Relationship Between Primary Production and Fish Production in Lake Tanganyika

Abstract

Primary production in Lake Tanganyika, 0.8 g C˙m−2˙day−1, is not high by comparison with other tropical lakes yet the fisheries of the lake maintain annual yields of 125 kg hectare−1 (1.3 g C˙m−2˙year−1). The efficiency of carbon transfer to the fishery from primary production is anomalously high among the lakes of the world and approximates the efficiencies of the most productive marine fisheries. The great antiquity of this lake may have allowed selection of the most efficient pelagic species and resulted, in turn, in a highly efficient pelagic ecosystem where carbon accumulates as fish at the top of the trophic pyramid rather than as algae at the bottom. However, estimates of heterotrophic bacterial production equal or exceed primary production by algae. The immense volume of anoxic deep water is the likely source of energy fixed in reduced substances that could allow such high rates of bacterial production. The study of the relationship between fish production and primary production in two other great African lakes, Kivu and Malawi, because of their quite different histories, would clarify the role of natural selection and bacterial production in determining the trophic efficiencies of tropical lakes with perennially anoxic deep water.