Long-lasting social bonds of a habitat-structured delphinid social system

Abstract

Owing to the large, three-dimensional, fluid nature of their aquatic environment, the impact of habitat configuration has rarely been investigated in cetacean societies. However, in some coastal areas such as large estuarine systems and lagoons, where environmental variables can be spatially structured, the role of habitat configuration in shaping dolphin societies should not be ignored. In the present study, we examined the social structure of Indo-Pacific humpback dolphins, Sousa chinensis, in waters off the Leizhou Peninsula (LZP), northern South China Sea, using an 11-year photo identification data set (2013–2023). We identified four mixed sex/age communities with segregated region preferences. Three communities exhibited a preference to waters of intermediate depth (5 m ≤ depth < 10 m), while one community preferred shallow waters (< 5 m in depth). Dolphins inhabiting Zhanjiang Bay and northern Leizhou Bay preferred deeper waters, probably a result of reduced access to the shallow waters in these areas. The double dekker semipartialling multiple regression quadratic assignment procedure (MRQAP-DSP) suggested that spatial overlap and gregariousness were the most significant predictors describing the LZP humpback dolphins' social structure. Community size and their geographic/social positions outperformed predation risk (as reflected by shark-inflicted scars) in shaping communities' sociality (measured as Strength, Eigenvector centrality, Reach, Clustering coefficient and Affinity). From our results, we suggest that dolphins with similar area preferences developed strong associations that were stable over time and a habitat-structured social network. This study contributes to our understanding of the complex social structure of coastal dolphins and provides new insights into dolphin behaviours that can be important for developing effective management strategies.