Spectral content shown in both (a) acoustic pressure and (b) particle acceleration domains for original field recordings of boat noise and ambient conditions, playback of ambient and boat-noise recordings in the field, and playback of ambient and boat-noise recordings in experimental tanks. Mean power spectral density of 1 min of each sound condition is shown. In both the pressure and particle acceleration domains, there is a clear difference between boat and ambient conditions, whether using playback or real noise, and in tanks or in situ. However, received levels of particle acceleration at the fish were higher in playback treatments than with motorboats. Sounds were analysed in MATLAB v2010a, fft length=sampling frequency (48 kHz for sound pressure and 44.1 kHz for particle acceleration, both result in 1 Hz bands).