太湖湖鲚种群结构演变特征、机制与生态调控研究

The Coilia ectenes taihuensis is a small pelagic fish which feeds mainly on zooplankton. Because of water eutrophication from the beginning of 1990's in Lake Taihu, the catches increased continuously, and the percentage of C. ectenes had increased in fish catches and the tendency of smaller-scale and low age fishery were more obvious. The number, density, fecundity and feeding habit of C. ectenes population were investigated. Meanwhile combining the historic data of water quality index and an investigation on plankton and fish assemblage in Lake Taihu, the dynamic variation of C. ectenes population resources and their responses to water eutrophication were analyzed, furthermore, the effect of high yield of C. ectenes on the variation of ecosystem structure is also the keynote. We will describe the food web by characterizing trophic relationships, main food sources of consumers and energy pathways between the components in the aquatic systems using traditional gut content analysis, stable isotope and fatty acid. The trophic relationships in different feeding typical fish were also studied, in order to regulate the structure and proportion of stocking fish species. The ultimate goal of regional classification and functional positioning of Lake Taihu is to attain rationale and sustainable utilizations of the fishery resources and improve the water quality in Lake Taihu.

太湖湖鲚是以食浮游动物为主的小型中上层鱼类。自1990年代初来，太湖水体富营养化程度日趋严重，而渔业捕捞总量持续快速增加，其中湖鲚产量及占总渔获量比重不断上升。太湖鱼类种群表现出的小型、低龄、底层和杂食的特征，凸显太湖水环境变化对鱼类结构的影响。项目通过对太湖湖鲚种群数量、密度、繁殖力以及食性等展开调查，结合太湖富营养化和蓝藻水华发生不同历史阶段的水质指标以及浮游生物和鱼类群落的时空分布特征，分析湖鲚种群数量与结构特征的演变对水体富营养化的响应机制以及高种群生物量对湖体生物群落影响；构建以湖鲚为基础的鱼类食物网结构与营养级关系，确定食物链传递途径及能流过程；通过与湖鲚相似食性鱼类及捕食者间的食物关系研究，提出鱼类放流种类和数量调整的建议，实现渔业增效和以渔改水生态调控的目标。

随着太湖水体富营养化加剧以及渔业资源的过度捕捞，太湖鱼类群落结构的小型化和单一化趋势加剧。针对这些问题，本项目在太湖不同类型湖区开展了全面的调查采样工作，系统研究了湖鲚种群结构的演变特征、机制与生态调控措施，主要研究结果如下：湖鲚年龄组成为0~4龄，0~1龄占92.4%，且湖鲚肥满度系数较小，群体偏向瘦削型。湖鲚的性腺春季开始发育，性体指标峰值出现在产卵盛期的夏季，且性腺发育速度随水温升高加快，最适繁殖温度为23~30°C。湖鲚主要以浮游枝角类、桡足类、虾类和幼鱼为食，其中枝角类（52.2%）和桡足类（40.3%）数量最多。食物选择性方面，湖鲚对大个体浮游动物有强烈的主动选择倾向，同时主动摄食特定的小型枝角类，且湖鲚与银鱼、似鱎等食性相似鱼类的食物竞争关系不激烈。通过以上分析可见，湖鲚食物来源丰富，小型个体生长快速，怀卵量大，且繁殖周期长；湖鲚对环境的适应能力强，在低溶解氧和较高温度条件下均能生长繁殖。因此，湖鲚种群在生长、繁殖和摄食等方面的特性决定了其在太湖鱼类群落结构中的优势地位。本研究同时也对太湖鱼类群落结构和多样性的空间分布特征进行了研究，并构建了以湖鲚为基础的鱼类食物网结构与营养关系，结果显示浮游植物等基础食源以浮游动物和虾等关键种为中间营养层，将其固定的碳源通过多条食物链最终传递给湖鲚等表层肉食性鱼类，而鱼类食物网能流途径的时空变化特征则表明鱼类食物来源的多样性以及较强的摄食可塑性。本研究最后通过原位围隔试验，研究受控条件下湖鲚与翘嘴鲌等肉食性鱼类间的捕食关系，分析实验水域翘嘴鲌的摄食生态学特征及能量传递效能，并估算出肉食性鱼类放流对湖鲚种群控制的适宜数量。在此基础上，结合湖鲚生长繁殖特性、水环境和种群动态综合模型评析结果，提出了太湖渔业放流结构调整与生态调控措施，并对渔业政策调整实施效果开展了追踪评估。