Population size survery of Yangtze finless porpoise in the Dongfengxisha waters of Yangtze River Estuary

Abstract:

The Yangtze River Estuary is one of the finless porpoise (Neophocaena asiaeorientalis) habitat with the high density. The Dongfengxisha waters located on the southwest side of Chongming Island in the Yangtze Estuary is a distribution hotspot of the Yangtze finless porpoise (N. asiaeorientalis). In order to clarify population dynamics of the finless porpoise in the Dongfengxisha waters, the visual survey and perennial observations were performed in this waters from 2014 to 2016. A total of six investigations covered 224 km length of the line transect and found 68 porpoises in 11 groups. The encounter rate is averagely 0.37 int./km from 0.12 int./km to 1.14 int./km. During 13 months of perennial observations, 340-353 porpoises in 123 groups were witnessed. The average group encounter rate was 0.38 and the average individual encounter rate was 1.07. Visible coefficient method estimated that the finless porpoise population was 11.1-62.7, with the average number of 31.6. Given that the shoal is located in the north of the Dongfengxisha waters and is hard for finless porpoise to survive, the population was corrected as 26.8. Since the finless porpoise ranges throughout the year in the waters, it is necessary to take intensive care and even establish a natural reserve.