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Theses

In situ quantification of brown trout movements

Abstract : Movements are a crucial aspect of ecology and evolution, as they determine population and community dynamics. Threats to these dynamics because of human perturbations are therefore a major concern for conservation. In this thesis, I studied movements in the Brown trout (Salmo trutta) in the context of stocking, i.e. the supplementation of wild populations with captive-bred strains from both, native and exogenous origin. For this purpose, I first developed a new genetic tool useful for detecting genetic structure in the brown trout, as well as hybridization with captive-bred strains, exhibiting high genotyping success and enabling to successfully identify patterns of isolation-by-distance. This tool was shown cost effective, and especially, should be useful for many population genetics studies on this species across its range. Then, I developed novel assignment approaches combining genetic data and stable isotopes, to study movements at the spatial scale of a river basin, which is of interest for applied matters such as management. This approach, based on machine learning, revealed high accuracy and power to discriminate and assign individuals to their population of origin. Further, I described the genetic effects of captive breeding on patterns of genetic diversity and differentiation, and found that captive-bred genotypes increased diversity and differentiation, and that expected natural patterns could be reversed in the case of higher frequency of captive-bred genotypes occurring at the level of populations. Then, I demonstrated that admixture between wild individuals and those carrying captive-bred ancestry affected dispersal patterns, that the two strains displayed different movement patterns in terms of propensity, distances, and direction, and that admixture between strains considerably reduced dispersal. Finally, I aimed at better understanding how individual, environmental and landscape related factors influence movements in natural populations; here I found that some determinants were universal across rivers, with larger individuals being more prone to movement for instance, or sites that are directly connected by the water flow, and those that are similar in terms of elevation and stream order exchanged more migrants. One the other hand, other drivers were context dependent, for instance the relations between movement patterns and position within riverscapes and habitat availability depended on the river basin considered. This thesis contributed to improve methods for studying movements, and to identify factors underlying patterns of movements at the scale of the river basin. The implications of my thesis are thus both fundamental and applied as a better understanding of movement patterns in the context of human perturbations is crucial for management and conservation.
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Keoni Saint-Pé. In situ quantification of brown trout movements. Ecology, environment. Université Paul Sabatier - Toulouse III, 2019. English. ⟨NNT : 2019TOU30207⟩. ⟨tel-02942828⟩

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