The population of finless porpoise in the middle and lower reaches of Yangtze River

Abstract

Based upon the data of ecological surveys of finless porpoise, Neophocaena phocaenoides, in the middle and lower reaches of the yangtze River and specimens collected in recent years, the current state of the porpoise was analysed and evaluated. Main results are highlighted as follows: (1) The porpoise distributes in the middle and lower reaches of the yangtze River, Yichang (1669 km from the estuary) is upper range of the distribution. The porpoise also distributed in Lakes Dongting and Poyang. The distribution patterns are clumped along the vertical direction of the rivet and shorewise along the horizontal direction of it. (2) The estimated population size of the porpoise is 2700 individuals. Density of population is highest in winter and lowest in summer. (3) Most common groups are of 1.5 individuals, which is about 88% in ratio. (4) It is reckoned theoretically that 539 new calves are born every year. Annual reproductive rate is 20%. (5) Though analysis and comparison the change of density of the populations among the river, Chinese coastal waters and Inland Sea of Japan, it is inferred that part of the population seems possibly to take long distance and large scale movement between the river and ocean, which is related with the reproduction.