Population Prediction of Finless Porpoise in the Yangtze River

Abstract

Finless porpoise is the only freshwater mammal in the Yangtze River basin, which has suffered a plummet in population these years. Our team mainly used Improved Leslie Population Model and Improved Differential Equation Model to predict the change of its population. Firstly, we predicted the population of finless porpoises 20 years later in 5 ex-situ reserves and analyse the influence caused by initial sex ratio. We used Leslie Population Model and improved it according to the characteristics of finless porpoises. We divided finless porpoises of different ages into five groups and used Siler's Competition Risk Model and PSO-MLE Algorithm to analyse their mortality. Using the models, we found that only when the initial sex ratio was 1:1 did the reproduction rate reach its maximum, and the population of finless porpoises could reach 1,336 after 20 years in this case. When the sex ratio was imbalanced, the greater the difference from 1:1, the fewer porpoises there were after 20 years. Lastly, we predicted how long it will take for the Yangtze finless porpoise to become functionally extinct without ex-situ conservation. We used Improved Differential Equation Model. According to the prevailing view of the criteria for functional extinction, it could be predicted that without protection, the finless porpoise will become functionally extinct in around 2038, from which we can see the importance of ex-situ conservation in finless porpoises’ protection.