Main characteristics of the biology of the trout ( Salmo trutta L.) in Lake Léman (Lake Geneva) and some of its tributaries

Divided between France (41%) and Switzerland (59%), Lake Leman is the largest lake in western Europe, with a surface area of 58 240 ha, (Fig. 1). The main physical, chemical and biological characteristics of this subalpine, mesoeutrophic lake, have been detailed in a report (C.I.P.E.L., 1984). The most important physical data concerning the basin flowing into the lake are shown in Fig. 1. Twenty-three species of fish have been reported (Laurent, 1972) but the fishing (Gerdeaux, 1988) is aimed principally at seven species: perch (Perca fluviatilis), whitefish (Coregonus lavaretus), Arctic charr (Salvelinus alpinus), brown trout (Salmo trutta), burbot (Lotta lotto), roach (Rutilus rutilus) and pike (Esox lucius). Catches of trout represent between 2% and 5% of the total annual tonnage of fish captured in Lake Leman. The main characteristics of the fishing and release of trout in Lake Leman in the course of the last 12 years are shown in Table 1. The lake trout is mainly caught within the lake (Fig. 2), either by amateurs using dragline from motorboats, or with nets by professional fishermen. Since 1950, the annual catch of trout declared by professional fishermen has varied between 9 and 32 tonnes/year (Fig. 2). The amateurs have recently (since 1986) been required to declare their catches: the latter were around three quarters of those of professionals (Fig. 2). Occasional catches of adult lake-dwelling trout are made by rod and line in the river, before or after spawning, but they remain poorly known, as they do not have to be declared.