Predation as a determinant of size structure in populations of crucian carp (Carassius carassius) and tench (Tinea tinea)

Abstract

AbstractPredation is an important structuring force in many fish assemblages and may have large, direct lethal effects on prey fish populations but also may affect growth rate and survival indirectly through shifts in behavioral patterns. Some species appear more sensitive to predation and earlier studies in a limited set of Finnish ponds suggests that crucian carp (Carassius carassius) is very sensitive to predation, which results in changes in population size‐structure and density. In this study we tested the effect of piscivore presence or absence on crucian carp populations by using data from a large number (>600) of Swedish lakes across a wide geographical area and ranging in size from small ponds to large lakes (0.02–4400 ha). We also included a second species, tench (Tinea tinea), in our analyses. The population size structures of crucian carp and tench were clearly related to the presence or absence of piscivores. In lakes and ponds without piscivores. populations were dominated by small‐bodied individuals. When piscivores were present, populations consisted almost exclusively of large individuals. Densities of crucian carp and tench were much higher in ponds and lakes without piscivores. There were no differences in size structure or relative abundance when catches from electrofishing were compared with gill net catches, suggesting that our results are not an effect of a behavioral shift in the presence of piscivores.