Acoustic occurrence, diel-vocalizing pattern, and detection ranges of southern right whale gunshot sounds off South Africa's west coast

Abstract

Southern right whales (SRWs), Eubalaena australis, have a cosmopolitan distribution in the Southern Hemisphere but are known to overwinter in four coastal breeding grounds off Argentina, Australia, New Zealand, and South Africa (International Whaling Commission [IWC], 2001; Jackson et al. 2016; Jefferson et al., 2015; Webster et al., 2019). SRWs perform seasonal migrations southwards in summer to Antarctic and sub-Antarctic waters where they feed mostly on copepods and krill (euphausiids), and northwards in winter to warm waters of the low latitudes for mating, calving, and nursing (Bannister et al., 1999; Best, 2007; IWC, 2001; Jefferson et al., 2015; Mate et al., 2011). However, Best (2006) and Mate et al. (2011) showed that the coastal waters of the South African west coast are also used as an austral spring/summer feeding ground by the portion of the population that remains there year-round. Seasonal acoustic occurrence of SRWs in South African waters is currently based on short-term shallow coastal (adjacent to the coast and within the 100 m isobath) research (Figure 1; Hofmeyr-Juritz, 2010; Vinding-Petersen,- 2016). An expansion of such acoustic work to more offshore waters (Figure 1) and more long-term programs is useful for a more comprehensive understanding of the species' seasonal occurrence patterns