Disentangling the Drivers of a Piscivorous Intra-Annual Cohort and the Contributions of Three Cohorts to Early-Year Class Strength in Pikeperch (Sander lucioperca)

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.