The Interannual Variability of the Fall Size of Young-of-The-Year Chub (Squalius cephalus): Influence of Phenology, Growth Patterns and Abiotic Factors

Long-term surveys confirm the rapidity of environmental and biological changes undergone by endangered species but that also concerned relatively “tolerant” species, especially common rheophilic such as European chub ( Squalius cephalus , Linnaeus 1758). As many organisms, fish are highly vulnerable during their first life stages. Body size is a determinant factor for ecosystem functioning to survive predators or winter conditions. While numerous studies has already demonstrated large variability autumnal hatched year, few have focused on factors explaining these interannual variations growth patterns underlying distributions. Using otoliths young-of-the-year (YOY), we studied how in fall sizes might be related varying phenology, temperature, hydrology patterns. YOY were sampled three sections same reach Rhône River with contrasted hydrological regime: an artificial deep lotic channel (the tailrace Bollène), bypassed section both lentic areas (former river before dam construction) reservoir waters. Sampling was performed each sector two thermally distinct years. Temperature had important effect phenology rate it not expressed similarly among sections. Fish earlier warmer year. positively correlated growing degree-days, relationships between years The faster section, differences varied In difference slight, almost significant, even if temperatures very different 2 considered. Autumnal could explained either due higher occurring final part period. Our results accordance general theory’s predictions relating individual they showed other mitigate influence temperature early