Effects of habitat complexity and prey abundance on the spatial and temporal distributions of perch (Perca fluviatilis) and pike (Esox lucius)

Structurally complex environments strongly affect the behaviours and foraging efficiencies of predators and prey. I studied temporal variation in the habitat distribution of perch (Perca fluviatilis) and pike (Esox lucius) in relation to habitat complexity and prey abundance in a lake. The study involved quantitative estimates of different habitat types, estimates of macroinvertebrate prey availability, and distribution and movement patterns of the fish. The numbers of 80-110 mm perch in the littoral zone decreased rapidly in spring, which was a result of either perch moving to the pelagic zone or predation mortality. Predation mortality is the most plausible explanation because piscivorous perch and pike >160 mm aggregated close to these high abundances of 80-110 mm perch, and 80-110 mm perch used only vegetated habitats as a possible protection against predators. Both the biomass and diversity of macroinvertebrates increased with vegetation density, whereas perch abundance was highest in an intermediate vegetation density. Pike size was inversely related to vegetation density as a result of potential cannibalism from the largest pike individuals, which preferred the tree structure habitat. Perch group size decreased with increasing vegetation density, and perch <80 mm always occurred in group sizes larger than three individuals and never occurred in the same groups as perch >160 mm. In contrast, perch >160 mm occurred at decreasing numbers with increasing group size and mainly stayed solitary or in pairs. Perch >160 mm showed no tendencies for homing behaviour and moved actively around the whole lake, whereas pike showed a strong homing behaviour. My study suggests that the structural complexity in the littoral zone can both qualitatively and quantitatively change the interaction between piscivorous predators and their prey.