Indo‐Pacific humpback dolphins (Sousa chinensis) in the Moyang River Estuary: The western part of the world's largest population of humpback dolphins

Abstract

Abstract Information gaps from uninvestigated habitats can hinder population assessments and the efficacy of conservation actions for marine mammals, particularly for populations of widely distributed species. The full extent of occurrence of the world's largest (putative) population of Indo‐Pacific humpback dolphins (Sousa chinensis) in the Pearl River estuary (PRE) is not known due to a poor understanding of the western boundary of the population's range. This information gap is the basis of the most critical obstacle for assessing the population's status. To determine the distribution and abundance of the PRE humpback dolphins in the far western portion of its range, systematic line‐transect vessel surveys were conducted in the Moyang River estuary (MRE) during 2013–2015. Photo identification of dolphins and cross‐matching of individual dolphins between different regions were also undertaken to examine individual movement patterns. The abundance of humpback dolphins in the MRE was estimated to be 528 individuals (coefficient of variation: 28.7–50.2%). Cross‐matching of individually identified dolphins from the MRE (present survey area) with those from other survey areas of the PRE showed that dolphins moved frequently across different regions of the PRE, indicating dolphins from both PRE and MRE comprise a single population (which is renamed to be the PRE–MRE population). The western boundary of this population appears to be in the waters on the eastern side of Hailing Island, as dolphins were never observed further west. Supporting around one‐fifth of the PRE–MRE population and providing a quarter of the habitat of the entire PRE–MRE population, the MRE clearly also deserves consideration for greater conservation measures. Strengthening the management with stringent controls over fishing activities in the MRE and establishing a marine protected area in the core habitat are recommended to facilitate better conservation for the entire PRE–MRE humpback dolphin population.