Abstract:   The world's largest population of Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary is exposed to some of the world's greatest concentration of anthropogenic threats; much of it due to the region's rapid urbanisation and industrialisation in recent decades. By assessing behavioural responses of humpback dolphins to long-term and large-scale environmental change in Hong Kong, and short-term but frequent behavioural disturbance due to unregulated dolphin-watch tourism, this study investigated humpback dolphins as a model system of a coastal delphinid in the coastal seas of the Anthropocene.

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Field surveys were conducted between 2011 and 2014 to identify humpback dolphins’ distribution pattern. Resource selection function was applied to model the dolphin's habitat selection process and quantify their long-term habitat preference. The results indicate that humpback dolphins display a heterogeneous pattern in habitat selectivity that is conditional to distinctive sets of key factors at different spatial scales. By using Landsat data and historic archives, and by quantifying a cumulative habitat loss over the past 40 years, this study reveals that during that time the natural shoreline providing critical ecological functions to humpback dolphins in Hong Kong has been drastically reduced. Occurrence probabilities reconstructed for the time-periods prior to major habitat alterations, and occurrence probabilities projected into future years (when all currently planned projects are to be completed) indicate a major drop of habitat use by the dolphins near previous reclamation areas. All current Marine Protected Areas for humpback dolphin conservation are already affected by the ongoing environmental change and this will intensify in the future.

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Shore-based scan-sampling surveys were conducted between 2013 and 2014 to identify a distribution pattern of the dolphins at one of their main feeding area in Hong Kong. With year-round sightings, the dolphins used this area selectively at different seasons and time of day. Only a small portion of the area was used as feeding location, within a narrow range of distances from shore, demonstrating a clear pattern of spatio-temporal fine-scale habitat selection that has not been accounted for in the current local conservation measures.

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Behavioural responses of humpback dolphins to small-scale dolphin-watch operations were investigated by tracking the dolphins' movement and recording fine-scale changes in the movement parameters. Analyses show that movement patterns of the dolphins, distinctive between behavioural states, were significantly altered by the presence of dolphin-watch boats. Multivariate models reveal that the disturbance by dolphin-watch operations can be seen as an external factor affecting the dolphins’ spatial decisions. Consequently, an appropriate regulatory mechanism is needed to manage the dolphin-watch tourism and minimise its impacts on the target species.

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In summary, this study quantifies humpback dolphins’ response to large long-term and short-term chronic anthropogenic impacts, and indicates that various human activities affect the dolphins' daily behaviour and habitat selection. The conservation actions that are currently in place are ineffective in protecting humpback dolphins from man-made threats and will not be effective in preserving their habitat in the long-term. This implies serious ecological consequences and an urgent need for science-based and habitat-oriented conservation strategy.