东洞庭湖长江江豚及其与鱼类资源相关性

为掌握东洞庭湖长江江豚种群动态分布规律及其与鱼类资源的相关关系,2012年6月~2017年12月,对东洞庭湖进行了54次长江江豚种群调查和8次水声学鱼类资源空间分布调查.调查结果显示：（1）共发现长江江豚1110头次,分布在湘阴-洞庭大桥之间长约65km的区域内;（2）100% MCP）、95% MCP、75% MCP和50% MCP下,长江江豚栖息地面积依次为161.3、114.26、76.95和64.31km²,占保护区总面积百分比依次为24.18%、17.13%、11.54%和9.63%;（3）不同水位条件下,长江江豚观测群次和头次差异显著,枯水期可观测到群次和头次最高,分别为（13.92±4.64）群次/次和（31.92±7.17）头次/次,丰水期观测群次和头次最低,分别为（5.17±1.64）群次/次和（17.25±7.46）头次/次;（4）水声学调查结果显示,2013年3月东洞庭湖鱼类资源平均密度最高为57.21尾/1000m³,东洞庭湖鱼类密度与水位呈弱负相关关系,相关系数r=-0.601（P>0.05）;（5）GIS模型分析结果显示,东洞庭湖鱼类资源低水位时期（枯水期和退水期后期）,集中分布于扁山至鲶鱼口区域,高水位时期,东洞庭湖鱼类资源分布较为分散;（6）方差分析结果显示,东洞庭湖低水位期鱼类资源水平密度分布不均,扁山至煤炭湾区域鱼类资源水平空间平均密度最高,与其它区域有显著性差异（P<0.05）,高水位时期鱼类分布较为均匀,方差分析显示,除煤炭湾至鹿角区域与城陵矶至洞庭大桥区域和扁山至煤炭湾区域分别有显著差异之外（P<0.05）,其他水域之间无显著性差异（P>0.05）;（7）Pearson相关性分析显示长江江豚头次与对应的鱼类密度呈显著正相关,R²=0.86,P<0.01,长江江豚可能具有随鱼群迁徙的行为特征.

Spatial distribution of the Yangtze finless porpoise and relationship to fish density in East Dongting Lake,China

The Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis) is a subspecies of finless porpoise and is known to live only in the middle and lower reaches of the Yangtze River and the adjacent Dongting and Poyang Lake. Since the 1990s the population has decreased dramatically due to habitat degradation, by-catch, water pollution and other human activities. The Yangtze finless porpoise was listed as an Endangered species on the IUCN Red List since 1996 and was listed as a top-level protected animal in China since 1989. The Dongting Lake, China's second largest freshwater lake, is located in the northern Hunan Province. The lake is at the south of the middle reach of Yangtze River and is divided into three parts:East Dongting Lake, South Dongting Lake and West Dongting Lake. Dongting Lake is important both at home and abroad due to the aquatic biodiversity, geographical location, and human activities. Dongting Lake has been for hundreds of thousands of years as one of the most important habitats for Yangtze finless porpoise. According to the population assessment by the Ministry of Agriculture and Rural Affairs in 2017, there are approximately 110 individuals (10.87% of the total population) living in Dongting Lake. To assess the population distribution of the finless porpoise and its relationship with fish density, 54 line transects surveys and eight hydroacoustic surveys were conducted in East Dongting Lake covering four hydrological seasons between June 2012 and December 2017. A total of 1110 individuals were observed, and they were primarily distributed in an elongated area approximately 35km long between Xiangyin County and Dongting Bridge. The natural habitat area of finless porpoise estimated by the method of minimum convex polygon (MCP) under the 100%, 95%, 75%, and 50% were 161.3km², 114.3km², 77.0km² and 64.3km² respectively, accounting for 24.2%, 17.1%, 11.5% and 9.6% of the whole finless porpoise protected area. Results of the one-way ANOVA revealed significant differences among observations during different hydrological seasons (P<0.05) and the highest frequency of groups and individuals of finless porpoise were observed (13.92±4.64 groups/survey and 31.92±7.17 ind./survey) during the dry season. The lowest frequency (5.17±1.64 groups/survey and 17.25±7.46 ind./survey) occurred during the wet season. Results of the hydroacoustic surveys showed that the highest fish density was 57.21ind./1000m³ in March 2013. There was a weak negative correlation (R =-0.601, P>0.05) between fish density and water levels in East Dongting Lake. ArcGIS modelling and hydroacoustic technology were combined to analyze the spatial distribution of fish densities, and the results showed that fish mainly distributed in Bianshan-Meitanwan (Area III), Meitanwan-Lujiao Port (Area IV) and Lujiao Port-Nianyukou (Area V) during low water (dry season and late stage of falling season). Fish were more disperse during high water. During low water of Dongting Lake, an uneven distribution of fish was found and significant differences existed between Area III and other areas (P<0.05) with the highest fish density (107.52±17.36 ind./1000m³). Except for the significant differences between Nianyukou-Leishi Port (Area VI) and Chenglingji-Dongting Bridge (Area I), and Area III (P<0.05), there were no significant differences between the other areas (P>0.05). The positive relationship between the number of porpoises and fish density (R²=0.86, P<0.01), analyzed by Pearson correlation, suggests that Yangtze porpoise possesses the behavior to track fish school. Future conservation on the Yangtze finless porpoise could be more effective if special measures are conducted to stop fishing and habitat degradation related to finless porpoises in East Dongting Lake.