Thinking the unthinkable: a candidate model for predicting sustainable yields of introduced fish species in African lakes

In fresh waters world-wide, Welcomme (1988), (1992) analyses over 1.5 million introductions of 291 species into 148 countries since 1900. Many of these introductions have been designed to enhance fisheries, although the majority have been carried out for aquaculture. Outcomes have been mixed, and so it would be helpful to try to ensure that future introductions are beneficial. Adverse effects include predation, competition, hybridization, introduction of disease and parasites, crowding, stunting and degradation of water quality (Welcomme, 1984), and there is evidently a need to better predict the ecological role and impact of an introduced species, and to obtain international agreement on its introduction. Guidelines to this effect have been published by FAO (Tiews, 1985). As (1986) points out, new introductions cannot be banned, and so this Chapter aims to assess the impact of potential new introductions of the freshwater sardine or Nile perch to African lakes by evaluating the balance of costs and benefits. A new model based on primary productivity is introduced to estimate potential sustainable yields.