夏、秋季长江口鱼类群落结构

Fish community structure of the Yangtze River Estuary in summer and autumn

为了解生境变动条件下长江口鱼类群落的特征,为其鱼类资源的管理提供依据,2010年5月中旬至9月在长江口进行了张网鱼类资源调查(除8月外,采样频率为1周1次)。结果显示,调查期间总共出现6种生态类群、39种鱼类,海洋洄游鱼类和河口定居性鱼类的种类数目分居1、2位,包含种类数目最多的科是鳀科(6种),其次虎鱼科和石首鱼科(4种),5-9月间种类和生态类群种类数目更替均无显著性差异;5-9月间各生态类群尾数/重量均以海洋洄游鱼类占首位,5-8月间各月平均每网尾数/重量均无显著性差异,但9月除了与7月尾数无显著性差异外,尾数和重量均较各月高,生态类群尾数/重量的排序变化均有统计学差异;对棘头梅童鱼、刀鲚、凤鲚、银鲳、灰鲳、龙头鱼等6种主要经济鱼类的幼鱼数量比例进行了分析,发现不同种类的变动有差异,如棘头梅童鱼、刀鲚、龙头鱼幼鱼基本呈下降趋势,而凤鲚则为上升趋势。此外,相同属的鱼类生态位有一定的分化,银鲳和灰鲳在时间上交替出现、而刀鲚和凤鲚在不同水域产卵,这是一种减少对食物、空间竞争的策略;按鱼类群落优势种综合丰盛度法,各月优势种比例均在95%以上,而各月间优势种更替无显著性差异;Bray-curtis尾数/重量相似性系数聚类分析和非度量多维标度分析在60%的水平上将群落分为组Ⅰ(5月-8月前半月)和组Ⅱ(8月后半月-9月)。此外,长江口虽仍是棘头梅童鱼、银鲳、灰鲳等重要经济鱼类的育幼场,但群落结构已有了变化,特别是中华鲟、鲥等珍稀鱼类的消失,反映了因过度捕捞、环境污染、水利工程建设等引起了长江口鱼类资源的衰退。

For studying the fish community characteristics influenced by the habitat variation in Yangtze River Estuary,which could be used to determine how to manage its fish resources usefully,fishes from Yangtze River Estuary were collected during summer（the second half month of May to August 2010）and autumn（September 2010）every week（every half a month in the first half of August）.During the study periods,39 species belonging to 6 fish ecological guilds and 20 families,12 orders were identified,most of them were marine migrant fishes（17 species）and estuarine resident species（14 species）,and Engraulidae had the highest numbers of fishes（6 species）,then followed by Gobiidae and Sciaenidae（4 species）.Cochran and Friedman test was used to indicate that species composition or numbers of each guild in each month between May and September had no significant difference,respectively.Marine migrant taxa were both the most important guild of abundance or catch in each month,and average abundance or catch per net showed no statistical variations between May and August,but it was higher in September than that from May to August（except average abundance in July）.Significant difference occurred in abundance or catch rank in each guild.Percentages of juveniles of 6 importantly commercial species（Big head croaker Collichthys lucidus,Japanese grenadier anchovy Coilia nasus,Osbeck＇s grenadier anchovy Coilia mystus,silver pomfret Pampus argenteus,dark pomfret Pampus cinereus,and Bombay duck Harpodon nehereus）were examined to exhibit the variability in rank-distributions,C.lucidus and C.nasus declined,by contrast,C.mystus increased,P.argenteus occured from May to August,while P.cinereus was observed during August to September.C.nasus spawn in fresh water,but C.mystus breed in the Estuary,which would reflect the temporal or spatial segregation of species of fishes belonging the same genus and were considered the ecological lysimilar,impling that they may reduce the competition for food or space during peak recruitment.According to the synthetic abundance method,dominant species dominated more than 95% of synthetic abundance,but no significant difference was observed among dominant species composition in each month.In addition,cluster analysis and non-metric multi-dimension scaling plot ordination of Bray-curtis similarity method based on abundance and catch showed that community could be divided into 2 groups on 60% similarity level,group Ⅰ consists of samples between May and the first half month of August,while group Ⅱ consists of fishes from the second half month of August to September.When compared with the previous study,although Yangtze River has still been the nursery and feeding ground for importantly commercial fishes,community structure has varied,and the major difference that could be observed is that the absence of rare species such as hilsa herring Macrura reevesii,Chinese sturgeon Acipenser sinensis.The study might reflect the degradation of fish resources due to overfishing,water pollution and large-scale hydrological project construction.