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5.1 Introduction

Information on the largest reservoir in Sudan, Lake Nubia, was summarized in an FAO/CIFA Technical Paper (Kapetsky and Petr, 1984). The second largest is the Jebel Aulia (or Gebel Aulia) Reservoir which is situated 45 km south of Khartoum. The available information is summarized in the following.

5.2 Jebel Aulia Reservoir

5.2.1 White Nile

The inflowing river of the Jebel Aulia Reservoir is the White Nile, which had its source at the Owen Falls dam in Uganda. The river discharges into the Nile at Khartoum. South of Khartoum the White Nile was impounded for water storage purposes in 1937 and this resulted in the Jebel Aulia Reservoir; its geographic position is presented in Figure 5.1.

5.2.2 Pre-impoundment study

No data available.

5.2.3 Limnology, hydrology and morphometry

The dam was constructed 377 m above sea level. The reservoir surface area ranges from 600 to 1 500 km2, maximum depth is 12 m with mean from 2.3 to 6 m, with a volume of 3.5 m3 (Vanden Bossche and Bernacsek, 1991, quoted from Welcomme, 1972). Khalid (1990) confirms a mean depth of 2.3 m and a capacity of 3.5 km3, with surface area of 1 246 km2. The lake's length of 500 km is quoted from George et al. (1985), and Khalid estimated the maximum width in the vicinity of the dam between 6 and 7 km.

The reservoir's level starts to drop in February and continues until the end of May. It reaches its maximum level in September. The amplitude of the water level movement is 6 m (Khalid, 1990).

The available physico-chemical data are summarized in Table 5.1.

5.2.4 Description of the fishery

Welcomme (1975) estimated the number of fishermen and boats in 1975 at 1 500 and 550 respectively. In 1982 these numbers were of the same order of magnitude, viz., 1 594 and 544 respectively (FAO, 1982; Kapetsky, 1986). Seines and gillnets are the principal gear on Jebel Aulia Reservoir, but castnets are also common (Henderson, 1975). Principal species exploited are Sarotherodon galilaeus, Oreochromis niloticus and Lates niloticus (Kapetsky, 1986).

5.2.5 Stock assessment Total annual yield

Reliable statistics do not exist for the Jebel Aulia Reservoir; however, various estimates were made of the yearly production. Henderson (1975) produced a range from 7 000 to 8 100 t for 1975 with a potential yield of 15 000 t (corresponding to 100 kg/ha/yr). A more precise value of 8 216 t was presented by FAO (1982) with a potential yield of 4 500 t or 30 kg/ha/yr. Asma (1985) calculated the maximum sustainable yield to be 7 363.860 t/yr. Kapetsky (1986) calculated an annual yield of 55 kg/ha for 1981–1982, based on the method of Henderson and Welcomme (1974). Catch rates

Khalid (1990) summarized some catch data obtained in May 1975. Catch rates were expressed in catch/day; data originated from the Fisheries Research Centre in Khartoum. It was not indicated how fish were caught. The following figures were deducted from the information presented by Khalid (1990). In 11 days of fishing 32 941 tilapias were caught (a mixture of Tilapia zillii, Tilapia galilaea and Oreochromis niloticus), weighing 19 696 kg, and 8 510 specimens of non-tilapias weighing 11 419 kg. Total production in 11 days was 31 115 kg or 2 829 kg/day. Fishing effort

(See section 5.2.4.) Apart from the number of boats, no information on fishing effort could be traced. Mesh selectivity

No information available to the author. Species composition

Over 95% of commercial catches from Jebel Aulia Reservoir consisted of seven families, according to Adam (1986). The family composition was as follows:

Mormyridae23.7 %
Mochokidae23.5 %
Schilbeidae21.1 %
Characidae13.4 %
Cyprinidae5.8 %
Bagridae5.2 %
Citharinidae2.8 %

Asma (1985) reported catches to consist of 54 fish species, 28 genera belonging to 13 families. Table 5.1 presents an overview of the most abundant fish species in commercial catches, with their vernacular names. Small clupeids

No data available. Biological data

Khalid (1990) investigated length/weight data of Oreochromis niloticus from the Jebel Aulia Reservoir. He established the following length/weight relationship:

log W = a + b log L

(W: body weight; L: body length)
a = 4.58213 and b = 3.03557

The following values of body length were assigned to age groups:

L1: 116 mmL4: 319 mm
L2: 194 mmL5: 360 mm
L3: 260 mmL6: 371 mm

He determined the Van Bertalanffy growth parameters for this species as well:

L ∞ = 450 mm; k = 0.2949/yr; t0 = 0.0109

5.2.6 Management

No information was found on management measures.

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