Fig. 1

Underwater source level measurements (dB re. 1 μPa RMS Hz^−0.5 at 1 m) made at a 1 V and b 3 V at angles of 0 °, 90 °, and 180 ° off-axis. The transducer was to be mounted on its side on the animal, such that the measurements at 90° are representative of sound levels in the direction of the animal’s head/ears while 0 and 180 ° indicate directions away from (approximately normal to) the animal. Note that at 1 V the source levels at low frequencies at angles of 90 ° and 180 ° started to approach the noise floor of the calibration equipment and the true source levels are likely lower than those shown