Response of migratory salmonid populations to global changes

• Main Author: Tréhin, Cécile
• Other Authors: Dynamique et durabilité des écosystèmes : de la source à l’océan (DECOD), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Agrocampus Ouest, Marie Nevoux, Étienne Rivot
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2022
• Subjects: Migratory fish; Life history strategy; Marine growth; Population dynamics; Poissons migrateurs; Stratégie d’histoire de vie; Croissance en mer; Dynamique des populations; [SDV.SA]Life Sciences [q-bio]/Agricultural sciences; Salmo salar
• Online Access: https://theses.hal.science/tel-03896540; https://theses.hal.science/tel-03896540/document; https://theses.hal.science/tel-03896540/file/fix_wr3yfQTF-trehin.pdf

This thesis aims to better understand the ecological and demographic processes determining life history traits and population structure in Altantic salmon Salmo salar populations. I test the hypothesis that growth is key to explain variations in adults returning to rivers to reproduce, with differencial responses between males and females. The project relies on the analysis of 21 to 47 years of empirical data from five monitored wild populations, and on the development of a population model with a focus on the marine phase of the life cycle. I show that high growth over first summer at sea favours early sexual maturation (thus a return to freshwater to reproduce). Females need to reach higher body size in order to mature.Individual growth over the first months of the marine migration declined over time. This temporal signal in growth over first summer at sea is common to several populations, underlying the effect of common environmental stressors. This response is combined with differences between populations, underlying that variability in age at return is partly due to factors specific to each population. Finally we show that post-smolt survival, depending on smolt size, and maturation rate, depending on sex and marine growth, ultimately condition age and sex structure in returns. However temporal variability of return rate and reproductive potential essentially relies on the survival rate of post-smolts. L’objectif de cette thèse a été d’acquérir une meilleure compréhension des mécanismes écologiques et démographiques qui déterminent les traits d’histoire de vie et la structure des populations de saumon atlantique Salmo salar. Je teste l’hypothèse que la croissance occupe une place centrale dans les variations des retours des adultes en rivière, avec des réponses différentes chez les mâles et les femelles. Le projet s’appuie sur l’analyse de 21 à 47 années de données empiriques provenant du suivi de cinq populations sauvages sud-européennes, et sur la construction d’un modèle de population centré sur la ...