Estimates of bio-sonar characteristics of a free-ranging Ganges river dolphin

Abstract

This paper reports the first known studies of the bio-sonar characteristics of an isolated free-ranging Ganges river dolphin, Platanista gangetica. The animal preferred to roam in a deeper tract of the otherwise shallow river. The click sounds of the dolphin were recorded over a period of 2 days on a 3.2-meter-long high-frequency hydrophone array composed of three hydrophones forming an equispaced linear array and another two hydrophones in conjunction with the central hydrophone forming an SSBL triangular array in a plane perpendicular to the array axis. The array was deployed both in horizontal and vertical configurations. The array structure provided 3-D measurements of the source location through measurement of the interelement time delay. Bio-sonar characteristics such as click duration, bandwidth, and interclick intervals in click trains have been reported. Measurements of dolphin track and the relative click levels on the array hydrophones have been used to obtain a preliminary characterization of the animal’s beam pattern.