Where to go in a highly developed area? -Utilization distribution of Indo-Pacific humpback dolphins in Pearl River Estuary, Hong Kong, China

Abstract

The Pearl River Estuary, China is reported to have the largest population of Indo-Pacific humpback dolphins (Sousa chinensis) in the world, while the region’s coastal development is also one of the most extensive. To examine area/habitat use pattern of humpback dolphins in Hong Kong, home range and core area utilization were estimated using dolphin sightings recorded from 2010 to 2012 by applying Kernel Density Estimates and local nearest-neighbor convex hull (LoCoH). Four spatially separated core areas were found, based on different behaviors. All core areas were either close to shore or sheltered by islands. Foraging and milling presented restricted core areas. Resting and socializing core areas were not evident. Range estimates for travelling behavior extended further than the range of other behaviors, suggesting two travelling corridors within Hong Kong waters; one connecting the northern Lung Kwu Chau Marine Park and western Lantau Island, and the other corridor connecting southern Lantau Island and Soko Islands. This indicates a connection between dolphins off northern and western Lantau Island and also between southern Lantau and Soko Islands. No connection was apparent between the core areas off The Brothers Island and the Marine Park, an area exposed to particularly heavy marine traffic. Incorporating individual movement and social data into the current analysis can further clarify the connectivity between all the core areas. It is of concern that less than 20% of the core areas are within Hong Kong's marine protected areas, which indicates the inadequacy of the current designation of local protected areas. Travelling ranges between southern Lantau and Soko Islands overlap with a principal shipping lane used by high-speed ferries operating between Macau and Hong Kong, posing a potentially severe threat in maintaining connectivity between these two areas.