Spatial and temporal separation of littoral zone fishes of Lake Geneva (Switzerland-France)

The spatial (distance from the shore) and seasonal (summer-winter) distributions of the ichtyofauna in the littoral zone of Lake Geneva were studied between October 1991 and December 1992. Gill nets were set simultaneously at three different sites of a chosen littoral zone: shore, middle and far (50, 300 and 550 m from the shore, respectively).The results show that in summer more species and individuals are present in the littoral zone than in winter. Throughout the year, species richness is greater at the shore site than at the middle or far site. In summer, total abundance is greater at the far site, whereas there are more fish at the shore site during winter. Perch (juveniles and adults), roach and gudgeon (adults only), have maximum abundance during the summer, while lake trout, grayling and whitefish (adults) have maximum abundance during the winter. For five species (adults only) the site comparison shows spatial segregation of the habitats: greater numbers of perch are present at the far site while roach, tench, lake trout and grayling prefer the shore site.