TEMPERATURE-MEDIATED AND LIGHT-MEDIATED PREDATION BY PERCH ON VENDACELARVAE

The perch foraging pattern in a Finnish lake (64 degrees N) was crepus cular and they moved into littoral areas at dusk and returned to deepe r waters by dawn. Predation on vendace larvae was guided by environmen tal cues, mainly temperature and light periodicity, which affected the density and foraging activity of perch in the littoral area. The avai lability and the vulnerability of different food categories were both responsible for the perch diet. The hypothesis that perch have a gener ally decisive role in the regulation of vendace larval abundance throu gh predation at the time of high vendace larvae concentration in the l ittoral area was not supported. We emphasize the need to evaluate biol ogical phenomena, such as predator-prey relationships, in the light of the relevant physical variables, and to do so within appropriate time and space scales, instead of relying on indirect estimates of the pre dator and prey population abundance and using their reciprocity as evi dence of the interaction. (C) 1996 The Fisheries Society of the Britis h Isles