Geographic variation of whistles characteristics of striped dolphin (Stenella coeruleoalba) between different areas of the Mediterranean sea.

The striped dolphin (Stenella coeruleoalba) is a cosmopolitan species distributed world-wide. It is generally abundant, but some populations face significant challenges, as in the Mediterranean Sea. The Mediterranean population is considered a distinct conservation unit by IUCN experts. Morphological and genetic studies strongly suggest that the Mediterranean and Eastern North Atlantic populations are isolated from each other, with little or no gene flow across the Straits of Gibraltar. Characteristic of vocal behaviour have been often used to distinguish populations of many cetacean species. This work describes the geographic variability of striped dolphin “whistles” vocalisation in the Mediterranean Sea. Acoustic data were collected from 1994 to 2004 in different areas of the Mediterranean Sea, using multiple platforms. Thirty independent sightings were made, approximately 19 hours of recordings were inspected and 1190 whistles were extracted and analysed. The results of this project show that the whistles emitted by the animals living in distinct locations are different. DFA analysis allows to correctly classifying the animals of the Eastern and Western portion of the basin in the 70% of the cases. Moreover, some characteristics of the whistles show a geographical gradual gradient. Different possible explanations of geographic variation are considered: ecologic, genetic, and social factors. The genetic distance among these subpopulations have to be verified but in the mean time they could be taken into consideration as conservation units for future conservation plans.