The seascape of Anthropocene: Spatio-behavioural dynamics of Indo-Pacific humpback dolphins (Sousa chinensis) in Hong Kong

Abstract

The availability and predictability of resource are thought to be among the key factors that determine the ranging pattern and socio-behavioural strategies of coastal dolphins. In Hong Kong, these are under enormous human pressure and fast diminishing due to many and ever-increasing development projects. No other delphinid population faces the intensity and multitude of impacts as those experienced by Indo-Pacific humpback dolphins in Hong Kong (HK) and the greater Pearl River Estuary (PRE). In this study, we investigate the spatio-behavioural dynamics of humpback dolphins and discuss our findings in the context of known population structure and local conservation needs. Kernel density estimates and Local nearest-neighbour Convex Hull (LoCoH) models constructed with 4-year (2011-2014) sightings records indicate four spatially separated core areas within shallow-water, island-associated inshore habitats. Foraging appears to be the key determinant of the dolphins’ overall distribution pattern, while the small and patchy but predictable foraging sites lead to the formation of small groups with fluid association between individuals. Spatial modelling depicts distance from shore and location as important variables in predicting foraging probability. Considering that the dolphins seen in HK waters represent part of a larger social network of the PRE population, and that HK waters represent only a small portion of the PRE ecosystem, the use of HK waters throughout the year indicates that this region of PRE represents an important area for the dolphins' overall energetic and socio-behavioural needs. Given the ongoing and vast development projects and heavy marine traffic across PRE, it is concerning that < 17% of core areas and < 7% of core foraging grounds are within the HK marine protected areas. Our findings highlight the importance of the understanding of animal behaviour and socio-spatial ecology in formulating effective conservation measures; and indicates the severe inadequacy of current protection measures in HK.