Figure 1
From: Wild harbour porpoises startle and flee at low received levels from acoustic harassment device
(a) AHD ping characterization and (b) acoustic startle response in the six tagged porpoises. (a) An example of an AHD ping recorded by a DTAG on a porpoise at 1 km distance from the sound source. The bandpass-filtered (10–46 kHz) AHD ping had a received sound pressure level of 132 dB re 1 µPa (rms). The plot depicts the cumulative energy of the ping, the spectrogram, spectral density plot (or power spectrum), and the waveform of the ping. Due to propagation properties of the shallow water at this exposure site, the received ping had a duration of more than a second, although the emitted duration was 500 ms. (b) The acoustic startle response was evoked by the AHD pings in four porpoises (HP1,2,3,6): sudden muscle flinches, measured by the derived acceleration (jerk), occur within 0.2 s of receiving the first ping. HP4 and HP5 received the lowest sound pressure levels (dB re 1 µPa, rms fast), as indicated by the legend, and did not startle to these pings.
