Habitat use of 0+year pike in experimental ponds in relation to cannibalism, zooplankton, water transparency and habitat complexity

Habitat use of 0+ year pike Esox lucius (mean 20-31 mm L-T) was evaluated in artificial ponds (surface area =16 m(2)) in relation to water transparencies (low and high), habitat complexity (low and high), food availability (zooplankton) and cannibalism (mortality in the ponds). Pike could choose freely between a structured area, an open water area and a structure and open water interface area. Habitat use shifted towards the structured habitat type in the presence of high habitat complexity and low water transparency. Both findings could be explained as a consequence of territorial behaviour. When cannibalism was intense, the proportions of pike using the structures were reduced and the largest pike, and hence the potential cannibals, were found inside the structures. Since the smallest pike were constrained to the unsheltered, and hence probably more hazardous, habitat outside the structures, this study suggests that mortality due to intra-cohort cannibalism may occur in an indirect as well as a direct way. (C) 2004 The Fisheries Society of the British Isles.