INTRODUCTION OF LAKE TANGANYIKA SARDINES INTO ITEZHI-TEZHI RESERVOIR, ZAMBIA

by

Raphael Mubamba
Department of Fisheries
P.O. Box 350100
Chilanga
Zambia

1. BACKGROUND

Lake Itezhi-tezhi, the second largest man-made water body in Zambia, was created in 1977 when it began filling up following the closure of the Kafue River at Itezhi-tezhi gap. At full capacity the surface area of the lake is 370km² and 90% of the area lies within the Kafue National Park. The deepest point of the lake is 55m and its mean depth is 15.4m.

Since the creation of the lake, a number of studies have been carried out. The Zambia Department of Fisheries began conducting some research work on Lake Itezhi-tezhi in 1979 through gill net surveys catch and effort assessment surveys and fish biology studies. A description of the changes that have taken place in the fish fauna of the lake is contained in Kapasa and Cowx (1991). From 1983 to 1985 the Zambia National Council for Scientific Research carried out the first detailed limnological studies on the lake (Obrdlik, 1985). The growth parameters and breeding biology of two fish species namely Alestes lateralis and Schilbe mystus have been studied by Mudenda (1986). In 1991 an ecological study of the lake was initiated by the Department of Fisheries in collaboration with SAREC of Sweden. On 8 March 1992 an echo-sounding survey of the lake was carried out by the Department of Fisheries.

The activities outlined above have shown that fish production in the lake varies from about 500–1000 tonnes per year and that the standing fish biomass does not probably exceed 3000 tonnes. It has also been found that the lake is oligotrophic and that it has moderate levels of Chl.a (mean = 3.11mg/m³). The lake is also quite rich in zooplankton and is dominated by the copepods, cladocerans and rotifers. The phytoplankton is dominated by the blue-green algae, mainly Microcystis spp. It has also been observed that the deep and open waters of the lake have little or no fish. The conductivity of the lake is about 230 microseimens per centimetre, more than double the value of Lake Kariba.

Because of the findings outlined above, it was decided by the Department of Fisheries together with the provincial authorities in Southern Province, that an alien fish species be introduced into the lake to utilise the empty pelagic zone in order to boost fish production and in the process to increase protein supply and employment opportunities for local people in particular and for the country as a whole (Mubamba, 1990). Because of the success story of the Limnothrissa in Lake Kariba (Bell-Cross and Bell-Cross, 1971; Balon, 1971) it was felt that the sardines could also colonise Lake Itezhi-tezhi without much difficulty. In the case of Itezhi-tezhi it was not necessary to introduce planktonic organisms to serve as a food resource for the sardines because the lake is already quite productive. With the high turn-over rate of the sardines reported elsewhere (Kenmuir, 1990) it is expected that the annual fish production in Lake Itezhi-tezhi would increase from the current levels of 500–1000 tonnes to something like 5000–8000 tonnes (Mubamba, 1992).

The present report is intended to give an account of the first introduction of the sardines (locally known as the Kapenta) into Lake Itezhi-tezhi.

2. METHODS AND RESULTS

The project began in March 1990 by conducting capturing experiments in Lake Kariba and Lake Tanganyika and by carrying out road transportation trials from the two lakes to Chilanga near Lusaka. At Lake Kariba the capturing experiments involved catching the sardines at night using paraffin powered pressure lamps and scoop nets in both the Sinazongwe and Siavonga sectors. At Lake Tanganyika the sardines were caught during the day (early morning and late afternoon) using shallow beach draw nets about 10m long and of mosquito netting material. The studies were conducted both in the Nsumbu and the Mpulungu waters of Lake Tanganyika.

A very high mortality (80–100%) of the sardines caught using scoop nets was experienced and most of the fish (sardine juveniles) died within an hour of being caught. The mortality in draw nets was lower, 50–80% within an hour. The smaller sardines of less than 15mm total length showed a lower mortality than those which were more than 20mm long.

In April 1990, live sardines (20 fish) were successfully transported in a plastic bag by road from Sinazongwe to Chilanga over a distance of about 200km. At Chilanga the fish were reared in a cage for two weeks. On two other occasions, some sardines from Lake Tanganyika were also successfully transported in open 60 litre capacity jerry cans over a distance of about 1,200km between Lake Tanganyika and Chilanga using a lorry. The first batch was caught at Nsumbu (Kasaba Bay, in May 1990) and the second at Mpulungu (Kasakalawe Bay, in November 1991). The 1990 batch (15 fish) was reared in a cage at Chilanga for three weeks while the 1991 batch (20 fish) was released into Village Reservoir (mean depth = 2–3m) also at Chilanga. The stocking was undertaken on 2 December 1991.

The length of the fish released in December 1991 ranged from 10–15mm and six of them were later caught on 4–5 May 1992 by a 12mm monofilament gill net at the size of 60–70mm in length. All the six fish were identified as Limnothrissa miodon. After dissecting two fish, it was observed that one was a female and the other a male. Both of them were in an active gonadal stage or approaching maturity. All the six fish were extremely fat.

2.1 Lake Itezhi-tezhi

2.1.1 The first release

The first release of the sardines into Itezhi-tezhi was conducted on 16 March 1992. The fry were caught at Kasakalawe Bay in the Mpulungu waters of Lake Tanganyika with the assistance of Blignaut Exports Ltd. The majority of the fry of 25mm total mean length were caught in mid-February 1992 and were kept in holding tanks where they were fed on ground sardine powder. Some fry, especially those less than 15mm were caught from 12–15 March 1992 and were also from Kasakalawe Bay.

Before flying to Itezhi-tezhi, the fry which had been kept in the tanks, were packed in one quarter water filled 5 litre polythene bags, at a density of about 70 fry per bag. Each of the bags was then inflated with industrial oxygen before being sealed. The bags were then placed in well insulated carton boxes. Each carton box contained four bags. There were 16 boxes altogether and these were transported from Mpulungu to Fort Rosa airstrip by road. The airstrip is near Nonde along the Mbala-Kasama road, over a distance of about 80km from Mpulungu. From Fort Rosa to Ngoma airstrip, the fish were shipped in a PIPER-SENECA II six sitter aircraft belonging to Blignaut Exports Ltd. The model of the plane is PA 34. The plane departed Fort Rosa at 11.00 hrs and arrived at Ngoma around 14.20 hrs. From Ngoma to Itezhi-tezhi, a distance of 21km, the boxes were transported by road again in an open Land Cruiser van.

Upon arrival, the fish were stocked at Musa Gate in the Southern basin of the lake in a depth ranging from 0.1 to 0.8m. This was done after allowing the water temperature in the bags to be equal to the water temperature of the lake. Then a little amount of Itezhi-tezhi water was slowly added to the bags before releasing the fry. The stocking exercise lasted from 15.00–16.00 hrs and was undertaken on a sandy to muddy beach in the park waters. The environmental conditions at the time of stocking were as follows;

The size of the sardines stocked ranged from 22.0–25.0mm total length. While the rest of the fry were being released, others were kept in a cage to monitor the survival and growth. Soon after being put in the cage it was observed that smaller fry were swimming near the surface and larger ones at the bottom of the cage.

There were about 4,500 fry of sardines which were airlifted and the mortality in transit was estimated to be 90%. This means that there were about 450 fry that were stocked in the first shipment. The fry which were held in the cage (fixed at about 0.8m depth) were still alive by 19 March 1992, three days after stocking.

2.1.2 The second release

The second release of the sardines into the lake was conducted on 20 March 1992. The majority of the fry shipped in the second trip were caught in Musende Bay at the new Samaki Fisheries jetty using a mosquito net. A small proportion of the fry was caught at Kasakalawe Bay.

After having registered an exceptionally high mortality in the first shipment, a few changes were made during the second shipment to increase survival. One of the courses of action taken, was the reduction of the number of boxes from 16 to 13 and then the volume of water in the 5 litre bags was increased from ¼ full to ⅓ full. In this way, the level of turbulence was reduced. In addition, larger temperature fluctuations were also reduced. The number of fry was maintained at about 90 per bag.

During the second shipment the fry were packed in bags at Mpulungu from 04.00–06.00 hrs before being delivered to Fort Rosa by road. The plane departed Fort Rosa at 11.00 hrs and arrived at Ngoma by 14.40 hrs. The fish were then quickly taken to the lake by road and were stocked at Quarry Bay, west of the Department of Fisheries harbour in the northern basin. While the rest of the fry were being released, a few were kept in a cage again for monitoring. The stocking lasted from 16.20–16.45 hrs and the fry were released in a water depth of 0.1–1.0m. The sediment at the stocking site was mainly mud mixed with little sand. The water temperature was 28°C. Weather conditions were choppy, wet and the sky was 100% overcast. The mean total length of the fry released was 18.45mm.

As a result of the changes made in the volume of water in the plastic bags, the mortality rate in transit was greatly reduced from 90% to 25%. The total number of fry shipped in the second trip was about 4,700. Allowing a transit mortality of 25%, there were about 3,500 live fry stocked in the second shipment.

3. CONCLUSION

During the month of March 1992, Lake Itezhi-tezhi was stocked with 3,950 fry of the sardines from the Mpulungu waters of Lake Tanganyika. Going by its size, Itezhi-tezhi may require about 20,000 fry to be fully stocked. Assuming the survival rate of 75% of the sardine fry, there will be need to make about 5 air shipments between Mpulungu and Itezhi-tezhi.

4. ACKNOWLEDGEMENT

The author wishes to thank the Government of Zambia through the Director of Fisheries, for funding this project. Other gratitudes go to Blignaut Exports Ltd. (Zambia) for cooperation in air shipments. Members of staff of the Department of Fisheries at Chilanga, Mpulungu and Itezhi-tezhi assisted greatly in the exercise. Many thanks are also extended to them.

5. REFERENCES

Balon, E.K., 1971. First catches of Lake Tanganyika Clupeids (Kapenta-Limnothrissa miodon) in Lake Kariba. Fish. Res. Zambia 5: 175–185.

Bell-cross, G. and B. Bell-cross, 1971. Introduction of Limnothrissa miodon and Limnocaridina tanganicae from Lake Tanganyika into Lake Kariba. Fish. Res. Bull. Zambia 5: 207–214.

Kapasa C.K. and I.G. Cowx, 1991. Post-impoundment changes in the fish fauna of Lake Itezhi-tezhi, Zambia. Journal of Fish. Biol. 39: 783–793.

Kenmuir, D., 1990. Sardines in Zambia. Fish Farming International, Vol 17, No. 7: 16–17.

Mubamba, R., 1990. Project Brief: Introduction of Kapenta (Limnothrissa miodon) into Lake Itezhi-tezhi. Dept. of Fisheries, Chilanga, Zambia. Unpubl. Report. 13p.

Mubamba, R., 1992. The first introduction of Kapenta into Lake Itezhi-tezhi.Dept. of Fisheries, Chilanga, Zambia. Unpubl. Report. 4p.

Mudenda, H.M.G., 1986. Preliminary investigations of some aspects of the biology and population dynamics of Alestes lateralis and Schilbe mystus. Dept. of Fisheries, Chilanga, Zambia. Unpubl. Report. 48p.

Obrdlik, P., 1985. Limnological research on Itezhi-tezhi Lake: Water Resources Research Unit. Environmental Research Laboratory Technical Report No. NCSR/TR/57, WRRU/28. National Council for Scientific Research, Lusaka, 47p.