Diel and seasonal distribution of perch in Lake Constance: a hydroacoustic study and in situ observations

摘要: A near-shore belt 50 km in length was surveyed parallel to the shoreline of Lake Constance, central Europe, with a single-beam echosounder five times between July 1993 and February 1994. The species age composition fish survey area investigated by gillnet fishing SCUBA-diving. In summer, horizontal distribution perch patchy. Population density declined from east west, highest densities occurred one shallow bay close ports jetties at steeper shores. During daytime, stayed sublittoral zone 3 15 m depth 2 6 above thermocline. Within this layer classes were separated spatially: relative number young-of-the-year whereas adult (2+ older) increased depth. At dusk migrated littoral zone, where they spent night resting on bottom. winter, under almost homothermal conditions, all ages located 35 70 contours, performed pronounced diel vertical migrations. They rested on, or to, bottom during daytime ascended up 20 below surface night. season, much more homogeneous than summer.