Pulsed sounds and Tail-slap in free-ranging Mediterranean striped dolphins

Striped dolphin (Stenella coeruleoalba), one of the most widespread cetacean species in the Mediterranean Sea, is an extremely vocal mammalian species, with a developed use of both vocal and non-vocal acoustic communication cues. However most of its visual and acoustic behaviour remains poorly studied. For the first time, the pulsed sounds of Stenella coeruleoalba were analysed in relation to the “tail slap” surface behaviour. The Tail-slap were recognized as a flat and noisy contact of the caudal section on the water surface with the animal in dorsal position. During the summers 2009-2010, continuous passive acoustic recordings and behavioural simultaneous data were collected, in an area of over 700 Km2, located in the Ionian Sea (Gulf of Corinth, Greece). Recordings were made in the proximity of the animals with a single hydrophone and a digital audio MAudio microtrack recorder. 63 surveys were made, 44 sightings were recorded, and 3.5 hours of behavioural observations and simultaneous recordings were sampled. Visual and acoustic data were broken down into 3-minute-intervals. For each 3-minute-interval, the number of pulsed sounds and the frequency of “Tail slap” were considered for statistical analysis. Statistical analysis showed a significant positive correlation (P<0.05) between pulsed sounds and “Tail slap” and a significant variation (P<0.05) in the number of pulsed sounds emitted, into the 3 minuteintervals, in relation to the presence or absence of the “tail slap”. In presence of the tail-slap, the number of produced pulsed sound increased. We suggest that, as reported for other species (i.e. Stenella frontalis), dolphins could be in alarming or stressing situations while producing the pulsed sounds associated with “tail slap”.