Understanding individual interactions within a community or population provides valuable insight into its social system, ecology and, ultimately, resilience against external stimuli. Here, we used photo-identification data, generalised affiliation indices and social network analyses to investigate dyadic relationships, assortative interactions and social clustering in the Australian humpback dolphin (Sousa sahulensis). Boat-based surveys were conducted between May 2013 and October 2015 around the North West Cape, Western Australia. Our results indicated a fission-fusion society, characterised by non-random dyadic relationships. Assortative interactions were identified both within and between sexes, and were higher amongst members of the same sex, indicating same-sex preferred affiliations and sexual segregation. Assortative interactions by geographic locations were also identified, but with no evidence of distinct social communities or clusters, or affiliations based on residency patterns. We noted high residency amongst females. Models of temporal patterns of association demonstrated variable levels of stability, including stable (preferred companionships) as well as fluid (casual acquaintances) associations. We also demonstrated some social avoidance. Our results point to greater social complexity than previously recognised for humpback dolphins and, along with knowledge of population size and habitat use, provide the necessary baseline upon which to assess the influence of increasing human activities on this endemic, Vulnerable species.