Source levels and propagation modelling of whistles from a free-ranging rough-toothed dolphin

Abstract

A lone adult individual of rough-toothed-dolphin had its acoustic behavior recorded with a calibrated system (Fostex FR22: 192 kHz sampling rate; C54 hydrophone: -165.0 dBV, 0.009 Hz–100 kHz). Moments when the animal approached and faced the hydrophone were noted. Whistles were counted in Raven 1.6 (Hann window, 512, 50% overlap). Duration (ms), minimum, maximum and peak frequencies (kHz), number of steps and step frequency (kHz) were extracted of whistles emitted when the animal was in a 1-m radius of the hydrophone. Source levels (SL) were estimated through power spectral density calculation in Matlab. SL at frequency parameters and at each whistle step were extracted and used in bellhop propagation models of a coastal scenario. 63 whistles were emitted within 1m. Frequencies ranged from 1.2 to 9.7 kHz and duration from 115.3 to 825.6 ms. Frequency and SL increased with step number, with 4.5 steps per whistle. Minimum frequencies (1.9 ± 0.6 kHz) had smaller SL (125.2 ± 4.2 dB re 1 μPa) and decreased to 100 dB before 500 m. Peak frequencies (6.7 ± 1.0 kHz) had mean SL of 149.5 ± 8.5 dB re 1 μPa and reached 2500 m with 100 dB. Higher frequencies reached longer distances and depths.