Trends in Fish Biomass Off Northwest Africa, 1960-2000

V. Christensen, P. A. Amorim, I. Diallo, T. Diouf, S. Guenette, J. J. Heymans, A. N. Mendy, M. Sidi, M. L. D. Palomares, B. Samb, K. A. Stobberup, J. M. Vakily, M. Vasconcellos, R. Watson, D. Pauly, (2005). paper presented at the Cartographie des prises halieutiques d’Afrique occidentale : 1950 à 2000 In Pêcheries maritimes, écosystèmes & sociétés en Afrique de l’Ouest : Un demi-siècle de changement, 24-28 juin 2002, Dakar, Senegal, 2005

We estimate biomass trends for demersal and large pelagic fishes, (i.e., excluding small pelagic and mesopelagic fishes) based on 17 Ecopath models from Mauritania, Cape Verde, Senegal, the Gambia, Guinea, and Guinea-Bissau, Sierra Leone and the open waters of the central east Atlantic, made to represent various time periods during the second half of the 20th Century. We use a published method developed for estimating fish biomass in the North Atlantic, and modify it to account for the specificity of West African fisheries and ecosystems. We show that, overall, fish biomass as defined here (i.e., excluding low-trophic level and small fishes) has declined over the forty year period from 1960 by a factor of 13. An implication of our results is that further increase in fishing mortality in the region will not lead to increased catches but will only drive biomasses further down. The economic and political consequences of our findings are briefly discussed.