Abstract
Information on the mean trophic level of fishery landings in Angola and the output from a preliminary Ecopath with Ecosim (EwE) model were used to examine the dynamics of the Angolan marine ecosystem. Results were compared with the nearby Namibian and South African ecosystems, which share some of the exploited fish populations. The results show that: (i) The mean trophic level of Angola’s fish landings has not decreased over the years; (ii) There are significant correlations between the landings of Angola, Namibia and South Africa; (iii) The ecosystem attributes calculated by the EwE models for the three ecosystems were similar, and the main differences were related to the magnitude of flows and biomass; (iv) The similarity among ecosystem trends for Namibia, South Africa and Angola re-emphasizes the need to continue collaborative regional studies on the fish stocks and their ecosystems. To improve the Angolan model it is necessary to gain a better understanding of plankton dynamics because plankton are essential for Sardinella spp. An expanded analysis of the gut contents of the fish species occupying Angola’s coastline is also necessary.
Highlights
African fisheries play an important role in food security and good nutrition on the continent, and supply up to 60% of the population’s protein intake in some sub-Saharan countries (Béné and Heck, 2005)
The main aim of this paper is to examine longterm changes in the trophic level of fishery landings in Angola and to test whether the mean trophic level of Angolan landings has declined over time
Considering that phytoplankton, zooplankton, small pelagics and Sardinella are the main sources of prey for all five compartments listed above, it is important for future studies and models of the Angolan marine ecosystem to focus on the productivity of plankton and the pelagic ecosystem. This analysis of Angolan landings and the Angola Ecopath with Ecosim (EwE) model showed a pattern of ecosystem dynamics similar to the pattern elsewhere in the large Benguela Current marine ecosystem
Summary
African fisheries play an important role in food security and good nutrition on the continent, and supply up to 60% of the population’s protein intake in some sub-Saharan countries (Béné and Heck, 2005). In the Benguela ecosystem, South Africa, Namibia and Angola all actively exploit their resources. Fisheries represent almost 9% of the GDP (gross domestic product) in Namibia, 4% in Angola and 0.5% in South Africa. The Angolan marine ecosystem is under the influence of two major current systems: the south-flowing warm Angolan Current and the northflowing cold Benguela Current. These two currents meet between 14 and 17°S at the Angola–Benguela front, impacting the whole water column and influencing the spatial distributions and diversity of the flora and fauna (Sumaila et al, 2005; Pichevin et al, 2005). Sardinella spp. together with Trachurus spp. constitute Angola’s most commercially important fish species
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