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Stratégies d'occupation spatiale en milieu lacustre : réponses de l'ichtyofaune dans un réservoir échauffé, non stratifié

Abstract : The study was conducted in an artificial reservoir, adjacent to a nuclear power plant, in which water temperatures are cool in the winter (8.2 – 12.4°C) and rise early in the spring (April : 14.7°C) nearly 5°C and 3°C over the temperature of its tributary (Moselle river), respectively. The absence of stratification (neither thermocline nor oxycline exist) and the constant water level provided a unique opportunity to observed fish distribution with low abiotic constraints. In one hand, temporal and spatial distributions of the fish community were studied in both littoral and pelagic area. The time survey separated two major groups of young of the year (YOY) according to their time of appearance; the first represented the progeny of early-spring spawning species whereas the second resulted from later-spawning species. Ontogenetic niche shifts of coexisting species were appreciated and for example during late spring and summer, the smallest white bream YOY (LT < 20 mm) were restricted to complex habitats whereas those of pumpkinseed occupied all available habitats. Growing white bream progressively migrated to open water before reaching pelagic areas. There, the vertical distribution of fish was studied using gill net time series. Seasonal and species-specific distribution patterns were highlighted. During the autumn, many species were sampled in deeper water whereas pumpkinseed was the only one sampled in abundance in the littoral zone. Pumpkinseed introduction success might be explained by both its late hatching and its opportunistic strategy in habitat selection enabling it to exploit space left vacant. In the other hand, life history reactions of fish exposed to heated waters were studied particularly in the pumpkinseed population. Fast growth among young of the year, precocious maturity and short life-span were observed, in contrast to related studies. The short life span appeared to be the price paid for early maturity in breeding fish, which suffered high mortality rates just after their first reproduction. These findings should prove helpful in predicting ecological responses to climatic change.
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Samuel Dembski. Stratégies d'occupation spatiale en milieu lacustre : réponses de l'ichtyofaune dans un réservoir échauffé, non stratifié. Ecologie, Environnement. Université de Metz, 2005. Français. ⟨tel-00145435⟩

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