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Master Thesis

Rôle des perchettes et impact de leur exploitation sur la structure trophique du lac d'Annecy : approche par modélisation écosystémique

Abstract : Lake Annecy has an oligotrophic status stable since decades. It is considered as productive, and support important fisheries, both anglers and professional (total fished weight estimated to 27 t.an-1). A preliminary recent model made with 'Ecopath with Ecosim' showed the main trophic paths, and the system stability. However, considering new data collected by direct measures (hydroacoustic), the importance of the biomass of juvenile perch (Perca fluviatilis) seems to be strongly under-estimated. This biomass seems to frequently reach a high level, about 5 to 10 times more important than the preliminary model estimation. The importance of the perch 0+ biomass raises questions on the lake capacity and the prohibition of fishing these juveniles. Moreover, fishing these perch 0+ is allowed on the lake Bourget, which seems to have a similar evolution toward an oligotrophic status as Annecy lake. That is why it would be useful to identify the impacts of this fishery to eventually build scenaris on other ecosystems and improve our knowledges of this key species in oligotrophic network. A recalibration of the model parameters gives us a picture of the ecosystem which fits better with our knowledge of the fish populations. Updated datas improve the model relevance and allow to estimate the lake capacity. The 'Ecopath with Ecosim' model shows the trophic structure of the ecosystem and the main trophic paths. A sensitivity analysis, which examined the effects of the perch 0+ parameters that changed a lot, shows the model robustness or fragility. Then, the impacts on the ecosystem of a fishery targeting the perch 0+ are simulated and discussed with the EcoTroph model. It allows to identify the effect of such a fishery on all the ecosystem and its production.
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Master Thesis
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Submitted on : Monday, January 20, 2014 - 9:13:52 AM
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Thibaut de la Chesnais. Rôle des perchettes et impact de leur exploitation sur la structure trophique du lac d'Annecy : approche par modélisation écosystémique. Sciences agricoles. 2013. ⟨dumas-00927496⟩

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