Preliminary investigation on characteristics of Indo-Pacific humpback dolphins (Sousa chinensis) in waters between Shangchuan Island and Hailing Island

The Indo-Pacific humpback dolphins (Sousa chinensis) of the Pearl River Estuary population are distributed from Lingding Bay to the waters around Shangchuan Island. To find out whether there are S.chinensis in the waters to the west of Shangchuan Island, a total of eight vessel-based line-transect surveys was conducted from 2013 to 2015 in the waters between Shangchuan Island and Hailing Island. The humpback dolphins were sighted in each of the surveys and 78 groups with 623 individuals were sighted in total, confirming the year-round occurrence of the dolphins in this area. Most of the sightings were made in the waters near Xiachuan Island, Mangzhou Island and nearshore waters of Dongping harbor and Miaowanjiao. Dolphin encounter rate was similar with those in the Eastern Pearl River Estuary (Lingding Bay) and the Western Pearl River Estuary. The group size of dolphins was larger and the individuals are younger in the survey area than in the adjacent areas, indicating that the waters between Shangchuan Island and Hailing Island is important habitat for S.chinensis and has great potential for protection.