Acoustic seasonality, behaviour and detection ranges of Antarctic blue and fin whales under different sea ice conditions off Antarctica

Abstract

Descriptions of seasonal occurrence and behaviour of Antarctic blue and fin whales in the Southern Ocean are of pivotal importance for the effective conservation and management of these endangered species. We used an autonomous acoustic recorder to collect bioacoustic data from January through September 2014 to describe the seasonal occurrence, behaviour and detection ranges of Antarctic blue and fin whale calls off the Maud Rise, Antarctica. From 2479 h of recordings, we detected D- and Z-calls plus the 27 Hz chorus of blue whales, the 20 and 99 Hz pulses of fin whales and the 18-28 Hz chorus of blue and fin whales. Blue whale calls were detected throughout the hydrophone deployment period with a peak occurrence in February, indicating continuous presence of whales in a broad Southern Ocean area (given the modelled detection ranges). Fin whale calls were detected from January through July when sea ice was present on the latter dates. No temporal segregation in peaks of diel calling rates of blue and fin whales was observed in autumn, but a clear temporal segregation was apparent in summer. Acoustic propagation models suggest that blue and fin whale calls can be heard as far as 1700 km from the hydrophone position in spring. Random forest models ranked month of the year as the most important predictor of call occurrence and call rates (i.e. behaviour) for these whales. Our work highlights areas around the Maud Rise as important habitats for blue and fin whales in the Southern Ocean.