Fisheries in the Nile System

Abstract

The contribution to fishery by the River Nile itself is far less substantial than that of the Nilotic lakes. Especially during the past decades the fish landings from the lakes rose considerably. Concomitant with a decreased salinity between the 1920s and the1990s, fish landings in Lake Borullus and Lake Manzala in the Nile Delta rose from about 6,000 to 50,000 t y−1 and from 12,700 to 55,000 t y−1 respectively. In both lakes the dominance of mullets in the catches changed into a dominance of tilapiines. The estimated annual catch in Lake Albert rose from 24,800 t in 1991 to 182,000 t in 2007 and the catch composition changed towards small sized species. In Lake Victoria, Nile perch and Nile tilapia were introduced in the 1950s to improve the dwindling catches of native tilapiines. Subsequently, predation by Nile perch, fishery and ecological changes caused a decline of the endemic haplochromines and many other native fish species. However, the stocks of Nile perch, Nile tilapia and the indigenous zooplanktivore Rastrineobola argentea increased strongly. After the Nile perch boom at the end of the 1980s, the annual fish production increased tenfold to about 1,000,000 t in 2005. During the same period the fishing effort had tripled. Initially Nile perch made up more than 70% of the fish landings, but by 2005 this had changed to 53% R. argentea and 26% Nile perch. Lake Tana's subsistence fishery with reed boats and small gill nets changed after the introduction of motorised boats and modern nylon gill nets in 1986. The total landings of the motorised boats increased to a peak 388 t y−1 in 1993 and were 292 t in 2006. A decrease in abundance by about 75% of the riverine spawning Labeobarbus species and the collapse of juvenile Labeobarbus during the 1990s were observed. Possibly with the exception of the Sudd swamps, all studied areas of the Nile system show signs of overfishing.