Contribution to a better knowledge of bycatch of fixed gillnets of shrimps (Farfantepenaeus notialis) in the Casamance estuary in Southern Senegal

International audienceThis study was carried out in Ziguinchor (Senegal) in southern Senegal where the coastal shrimp Farfantepenaeusnotialisis exploited by a small-scale fishery whose activities have been mainly oriented for several years. Data were collected downstream Casamance Estuary from 26 July to 31 August 2016 at two landing sites: from July 26 to August 12 in Boudodyand then from August 16 to 31under the bridge Emile Badiane. During this period, the landings of 61 fishermen were studied. Those fishermenwere selected at random or through contacts established by the Ziguinchor Regional Fisheries and Surveillance Service. Thecollection was carried out three times a week with fishermen returning from fishing between 9 PMand 10 AM.Juvenile fish are the main bycatch of thistype of fishing gear (86.85%), followed by crustaceans (13.13%) and cephalopod molluscs(0.02%). Most ofthese captures (89.54%) are discarded, 10.46% are retained. Some 39 species constitute the bycatch of fixed net used inshrimp fisherydownstream Casamance estuary. Therearefour species regularly found in fishermen's nets, 1 quite frequently, 5 of them are retrieved occasionally and 29 are erratic. Ethmalosa fimbriata, accounting for almost 60.74%of catches, is the main bycatch species found in fixed net. 64% of species caught belong to the category of minor concernsand 10% are labelledas threatened species(vulnerable and endangered). Out of those 39 species, 13 are estuarine of marine origin and 13 are marine estuarineand 21 of them are predatory species of the second trophic level. Bycatchdiscards account for 140 kg. Some species, mainly juvenilefish, discarded by fishermen are salvaged for human and / or animal consumption. Others arekept by fishermen and are eate

Changes in the trophic structure, abundance and species diversity of exploited fish assemblages in the artisanal fisheries of the northern coast, Senegal, West Africa

International audienceThis work investigates the effects of changes in both fishing pressure and the environment on the trophic dynamics, abundance and diversity of species in the artisanal commercial fisheries off the northern coast of Senegal. Using artisanal commercial fishing data (provided by the Centre for Oceanographic Research of Dakar-Thiaroye [CRODT] in Senegal), we identify changes in the catch per unit effort, mean trophic level, biomass trophic spectrum and species diversity between two fishing periods (1990-1999 and 2000-2009). Decreases in mean trophic level, the biomass of high trophic level species and indices of species diversity between 1990 and 2009 were observed in commercial catches. These decreases were then related to changes in fishing pressure, fishing strategy and the combined effects of fishing and environmental factors (as derived from satellite observations). This paper helps to better inform the management of fisheries resources by providing decision makers with more effective biological indicators that incorporate the effects of fishing pressure and environmental change and that are applicable at local, regional and global scales