Another potential disaster? On a proposal to introduce Nile perch, Lates niloticus , into Lake Kariba (Zambia/Zimbabwe)

Abstract

The introduction of Nile perch, Lates niloticus, into Lake Victoria resulted in a massive increase in fish catches, but with significant ecological costs. These included the near extirpation of the 500+ endemic haplochromine species and the eutrophication of the lake. A proposal to introduce Nile perch into the artificial Lake Kariba (Zambia/Zimbabwe) is of concern, therefore, because of potentially adverse impacts on its fisheries and biodiversity. It is very unlikely that Nile perch would improve the fisheries in Lake Kariba, as it did in lakes Victoria and Kyoga, because this lake is oligotrophic and much less productive. The principal fishery in Lake Kariba is already in difficulty, owing to overfishing, and Nile perch could reduce catches further. The biomass of other native fish species is very low and would be unlikely to support a significant Nile perch population. Lake Kariba has already experienced a major loss of biodiversity as river-adapted fish species have not been able to adapt to lacustrine conditions. The non-native Nile tilapia, Oreochromis niloticus, has also replaced the endemic tilapia species in the middle Zambezi system and the Nile perch could bring about a further loss of biodiversity. The ecological costs of its introduction into Lake Kariba would not be justified by an increase in fishery productivity, and the possible introduction of Nile perch should be forcefully rejected.