Hydropeaking and Channelization Threaten Young‐of‐the‐Year Fish—The Case of the Chub ( <i>Squalius Cephalus</i> L.) in the Rhône River

ABSTRACT Hydrological and geomorphological alterations of rivers disrupt the natural spatial and temporal dynamics of aquatic species habitats, which constrains the life cycle of aquatic fauna. While many studies have focused on the impact of these alterations on the adult stages of fish species, few studies have examined their effects on larval settlement and the persistence of young‐of‐the‐year (YOY) in later developmental stages, the survival of which is critical for overall population dynamics. In this study, we collected samples from different developmental stages (larvae, postlarvae, juveniles) of chubs ( Squalius cephalus L.) every 15 days for 2 years in three reaches of the Rhône River and compared the results in the context of different hydrological (i.e., hydropeaking) and geomorphological (i.e., channelization) conditions. We found that higher abundances of young chubs (especially those in the larval and postlarval stages) were related to a greater diversity of floodplain channels, even in the case of hydrological alterations. However, hydropeaking generally induced a decrease in larval settlement success during extreme episodes. Consequently, there were low abundances of individuals in young developmental stages in the reach affected by a combination of geomorphological and hydrological alterations. In addition, the presence of diverse floodplain channels was highly important for fish movement across different habitats during development. Thus, our study highlights the critical role of floodplain channel diversity during the first year of fish development and its importance in buffering the deleterious effects of hydrological alterations.