Autumnal shift from diurnal to nocturnal peaking feeding activity of Rutilus rutilus in boreal lake littoral zones

The possibility that the feeding activity of roach Rutilus rutilus shows an autumnal shift towards hours of lower light intensity in shallow and illuminated habitats in temperate watercourses as a consequence of relatively increasing daytime predation risk was tested in a littoral zone of a large boreal lake using trapping experiments. Autumnal feeding activity of R. rutilus first showed a striking shift from day to twilight when water temperature fell from 20 to 10 degrees C, and a low but steady night activity prevailed in late autumn, when temperature had fallen to 5 degrees C and the length of the night had increased. The size of the captured littoral R. rutilus also increased throughout the autumn. Both shifts may be linked to increasing daytime predation risk and decreasing food demand and availability. (C) 2008 The Author Journal compilation (C) 2008 The Fisheries Society of the British Isles