Studies have revealed that parts of the population of chinese white dolphins are experiencing rapid decline

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Chinese white dolphin mother and son, the mother has been injured. Photo courtesy of the scientific research team of the Institute of Deep Sea of the Chinese Academy of Sciences, photographed by Zheng Ruiqiang

Recently, the research team of Li Songhai of the Institute of Deep-sea Science and Engineering of the Chinese Academy of Sciences (hereinafter referred to as the Institute of Deep Sea) cooperated with the research team of Liu Wenhua of Shantou University to publish academic papers in the international journal Frontiers in Marine Science. The study integrated the institute of deep-sea and Shantou University’s individual photo databases from 2015 to 2019 to model the population of Chinese white dolphins in Sanniang Bay and its adjacent waters in Guangxi To assess the dynamic development trend of this population. The results of the study showed that the Chinese white dolphin in Sanniang Bay and its adjacent waters in Guangxi was a relatively closed population, and the survival rate of the Chinese white dolphin population fluctuated greatly during the survey, suggesting the presence of high-intensity marine stressors/stressors in the area. The study reveals for the first time that the Chinese white dolphin in the area is experiencing rapid population decline in the near future, with populations falling by a third in less than five years, and stresses the importance of high-resolution data for us to grasp the status of wildlife populations.

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Chinese White Dolphin Adult and Cub Picture Source: Marine Mammals of the World

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Chinese white dolphins in Sanniang Bay and its adjacent waters in Guangxi. Photo courtesy of the scientific research team of the Institute of Deep Sea of the Chinese Academy of Sciences, photo by Lin Wenzhi

The Chinese white dolphin (Sousa chinensis) is one of the four species of the camel dolphin genus, which is a national first-class protected animal in China and is assessed as a “vulnerable” species by the International Union for Conservation of Nature (IUCN). It is mainly distributed in shallow waters near the shore from the eastern Indian Ocean through Southeast Asia to the mouth of the Yangtze River in central China.

In China, Chinese white dolphins are scattered along the southeast coast, including Xiamen Bay, the west coast of Taiwan Island, the Pearl River Estuary, Zhanjiang, Beibu Bay (including Sanniang Bay) and the southwest waters of Hainan. Since human society entered the era of industrialization, the survival of the Chinese white dolphin has been severely threatened. In the late 1990s, due to the large-scale reclamation of land in the northern waters of Lantau Island in Hong Kong, China, the research and conservation of Chinese white dolphins entered the attention of researchers and conservation workers for the first time. In the inland waters, it was only in recent years that a more systematic study of the ecology of chinese white dolphin populations has been initiated.

Between 2015 and 2019, the research team of the Institute of Deep Sea and the research team of Shantou University conducted a total of 112 days of field investigation in Sanniang Bay and its adjacent waters in Guangxi Province, and successfully identified 198 dolphin individuals, including 147 highly recognizable individuals (D≥3). In the combined dataset, the cumulative identification curve reached the plateau period in early 2017, i.e., full population coverage was achieved; of which 123 individuals (83.7%) were witnessed more than 5 times, making it the highest quality individual identification database for this population to date.

By constructing a Robust design model, the study proposes that the number of Chinese white dolphins in the waters of Sanniang Bay dropped from 156 in 2015 to 102 in 2019. Correspondingly, the research team recorded a large number of dead dolphin individuals during the investigation. In December 2015, for example, three fresh bodies were found. Unfortunately, no detailed autopsies were performed on the deceased individuals at the time. As a result, the research team was unable to assess the population’s major threats through cause-of-death identification.

The study also found that the survival rate of Chinese white dolphins in this area (0.88-0.92) was significantly lower than that of Chinese white dolphins in Xiamen (0.976), Taiwan (0.985) and Hong Kong (0.980). In addition, survival rates across age groups and genders also differ from our conventional understanding. In general, juvenile dolphins are vulnerable to attack or prey, while in adult individuals, males often fight over mating rights. Therefore, the survival rate will generally show a trend of juvenile < adult males < adult females. But in the population of white dolphins surveyed, the team found that the survival rates of adult females were relatively stable, but the survival rates of young and adult individuals of unknown sex fluctuated sharply in the short term. Based on this, the research team proposed to investigate the possibility of some kind of lethal marine stress source in the Chinese white dolphin in the sea area from 2015 to 2017, causing the population to experience rapid population decline during this time. (Source: China Science Daily Zhang Qingdan)

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