Characterization and comparisons of click trains of Tursiops truncatus and Stenella coeruleoalba in the central Mediterranean sea

The present work focused on the characterization and comparison of click trains recorded from two Mediterranean odontocetes species: Stenella ceruleoalba and Tursiops truncatus. Acoustic data were recorded in two different areas of the central Mediterranean: the strait of Sicily and the Ionian sea. Two different acquisition systems were employed: a) recording in a band from 100 to 150.000 Hz, b) recording in a band from 0 to 48000 Hz. Acoustic data were analyzed by using the Avisoft SASLab Pro software, applying a high-pass filter of 3 KHz. The identification and the selection of individual click train were made manually, then the software measured automatically the following temporal parameters: number of pulses, duration of click train (ms), and relative pulse rate (Hz). In total we analyzed 349 click trains. Because data were not normally distributed, the Mann-Whitney U Test was carried out in order to compare: 1) the two areas, for each species; 2) the two species; 3) the two species for each area. For Tursiops truncatus the number of pulses and the duration were greater in the Ionian sea while the pulse rate were greater in the Strait of Sicily. For Stenella ceruleoalba the duration was grater in the Ionian sea. If we pool together data from the two sites, Tursiops truncatus showed an higer pulse rate than Stenella ceruleoalba. This result is consistent if we consider only the data of the Sicilian channel. In the Ionian sea, pulse rate didn’t show any difference among species, while the duration and the number of pulses were higher for Tursiops truncatus. The results of this study show that it is possible to identify acoustically the two studied species by analyzing their click trains, considering also the location were the recordings were made.