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In the context of the River Rhône restoration programme, the objective of this study was to assess the dispersal and population connectivity of the European chub, Squalius cephalus (Linnaeus, 1758) in a section of the natural, free‐flowing part of the lower River Rhône.The elemental water signatures for Sr:Ca and Ba:Ca were measured at seven stations within the river section, including its tributaries and backwaters, to determine whether they could be differentiated by microchemistry. From August to October the signatures differed among three sectors of the study reach: the Rhône; the Ardèche; and the backwaters.The elemental signatures of the otoliths of 178 young‐of‐the‐year (YOY) chub from the stations were measured to assess spawning areas and identify early migratory life histories. Analyses of otolith microchemistry identified the natal origin of 95% of the fish. Sr:Ca signatures of otoliths showed early downstream migration for 30.4% of the YOY chub; however, 70% of the fish recruited relatively close to their spawning origin suggesting a potential inshore retention of fish.The results showed (i) a non‐negligible contribution of the tributaries and backwaters in the recruitment of fish into the main channel; and (ii) the ability of chub to migrate over several kilometres during their first few months of life.This study shows that the combination of water and otolith microchemistry analyses of fish growth increases the understanding of fish life history. Moreover, the study revealed that half of the YOY fish from this river section came from the tributaries and the other half came from reproduction in the River Rhône (despite its high anthropization).These methods offer promising future applications of otolith microchemistry for river management in the context of ecological rehabilitation, especially to assess the effectiveness of measures applied in the restoration of floodplain connectivity for riverine fish population conservation. [ABSTRACT FROM AUTHOR]

This assesses features of otoliths from laboratory‐reared embryos, larvae and juvenile European chub Squalius cephalus from hatching to 180 days post‐hatching (dph). We observed the development of the three pairs of otoliths (lapilli, sagittae and asterisci) and more precisely shape changes, as well as timing and deposition rate of increments of the lapilli. The lapilli and the sagittae were present at hatching, whereas the asterisci formed between 20 and 30 dph. The lapillus and sagitta shapes were round until 20 dph. From 60 dph the anterior and the posterior rostra of the sagittae were well developed, but very thin, making this otolith too fragile to manipulate for further studies of shape and validation of otolith increment deposition rate. The lapilli provided reliable age estimates for free embryos, larvae and juveniles up to 120 dph. However, caution should be taken when ageing fish older than 150 dph as an underestimation was noticeable. The regression of the number of otolith increments on age showed a slope and an intercept not significantly different from 1 and 0, respectively, which indicated that otolith growth increments were deposited on a daily basis, with the first microincrement occurring at hatching. Increment counts were consistent between three interpreters, indicating a consistent and reliable age estimate. This study validates that the otolith increment deposition rate can be used to assess hatching dates and daily growth of wild S. cephalus under 150 dph and in environments similar to the conditions used in this study. [ABSTRACT FROM AUTHOR]

Floods are known to be the major source of natural variability and disturbance in stream ecosystems. However, the management and channelisation of large rivers have impacted the fluvial geomorphology and disconnected the main channel and floodplains used as nurseries by many species of fish. This study examines the influence of a first autumnal flood event of the Ardèche River on the roach population, Rutilus rutilus (Linnaeus, 1758), in the Caderousse reach on the Rhône River. This influence was evaluated through an analysis of the spatial distribution for the abundance and size of juvenile roach and an analysis of otolith shape. Juvenile roach from the three sections of the reach formed well-defined local populations before and after the flood event. Juvenile roach were always more abundant in the less modified section ( BPS) of the river than in the other sections ( RES and TAIL). While the original primary river channel was directly impacted by the flash flood, no significant difference in otolith shape was observed before or after the flash flood. Our results suggest that this part of the reach provides refuge habitats used by fish during high flow events. [ABSTRACT FROM AUTHOR]