ALCOM Field Document No. 29

	Utilization of small water bodies, Botswana: Report of activities towards fisheries exploitation, 1992–1993
	CONTENTS

By U.P. Nermark
Aquaculturist
(Associate Professional Officer)
ALCOM

and T.G. Mmopelwa

Funding Agencies:

SWEDISH INTERNATIONAL DEVELOPMENT AUTHORITY
BELGIAN ADMINISTRATION FOR DEVELOPMENT CO-OPERATION

Executing Agency:

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Harare, Zimbabwe, December 1994

PREFACE

This document describes pilot activities -- testing and demonstration -- carried out during 1992–93 to tap the fisheries of selected small water bodies (reservoirs) in Botswana.

In 1992, test fishing was done at four reservoirs including Semarule dam where it had been already initiated earlier. Two fishing gears -- the Drottningholm nets and monomesh multifilament nets -- were tried out and compared. The results are described in this paper.

A reservoir inventory was prepared on the basis of both available information and field visits. These results will be presented in a separate field document.

The paper also discusses choices concerning various fisheries management strategies for the reservoirs. Management suggestions are made about some of the reservoirs.

These activities were carried out by the Fisheries Section, Ministry of Agriculture, Botswana, with assistance from ALCOM, which provided the services of an aquaculturist (Associate Professional Officer). The activities constituted the third phase of ALCOM's assistace to Botswana to utilize its small water body fisheries. During the first phase which started in 1989, a socio-economic study was carried out on fish-eating habits and fishing activities. (See ALCOM Field Document GCP/INT/436/SWE.12) During the second phase, the species composition in selected reservoirs, their relative abundance, and water quality were studied.

ALCOM is a regional aquaculture and fisheries programme of the FAO (Food and Agriculture Organization of the United Nations). Based in Harare, Zimbabwe, it covers all the member-countries of SADC (Southern African Development Community) -- Angola, Botswana, Lesotho, Malawi, Mozambique, Namibia, Swaziland, Tanzania, Zambia, Zimbabwe.

The aim of ALCOM is to assist member-countries improve the living standards of rural populations through the practice of aquaculture. Toward this end, pilot activities are conducted in member-countries to demonstrate new techniques, technologies or methodologies. Successes achieved, ideas derived, lessons learnt, are applied on a wider scale by member--governments.

ALCOM is funded by Sweden and Belgium. Its preparatory phase began in 1986, and its first implementation phase in 1990.

ALCOM Address:

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CONTENTS

SUMMARY

1.   INTRODUCTION

2   ASSESSING THE POTENTIAL FOR FISH PRODUCTION

2.1   Botswana people like fish
2.2   Compilation of inventory over reservoirs in eastern and southeastern Botswana
2.3   Selection of reservoirs
2.4   Biophysical assessment

2.4.1   The Drottningholm test-fishing method
2.4.2   Species composition
2.4.3   Catch per unit effort (CPUE)
2.4.4   Water parameters
2.4.5   Comparison of multimesh test-nets and the monomesh nets

2.5   Socioeconomic assessment
2.6   Assessment conclusion

3   ACTIVITIES TOWARDS FISHERIES EXPLOITATION AND RESULTS

3.1   Fisheries intervention

3.1.1   Reservoirs in communal areas
3.1.2   Reservoirs under Water Utilities Corporation, WUC
3.1.3   Fishermen training course
3.1.4   Workshop on small reservoir fisheries for Fisheries Section staff
3.1.5   Catch statistics

3.2   Trials of gears for fishery exploitation

3.2.1   Multifilament gill nets
3.2.2   Seine net
3.2.3   Trap

3.3   Market study

4   CONCLUSIONS AND RECOMMENDATIONS

4.1   Socioeconomic aspects
4.2   Legislative aspects

4.2.1   Ownership of reservoirs in communal areas
4.2.2   Reservoirs under WUC

4.3   Biophysical aspects

4.3.1   Inventory of reservoirs
4.3.2   Future stock assessment methods
4.3.3   Estimating the yield from reservoirs
4.3.4   Stocking and choice of species

4.4   Choice of management strategy

5.   REFERENCES

APPENDICES

1.   The Drottningholm Test Fishing Method
2.   Management suggestions for some selected reservoirs

TABLES

1.   Characteristics of the 11 selected reservoirs at full water level
2.   Species found in reservoirs test-fished
3.   Catch per unit effort (CPUE) in g/net (non-normalized) from one test-fishing exercise in each reservoir, March 92 – May 92
4.   Water quality parameter in the fished reservoirs 03/92–05/92
5.   Results from fishing with multifilament nylon gill nets, Semarule reservoir, December 1991
6.   Results from fishing with multifilament nylon gill nets, Semarule reservoirs, May 1992
7.   Results from fishing with multifilment nylon gill nets, Bokaa reservoir, April 1992
8.   Results from fishing with multifilament nylon gill nets, Gaborone reservoir, April 1992
9.   Catch in cylindrical wire mesh trap in Gaborone reservoir (15h00 effective fishing)

FIGURES

1.   CPUE for total catch (+/- STD) from test-fishing in the different reservoirs October 90 – October 91

2.   CPUE for total catch (+/- STD) from test-fishing during a year cycle in Semarule reservoir, October 90 – October 91

3a.   Length frequency for O. andersonii (as % of sample) in Mmakgodumo, February 91. (Including 6.25 and 8mm mesh panels)

3b.   Length frequency for O.andersonii (as % of sample) in Mmakgodumo, February 91 (Including 6.25 and 8mm mesh panels, but excluding size classes below 57mm)

4.   Length/weight correlation for O.andersonii in Mmakgodumo, February 91

5.   Length frequency for O.andersonii (as % of sample) in Semarule, October 90 – October 91

6.   Length/weight correlation for O.andersonii in Semarule

7.   Temperature in Semarule, October 90 – October 91

8.   pH and transparency in Semarule, October 90 – October 91

9.   CPUE for total catch (+/- STD) from test-fishing in the different reservoirs March 92 – May 92

SUMMARY

ALCOM has been assisting the Fisheries Section, Ministry of Agriculture, Botswana in implementing the project “Development of small reservoir fisheries”.

During phase one, a socio-economic survey around seven smaller reservoirs showed that there is sparse hook and line fishing on those reservoirs. The survey repudiated earlier assumptions that people in eastern Botswana do not eat fish and suggested that availability and knowledge concerning how to cook fish are the main constraints preventing people from eating more fish. The survey also concluded that fishing is a part-time activity.

These findings led to the second phase with a biophysical study of eight selected reservoirs through test fishing using the Drottningholm method. A total of 15 different species were found; the CPUE was calculated both by species and by total catch for each reservoir. The catch was dominated in mass by Oreochromis andersonii in four reservoirs, by Clarias gariepinus in three and by small Barbus spp in one reservoir.

During the second phase, Semarule dam (37 ha when full) was chosen as a reference for a one-year test-fishing cycle. Five different species were found but catches were usually dominated in mass by O. andersonii. Seasonal changes could be registered. During the period October – December 1990 and September – October 1991 the catch was dominated by the small pelagic Barbus paludinosus.

These two phases brought home the fact that fish are there but the stock is unexploited because of the lack of fishing knowledge of the local population who would like more fish if it was possible. ALCOM and the Fisheries Department therefore started a third phase in 1992 which focused more on exploitation of Small Water Bodies than on assessment.

Through collaboration with the Water Development Section (WDS) in the Ministry of Agriculture (MoA), fisheries has now been included in the water development policy as an activity in multipurpose dams. The policy has been approved by the MoA Policy Committee. But the project faced problems in getting starting with the exploitation of reservoirs in communal areas. The problems were (i) legislation; it was not possible to get a clarification on who had the legal right over the use of reservoirs and (ii) the drought in Botswana during 1992, when four of the first test-fished reservoirs dried out and little water remained in the rest.

Because of these constraints, work began with the perennial bigger reservoirs under the Water Utilities Corporation (WUC) which has a legal framework for utilizing these waters. After discussions with WUC's Dam Amenity Committee, an increase of 4 up to 9 fishing licences were granted. Each license represents an average of three fishermen and the use of 15 gillnets (25 m long/net mounted) per day all year. Meetings were held on a regular basis with WUC where the fisheries agreements for the different reservoirs were amended.

A training course was held at Gaborone reservoir for fishermen representing three licenses. Catch recording forms were edited and introduced to the licensees. Collection of monthly results was initiated. Spreadsheets for recording monthly and yearly statistics were created for the Fisheries Department.

A workshop on small reservoir fisheries and management was held in Maun (December 1992). Results from ALCOM activities and a practical test-fishing exercise using the Drottningholm method were presented.

A small marketing study in 1992 showed that big-sized bream was accepted by both supermarkets and restaurants in Gaborone and Molepolole. They said they needed a reliable and regular supply of properly handled fish.

During 1992 three additional reservoirs were test-fished, and two species, not previously recorded from test-fishing, were caught. One test-fishing exercise was also repeated in the reference reservoir, Semarule dam. A comparison was made between the Drottningholm test-nets and monomesh multifilament nets. The results are described in this paper.

An inventory was prepared based on available information gathered from the WDS and WUC as well as from field visits. More than 300 small reservoirs ranging in size from 0.2 to 130 ha have been built in rural areas of southeastern and eastern Botswana for livestock use. Three bigger reservoirs, 600 – 1900 ha, have also been constructed to supply drinking water to the main urban centres. The total estimated surface is 1390 ha for the 314 listed smaller reservoirs plus 4255 ha under WUC. WDS has indicated that perhaps as many as 50% of the smaller reservoirs (under 10ha) do not hold water any longer because of siltation and old age.

This paper also discusses the choice of different management strategies and makes suggestions for some selected reservoirs.