太湖鱼类群落变化规律、机制及其对环境影响分析

Changes of Fish Community,the Mechanism of Changes,and the Effects of the Changes on Environment in Taihu Lake

通过渔获物调查并结合历年鱼类渔获统计资料,用Wilhm改进式计算鱼类组成的均匀度指数,研究了太湖鱼类群落组成变化的规律。用鱼类食物个数组成比例、体积组成比例及食物重叠指数等定量指标,分析了富营养化条件下太湖主要鱼类的食物组成特点及相互关系;并根据渔获物统计资料,用SAS软件建立最优回归模型作为辅助手段,分析了鲚与主要鱼类数量变化间可能存在的关系,探讨太湖鱼类群落演替的内部机制。结果表明:(1)太湖鱼类群落组成变化的规律表现为鱼类种类在不断减少,鲚为绝对优势种,总量快速上升,鱼类组成的均匀程度逐年下降,鲚、鲤、鲫等鱼类年龄结构低龄化趋势加强;(2)富营养化条件下,太湖主要鱼类的食物组成特点及相互关系是鲚主要摄食枝角类,太湖新银鱼主要摄食桡足类,它们的主要食物有很大差别;鲚和鲢、鳙食物中浮游动物组成比例几乎相同,在蓝藻没有暴发期间存在食物竞争;翘嘴鲌、蒙古鲌的主要食物是鲚和小型鱼类,它们之间有捕食与被捕食关系;鲤主要摄食水生植物和底栖动物,鲫主要摄食蓝藻,鲚与鲤、鲫可能存在功能上相互促进的共生关系。这些食物关系和鲚与主要鱼类数量变化的最优回归模型结果相一致。太湖鱼类群落演替的内部机制是特有的鱼类间相互关系,而环境变化通过这种相互关系起作用。鱼类群落变化对环境的主要影响是浮游动物食性鱼类数量的快速上升,对浮游动物的牧食压力不断增加,可能使藻类更易暴发;鲢、鳙、鲫主要摄食蓝藻,可能有抑制蓝藻暴发的作用。控制鲚数量快速增加的有效调控途径是降低捕捞强度,增加鲚捕食者——鲌、食物竞争者——鲢鳙的数量。

Based on the statistics of fish catches and calculating the evenness index in Wilhm＇s method, the changes of fish community composition in Taihu Lake were studied ; for the purpose of analyzing the interior mechanisms of the changes, with the index such as individual composition, volume composition and diet overlap, the mutual food relationships among main fishes were analyzed; optimization regression model was also used to help study the mutu- al relationship. Results were as follows. 1 ） Fish species were decreasing ; most of the total fish catches were Coilia ectenes taihuensis Yen et Lin which was increasing very quickly. The evenness index H decreased at the trend of H = -0. 0465t ＋2. 5339. 0^ ＋ individuals of C. ectenes taihuensis, Cyprinus earpio （L） and Carassius auratus （L） had been increasing in their percentages of catches. 2） The mutual food relationships among main fishes were that： there were intense competition between C. eetenes taihuensis and Hypophthalmichthys molitrix （C et V） and Aristichthys nobilos （Rich）, partially intense competition between C. ectenes taihuensis and Neosalanx tangkahkeii taihuensis Chen; the main predators were topmouth cuher （Erythroeulter ilishaeformis Bleeker and E. rmongolian Basilewsky ） which mainly preyed on C. ectenes taihuensis and other small fishes ; the result of optimization regression model also expressed the same result as the mutual food relationships among main fishes. It can be eonelluded that： The interior mechanisms of the changes were the mutual food relationships among main fishes. Exterior environmental factors affected the changes through the special relationship. The effects of the changes on environment in Taihu Lake were that ： the increases of planktivirous fishes such as C. eetenes taihuensis indirectly promoted blue-algae by feeding on large amount of zooplanktons ; H. molitrix, A. nobilos and C. auratus mainly fed on blue-algae, which may constrain the burst of blue-algae. The effective method to smooth the rapid increases of C. ectenes taihuensis is to maintain the population of its predators such as E. ilishaeformis and E. rmongolian and of its competitors such as H. molitrix and A. nobilos by controlling the overfishing and proliferate matures.