Ocean. With the use of a higher sampling rate, the acoustic parameters of S. frontalis whistles have changed significantly and became more similar to those reported for North Atlantic populations.

High-frequency social communication in Sotalia guianensis.

This study aimed to investigate the use of high ultrasonic frequencies (above 40 kHz) in the Sotalia guianensis whistle repertoire. The whistles were classified as high-frequency (HF) whistles and very high-frequency (VHF) whistles. Seven parameters were extracted and a general linear mixed effects model was performed between the total number of whistles and VHF ones. Frequency parameters of HF and VHF whistles were the highest reported for this species so far. However, VHF whistles were rare and occurred in situations of high acoustic activity, which may represent a strategy used by dolphins to deal with higher levels of vocalization rates.

Whistle comparison of four delphinid species in Southeastern Brazil.

The present study evaluates variations in frequency and duration parameters of whistles of four dolphin species (Sotalia guianensis, Steno bredanensis, Stenella frontalis, and Tursiops truncatus), recorded in the Rio de Janeiro State Coast, Southeastern Brazil. A total of 487 whistles were analyzed. Acoustic parameters of the whistles were classified to species by discriminant function analysis. Overall classification score was 72.5%, with the highest classification score obtained for whistles of S. bredanensis and the lowest obtained for S. frontalis. Most differences were among S. bredanensis and S. guianensis, species that did not have their repertoires compared in other studies.

High-frequency whistles of Guiana dolphins (Sotalia guianensis) in Guanabara Bay, southeastern Brazil.

Guiana dolphins produce whistles with a higher frequency and less complexity than most other delphinid species. The present study used a recording system with sampling rate of 192 kHz to describe the high-frequency whistles of Sotalia guianensis in Guanabara Bay, Rio de Janeiro. Eleven acoustic parameters (start, end, minimum, maximum, delta, center and peak frequency, duration, and frequency at 14, 12, and 34 of duration) were measured for all whistles. Whistles with a fundamental frequency up to 66.7 kHz were reported, thereby expanding the known frequency range of this species.

Underwater noise in an impacted environment can affect Guiana dolphin communication.

This study focused on whistles produced by Guiana dolphin under different noise conditions in Guanabara Bay, southeastern Brazil. Recording sessions were performed with a fully calibrated recording system. Whistles and underwater noise levels registered during two behavioral states were compared separately between two areas. Noise levels differed between the two areas across all frequencies. Whistle duration differed between areas and was negatively correlated with noise levels. Whistling rate was positively correlated with noise levels, showing that whistling rate was higher in noisier conditions. Results demonstrated that underwater noise influenced Guiana dolphin acoustic behavior.