While fish has never been a part of their traditional diet, people in eastern and southern Botswana living around reservoirs do eat fish -- mainly sun-dried, fried or tinned. Many households do not know how to cook fresh fish but they do like fish.
Few people have shown any interest in fishing: they have neither the knowledge nor the time. Other activities such as arable farming take up most of the time during the farming season; and most of them do not live close to dams.
It is recommended that the work of ALCOM and the Fisheries Department in making people aware of the fish resource in reservoirs should continue. This food resource could act as an addition to the diet. More demonstrations on how to catch fish and how to cook it are necessary; this will be the only way to encourage fishing and fish-eating. But the price of fish has to be lower than that of meat; and it must be competitive with the price of tinned fish.
It is also important that before any licence for fishing is approved, fishermen get practical training on fishery biology, fishing gears, cooking demonstrations, marketing and regulations concerning health and hygiene.
There is still a need to resolve the problem of ownership, mainly for communal reservoirs.
Through collaboration with the Water Development Section (WDS), fisheries should be included in the Water Development Policy of the Ministry of Agriculture.
In papers presented at the workshop on environmental protection laws/acts at Kasane (22–23 April, 1991) and at the annual staff conference (23–27 November 1992), Mr. T.G. Mmopelwa emphasized the fact that laws regulating the use of fish resources are an important management tool.
It is very important for legislation to be developed, which will enable the Fisheries Section to monitor and regulate fishing activities in reservoirs. At present, ownership and exploitation of reservoirs are not well established.
Dam groups must be revitalized/reactivated because they are not functioning. The constitution for the groups has to be amended. They must be properly registered to avoid future uncertainty about land and water rights.
One paragraph included in the new Agricultural Water Development Policy states that the newer multipurpose reservoirs will be administered by Ministry of Agriculture (MoA) through the local Regional/District Agriculture offices (RAO/DAO). That means that if a user keeps the resource idle, or if he doesn't follow the agreement, the RAO/DAO will be able to cancel the lease and let another individual/group take over the lease. Hopefully the same regulatory powers should also be exercised with the older reservoirs if they are mis-managed or not managed at all.
For these reservoirs, legislation concerning reservoir use exists. On these dams, it is important to spot and discourage illegal fishing activities. The problem though, is that if illegal activities are reported, it is very difficult to prosecute as the legal text is not specific enough.
The information on available surface area and storage capacity is inaccurate for the majority of reservoirs, mainly due to the effects of siltation. Reliable information is available at present only for reservoirs constructed during the last few years. Questionnaires about the status of reservoirs that have been sent out to all districts in the eastern and southeastern region, will hopefully indicate which reservoirs could be considered for fisheries activities. It is important to maintain and update the inventory since it will facilitate the planning of reservoir fisheries.
Based on the CPUE from one year's test fishing at Semarule dam using the Drottningholm method (see Figure 2), it is shown that the catchibility of fish is constant during the months of January, February and March. During this period the confidence intervals are also smaller. If we consider that fish populations in the other small water bodies in eastern and southeastern Botswana show the same yearly dynamics, test fishing should preferably be performed during this period. This will provide a useful tool for decisions on fishing curbs during certain times of the year, i.e. during the breeding season.
Test fishing is an essential tool for experts and decision-makers on fisheries management. Continued test fishing is also recommended to monitor changes. Without this, it would be difficult to explain to fishermen why certain restrictions may have to be imposed. It gives us valuable baseline data on species composition and relative abundance, but it has to be followed up with trials using other fishing gear. Therefore, a single test-fishing exercise using the Drottningholm method does not on its own serve as an effective instrument for recommending a piece of fisheries regulation.
The Drottningholm method is rather expensive for most developing countries since the net material has to be imported. One recommendation would be to make test nets of stronger twine. The number of panels could be decreased and the length of panels increased because of the catch of big fish. Ultimately a method should be found that is good both for sampling/monitoring and for recommendations on the type and number of gear adjusted to suit local conditions to be used by the country's fisheries staff. The aim should be to be able to purchase the material for these nets on the local market.
Usually small reservoirs are considered to be highly productive. These waters are generally shallow and fed by nutrients from brief heavy rains. This facilitates plankton and larger plant (macrophyte) growth and the build-up of rich bottom sediments, which are food for many species of fish.
What makes it so difficult to estimate the production of small reservoirs is the fact that they are not a stable environment, they vary so much over the year both in surface and in chemo-physical aspects. After heavy rains the reservoir may lose some of its nutrients as well as some fish if the water spills out of it. This happens sporadically and only for a short period. Initially, turbidity increases and photosynthetic activity drops. During the high water level, some land will be immersed by water; plant material and other nutrients such as animal dung will therefore be dissolved. When turbidity decreases, the primary production will increase. Because of variations in the water level, water temperature in shallow reservoirs changes a lot over the year. During the colder and dryer months, breeding and feeding areas will decrease and during extended drought periods, many shallow reservoirs dry out totally.
In Zimbabwe the Department of National Parks and Wildlife Management has estimated the yield from Lake Chivero on the basis of further management at 250 kg/ha/year. This is a big and very productive reservoir. The yield from smaller reservoirs in Botswana may be good, but lower than Chivero because of poorer soils and lower winter temperature, although if there is a lot of cattle around this would tend to increase the productivity by fertilization.
In reservoirs with few species, it may be possible to increase production by introducing additional species. These species can help to utilize a food source presently not exploited or control the population of another fish species and increase the production/variation of fish for human consumption.
In a country like Botswana, where reservoirs can dry out during extended dry periods, it's essential that the Fisheries Section is given the capacity to restock these waters. Species most in demand in the market could then be chosen for stocking. These would preferably be local species, but in isolated reservoirs it may also be possible to introduce exotic species if there is a market for them.
The local species in the highest demand are the different bream species (O. andersonii, O. mossambicus, O. macrochir, T. rendalli). The African catfish (C. gariepinus) may also be stocked in some reservoirs (i) to feed on the huge number of tadpoles in the dam and (ii) because it is more resistant to drought conditions. This will increase the fish biomass of reservoirs.
Exotic species to be considered could be other bream species, bass (such as Micropterus spp.), and species of carp. The common carp, C. carpio, is already introduced in the region and is caught by fishermen in Gaborone reservoir. Bass was introduced in one reservoir, but was never restocked after the reservoir dried out during the 1980s.
Before any choice of further management, general considerations have to be taken in account, such as:
The training of fishermen to make them more efficient in fishing and better aware of customer requirements as regards hygiene, storage and reliable delivery of fish.
Further market studies need to be done to find a market also for the other species caught: African catfish, butter catfish, carp and Labeo spp.. This is very important as only a part of the catch from reservoirs in the region consists of bream (Bokaa 0–10%, Gaborone 30–60%, Semarule 60–80%).
Length frequency distribution is an important aspect. Fig 5 shows how the length frequency distribution varied for O. andersonii over a full one-year test-fishing cycle in a 37 ha reservoir. From this result, and from results of fishing with multifilament nets (Tables 5–8), it can be clearly seen that reservoirs in Botswana are under-fished - so many big-sized fish are caught.
Collaboration with the Water Utilities Corporation (WUC) has been quite fruitful; it should continue and possibly grow stronger. Even if there aren't enough staff, the Fisheries Section (FS) and the WUC should try to be present at reservoirs more often -- to support the licensees, and to observe fishing and other activities around the reservoirs. It is recommended that the Fisheries Section should actively advise the Corporation on fisheries activities and recommend amendments to fisheries agreements. The licensed gill-net fishermen should be given continued support by fisheries extension staff, and recording of catch should be regularly monitored.
A proposed management decision tree, based on the experiences in Botswana, is illustrated below in Fig 10.
Management suggestions for selected reservoirs are presented in Appendix 2.
