Size-dependent predator-prey relationships between perch and their fish prey

Size-dependent interactions between piscivorous perch Perca fluviatilis (age greater than or equal to1 year) and their fish prey age 0 year perch, pikeperch Sander lucioperca and roach Rutilus rutilus in the biomanipulated Bautzen Reservoir indicated that the highest ratio of prey total length (L-T) to predator L-T was 59%. Perch L-T and prey fish L-T were positively and linearly related. Perch L-T was strongly related with both gape width and gape height. Within the range 80-110 mm L-T, the gape height of perch exceeded gape width, while beginning at 120 mm L-T the gape width exceeded gape height. The minimum, maximum and mean prey L-T and prey body depths of all three prey species increased with increasing predator size. but the increases in mean sizes of perch and pikeperch as prey were less than that of roach. The low limit of the 'predation window' observed in this study coupled with results of previous studies on perch in the Bautzen Reservoir indicated that perch had a major impact on the population dynamics of both perch and pikeperch. (C) 2003 The Fisheries Society of the British Isles.