Bottlenose Dolphin (Tursiops truncatus) Whistle Modulation during a Trawl Bycatch Event in the Adriatic Sea

Marine mammal vocal elements have been investigated for decades to assess whether theycorrelate with stress levels or stress indicators. Due to their acoustic plasticity, the interpretation ofdolphins' acoustic signals of has been studied most extensively. This work describes the acousticparameters detected in whistle spectral contours, collected using passive acoustic monitoring (PAM),in a bycatch event that involved three Bottlenose dolphins during midwater commercial trawling.The results indicate a total number of 23 upsweep whistles recorded during the bycatch event, thatwere analyzed based on the acoustic parameters as follows: (Median; 25th percentile; 75th percentile)Dr (second), total duration (1.09; 0.88; 1.24); fmin (HZ), minimum frequency (5836.4; 5635.3; 5967.1);fmax (HZ), maximum frequency, (11,610 11,293; 11,810); fc (HZ), central frequency; (8665.2; 8492.9;8982.8); BW (HZ), bandwidth (5836.4; 5635.3; 5967.1); Step, number of step (5; 4; 6). Furthermore, ourdata show that vocal production during the capture event was characterized by an undescribed todate combination of two signals, an ascending whistle (upsweep), and a pulsed signal that we called"low-frequency signal" in the frequency band between 4.5 and 7 kHz. This capture event reveals anovel aspect of T. truncatus acoustic communication, it confirms their acoustic plasticity, and suggeststhat states of discomfort are conveyed through their acoustic repertoire.