Estimates of Potential Fish Yield for the Nasser Reservoir, Arab Republic of Egypt

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Abstract
Available biological and hydrographic information on Lake Nasser was examined to provide guidelines for future development of the fisheries. Not enough consistent data were available to allow precise estimates of fishing-stock interrelations; however, an approximation of potential yield was derived from subjective evaluation of limnological characteristics of the lake. Morphoedaphic factors were utilized to establish a numerical expectation of yield in relation to other tropical lakes and reservoirs. Two other models based on estimated zooplankton biomass and an assumed net gain in productivity in Lake Nasser at the expense of a yield loss to the Mediterranean fishery provided order-of-magnitude agreement. Potential yield estimates for Lake Nasser (including its southern portion, Lake Nubia, Sudan) were 23,000 metric tons (MT) of fish annually, providing the reservoir fills to its expected maximum (180 m), or 12,000 MT if it remains at its 1973 level of about 160 m. These estimates are considered sufficiently reliable to guide future development of the fishery.There is little evidence to support the existence of stock overexploitation. Tilapia nilotica, however, the major species entering the fishery, has been subjected to potentially damaging fishing practices on its breeding grounds. These practices combined with water level drawdown, inadvertently timed to perturb Tilapia fry inhabiting the shallow nursery areas, may unduly stress a prime species largely responsible for the current success of the fishery.Management recommendations for the Nasser–Nubia Reservoir include a regular program of monitoring both stocks and harvest, especially for Tilapia. Development emphasis should be placed on improving the logistics of the fishery rather than increasing the number of fishermen, at least until the lake area expands substantially.

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