Vessel noise experienced by free-ranging shortfinned
pilot whales. We deployed digital acoustic
recording tags (DTAGs; Johnson & Tyack 2003) on
short-finned pilot whales Globicephala macrorhynchus
(pilot whales hereafter) off the coast of Tenerife,
Canary Islands, Spain, during 2003 and 2005. The tags
sampled 16 bit audio at 96 kHz (2003) or 192 kHz
(2005). Several sequences of elevated noise levels from
vessels in the vicinity of tagged whales were identified.
To document the variability of noise levels experienced
by free-ranging pilot whales, we quantified the
noise level of 2 sequences of background noise and 6
sequences of vessel noise in which the tagged whale
moved little and consequently produced little flow
noise. A 50 s window from each sequence, centred on
the point of highest noise intensity, was filtered (2 to
12.5 kHz, 4-pole Butterworth filter) and analysed in
1 s blocks for RMS (root mean square) noise level in
communication frequencies.