Investigations On Distribution,Population And Fishery Resources Of Chinese White Dolphin (Sousa Chinensis) In Jiangmen Waters Of Guangdong Province

The Indo-Pacific humpback dolphin(Sousa chinensis),also known as the Chinese white dolphin,is a small dolphin which distributes in estuarine and inshore waters of Indian,the coastal waters of Southeastern China and Southeast Asia.The Indo-Pacific humpback dolphin is classified as "Near Threatened" by the International Union for Conservation of Nature due to the proximity of much of their habitat to areas of intensive anthropogenic activities.It has been investigated on the ecology and biology in the past 10 years in the east of the Pearl River Estuary.However,there is little survey for S.chinensis along the west Pearl River Estuary,especially the specific populations and fishery resources status.Jiangmen waters acts as an important channel of Pearl River Estuary and the Beibu Gulf,and is of great significance to study the population,distribution pattern,behavioral ecology,habitat environment and activity patterns.In this study,field survey is conducted in Jiangmen waters from 2012 to 2016 about the population size and fishery resources of S.chinensis for the first time.Photo-identification studies are conducted to get the number of S.chinensis and age composition data and then the database of individual identification of Jiangmen waters are established.The map of distribution sites is drawn with the GPS data from the photos and records.In the meantime this article analyses the variety of population distribution.The investigation on fishery resources is conducted in three periods including spring,autumn and winter in Taishan waters of Jiangmen,and the status of fishery resources is evaluated and investigated.This article analyses the relevance between the population size of S.chinensis and the amount of fishery resources,and the factors of habitat selection.The results are listed below:1.S.chinensis mainly distribute near the Guohua power plant to Dajin Island.The population distribution becomes wider over the three years and is fragmentary near the Shangchuan Island and Dajin Island.It is worth noting that the S.chinensis arewitnessed higher frequency during the field survey in the Guohua power plant.And there are lots of sail boats,human activities and populated water from power factories.Why the S.chinensis prefers this habit still remains unknown.We should focus on the water quality of the sea area and fisheries resources research to explore the factors affecting the distribution of white dolphins.2.Byusing the photo-identification,352 individuals with remarkable characteristics are identified respectively based on pigmentation and speckle patterns,nicks and so on in Jiangmen waters.We find that the growth rate is rising which suggests that there are some individuals which have been not found and identified in this waters.This article speculates that the increase of the population of Chinese white dolphins in Jiangmen waters is likely to migrate to the west of the Pearl River Estuary,and the dolphin in these waters may exist individual migration and communication.3.The amount of fishery resources has increased first and then sharply decreased in recent five years.From 2012 to 2015,the amount of fishery resources in Jiangmen sea area is gradually increasing,and the amount of fishery resources drop sharply in 2016.It is same to the prey fish resources density.The number of catch species in Jiangmen waters has not changed much since 2013.The dominant species,the number of dominant and the proportion are also various in different year and season.The level of biodiversity and species richness is slightly low in this water and there is no significant difference in biodiversity between different stations.Fishery resource is an important factor of affecting the distribution of Chinese white dolphins.There is a significant correlation between the number of Chinese white dolphins in Jiangmen sea area and the amount of fishery resources.4.Additionally,threat factors including the construction of the port,heavy marine traffic,extensive aquaculture,and over fishing are proposed based on the present studies.At last some measures are provided for the conservation in order to decrease the threats.