Assessment and Production of Characid Fish at White Nile River

International Journal of Environment and Bioenergy, 2012, 2(3): 137-145 International Journal of Environment and Bioenergy ISSN: 2165-8951 Journal homepage: www.ModernScientificPress.com/Journals/IJEE.aspx Florida, USA Communication Assessment and Production of Characid Fish at White Nile River

Fathi Mirghani Yousif 1, *, Asma Abdel Rahman Ahmad 2

1 Ministry of Animal Resources and Fisheries, Administration of General Fisheries and Aquatic Resources, Natural Fisheries Department, Khartoum, Sudan 2 Faculty of Science, University of Al-Neelain, Khartoum, Sudan

* Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: 002491116309.

Article history : Received 25 June 2012, Received in revised form 1 August 2012, Accepted 5 August 2012, Published 7 August 2012.

Abstract: This study was conducted from November 2007 to October 2008 at two main fishing sites in Jebel Aulia Reservoir, which were Jebel Aulia site 45 km south Khartoum city and Kosti site about 355 km southward Khartoum city. This study concentrated on two genera family Characidae, which were Hydrocynus forskalii , Hydrocynus lineatus , Hydrocynus brevis , Alestes baremoze, Alestes dentex and Alestes nurse . The results were analyzing using standard approaches and advanced computer programmes (PAST and FISAT II FAO-ICLARM). The estimated productivities were 77.02 kg/km 2 at Jebel Aulia and 499.71 kg/km 2 at Kosti site, respectively. Nevertheless, fishing effort in Kosti nearly is double Jebel Aulia site by using one type of fishing–net during period for fishing. For genus Alestes in Jebel Aulia site, exploitation ratio was between 0.52 and 0.90, while that for genus Hydrocynus was between 0.60 and 0.70. In addition, in Kosti exploitation ratio for genus Alestes was between 0.37 and 0.54, and that for genus Hydrocynus was between 0.41 and 0.58. The recommended exploitation ratio level was 0.5.

Keywords: assessment; production; characid; fish .

1. Introduction

Int. J. Environ. Bioener. 2012, 2(3): 137-145 138

The basic purpose of fish stock assessment is to provide advice optimum exploitation of group of organisms of one species, which have the same parameters and inhabit particular geographical area (FAO, 1989). Stock assessment of tropical resources has been developed tremendously through the work of Pauly (1980). The Russian Research Expedition (1964) reported that the area extending from the Jebel Aulia Dam to Kosti was the most suitable area for commercial fishing operations. This area is about 120,000 ha with potential for annual catch of 36,000 tons. The annual fish catch reported for the northern part of the White Nile was 1,890,520 kg and 1,945,582 kg for the southern region (Hamaza, 1981). Henderson (1975) reported that the potential production of Jebel Aulia reservoir was 15,000 tons while the actual production ranged from 7,000 tons to 8,000 tons annually equivalent to 100 kg/ha/yr. A more precise value of 8,216 tons was presented by FAO (1982) with a potential yield of 4,500 tons and an annual yield of 30 kg/ha/yr. Kapetsky (1986) calculated an annual yield of 55 kg/ha for 1981-1982. Ahmed (1989) recorded that the potential productivity of the reservoir was about 114 kg/ha and the maximum sustainable yield of fish for the whole reservoir was estimated to be 7,364 tons/year. He concluded that the stock will be depleted if fishing pressure continued to increase. There was reduction of species diversity and average size in northern side of the Jebel Aulia Dam Reservoir. Everett (1995) estimated the potential production in Jebel Aulia Dam reservoir at about 11000 tons/yr. Bellman (1998) highlighted over fishing problem in the northern part of the reservoir from Kosti northward. The Fisheries Department of Khartoum state (2003) estimated the total annual fish yield of Khartoum State to be 10,000 ton/yr. The northern regions of Jebel Aulia Dam Reservoir contributed a half of this annual yield. Abdel Rahman (2003) estimated the total annual yield in Jebel Aulia Dam to be 115,732 kg and the maximum sustainable yield 90,706 kg. According to Ministry of Animals Resources and Fisheries of the Sudan (2006) the potential storage of fishes of Jebel Aulia Dam was around 15,000 ton/yr while the actual exploitation of the stock was 8,000 ton/yr. The aim of this study is to make quantitative predictions of the productivity, carrying capacity, degree and draw backs of exploitation as well as the relations of fish populations to environmental changes.

2. Materials and Methods

The study started in November 2007 and was terminated in October 2008, and sampling took place three times every month. The samples were randomly selected from commercial catch to cover night and day catches. Experimental fishing was performed using multi-filaments nets twine No. 6, 50 m length, 1.5 m depth and 4 cm mesh size, and twine No 6, 50 m length, 1.5 m depth and 6 cm mesh size. Characids collected were identified up to the species level following: Boluenger (1907), Sandon (1950), Abu

Giederi (1984) and Bailey (1994). The 1931 specimens were collected from Jebel Aulia and 557 specimens from Kosti. Catch composition was analyzed by number and weight expressed as percentages of all families in the same catch. Total length and standard length of individual fish were measured to nearest mm using measuring board. The body weight was measured to nearest gram using digital weighting balance version FRUIT 2000B. Morpho Edaphic Index (MEI) in kg/ha/year was estimated according to Henderson and Welcome (1974), and the biomass was estimated using swept area method of Pauly and Murphy (1982). The catch ability potential was estimated by the empirical formula of Pauly (1980), and the rate of exploitation was estimated by the model of Beverton and Holt Modal (1966).

3. Results and Discussion

There were full time, part time and occasional fishermen practicing fishing in Jebel Aulia. While at Kosti only full time fishermen are practicing fishing activities. This indicates over exploitation of characid fishes at Jebel Aulia site.

3.1. Fish Biomass

The fish biomass assessment determination in the two sites of Jebel Aulia Reservoir was calculated by swept area method. In Jebel Aulia site, the fish biomass of family Characidae was 377.02 kg/km 2, while in Kosti site was 499.71 kg/km 2 (Table 1).

Table1 . Characids fish biomass at Jebel Aulia Reservoir in the two sites of the studies during 2007/2008

Parameter C/F Time Area survey Velocity of the X1 X2 study site (h) (km²) mesh (km/h) Jebel Aulia site 0.578 11.35 2.456 0.22 0.51 0.015 Kosti site 0.347 7.19 1.131 0.16 0.51 0.015

3.2. Stock Assessment of Characid

The potential of characid fish production in Jebel Aulia Dam Reservoir in the flooding season in summer 2008 is 90.164 kg/ha/yr (Table 2) and at Kosti site it was high production in winter 113.023 kg/ha/yr. The average production in Jebel Aulia Dam Reservoir was 77.213 kg/ha/yr, and it was 94.263 kg/ha/yr at Kosti site (Table 2).

Table 2 . Potential of production of characids fish in Jebel Aulia Dam Reservoir during 2007/2008 at Jebel Aulia and Kosti sites Seasons Jebel Aulia site Kosti site

Conductivity Fish Conductivity Fish (kg/ha/yr) (µmho/cm) (µmho/cm) (kg/ha/yr) Winter (from November 231.75 75.738 243 113.023 2007 to February 2008) Summer (from March to 275 90.164 199 92.558 June 2008) Autumn (from July to 200.5 65.738 166 77.209 October 2008)

3.3. Catch per Unit Effort (CPUE)

This is estimated using the catch per unit effort (CPUE) from the experimental fishing. The catch per unit effort (CPUE) for family Characidae was estimated by empirical formula:

In Jebel Aulia site, CPUF = 0. 578 ×1000 = 20.7 kg / km 2 2.456 × 11.35 In Kosti site, CPUF = 0.347 × 1000 = 42.6 kg / km 2 1.131 × 7.19

The above result indicates that the yield (as CPUF) at Kosti area is almost two times that of Jebel Aulia fished by the same gear and for the same fishing duration (Effort).

3.4. Exploitation Ratio of the Characid

Exploitation ratio of family Characidae in Jebel Aulia site was given in Tables 3 and 4. The lowest total mortality (Z) was 0.34/yr for H. lineatus and H. brevis, while the highest value of Z was 0.53/yr for Alestes baremoze . In Kosti, the lowest value of Z was 0.256/yr for B. nurse , whereas the highest one was 0.957/yr for H.lineatus (Tables 5 and 6).

Table 3. Natural mortality (M) and total mortality (Z) of characids fish in Jebel Aulia during 2007/2008 Characidae sp TL (cm) (K) Temp. (oC) L mean L¯ M Z Alestes baremoze 26.3 0.0776 25.9 18.98 5.1 0.1514 0.53/yr Alestes dentex 29.2 0.0499 25.9 17.34 5.5 0.2438 0.50/yr Alestes nurse 19.1 0.1374 25.9 11.89 4.8 0.1373 0.140/yr Hydrocynus forskalii 46.2 0.0306 25.9 22.69 8.6 0.1558 0.519/yr Hydrocynus lineatus 40.8 0.0236 25.9 21.83 8.7 0.1359 0.34/yr Hydrocynus brevis 52.1 0.0209 25.9 24.31 7.0 0.1175 0.336/yr

Table 4 . Determination of exploitation ratio in Jebel Aulia during 2007/2008 Characidae sp Alestes Alestes Alestes Hydrocynus Hydrocynus Hydrocynus baremoze dentex nurse forskalii lineatus brevis Total mortality (z) 0. 53/year 0.50/year 0.140/year 0.519/year 0.34/year 0.336/year Natural mortality (M) 0.151 0.244 0.137 0.15584 0.136 0.118 Fishing mortality (F) 0. 379 0.26 0.126 0.358 0.204 0.219 Exploitation ratio (ER) 0.72 0.52 0.90 0.70 0.60 0.64

3.5. Discussion

Exploitation ratio (ER) of family Characidae species in Jebel Aulia site is above the recommended level (0.5), specially for the genus Alestes which ranged between 0.52 – 0.90. That of genus Hydrocynus was between 0.58 and 0.68. In Kosti area exploitation ratio was optimum or below to recommended level. This indicates the stress or overfishing in Jebel Aulia sites. This result is in agreement with Ahmed (1985). The study conducted by Hamaza (1981) stated that overfishing is the one of the major problems in the White Nile because continuous fishing being carried out during most of the year. The study conducted by Ahmed (1985) in the vicinity of dam (up to 10 km) indicated that no direct overfishing can be proved (the exploitation reached the maximum allowable level). Exploitation ratio of the indicated species was higher, and there is decrease in species diversity. Further studies over time are needed to detect the rate of fishing to total mortality for the viable fish species of the White Nile. Kawai (1994) affirmed a continuous decline in yield of fish genera in the northern part of Jebel Aulia Reservoir. Assessment of reservoir fisheries in the present study potential yield at Jebel Aulia was estimated at 377.02 kg/km 2 year for family Characidae. It was estimated as

499.71 kg/km 2 at Kosti. Fisheries Department of Khartoum state (2003) estimated that over 70% of the catch came from the area between Jebel Aulia Dam and Kosti.

Table 5. Natural mortality (M) and total mortality (Z) of characids fish in Kosti during 2007/2008 Characidae sp TL (cm) (K) Temp. (oC) L mean L¯ M Z Alestes baremoze 38.6 0.8029 26.3 19.03 14.6 0.151 0.258/yr Alestes dentex 33.2 0.0840 26.3 13.88 8.9 0.150 0.326/yr Alestes nurse 20.2 0.223 26.3 12.99 6.7 0.160 0.256/yr Hydrocynus forskalii 71.3 0.1155 26.3 24.65 14 .8 0.321 0.547/yr Hydrocynus lineatus 51.9 0.4784 26.3 24.50 10.8 0.525 0.957yr Hydrocynus brevis 32.8 0.9179 26.3 25.04 16.5 0.354 0.834/yr

Table 6 . Determination of exploitation ratio in Kosti during 2007/2008 Characidae sp Alestes Alestes Alestes Hydrocynus Hydrocynus Hydrocynus baremoze dentex nurse forskalii lineatus brevis Total mortality (z) 0.258/yr 0.326/yr 0.256/yr 0.547/yr 0.957/yr 0.834/yr Natural mortality (M) 0.151 0.150 0.161 0.321 0.525 0.354 Fishing mortality (F) 0.107 0.176 0.096 0.226 0.432 0.48 Exploitation ratio (ER) 0.41 0.54 0.37 0.41 0.45.0 0.58

The analysis of the rate of change in the two sites showed that the population of the fish in this reservoir has increased by 10.5% of the initial stock size in the duration of the study period (Ahmed, 1985). The conclusion was that Jebel Aulia Reservoir was still a productive source, if optimally exploited and the exploitation ratio is not allowed to exceed 0.5, and if the broad stock and recruits are protected by legalization and close observation of the fishing activity. Extrapolating from the 10% increase recorded for the duration of year of the study indicated that the stock size of the fish population in the reservoir could be doubled in about 20 years time if these of stocks are properly maintained (Ahmed, 1989). The present situation is that in spite the suggested over fishing of most parts of the reservoir there were a few fish species whose populations could withstand further exploitation. The most important species in the term of economic vialability and the popular preference of Characidae fish presented it at the danger zone and their population needs to be protected and preserved specially at Jebel Aulia site.

From the presented study in Jebel Aulia Dam the average biomass of family Characidae was 77.213 kg / ha/yr, while in the Kosti area the average biomass was about 94.263 kg /ha/yr. Henderson (1975) used different method (morpho–edaphic index) and reported that fish potential biomass was 100.0 kg/ha. Ahmed (1985) reported that the fish biomass was 114.0 kg/ha in the northern part of the reservoir. Katespaky (1986) calculated an annual yield of 55 kg/ha for 1981-1982 based on the method of Henderson (1975) and Welcomme (1974). Ahmed (1985) showed some stability of the fish biomass over the reservoir, and due to similarity of the method at low value of 55 kg/ha was reported by Katespaky for the year 1981-1982. This may be due to the different method used for the determination of the fish biomass or may be due to other ecological, environmental factor not encountered in this study. Bashier (2007) reported that the biomass of the area under investigation decreased from south to north in the study area. The fish biomass account in Kosti at mid-stream was 122.65 kg/ha and Goli at the north part was 88.44 kg/ha. This confined the result of the present study where the biomass of the fish in Jebel Aulia was 77.213 kg/ha and 94.263 kg/ha for Kosti sites.

4. Conclusions

(1) It is apparent that a serious attention needed to be given to revise fish stock assessment. (2) Loss in species diversity and reduction of family Characidae abundance is noticed in the study area. Beside, the majority of the catch in the two sites was composed of under sized fishes. (3) Reduction in fish production came more likely as the result of the use of illegal gears. Gill nets are highly selective and their selectivity may passively affect the fish stock through: (a) decrease in yield due to intensive fishing, (b) direction of catching effort towards specific species, and (c) over-fishing due to long-term practice.

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