Figure 3.

Diving and foraging behaviour of porpoise hp12_293a around the time of passage of a presumed fast ferry. (c–f) A close-up of the period delineated by the grey frame in (a,b). (a,d) 16 kHz TOLs (0.5 s trimmed mean averages over 1 ms measurements). (b,e) Dive profile with the time during which the porpoise produced regular and buzz clicks marked in blue and red, respectively. The thick black lines above the profile in (b) show the times with audible vessel noise in the recordings. The yellow overlay marks the period when the ferry noise was clearly audible above other vessel noise. Shading marks the civil twilight and night-time. (c) Spectrogram composed of power spectral densities in 1 Hz bands. The broadband vertical bands indicate noise when the porpoise surfaces. (d,e) Detail of TOL and dive profile during the close-up interval. (f) Acceleration. The oscillations in the x- and z-axes (i.e. the animal's longitudinal and ventro-dorsal axes, respectively) indicate propulsive motions.