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Geographic variation in fin whale (Balaenoptera physalus) calls in the Weddell Sea, Antarctica
Victoria R. Field, Elke Burkhardt, Ilse Van Opzeeland
Currently, little is known about the population identity of fin whales (Balaenoptera physalus) in Antarctic waters. Initial analyses of acoustic recordings from the Southern Ocean (SO) have shown that fin whale calls differ between regions, possibly representing different fin whale populations. In the Atlantic Sector of the Southern Ocean, the typical fin whale low frequency (LF) 20-Hz song is often accompanied by simultaneous higher frequency (HF) component at around 89 Hz or 99 Hz. However, the distribution of these call types throughout the area and whether there is a clear spatial separation between these call types is so far unknown. In this study, fin whale call characteristics were analysed and compared between two recording locations: the Greenwich Meridian (from 2009 and 2011) and Elephant Island (from 2013 and 2015). The HF call component was found to be significantly (p-value < 2.2e^-16) unique in its peak frequency at the two locations, with 99 Hz (97.14 Hz ? 3.19) at Greenwich Meridian and 86 Hz (86.26 Hz ? 1.36) at Elephant Island. The inter-pulse interval (IPI) of LF and HF calls also differ between geographic regions, with a median IPI of 14.5 seconds at Elephant Island and a median IPI around 10 seconds at the Greenwich Meridian. Variations in fin whale song IPIs were also investigated and revealed that song also varies at the two recording sites. Fin whale song at Elephant Island was dominated by a singlet song type whereas fin whale song at the Greenwich Meridian featured mainly a triplet song type. The characteristic elements for fin whale calls examined in this study all indicate that the fin whale calls recorded at Elephant Island and Greenwich Meridian belong to two distinct acoustic populations. An understanding of how potentially distinct fin whale stocks utilize different geographic regions of the Southern Ocean is fundamental for management and conservation measures aiming to improve the conservation status of this vulnerable species.