Caracterização acústica dos assovios do golfinho-pintado-Pantropical (Stenella attenuata - Gray, 1864) (Delphinidae: Cetacea), na Bacia de Santos, Brasil, Oceano Atlântico Sul

Abstract

The Pantropical spotted dolphin (Stenella attenuata) is a species oceanic delfin little known in terms of acoustic repertoire. The present study had as objective to enhance the knowledge about the whistles produced by the species in the region of the Bacia de Santos, Brazil (South Atlantic population). The data came from the Projeto de Monitoramento de Cetáceos da Bacia de Santos (PMC-BS), collected from a hydrophone arrangement APC 42-1021 (sampling rate: 192kHz) towed by a vessel, associated to the visual confirmation of the species. 83 whistles were identified in one hour and seventeen minutes of recording effort, of which 10 acoustic parameters were extracted: minimum, maximum, beginning and ending frequencies (kHz), frequency range (kHz), duration (s), number of inflection points, number of steps, presence/absence of harmonics, initial/final slope. The visual contours of the signals also were analyzed, divided into 6 categories: ascending, descending, multi, ascending-descending, descending-ascending and constant. The duration of the whistles ranged from 0.098 to 1.650s (mean 1.3s ± 1.43), the beginning frequency ranged from 4.67kHz to 22kHz (mean 10kHz ± 3.52), ending frequency from 5.72kHz to 30kHz (mean 15kHz ± 5.9). The minimum frequency presented values between 4.22kHz and 12.63kHz (mean 8kHz ± 1.5), and the maximum frequency from 11.12kHz to 31kHz (mean 19.7kHz ± 3.5). The frequency range presented minimum and maximum values of 14.31kHz and 22.71kHz, respectively (mean of 11.65kHz ± 3.4). The number of inflection points ranged from 0 to 4 (mean 1.48 ± 1.18), number of steps from 0 to 15 (mean 2.3 ± 2.3) and about 37% of the whistles presented harmonic (1 by signal). Of the whistles, 82% had a positive initial slope and 64% presented a positive final slope, with 38.5% classified as multi, being the dominant contour category in the population. In the comparison of the results of the present study (South Atlantic) with studies done in other locations (North/South Pacific), the data presented little variation. The exception was duration, which was higher in the present study (mean of 1.3s ± 1.43) when compared to the specie’s study in the Pacific (mean between 053s - 09s). This is a pioneering study for the Brazilian coast, thus demonstrating the viability of a more comprehensive systematic study in the region to further enhance the knowledge of the specie’s whistle.