A model of trophic flows in the northern Benguela upwelling system during the 1980s

A model of trophic flows through the northern Benguela between 1980 and 198 9 was constructed using the ECOPATH approach. The model serves to close the temporal gap between models of the system for the 1970s and 1990s. The aim is to provide a workable model, with the intention of encouraging scientis ts working on different components of the ecosystem to collaborate to impro ve and update the model for more recent years. Ultimately, this type of mod el may form a basis for multispecies management approaches in the region. B y the 1980s, sardine Sardinops sagax and hake Merluccius spp. stocks in the northern Benguela had both undergone a decline, yet were still heavily fis hed. Horse mackerel Trachurus trachurus capensis had increased over the pre vious decade and was the dominant pelagic species during the 1980s, with hi gh catches. Production by some groups, such as goby Sufflogobius bibarbatus , mesopelagic fish and demersal fish, was insufficient to sustain other com ponents of the system. In all, 1.5 million tons of goby, 1.7 million tons o f mesopelagic fish and 0.7 million tons of demersal fish (excluding hake) w ere required to support predators in the northern Benguela. Total biomass i n the northern Benguela during the 1980s was high, comparable to that of th e Peruvian system in the 1960s and almost double that of the northern Bengu ela during the 1970s. Horse mackerel and hake catches were both high, with fishing on hake being ecologically more expensive. Biomass of benthic produ cers, meio- and macrobenthos were a quarter of the total biomass of these g roups in the southern Benguela. The sensitivity of the model to parameter e stimates is highlighted. Uncertainty about some of the parameters, thought to have major influences on the functioning of the model, is explored.