The habitat use and behavior of Indo-Pacific humpback dolphins (Sousa chinensis) and Indo-Pacific finless porpoise (Neophocaena phocaenoides) in Hong Kong SAR waters

Both Indo-Pacific humpback dolphins (Sousa chinensis) and Indo-Pacific finless porpoise (Neophocaena phocaenoides) occur regularly in Hong Kong Special Administrative Region (SAR) waters. The range of each species overlaps... [ view full abstract ]

Both Indo-Pacific humpback dolphins (Sousa chinensis) and Indo-Pacific finless porpoise (Neophocaena phocaenoides) occur regularly in Hong Kong Special Administrative Region (SAR) waters. The range of each species overlaps and each are exposed, to differing degrees, to the same anthropogenic activities, such as noise, ship strike, bycatch in fisheries, and contamination of their habitat and prey resources. So as to better understand fine scale habitat use and the factors which influence distribution patterns, acoustic tools were used to study selected areas within Hong Kong. Acoustic loggers were deployed between July 2015 and November 2018. As dolphins prey on soniferous fishes, acoustic detectors were also able to provide information on the overlap of both fish and marine mammal detections. A General Additive Model (GAM) which included a number of environmental parameters (e.g. tidal height and state, temperature, and rainfall) was used to assess the factors which could contribute to marine mammal occurrence. The results indicate that both scies of marine mammals were present year round in the areas of study, although there were both seasonal and diurnal patterns of occurrence. Feeding dominated during certain tidal periods and the occurrence of small fishing vessels also appeared to increase during these periods. Acoustic tools are easy to use, economical to deploy and can provide continuous data sets thus making them ideal fr such studies. the information provided on long term habitat use and key behaviours provide critical information for managers.