Aquatic Mammals (1996)


A comparison of the acoustic waveforms of three different species, Phocoena phocoena, Phocoena sinus and Neophocaena phocaenoides of the sub-family Phocoeninae is made with the species Phocoenoides dalli of the subfamily Phocoenoidinae. The comparison is based on the successful mathematical modelling and identification of the clicks. As remarkable as it may seem, the polycyclic sonar signals of these species have the same basic wave shape in common, despite their somewhat longer time-duration frequency bandwidth product in relation to a Tursiops type click which lasts only a few cycles. In-depth analysis for the type of sonar click of the Phocoeninae subfamily reveals both a representation by a single pulse and a decomposition into a main pulse, followed within 16-20 µs after onset by an important reverberation. Both pulses can be modelled by the Gabor time function. For the P. dalli species we find a decomposition into three elementary pulses together giving rise to the unusual time duration of the click of 100 µs. The time difference between those first two pulses of the click—with identical dominant frequency—is conjectured to be an important parameter in the identification of the acoustic behaviour and is probably attributable to a morphological distinction inside the animal’s head. This supports acoustically the subfamilial partition. Cluster analysis applied to the two highest ranking parameters of the click description. i.e. dominant frequency and either time duration or frequency bandwidth reveals a striking overlap in similarity in the click structure of the three members of the subfamily Phocoeninae and a distinguishing characteristic for the subfamily Phocoenoidinae. A cluster of clicks for Tursiops (open water) is added to this scatter plot as a reference to species with a different (higher) relative frequency bandwidth. As a linear, non-parametric measure of similarity in waveform, the cross-correlation factor for normalized frequency scale between P. sinus, P. phocoena and N. phocaenoides is calculated as 0.73 and 0.76.