Data from: Northern bottlenose whales in a pristine environment respond strongly to close and distant navy sonar signals

Impact assessments for sonar operations typically use received sound
levels to predict behavioural disturbance in marine mammals. However,
there are indications that cetaceans may learn to associate exposures from
distant sound sources with lower perceived risk. To investigate the roles
of source distance and received level in an area without frequent sonar
activity, we conducted multi-scale controlled exposure experiments (n = 3)
with 12 northern bottlenose whales near Jan Mayen, Norway. Animals were
tagged with high-resolution archival tags (n = 1 per experiment) or
medium-resolution satellite tags (n = 9 in total) and subsequently exposed
to sonar. We also deployed bottom-moored recorders to acoustically monitor
for whales in the exposed area. Tagged whales initiated avoidance of the
sound source over a wide range of distances (0.8–28 km), with responses
characteristic of beaked whales. Both onset and intensity of response were
better predicted by received sound pressure level (SPL) than by source
distance. Avoidance threshold SPLs estimated for each whale ranged from
117–126 dB re 1 µPa, comparable to those of other tagged beaked whales. In
this pristine underwater acoustic environment, we found no indication that
the source distances tested in our experiments modulated the behavioural
effects of sonar, as has been suggested for locations where whales are
frequently exposed to sonar.