Piscivory, Growth, and Size-Selective Mortality of Age 0 Pikeperch (Stizostedion lucioperca)

Abstract

Year-class strength of pikeperch (Stizostedion lucioperca), indexed as the age 0 abundance in trawl surveys, varied 300-fold in the northern part of Lake IJssel, The Netherlands, over the period 1966–89. Both mean length and year-class strength of age 0 pikeperch in November were highly correlated with mean summer temperature. Depending on the environmental conditions, especially water temperature and availability of food, the initially unimodal length frequency distribution of age 0 pikeperch developed into a positively skewed, bimodal or negatively skewed distribution towards the end of the summer. Strong year-classes were characterised by larger mean lengths and a negatively skewed frequency distribution, while weak year-classes were smaller and positively skewed. Stomach contents consisted of zooplankton and macrofauna for the smaller specimens and of age 0 smelt (Osmerus eperlanus) for the larger pikeperch (> 10 cm). Body energy content increased with fish length, and differences in proximate analysis were more pronounced later in the season. The condition of nonpiscivorous age 0 pikeperch was low and decreased over time, while that of piscivorous pikeperch increased. The onset of piscivory, favoured by high temperatures during summer, has a direct positive effect on the growth and survival of age 0 pikeperch.