摘要
瑞典四大湖(维纳恩、韦特恩、梅拉伦和哈马伦湖)的鱼类资源极其丰富,分布有红点鲑、鲑、鳟、白鲑、河鲈、梭鲈、白斑狗鱼和鳗鲡等经济物种。研究表明,筑坝、航运、富营养化和过度开发等所产生的物理、化学和生物因素会对湖中的经济物种产生影响,导致湖中原有物种资源的种类组成发生变化。由于近年来的人类活动的影响,上述湖泊中原有鱼类组成中的优势种群发生了变化,一些物种消失了,一些新的物种在湖中出现,其原因主要是富营养化、鳗鲡和龙虾丰度的改变以及过度捕捞。过度捕捞在某种情况下是大湖的渔业生产引起的——在一个捕食者和竞食者同时存在的环境中,如果食物资源非常充足,鲑科鱼类以及梭鲈等鱼类在生活史上会倾向于在性成熟状态下生长,但在常规可捕规格的选择性调控下,这些物种会因产卵群体太小而导致资源量急剧下降。
The four largest Swedish lakes, Vanern, Vattern, Malaren, Hjalmaren, host important commercial fisheries for char, salmon, trout, whitefish, vendace (cisco), perch, pike-perch, pike and eel, i.e. highly diverse biological resources. Case studies illustrate physical, chemical and biological impacts on some of these commercial species caused by constructions of dams and ship canals, eutrophication, and overexploitation. Although some original species have been lost and a few new species have been added, the recent human interference has basically caused major shifts in dominance of the fish community structures because of eutrophication, alterations in the abundance of eel or crayfish, and due to overfishing. The latter is in some cases caused by the Great Lake Fishery Paradox—in an environment with several predators and competitors, but with ample food resources, especially salmonid fish but also species like pike-perch may adapt a life history favoring growth over sexual maturation. If harvested at a conventional size these populations will decline rapidly due to too small spawning stocks.
