Abstract
In Guinea, was highlighted by various authors that the intensification of the exploitation of demersal resources over recent decades has led to a general decline in abundance. This intensification is supposed to have also induces changes in the specific and multi-functional structure of the fish assemblages of this zone, but few studies have Judging far, most previous work on these resources with relevant strictly mono-specific approaches and strictly taxonomic approaches. In this context, the aim of this thesis is to contribute to a more complete ecosystem diagnosis of the current state of the Guinean marine resources and in particular whether the taxonomic and functional diversity of fish assemblages was affected by fishing. Data from scientific trawl surveys collected on Guinean continental shelf between 1985 and 2012, statistics on catches of fishing and seventeen functional traits related to locomotion functions and food purchase 50 groundfish species are studied diversity through various indicators to analyze the impact of fishing.The results show that the intensification of fishing has had significant effects on certain general characteristics of the population in question. Since 1985, we thus observed a drop in the density and the mean trophic level of fish and a turnover of dominance, whereby major species of high commercial value, characterized by substantial body masses and slow growth are gradually replaced by species of smaller sizes at lower commercial value and rapid growth. There is also a significant decrease in functional richness whose evolution confirms the results obtained from the taxonomic assessments and confirms that the coastal ecosystem of the continental shelf is disrupted in connection with fishing pressure.