Modeling demographic parameters of an edge-of-range population of Indo-Pacific humpback dolphin in Xiamen Bay, China

Abstract

The Indo-Pacific humpback dolphin (Sousa chinensis) is a species vulnerable to extinction. One population of this species, located in Xiamen Bay, China, has been extensively studied so as to estimate its abundance. However, the demographic dynamics of this population are not fully known. To study survival and the size of this population, monthly photo-identification surveys were conducted from August 2010 to July 2015. A total of 157 dolphin sightings were recorded and 60 individuals were successfully photo-identified for use in mark–recapture analysis. The super-population size estimated by POPAN modeling suggested that 64 individuals were present in Xiamen Bay during the study period, and the most recent annual population size was estimated at 58 individuals (using both a Huggins closed capture model and a POPAN model). A Cormack–Jolly–Seber model estimated an annual survival rate of 0.976, which remained constant throughout the study period. However, a low level of birth rate and/or calf survival, which was indicated by the low probabilities of entrance into marked population, may not support the long-term persistence of this population. Based on these findings, we propose that a comprehensive assessment of anthropogenic impacts on this population should be performed and actions should be taken accordingly, to limit mortality and increase the birth rate.