Abstract

Using pikeperch (Sander lucioperca) as a model species, we investigated the factors influencing fluctuations in the abundance of piscivorous intra-annual cohorts and assessed the role of three distinct cohorts: extremely small (ES), ordinary (or mid-sized) fingerlings, and piscivorous in shaping year-class strength. Our analysis was based on 13 years of data (2003-2024) collected in the Lipno Reservoir, Czechia. Using LASSO for variable selection among 45 potential covariates and subsequent Generalized Additive Model (GAM) construction, our results revealed that a higher abundance of ES conspecifics and young-of-the-year (YOY) perch, coupled with increased densities of large cladocerans in July, positively impacted the abundance of the piscivorous intra-annual cohort. The abundance of 1+ pikeperch was positively influenced by the abundance of piscivorous and ordinary cohorts recorded in the preceding year. We concluded that all three intra-annual cohorts contribute to the year-class strength of pikeperch, with piscivorous and ordinary cohorts having a more direct effect, while ES intra-annual cohorts indirectly support the piscivorous cohort by serving as prey.