The acoustic channel is important for communication in otariids (fur seals and sea lions). Discrimination between species, sex or individuals is essential in communication; therefore insight into the role of vocalisations in recognition is vital to understanding otariid social interactions. We measured vocalisations and their use in discriminating sex and species in male Australian sea lions (Neophoca cinerea). Barking calls of mature males were recorded and analysed based on five acoustic parameters. A discriminant function analysis classified calls to the correct individual at a classification rate of 56%, suggesting that male barking calls are individually distinctive with the potential to facilitate individual vocal recognition. Playback experiments were used to assess the role of vocalisations in sex and species recognition both in and out of the breeding season. Males showed significantly stronger reactions to both conspecific and heterospecific males than they did to conspecific females and were most responsive during the breeding season. Australian sea lion males have the most depauperate vocal repertoire of any otariid. This simple repertoire may reflect the ecological circumstances in which these animals breed, with very low colony densities, asynchronous breeding and low levels of polygyny. Yet even in this simple system, males are able to discriminate between males and females of their own species, and distinguish the calls of conspecifics from other species. The barking calls of male Australian sea lions have sufficient information embedded to provide the potential for individual discrimination and this ability will be assessed in future studies.