Demography and population trends of the largest population of Indo-Pacific humpback dolphins

Estimates of demographic parameters and predictive modeling of population viability furnish baseline evidence for informed management of species and populations. There are very few examples of such approaches involving cetaceans due to often limited fundamental data, which frequently impairs the effectiveness of conservation. In this study, we estimate demographic parameters for the Indo-Pacific humpback dolphins, Sousa chinensis, from the Pearl River Estuary (PRE), China, based on a life-table constructed using data from stranded animals. We apply current abundance estimates and use an individual-based Leslie-matrix model to predict the population fluctuation by factoring in parameter uncertainty and demographic stochasticity. Our estimates indicate a continuous rate of population decline of 2.46% per annum, albeit with considerable variation. If the estimated rate of decline remains constant, 74.27% of the current population is projected to be lost after three generations and 57.60% of model simulations meet the criteria for classification as endangered under Criterion A3, applying IUCN Red List Categories and Criteria Version 3.1. However, as PRE is among the fastest economically growing regions of China and the world, the estimated rate of decline may further accelerate in a near future and the projected risk of extinction may be higher. Effective conservation measures are much needed and should be seen as a matter of urgency in management plans targeting PRE and environs.

► Demographic rates were estimated for Sousa chinensis from the Pearl River Estuary. ► A 2.46% annual decline in abundance was estimated, albeit with some variation. ► On average, 74.27% of the current population is projected to be lost in three generations. ► A conservation status classification as EN is most likely, while CR or VU status is plausible. ► It is suggested that the IUCN global classification of Sousa spp. be reconsidered.