Survival rate and population size of Indo-Pacific humpback dolphins (Sousa chinensis) in Xiamen Bay, China

The survival rate and population size of Indo-Pacific humpback dolphins (Sousa chinensis) in Xiamen, China, were estimated from vessel-based surveys during 2007-2010. Over the course of 202 d (881.1 observation hours), 76 groups were observed, and 52 dolphins were successfully identified. The Cormack-Jolly-Seber model estimated a constant apparent survival of 0.948 (95% CI: 0.922-0.966). Based on the open/POPAN model, the population size was estimated at 70 individuals (95% CI: 63-88). To explore the effect of uneven yearly survey effort, we pooled the data with seven sampling occasions with similar effort. This data set generated similar results of a constant survival of 0.957 (95% CI: 0.918-0.978) and population size of 72 (95% CI: 65-88). The small population size of the Xiamen humpback dolphins satisfies the Critically Endangered criterion of IUCN (D), and emphasizes urgency of the need for protection of the population. Improved monitoring efforts should be focused on enhancing our understanding of current status and evaluating impacts of all anthropogenic activities. A conservation plan for the population should also be drawn up.