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African Journal of Marine Science

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

LJ Shannon, A Jarre-Teichmann

Abstract


A model of trophic flows through the northern Benguela between 1980 and 1989 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 scientists working on different components of the ecosystem to collaborate to improve and update the model for more recent years.
Ultimately, this type of model may form a basis for multispecies management approaches in the region. By the 1980s, sardine Sardinops sagax and hake Merluccius spp. stocks in the northern Benguela had both undergone a decline, yet were still heavily fished. Horse mackerel Trachurus trachurus capensis had increased over the previous
decade and was the dominant pelagic species during the 1980s, with high catches. Production by some groups, such as goby Sufflogobius bibarbatus, mesopelagic fish and demersal fish, was insufficient to sustain
other components of the system. In all, 1.5 million tons of goby, 1.7 million tons of mesopelagic fish and 0.7 million tons of demersal fish (excluding hake) were required to support predators in the northern Benguela. Total biomass in the northern Benguela during the 1980s was high, comparable to that of the Peruvian system in the 1960s and almost double that of the northern Benguela during the 1970s. Horse mackerel and hake catches were both high, with fishing on hake being ecologically more expensive. Biomass of benthic producers, meioand macrobenthos were a quarter of the total biomass of these groups in the southern Benguela. The sensitivity of the model to parameter estimates is highlighted. Uncertainty about some of the parameters, thought to have
major influences on the functioning of the model, is explored.



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