Seasonal occurrence of fin whale song off Juan Fernandez, Chile

Abstract

Fin whales Balaenoptera physalus were the species of baleen whale most widely caught by commercial whaling fleets off the Chilean coast and are globally classified as Endangered. However, very little is known about the present distribution and seasonal movements of fin whales off the coast of Chile. Passive acoustic data collected at the HA03 station of the Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organization off the Juan Fernandez Archipelago (JFA) between 2007 and 2016 were analyzed. The temporal occurrence of fin whale song was examined using automatic detection via spectrogram crosscorrelation of song notes and by calculating the average acoustic power in the frequency bands of fin whale song. Fin whale song off JFA was composed of regular 17 Hz notes associated with high-frequency components at 85 Hz, with singlet phrasing at a dominant primary inter-note interval of 14.4 s and a secondary interval of 30.8 s. There was a clear seasonal pattern in acoustic presence that was consistent across all years: low or no song during the austral summer and a peak in song occurrence in austral winter. A propagation loss model estimated the detection range at this site to be 186 km. Where the fin whales that are heard off JFA spend the summer months remains an open question. Possible locations include the Western Antarctic Peninsula and/or off northern-central mainland Chile. Further studies should be pursued to better understand the distribution and seasonal movements and to support the conservation of this Endangered species.