Acoustic and behavioural changes by fin whales (Balaenoptera physalus) in response to shipping and airgun noise

Abstract

Non-lethal behavioural effects of underwater noise in marine mammals are difficult to measure. Here we report acoustic and behavioural changes by fin whales in response to two different types of anthropogenic noise: shipping and airgun noise. Acoustic features of fin whale 20-Hz song notes recorded in the Mediterranean Sea and Northeast Atlantic Ocean were compared for areas with different shipping noise levels, different traffic intensities in the Strait of Gibraltar and during a seismic airgun array survey. In high noise conditions 20-Hz note duration shortened, bandwidth decreased, centre frequency decreased and peak frequency decreased. Similar results were obtained in 20-Hz song notes recorded during a 10-day seismic survey. During the first 72h of the survey, a steady decrease in song received levels and bearings to singers indicated that whales moved away from the airgun array source and out of our detection area, and this displacement persisted for a time period well beyond the 10-day duration of seismic airgun activity. This study provides evidence that male fin whales from two different subpopulations modify song characteristics under increased background noise conditions, and that under seismic airgun activity conditions they leave an area for an extended period. We hypothesize that fin whale acoustic communication is modified to compensate for increased background noise and that a sensitization process may play a role in the observed temporary displacement. The observed acoustic and behavioural changes of this endangered species are discussed in the context of reproduction success and population survival.