The Effects of Resource Availability and Distribution on Size Class Interactions in Perch, Perca fluviatilis

Abstract

The relationships between foraging efficiencies and prey species and size were investigated in laboratory and field studies of the perch, Perca fluviatilis. When fed Daphnia in the laboratory, small perch (one year old, 1+) had both a higher capture rate and a lower handling time than large perch (two year old, 2+). When perch were fed Cyclops no significant effect of age class on capture rate was found. Large perch had a higher capture rate than small perch when feeding on chironomids and Sialis and a lower handling time when feeding on Sialis. Although the capture rate of chironomids at low prey densities was greater for 2+ perch than for 1 + perch, the lower metabolic demands of 1 + perch enabled them to obtain a higher net energy intake. Due to their lower metabolic demands and higher capture rate when fed cladocerans in the laboratory, small perch were predicted to have a higher competitive ability in the pelagic habitat of lakes. This prediction was verified in a field experiment as 1 + perch had both a higher growth rate and a greater ability to withstand resource depression. When alone 1+ and 2+ perch utilized the same food resources, but when they coexisted, their diets differed. The superior competitive ability of 1+ perch in the pelagic habitat is probably responsible for the previously observed age-class, habitat segregation that occurs in the summer during periods of low food availability. The tendency for perch populations to become stunted is most likely due to the large pelagic and small littoral zones in many lakes as well as the higher temperatures during the summer. Both of these factors favour smaller perch.