Assortative interactions revealed in a fission-fusion society of Australian humpback dolphins

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 patter...