Apparent Sonar Clicks from a Captive Bottlenosed Dolphin, Tursiops truncatus, when 2, 7 and 38 Weeks Old

Abstract

A two-week-old dolphin produced clicks with peak energy as high as 60 kHz. At 7 weeks some clicks from the same dolphin peaked between 10 and 20 kHz. At 38 weeks it produced clicks with peak energy as high as 120 kHz (−10 dB BW 100 kHz), similar clicks were recorded from its mother and another adult female in the same pool. There was a 1/1 ratio between the −10 dB bandwidths and the respective spectral peak frequencies. Click duration was less than 50 µsec. Observations of the dolphins orientation relative to the hydrophones indicated that the selected clicks were recorded close to the beam axis. The click train from the two-week-old dolphin had click intervals from 70 to 2.5 msec. The intervals changed in a cyclic pattern with a decreasing mean interval as the dolphin approached the hydrophone. The possible implications of these observations for the click producing mechanism are discussed.