Piscivorous eels in Lake Constance : can they influence year class strength of perch?

Abstract

Research on predator-prey relationships in the littoral zone of Lake Constance showed that eels (Anguilla anguilla (L.)) were the most numerous piscivorous predators in the shallow water zones up to 3-metres depth in 1992. From July on fish was the most important component of the diet of eels. Perch (Ferca fluviatilis L.), burbot (Lota Iota (L.)) and bream (Abramis brama (L.)) were the most frequently consumed fish. As 61% of all identifiable fish the eels had consumed were perch, an attempt was made to estimate the impact of eel predation on the young-of-the-year (y-o-y) of the perch population. Consumption by the total eel population never exceeded the amount of perch fry consumed by adult, cannibalistic perch estimated in other studies, but it seems possible that eel predation could have an adverse influence on weak year classes. Further reoligotrophication of the lake might lead to even higher fish consumption by the eels due to declining benthic production and consequent increased predation pressure.