Scheme of the hydrophone system and its geometry.

The towed linear array is composed by 2 Medium frequency hydrophones Benthos AQ4 (Benthos, Falmouth, USA) with broadband preamplifiers HP/02 (Magrec, Devon, UK) incorporating a low cut filter set to provide -3dB at 100Hz, and 2 spherical ceramic hydrophone elements (Seiche UK Ltd) with high frequency preamplifiers with a 2kHz low cut filter. A 200m cable connected the array with the electronic component through a junction box. Recordings were digitalized at a sampling rate of 192 kHz and directly visualized on a laptop.