Communication is primordial for survival of animal species as signals are involved in many social interactions (mate selection, parental care, and collective behaviours). The acoustic channel is the primary modality used by birds and mammals to reliably exchange information among individuals. In group-living species, the propagation of vocal signals is limited due to the density of individuals and the background noise. Vocal exchanges are therefore challenging. This study is the first investigation into the acoustic communication system of the Cape fur seal (CFS), one of the most colonial mammals with breeding colonies of hundreds of thousands of individuals. We described the acoustic features and social function of five call types from data collected at two colonies. Intra-species variations in these vocalizations revealed their ability to convey information about the age and/or sex of the emitter. Using two classification methods, we also found that the five call types have distinguishable frequency features and occupy distinct acoustic niches indicating acoustic partitioning in the repertoire. The CFS vocalizations appear to contain characteristics advantageous for discrimination among individuals, which will enhance social interactions in their noisy and confusing acoustic environment. This study provides a basis for our understanding of the CFS acoustic communication system.