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Variations ontogéniques et spatio-temporelles des écophases larvaires des poissons : évaluation de la condition nutritionnelle et détermination des périodes critiques

Abstract : As a deterministic factor in recruitment, the study of the survival success of fish larvae has since the work of Hjort (1914) become crucizl to understanding variations in population dynamics. Nutrition and the consequences of larval starvation are now widely accepted as major sources of variability in survival , explaining that the number of offspring recruiting the adult population is not proportional to the spawning biomass. It is in this context that this thesis was written with the aim of identifying in situ the critical periods (i.e. high mortality stages) of the larval development, and defining the environmental conditions that are favourable to them using biochemical and histological condition indices. By carrying out several winter and spring surveys, mainly in the Eastern English Channel and North Sea, data on distributions, abundances and larval conditions have been acquired. A lower larval abundance has been highlighted compared to the 90s, particularly for species that have already shown a decline in their stock since the warming of the waters in the late 90s. This decrease in abundance could be linked to a decrease in areas favourable to good condition, particularly for sole. As the histological indices were defines experimentaly, these indices were calibrated using literature and statistical tools in order to obtain a method more adapted to the larvae collected in situ. This new approach was coupled with a growth index to define for three key species (sole, sprat and whiting) the zones, periods and environmental conditions favourable to good larval condition and growth during the critical first feeding period. Finally, these indices were coupled with a lipid index to define variations in the condition and energy allocation strategy of plaice larvae during ontogeny, showing a change from a growth strategy to one of creating energy reserves at the entrance to metamorphosis (transition from larval to juvenile phase). These results suggest several potential critical periods during development and, depending on the species, the environmental parameters increasing the probability of survival are variable. These condition results should be considered in ecosystem models to better understand the factors of variation in fish recruitment.
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Julien Di Pane. Variations ontogéniques et spatio-temporelles des écophases larvaires des poissons : évaluation de la condition nutritionnelle et détermination des périodes critiques. Biologie animale. Université du Littoral Côte d'Opale, 2019. Français. ⟨NNT : 2019DUNK0540⟩. ⟨tel-02480814⟩

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