Ecosystem structure and dynamics of the marine system of Sierra Leone for three time periods: 1964, 1978 and 1990

Abstract

We present the key feature of a quantitative food web model for the shelf and slope waters off Sierra Leone, constructed using the Ecopath with Ecosim software. Three periods are represented: 1964, based on data from the Guinean Trawling Survey, complemented with field data on lower trophic levels gathered in the late 1950/early 1960s and published by A.R. Longhurst; 1978, for which fish abundance data from an ex-USSR survey exist, along with related, scattered fisheries information; and 1990, for which a fair amount of fisheries data exist, along with the results of a Spanish trawl survey. Demersal fish biomass appears to have declined linearly from 1964 to 1990, due to the massive increase of the catches of distant water fleets operating in Sierra Leone, resulting in different flow structures for the food webs of these two periods.