A SURVEY OF THE SPAWNING OF PERCH (PERCA-FLUVIATILIS), PIKE (ESOX-LUCIUS), AND ROACH (RUTILUS-RUTILUS), USING ARTIFICIAL SPAWNING SUBSTRATES IN LAKES

The development of spawning in perch, pike and roach in Lake Geneva ha s been studied by means of artificial spawning substrates, laid at dif ferent depths, from 1984 to 1993. In Lake Geneva, perch spawned in May . A rise of surface water temperature up to 14 degrees C stimulated sp awning activity while bad weather (surface temperature at 10 degrees C ) induced a spread of the spawning period over more than one month. Th e spawning period was delayed in years when the mean width of perch eg g-ribbons was the largest; this corresponded to the biggest females. A t the beginning of the spawning period (early in May), perch preferent ially chose a depth of 4 m to spawn. In contrast, at the end of the sp awning period, maximum spawning intensity was observed at a depth of 1 2 m. This phenomenon more pronounced when water temperature rose above 14 degrees C in the top 4 m while it remained below 12 degrees C at a depth of 12 m Pike spawned at thp end of April and at thp. beginning of May in Lake Geneva. They preferred spruce branches among the differ ent spawning substrates that we tested in Lake Vouglans. When the wate r temperature increased at the surface of Lake Geneva, pike preferred to lay their eggs on substrates set at 3 m depth where the temperature was cooler than in the surface layer (10.5 degrees C vs 14 degrees C) . Roach spawned during the last two weeks of May or during the first t wo weeks of June in Lake Geneva, depending on water temperature. Spawn ing had generally been spread over a week, but a sudden decrease of wa ter temperature could slow spawning intensity. Roach were able tn lav their eggs On natural or synthetic substrates, located 0.5 m below the surface near the shore as well as, at a distance of several hundred m etres from the shore. The survival of eggs was always above 90% for pe rch and roach and generally above 70% for pike.