Bio-duck is a quacking-like sound which was first reported in the open ocean by submarines in the 1960s. It is recorded frequently around the coasts of Australia, and in particular in the Perth Canyon. The sounds were originally detected by sonar operators on Oberon-class submarine. They are audible with frequencies from 50 to 300 Hz. The duration of the calls is between 1.6 and 3.1 seconds. The sounds occur many times per day from winter to October, and then taper off until December; they are not heard again until the next summer.