Video 2.1. Conditioned response of hammerhead sharks (S. lewini) to sound

First, showing the swimming behaviour of three young hammerhead sharks during a 2 kHz control signal (at 149 dB SPLrms at 1 m). The flashing speaker icon indicates the location of the active speaker. Note that the sharks continue their normal swimming behaviour during the control signal. Second, showing how the conditioned hammerhead sharks react to a 400 Hz signal (at 135 dB SPLrms at 1 m), indicated by the flashing speaker icon at the location of the active speaker. After signal onset the sharks swim faster and change swimming direction more frequently (arousal state). Note that in the aroused state the sharks swim closer together to form a group, which is led by the largest animal.