Table 2.

Distances from the sound source (km) at which, compared with undisturbed behaviour, there was a population-level decrease of 25%, 50%, 75% and 100% in the buzzing rate during sound exposure trials i.e. ship noise and airgun pulses (a–d, figure 2). The estimated SEL at these distances are given both as unweighted and HF-weighted [23] values (figure 1). The cells highlighted with grey represent ranges where the computed SELs that the whales were reacting to were below background noise level. The values in the grey cells indicate the maximum background levels measured at these ranges. The interquartile range of background levels at these ranges were 113–119 dB re 1 µPa²-s in unweighted data and 95–97 dB re 1 µPa² s in HF-weighted data. Background levels were adjusted to the mean duration of the airgun pulses (1.34 ± s.d. 0.56 s, figure 1).

decrease in buzzing rate (%)	distance to sound source (km)	unweighted SEL (dB re 1 μPa2 s)	HF-weighted SEL (dB re 1 μPa2 s)
25	16 (a)	<134	<107
50	12 (b)
75	10 (c)
100	approximately 7–8 (d)	<135