Stingray sociality – A case study for the utility of heterarchical analysis in understanding animal societies (#151)
Sharks and rays aren’t typically considered social creatures, but many have the brain capacity necessary to develop and maintain complex social repertoires. Smooth stingrays reportedly form large breeding aggregations and have the brain size and complexity necessary for social behaviour, yet no formal assessment of their sociality exists. In Jervis Bay, Australia, smooth stingrays have been provisioned food at a local boat ramp since 1985. We took advantage of their attraction to this site to conduct a heterarchical analysis (dominance hierarchy and social network analysis) based on their agonistic interactions. We observed a stable, relatively linear but shallow dominance hierarchy dominated by a single individual. Social network analysis revealed a non-random social network centred on the dominant individual. The observed social structure was thus reflective of a despotic society. Contrary to previous research, size did not predict dominance but it was correlated with network centrality. The factors determining dominance of lower ranks were difficult to discern. This study provides the first heterarchical assessment of stingray sociality, and supports our hypothesis that this species is capable of social organisation. Given higher dominance and centrality relate to greater access to the provisioned resource, the observed social structure likely has fitness implications.