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Master Thesis

Méta-analyse des données de campagnes de chalutages démersales en Mauritanie de 1982 à 2011

Abstract : In this work we analyze the demersal monitoring surveys date carried out by IMROP in the Mauritanian EEZ from 1982 to 2011. This analysis uses four quantifiable and verifiable indicators on the evolution of these data, and the status of implementation of these surveys. First, we observed the periodicity and regularity of these surveys. In total 62 demersal surveys were carried out, with an average of two surveys per year. None of the four hydrological seasons in Mauritania has been covered regularly by these surveys. The cool season is the season during which most surveys were carried out, 25 in total, followed by the warm season with 17 surveys. Since 2004, a decrease in the number of campaigns carried out in the two- inter-seasons is observed. The evolution of the intensity of sampling through the number of trawl stations and the medium depths change, highlight, in general, an increase in the number of trawl stations since 2003. Similarly, a net increase in the average depth of fishing is observed since 2004. The accumulation curves for three surveys in 2004, 2008 and 2011 show that the sampling effort was probably sufficient to detect the majority of catchable taxa present in the Mauritanian EEZ. 645 taxa were identified during the surveys, 80% of fish. In the early 2000s, an improvement in the identification of species is noted. The analysis of the "presence / absence" of taxa shows that 42 taxa are absent in the catch from 1982 to 1995, but present in the following years, and four species have disappeared in the catch after a presence, especially in the years 1990. Finally, analysis of size frequency data collected during demersal surveys from 1986 to 2011, enabled to distinguish two periods: the late 1980s - early 1990s, marked by a significant number of individuals measured, and the late 1990s to 2011 characterized by a decrease of more than 60% of measured individuals. The last period was marked by a very low number of individuals measured for the 25 species that are the subject of systematic measurements during demersal surveys from 2004 to 2011.
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Hammoud El Vadhel. Méta-analyse des données de campagnes de chalutages démersales en Mauritanie de 1982 à 2011. Environnement et Société. 2016. ⟨dumas-01364915⟩

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