by
C.J. Vanderpuye
University of Ghana
Legon, Ghana
| Summary |
| The Volta lake is one of the largest man-made lake in the World. Annual fish catch is around 40 000 t per year. Present management trend aims at obtaining a safe biological yield (SBY). The Sub-Committee for Fisheries and Hydrobiology under the Chairmanship of the Chief Fisheries Officer provides a forum for the discussion of scientific and technical findings concerning the lake. Major problems in planning fisheries development concern the estimation of the stocks, fishery catch statistics and fishery regulations. Lack of funds and local experts impede good management. |
1. INTRODUCTION
In terms of surface area, Volta lake is the largest man-made lake in the world (Bernacsek, 1984). It has a surface area of 8 700 km2; a maximum depth of 75 m; an average depth of 18.8 m; a shoreline length of 5 200 km and a shore development factor of 16.0
The lake has been created primarily for hydroelectric power generation. Comparison of revenues from commercial fish catch and power generation for the years 1977 and 1978, however, seems to suggest that revenue from fish catch may be several fold that from power sale (Vanderpuye, 1985). From 1970 to 1977, the total fish catch from the lake fluctuated around 40 000 tonnes. (The annual catch from the lake usually accounts for about 20% of the total marine and freshwater catch). Though this is considered substantial, it is contended that with refinement in management techniques much more can be realized.
2. THE FISHERY
Owing to the presence of flooded trees and brush in the lake basin, the main finding gear employed in the fishery has been the static type. Coppola and Agadzi (1977) estimated the following statistics for the year 1977: average of 61 000 units of gillnets 370 cast nets, 10 500 lines and 4 000 traps were used per day; there were 1 500 fishing villages scattered around the lake; total number of fishing canoes was 13 800 and full-time fishermen, 20–600. Bazigos (1974) described such a fishing industry as “diffused, disordered and in the first stage of evolution”. This is characteristic of many of the inland fisheries of Africa, especially, the reservoir fisheries.
3. MANAGEMENT
3.1 Objective
This has been the attempt to realize The Maximum Sustainable Yield (MSY). Needless to say, owing to the magnitude of the lake and difficulties attendant to estimation of the commercial catch and fish population size, this objective has proved idealistic. Consequently, present trend in management has been towards the realization of Safe Biological Yield (SBY). (These terms have been used as defined by FAO (1979)).
3.2 Structural Organization
Since its creation in 1946, the Fisheries Department has been the sole agency which advises the Government on matters relating to general conservation of both freshwater and marine fish stocks. In this role, it formulates for the Government, regulatory measures which are finally fashioned into Legislative Instruments.
In 1968, however, when the multi--agency Volta Lake Research and Development Project was formed, a structural organization peculiar to Volta Lake was set up to advise the Chief Fisheries Officer in the rational harvest of the fish resources of the mammoth reservoir. The organisational set-up is outlined in Fig. 1. It was modelled on the present concept of integrated multi-disciplinary approach to solution of problems pertaining to perturbations in the ecosystem.
There is a Project Manager who oversees the whole Project. His duties include coordination of activities of the various sub-committees and units of the Project, determination of priorities, and minimization of duplications in the function of the various units.
Unfortunate to relate, due to financial constraints (following expiry of UNDP assistance in 1977), this set-up is considerably crumbled and it is due to be dismantled in March next year (1986). Thereafter, it is being proposed that the Volta Basin Research Project of the University of Ghana and the Institute of Aquatic Biology take over the research aspect while the Fisheries Department takes over the development programmes and fish-catch statistics. The Volta River Authority will continue to be responsible for the public health aspect.
The major objectives of the various units in this organization, are presented in Vanderpuye (1984). While there is a considerable interaction between the sub-committees and the units (web-type of relationship), discussion in this paper will concern itself principally with those units under the sub-committee for Fisheries and Hydrobiology whose activities relate directly to the theme of this Symposium.
The Chief Fisheries Officer is the Chairman of the Sub-committee for Fisheries and Hydrobiology. Other members include: the Project Manager, the Director of the Institute of Aquatic Biology, and the Chairman of the Volta Basin Research Project of the University of Ghana.
The Committee provides a forum for thorough discussion of scientific research findings. Implementable resuls are passed on to the Development Unit and thereafter to the Extension Unit.
While the Extension Unit was originally planned to part of the Poject, in practice, it is made up of Fisheries Department staff who report directly to the Chief Fisheries Officer. The Chief Fisheries Officer is the only person who advises the Government on conservation of the stocks. And since this function and that of extension mesh, this arrangement has been found to be convenient.
There is always feed back from the Extension Officers through the Chief Fisheries Officer to the Sub-committee. This results in the necessary adjustments being made in the implementation of the programmes. In this respect, the role played by the Socio-Economic unit needs mentioning. This unit usually carries out socio-economic surveys to assess the impact on the industry of the introduction of a new technology or method and its probable degree of acceptability.
4. MAJOR PROBLEMS ENCOUNTERED DURING PLANNING AND IMPLEMENTATION
4.1 Estimation of the Stock and Commercial Catch
Scientific planning should be based principally, on knowledge of (1) the size of stocks, and (2) the magnitude of the input and the total catch by the commercial fishery.
4.1.1 size of the stocks
The problems attendant to the assessment of the stocks in the Volta are common to all African reservoirs. For some time now these have engaged the attention of Stock Assessment wing of CIFA. Major effort has been in the area of finding quicker methods of assessing the magnitude of the stocks. The development and refinement of the Morpho-Edaphic Index (MEI) (i.e. Total Dissolved Solids/Mean Depth) for African inland waters seems to be the major achievement in this endeavour. Quite recently, Bernacsek (1984) reported that an MEI specific for African reservoirs has been developed. This means that yield from African reservoirs can now be predicted with relatively smaller associated error than has hitherto been possible.
4.1.2 The commercial catch statistics
These have been the responsibility of the Catch Assessment Unit. The Unit works closely with the Stock Assessment Unit. Jointly, the programmes of the two Units aim at obtaining the closest possible assessment of the abundance and distribution of the important commercial fish species so that the maximum possible exploitation may be planned and future catches predicted.
The input into the fishery as well as the total catch are estimated from the results of probability surveys. Parameters are estimated with associated error of 5%. A methodology (based on multi-stratified sampling technique) first developed for the Volta has been extended to the other large African reservoirs (i.e., Kainji, Kariba, Nasser, Kossou) and Lake Tanganyika (Bazigos, 1974).
Major problems encountered in our attempt to make reliable estimates include: (1) inability to complete surveys owing to logistic problems and (2) lack of effective supervision of field staff.
Following these problems, various mathematical models have been used to extrapolate and intrapolate scanty field data to give estimates (Coppola and Agadzi, 1976 and 1977).
4.2 Regulatory Measures
Formulation of regulatory measures based on scientific data for reservoir of this magnitude is a formidable task. Aside of size, are the usual problems attendant to the determination of rational harvest of individual species in a multispecies fishery (FAO, 1978).
Our initial approach to conservation when the abundance of the lake fish stocks was high was to allow the fishery to expand (a slow process) while we monitored biological indices of overfishing. A fishing pressure index developed by Vanderpuye (1972) helped in determining which fish species were being over-harvested and which were being under-harvested. Later, a minimum mesh size (100 mm) was determined based on the average size at first maturity of Sarotherodon galilaeus, the species with the highest fishing pressure index. Since then, the species composition has continued to change thus rendering meaningless, the 100-mm mesh size restriction which is still in operation. We recognize the need to review the mesh size periodically. Unfortunately, however, we no longer have the resources to do it.
To ensure that under-size meshes do not get to the fishery, we have banned the importation of such meshes. Notwithstanding this ban, some small meshes still filter to the lake area from neighbouring countries.
A singular unforeseen development which has been the source of considerable worry to the Fisheries Development, in recent times, has been the adaptation of the static gillnet into a kind of purse-seine net. (It was thought that the standing trees would continue to constitute built-in check against the use of moving gear for some time). This goes by the local name: “winch net”. The adaptation is accomplished by suspending wroughtiron rings (3–5 m in diameter) from the lead-line with lengths of cord (about 1–2 m). A drawing cord which passes through the rings ensures that the net is transformed into a purse seine.
The net is operated by 6–8 fishermen who set the net in form of a semicircle. The ends of the net and the drawing cords are drawn (the latter faster than the former) until the gillnet becomes a purse. This operation has been possible following the gradual decay of the trees in many areas of the basin.
From conservation point of view, the main objection to the use of the net is the small meshes (sometimes as small as 25 mm) used in its construction. Although there are a large number of small-size adult fish (especially, the very abundant clupeids) in the lake, the Fisheries Department contends that the net catches the juveniles of many of the commercial species as well. There is presently inadequate data to back this claim. In the meantime controversy ranges between the Department and the operators of the new net who think that they should rather be complimented for evolving an effective net for catching the small-size fishes.
4.3 Enforcement of Legislation
This has been largely ineffective due to the sheer size of the lake. Staffs of the Fisheries Department and the police are no match for the 22 000 fishermen operating from diffused landing points scattered all over the lake shore. Consequently, it is only occasionally that a culprit is brought to book. Much more is achieved through radio broadcasts. On several instances, villagers, on their own, have arrested and sent to the police, law-breakers. These include those who use explosives, chemicals and poisonous herbs for fishing.
5. DISCUSSION
The Volta Lake Research Project which assists the Chief Fisheries Officer in the management of the Lake was conceived on the current concept of multidisciplinary approach to solutions of problems relating to perturbations in the ecosystem. It is made of 3 major sub-committees of which the Subcommittee for Fisheries and Hydrobiology is one. Sub-division of this Sub-committee into smaller specialized units ensures that problems relating to fisheries are tackled with efficiency by experts specialized in these areas. A Fisheries Manager (whose post has never been filled) would normally, coordinate activities, synthesize research findings, and provide guidelines for overall development of the lake fisheries. A Development Planning Officer, who was later appointed, to some extent performed the functions of this Officer.
Though this organization seems impeccable on paper, on the ground there are a few problems which militate against efficiency. The major of these are: (1) insufficient funds to run such an organization; and (2) insufficient local experts to man the various specialized units. These problems started showing up following the expiry of the UNDP assistance.
Sound management should be based on scientific information. When the Project was fully manned, adequate information was available upon which rational exploitation of the fishery resources was planned. Developmental projects were also based on such information.
Enforcement of regulations for a lake of this magnitude has proved a formidable task; consequently, only a few regulations exist on the statute books. Mesh-size restriction has been enforced by banning the importation of meshes smaller than 100 mm. This has proved the best management measure in our circumstances. There is however, the need to monitor and adjust the minimum mesh size with time.
The evolvement of the ‘winch net’ is an unforeseen development which, according to the Fisheries Department, is doing considerable harm to the stocks; the net is consequently banned from the lake fishery. Since research results have shown that offshore stocks are made up of preponderantly smallsize clupeids (Vanderpuye, 1973), it will be necessary to determine the effect of the net on the stocks as soon as possible. Failure to do this might result in wastage of fish biomass through natural mortality.
6. REFERENCES
Bazigos, G.P., 1974 The design of fisheries statistical surveys - inland waters. FAO Fish.Tech.Pap., (133):122 p. Issued also in French and Spanish
Bernacsek, G.M., 1984 Guidelines for dam design and operation to optimize fish production in impounded river basins (based on a review of ecological effects of large dams in Africa). CIFA Tech.Pap. (11):98 p.
Coppola, S.R. and K. Agadzi, 1976 Frame surveys at Volta Lake (Ghana). Volta Lake Research and Development Project. Statistical studies. Rome, FAO, FAO/GHA/71/533/St.S/5:148 p.
Coppola, S.R. and K. Agadzi, 1977 Evolution of the fishing industry over time at Volta Lake, 1970–76. Volta Lake Research and Development Project. Statistical studies. Rome, FAO, FAO/GHA/71/533/St. S/6:41 p.
FAO, 1978 Some scientific problems of multispecies fisheries. Report of the Expert Consultation on management of multispecies fisheries. Rome, Italy, 20–23 September 1977. FAO Fish.Tech.Pap., (181):42 p. Issued also in French
FAO, 1979 Interim report of the ACMRR Working Party on the scientific basis of determining management measures. Rome, 6–13 December 1978. FAO Fish.Circ., (718):112 p.
Vanderpuye, C.J., 1972 Fishery resource assessment and monitoring in the development and control of fisheries in Lake Volta. Afr.J.Trop.Hydrobiol.Fish., Spec.Issue 2:115–34
Vanderpuye, C.J., 1973 Population of Clupeids in Volta Lake. Ghana J.Sci., 13(2):179–93
Vanderpuye, C.J., 1984 Volta Lake (Ghana). CIFA Tech. Pap./Doc.Tech.CPCA, (10): 261–319
Vanderpuye, C.J., 1985 Evaluation guidelines for rational planning and management of tropical and subtropical inland fisheries (Africa). A paper written at the request of FAO (mimeo)
