Odontocetes are capable of producing high frequency sonar signals and of processing the environment information contained in the sonar echoes. The goal of this study was to detect the time and spectrum characteristics of echolocation signals and sonar capabilities of finless porpoises (Neophocaena Phocaenoides). The main results and conclusions are summarized below:
Both riverine and inshore populations of finless porpoise produce “typical” high-frequency, narrow-band, and short-time duration phocoenid clicks, neither of them emits low-frequency (<70 kHz) sonar component. Comparison of echolocation signal characteristics between the two populations indicated that the waveform structures and frequency spectra are similar, while the acoustic parameters are significantly different (one-way ANOVA, p<0.05).
The echolocation appears shortly after birth (at least at days 22 postnatal) in Yangtze finless porpoise. The clicks of neonatal porpoise in the first recorded click train were indistinguishable from those of adults.
Results acquired from the methods of geometry and mathematics indicated that the double- and multi-pulse structure of echolocation signals in Yangtze finless porpoise is not caused by the phonating porpoise itself, but by the multipath propagation of the signals.
In open waters, the source levels (SLs) of echolocation signals in Yangtze finless porpoise are highly range dependent. From a relationship between interclick intervals (ICIs) and range to the hydrophone and from the estimated strengths of various of targets, the largest detection distances of the finless porpoise was estimated to be 11.5 m for a single fish, 2.6 to 7.9 m for gillnets, and 20.2 m for other conspecific individuals at normal incident angle.