大型通江湖泊洞庭湖的鱼类物种多样性及其时空变化

为了解通江湖泊鱼类物种多样性现状,于2004年3月-2004年12月和2005年5月对洞庭湖城陵矶、岳阳和沅江三个区域的鱼类进行逐月调查.共鉴定鱼类69种,隶属6目14科44属,其中59.4%为鲤科鱼类.以种类数和多样性指数分析了群落多样性特征,结果表明洞庭湖鱼类种类多样性较高,且时空变化较大.一般地,湖区与长江干流的距离越近,种类数达到峰值的时间就越早;鱼类多样性在春夏季高于秋冬季,在南洞庭湖高于其它两个区域.以优势度>5000为标准,全湖有17种优势种,其中80.0%为湖泊定居性鱼类.在生态类群方面,湖泊定居性鱼类种类最多,占总种类数的74.0%;江湖洄游性鱼类最少,占13.0%.对比分析显示,由于生境丧失、天然苗种资源衰退和过度捕捞等原因,洞庭湖鱼类多样性较20世纪70年代明显下降,洄游鱼类种类数减少;通江湖泊鱼类多样性明显高于阻隔湖泊,表明江湖阻隔造成鱼类多样性下降,因此,加强江湖连通是保护鱼类多样性的有效手段.

Diversity of fish species and its spatio-temporal variations in Lake Dongting, a large Yangtze-connected lake

To evaluate the fish diversity of Yangtze River-connected lakes, a monthly survey offish assemblage was carried out in the Lake Dongting in the middle basin of the Yangtze River in March-December, 2004 and May, 2005. Three sampling areas along a transect from the Yangtze River mainstream to the lake center, i.e. from lake mouth (Chenglinji) to East Lake Dongting (Yueyang) and South Lake Dongting (Yuanjiang) were selected. Totally 69 fish species belonging to 6 orders, 14 families and 44 genera were recorded. Cyprinids were the richest, accounting for 59.4% of total fish species. Species numbers and diversity indices showed that fish diversity of the lake was high, with great spatial and temporal variations. Generally, higher diversities occurred in spring and summer than in autumn and winter, and in South Lake Dongting than in the other areas. With regard to species numbers, the smaller the distance between sampling area and Yangtze River mainstream was, the earlier the diversity peak was reached. Dominant species were determined as species with the value of dominance over 5000. There were 17 dominant species in the lake among which 80.0% were limnicolous species. With regard to ecological groups, limnicolous species dominated the lake, accounting for 74.0% of the total species, while river-lake migratory species was the least, being 13.0% of the total. In comparison with that of 1970s, fish diversity of Lake Dongting had been dramatically decreased, especially for migratory species, and it was mainly due to the loss of habitats, decreased fry resource and over-fishing. Analysis also showed that fish diversities in Yangtze River-connected lakes were much higher than those of disconnected lakes, indicating that river-lake isolation results in species decreasing. Thus, increasing river-lake connectivities is important to the conservation of fish diversity in the Yangtze River floodplain.