Lake Constance fisheries and fish ecology

Abstract

This paper summarizes changes in the fish species list and in fishery yields in Upper Lake Consiance during the last century. Species richness has remained nearly unchanged since the end of the last century, although three species and one form of whitefish have been lost from the lake probably as a result of eutrophication and four other species have been introduced either accidentally or intentionally. Fisheries yields have increased since the 1950s because eutrophication enhanced fish production and fish stocks were exploited more intensively with highly efficient nylon nets. With increasing lake trophy during the 1960s and 1970s, the proportion of coregonids in commercial catches decreased, whereas the proportion of perch and cyprinids rose. The recent oligotrophication of the lake is reflected in an augmenting proportion of whitefish in commercial catches and an increasing age-at-capture. Lake whitefish (Coregonus lavaretus) and Eurasian perch (Perca fluviatilis) are commercially the most important fish species in Lake Constance. Their ecology has been studied intensively during the last decade, while most recently the littoral fish community has been included in our research activities. The effects of newly introduced and rapidly spreading ruffe (Gymnocephalus cernuus) on the native fish fauna are of special concern to fishery managers and will be a central topic of future research.