APPENDIX D
PAPERS PRESENTED AT THE SYMPOSIUM (continue)

ANNEX 1.7
Distribution and Relative Abundance of Fish Stocks in Uganda Waters of Lake Victoria

by

G.B. Mbahinzireki
UFFRO, Jinja, Uganda

INTRODUCTION

The last stock assessment survey of the whole Lake was carried out between 1969 and 1971 (Kudhongania and Cordone, 1974). The present report is based on results obtained in 1977 when certain defined areas of Uganda waters were trawled. The original plan was to assess the demersal fish stocks on a quarterly basis. However, this was not possible. The results presented in this report therefore are limited. Despite this fact, they are of special interest to fishery biologists, for instance, some of the species were recorded as rare or missing in the trawl catches yet others were well represented as reported by the previous investigators.

SAMPLING

The Ugandan portion of Lake Victoria was divided into four transects (Figure 1), each of which was sub-divided into 10-m depth intervals. Each depth interval was trawled twice using R.V. IBIS and a 40-mm codend. Each trawl lasted 30 minutes and was conducted during daytime (06.00–19.00 h). A total of 22 fishing hauls were made. Waters less than 4 m deep were not trawled due to the restrictions imposed by the draught of the fishing vessel. Furthermore, some depth ranges did not exist along all the transects and others were even unsuitable for bottom trawling (e.g., rocky and muddy bottoms).

Wherever possible, fish specimens were sorted out into species (excluding haplochromines) and their total weight determined. Rastrineobola argentea (and possibly smaller species of Barbus) was not separated from the bulk of the haplochromines.

OBSERVATIONS AND CONCLUSIONS

The following observations were made from this limited data (Table 1):

1. The haplochromine species complex contributed about 80% (by weight) of the total catch of the demersal fish stock in this part of the lake, followed by Bagrus docmac (7.7%), Synodontis spp. (4.6%), Protopterus aethiopicus (3.7%), Clarias mossambicus (3.3%) and the other species, including a few species of the tilapiine cichlids together constituted less than 1% (Figure 2).

2. Most siluroids (B. docmac, C. mossambicus and species of Synodontis) were represented almost in all water depth zones, especially the latter two species being more abundant in deeper waters. B. docmac was confined to waters less than 60 m. Xenoclarias sp. occurred mainly in deeper waters and Schilbe mystus occupied waters less than 40 m deep.

3. Among the species of tilapiine cichlids, only O. niloticus, O. variabilis and O. esculentus were caught in smaller quantities. Not even a single specimen of the genus was caught in transects I and II (Eastern Section of the Lake Region). T. zillii and O. leucostictus were absent in all trawl catches made.

4. Species of tilapiine cichlids, along with P. aethiopicus and Barbus spp. were too confined in waters of less than 40 m deep.

5. There was a general decline in number of species with lake depth.

6. Other fish species recorded as absent from the trawl catches included: Lates niloticus, Labeo victorianus, Alestes spp., Mormyrus spp. and Mastacembelus frenatus, although these species were reported present in catches made by Kudhongania and Cordone (1974).

7. Sandy bottom generally gave a poor catch, notably dominated by haplo-chromines.

It should, however, be noted that fish species reported as missing from the catches, may not be entirely absent in this Lake region. It is possible some species occurred in areas which were not fished. Such areas included waters less than 4 m deep and the chances of catching rare fish species would be very low. Lack of knowledge of the efficiency of the fishing gear limits the kind of interpretations one can make from such results. More trawl surveys would have been useful in answering some of these questions. The findings, nevertheless, shed some light on the changes which have been taking place since the completion of the first fish stock survey. Great changes in the fisheries of Lake Victoria have taken place as evidenced by reports presented in this Symposium.

REFERENCES

Kudhongania, A.W. and A.J. Cordone, 1974. Bathospatial distribution pattern and biomass estimates of the major demersal fishes in Lake Victoria. Afr. J. Trop. Hydrobiol. Fish., 3(1):15–31

Table 1(i): Bottom trawl catch rates (kg/h) of various fishes in Lake Victoria, Uganda region
(weight by depth intervals)

(a) by fishing transects

Transect 1

Missing fish species: Tilapia, Oreochromis spp., Labeo victorianus, Alestes spp., Mormyrids, Lates niloticus, Mastacembelus frenatus

Table 1(ii)

Transect 2

Missing fish species: Tilapia, Oreochromis, Protopterus aethiopicus, Barbus, Labeo victorianus, Alestes, Mormyrids, Lates niloticus, Schilbe mystus, Mastacembelus frenatus

Table 1(iii)

Transect 3

+ plentiful Rastrineobola argentii

Missing fish species: O. leucostictus, T. zillii, O. niloticus, Labeo victorianus, Alestes spp., Mormyrids, Lates niloticus, Schilbe mystus, Mastacembelus frenatus

Table 1(iv)

Transect 4

* net stuck and some fish escaped
- data not available or quantity unknown

Missing fish species: T. zillii, O. esculentus, Labeo victorianus, Mormyrids, Lates niloticus, Schilbe mystus, Mastacembelus frenatus

Table 1(v)

(b) by the lake region (all transects combined)

- data not available

Missing fish species: Lates niloticus, Alestes spp, Mormyrids, T. zillii, O. leucostictus, Mastacembelus frenatus

TRANSECTS I-IV

Figure 1 Sampled Transects (1–5) of Uganda waters of Lake Victoria

Figure 2 Percentage of total catch of various fishes in Lake Victoria (Uganda sector)

ANNEX 1.8
The Current Status of the Fisheries in Tanzania Waters of Lake Victoria

by

E.F.B. Katunzi
Mwanza Fisheries Research Centre,
Mwanza, Tanzania

GENERAL OBSERVATIONS

There is no proper record of fishing trends as no stock assessment has been made since 1974. There is an urgent need for the authorities to set up an effective rational machinery for proper development and management in the Lake mainly to save the diminishing species. As for Rastrineobola, Lates and Haplochromis there is a need to determine the potential annual yield. Maintenance of an optimal level of exploitation could be based on such regulatory measures as licencing, restriction of gears, fishing seasons and grounds - and a proper biological monitoring of the stocks. A joint venture in development and management of the resources among the riparian states is recommended.

The food situation in Tanzania is worsening each year. It is thus a national priority to aim at food self-sufficiency. Tanzania, having the largest share on Lake Victoria waters, could exploit this priviledge and attain a satisfactory level of fish protein production. About 95% of the fishing is operated by private artisanal fishermen who, due to lack of modern fishing equipment, have been forced to exert fishing pressure on the littoral resources. Lake Victoria in general does not have a long history of mechanized fishing, although the earliest experimental trawling was done by Graham, between 1927 and 1928 with a small beam trawl.

Subsequent trawling followed under the now defunct East African Community. Presently fishing operated by using gillnets, beach seines, traps and on a small scale, longlining. Trawling is limited to a few government-backed institutions, and private wealthy individuals. Trawling is mainly concentrated in the Mwanza gulf where about eight trawlers of varying capacities operate.

The commercially exploited stocks include Haplochromis, Rastrineobola, Lates niloticus, Bagrus docmac, Clarias mossambicus, Protopterus aethopicus, Mormyrus and Synondontis. The migratory species Labeo, Schilbe, Alestes and Barbus are also exploited more seasonally.

Most of the Haplochromis catch finds its way to the fishmeal factory based in Mwanza, but a locally sun dried product is packed and exported abroad. In some areas like Bukoba, they are smoked and used for human consumption, whereas in the Ukerewe Islands, they are eaten fresh. Since it is a very useful resource it is essential to devise a proper technique for their rational exploitation. At the moment there are no records on the stock size, neither are there appropriate future management and development strategies for maintaining or improving the fishery. Casual observations and interview with the local fishermen express negative attitudes toward dependency on fisheries as a means of subsistance. The catches of some species are diminishing drastically although those of Bagrus, Protopterus and Clarias, have remained more or less steady. It is anticipated that with further exploitation of the offshore fish resources, catches may increase.

Lates niloticus is contributing greatly to the urgently required animal protein. For the past few years, the species has been recorded in small quantities from the catches. At present it seems to be dominant. As for the other fish stocks, there is no recent reliable information on the potential yield, but with further exploitation, the catch rate can increase. The high rate of predation by Lates appears to be the cause of depletion of a number of species in the Lake. In the Mwanza gulf for instance, a number of haplochromine species are disappearing from their special habitats. Catch rates in places where the trawling pressure is minimal are also declining. A marketing survey made by the Fisheries Training Institute based at Nyegezi-Mwanza, has revealed that, despite the negative attitude of a few local people, Lates is fetching as good market prices as “tilapias”, Bagrus and Clarias.

The fishery for tilapiine cichlids is among the oldest fisheries in the Lake. The species exploited are now mainly O. niloticus, O. variabilis although O. esculentus, O. leucosticus and T. zillii also occur occasionally. There is an outcry from the public that “tilapias” are missing in the market, but this claim dates from long before the introduction of the Nile perch when the use of beach seines in the breeding grounds seems to have been the major cause for a collapse of these tilapiine cichlids.

The Rastrineobola fishery is a recent one and appears under exploited although the stock size is unknown. The potamodramous species of Labeo, Schilbe, Alestes, Barbus and Synodontis have now virtually disappeared from the catches. Historically these were major fisheries in the Lake but now are occasionally caught with gillnets. It has been established that the tendancy by fishermen of catching the gravid fishes moving upstream for breeding has been the main cause of depletion of these fishes (“recruitment overfishing”).

The overall impression of the fisheries is that there is a progressive decline in output. An integrated approach is urgently required to secure the best advantage for the surrounding population. It has become indispensable to optimise fishing conditions for artisanal fishermen whose attitude toward progressive fishing is declining. This only becomes effective when policy issues of the three riparian states are coordinated centrally. Collaboration in fisheries among the East African countries dates back to 1947. However, this international machinery disappeared with the collapse of the East African Community. A new cooperative mechanism is required through a centralized body which would provide for planning, the overall direction and coordination of technical programmes on management issues. This body should among other things be entrusted with a mandate to plan a concrete action programme for the rational development and management of the lake fisheries.

With the success of these joint activities in such fields as training, survey of resources, the related projects could be organized. Technical support for the fisheries activities of both national and regional fisheries bodies, could be effected in solving problems of mutual interest. To this effect it is recommended that a strong international machinery be set up and given a mandate to effect the proposed development and management of the fisheries.

Statistical information on the fisheries is inadequate and not much can be deduced from it. Similarly the baseline data on the major lake fisheries (species composition, population parameters, fisheries' characteristics, social-economic consequences of the automation in fisheries, limnology and hydrobiology) is not updated. Since the Lake waters do not respect the national boundaries, regional cooperation on such information becomes justifiable.

Most of the fishing operations of Lake Victoria are basically artisanal. It is therefore necessary to seek information on the current state of traditional artisanal fisheries. Management procedures are important in order to lay down the framework for the relevant improvement on their fishing techniques. There ought to be new improved techniques in order to maintain continuous optimal fishing as suggested by the stock assessment experts.

The message to all national delegates is that each in his own capacity should initiate plans leading to joint fisheries activities among the three countries sharing Lake Victoria. It is only through this approach that development and management of the lake fisheries could be effected.

ANNEX 1.9
Preliminary Results of an Evaluation of Fishing Trends in the Kenya Waters of Lake Victoria from 1981 to 1982

by

O.M. Mainga
Kenya Marine and Fisheries
Research Institute, Nairobi, Kenya

INTRODUCTION

In Lake Victoria (Kenya), catch assessment surveys on the artisanal fishery have been conducted under the auspices of the now defunct East African Freshwater Fishery Research Organization (Wetherall, 1974; Wanjala and Marten, 1975; Marten, 1979). In 1980 the newly formed Kenya Marine and Fisheries Research Institute initiated a full time catch and gear monitoring programme scheduled eventually to cover most of the landing beaches, both marine and freshwater of Kenya. The main aim of this programme is to provide the necessary information needed in the determination of the optimum level of utilization of the fishery resources, a prerequisite in conservation policy formulation. Although catch assessment surveys in Lake Victoria have been done in the past with varying degrees of success there are constant changes affecting the fisheries (including such factors as biological, physical and socio-economic variables), that the need for up-dating the results become crucial almost as soon as the preceeding survey results are out. The purpose of this paper is to provide provisional information on changes in fish populations (species composition, catch-rates) and on effects of types, quantities, of fishing gear used in the Kenya waters of Lake Victoria, and to suggest ways of exploiting the fishery rationally. The catch and effort assessment survey was conducted on 16 beaches around Lake Victoria (Kenya) during the period January 1981 to January 1983. A great deal of information was obtained during the survey, which is still continuing, but only part of it will be dealt with in this preliminary report. The importance of this important background information in the eventual objectives of this project cannot be overemphasized (Stevenson, Pollnac and Logann, 1982).

Materials and Methods

The Institute has 16 manned landing beaches scattered around the Kenyan shores of Lake Victoria each with 2 to 3 field recorders. These beaches are, from north to south, Port Victoria, “Uhanyam Misori”, Luanda (= “Lwanda”) Kotieno, Kaloka, Dunga, Kusa, Rota, Kendu Bay, Homa Bay Lwanda Gembe Mbita, Sindo, Sori and Muhoro (Figure 1). Apart from Port Victoria, Karungu and Muhoro etc. which are on the open waters of Lake Victoria, the rest of the beaches are situated around the Nyanza Gulf proper.

The field recorders posted at these beaches collect data on the fisheries both physically (by weighing and measuring the catches, after grouping them into species or genera, using respectively, a weighing balance and a length measuring board) and orally (by interviewing the fishermen on such factors as the areas frequented, time spent fishing, boat number and ownership, type and propulsion method, crew composition and gear type used). The mean number of boats observed per beach is 23. The data is collected on all working days except Sundays, and the reports are submitted monthly to the Institute's freshwater laboratory in Kisumu for analysis. Further details on catch assessment methodologies can be found in Bazigos (1971), whose format we adopted with some modifications, Wetherall (1974) and Stevenson, Pollnac and Logann (1982).

RESULTS

The catch and effort data obtained so far are not adequate to enable estimation of maximum sustainable yield and standing biomass for the Kenya waters of Lake Victoria. Therefore the use of an exponential surplus-yield model given by Fox (1970) requires the collection of more data. Great variability in catch and effort data has been noted and correlation coefficient of the regression of cpue against effort is extremely low (0.07).

There is seasonal variation in fish landings. The number of fishing canoes is estimated to be 4 000–5 000 according to records of the Fisheries Department, Nairobi. The present annual catch is put at about 77 000 t.

Data from nine beaches (the beaches were chosen at random out of the original 16) were analysed in detail for species composition and gear utilized in catching the various fish species. From the sample beaches it was found that the landings were dominated by Lates niloticus, which accounted for about 71.2% of the total fresh weight (Table 1). This was followed by Rastrineobola argentea (19.6%), “tilapias” (dominated by Oreochromis niloticus) (5.2%) Haplochromine species (1.4%) and Clarias mossambicus (1.1%). All other fish species scored less than 1% by weight of total landings.

The predominant fishing method was gillnetting, accounting for about 72% by weight of all the landings, this was followed by mosquito seining (16.6%), beach seining (7.4%), longlining (4.3%) and trapping (0.1%).

A point method whereby a fish species caught by a given gear scores 1 point for that particular gear was used to construct Table 2. This gave the percentage point distribution of gear used in catching the various fish species in the areas; and the corresponding percentage points scored (i.e., gear dominance) when compared with the total percentage catch contribution of the various fish categories (i.e., % gear dominance/% weight contribution of fish species) gave the following ratios:

1. Large sized fish (i.e., the large predators and Oreochromis niloticus, which were caught predominantly by medium to large meshed gillnets and longline), 1:1.6,

2. Small sized pelagic fish (i.e., Rastrineobola argentea, caught predominantly by mosquito seines), 1:3.2, and

3. Potamodromous and other small sized species (i.e., the Mormyrids, Barbus spp; Schilbe mystus, Synodontis spp. Labeo victorianus, haplochromine etc.) 1:94.5. The significance of these ratio figures is discussed below.

DISCUSSION

(a) Fish Stock and the Role of Different Fishing Gear

Though the results presented above are still provisional, pending a more careful analysis and further investigations (which is expected to cover a longer period of time), they do however make one point clear: the Catch Assessment Survey (CAS) method of stock assessment, when carried out with sufficient precision, can be a good method sufficient for most advice to the policy makers, without recourse to more detailed models. The yield figures for the Kenya part of Lake Victoria are perhaps too optimistic, but a review of the past estimate figures make our estimates very compatible.

Over the past decade since Wetherall's report of 1974 there has been a dramatic increase in annual catch figures for the Lake Victoria (Kenya) region. For instance, the catch has risen from 18 500 t in 1970 to about 57 450 t in 1982 according to the estimates given by the Fisheries Department. This is almost a threefold increase in the annual landings over the decade. The increase in total catches also correspond favourably with the increase in landings per canoe-day cpue over the same period: 25 kg in 1972 (Wetherall, 1974), 27 kg in 1978, and 63 kg in 1981 (Mainga, 1982).

If there has been almost a three-fold increase in the Lake Victoria (Kenya) landings over the decade, then our estimates of the maximum yield should triple that of the 1970s. Wetherall's estimates of the annual landings from the Kenya waters in 1972 was about 25 000 t (the range was 20 000–30 000 t). Butcher and Colaris (1975) estimated the maximum yield to be 25 000 t. A three-fold increase in catches over the last decade would bring the present annual landings to about 77 000 t in 1983 which is possibly close or above the maximum sustainable yield.

The percentage species composition of the landings have changed dramatically over the decade. Two fish species have shown a tremendous increase in their percentage contribution to the total catches over the years: Lates niloticus (from 0.1% in 1972 to 63.6% in 1981) and Rastrineobola argentea (from a negligible amount in 1972 to 20.7% in 1981) (Mainga, 1982). Haplochromis species formerly the single most dominant contributor of all the catches combined, has shown one of the sharpest declines (from 20% in 1972 to peak 48.6% in 1978 to a mere 2.7% in 1981). Over the same period the majority of all other species, especially the potamodromous ones, have exhibited varying degrees of decline in the fishermen catches. The present results predict a similar trend for these species.

The distribution of gear type have also changed considerably over the years. This has been confirmed by the report by Muller, Benda and Powell (1982). The present results compared to similar data collected in 1974 (Rinne, 1975), indicates that there has been a three-fold increase in the use of gillnets, a four-fold increase in the use of traps, a slight increase in the use of longlines (hooks); a 2.7 times decrease in the use of beach seines, and a two-fold decrease in the use of mosquito seines. The changes in gear type is an indication that the fishing strategy employed by the fishermen also change according to the available fish species (Henderson and Welcomme, 1974; Marten, 1979).

In an exploited fishery, such as the Nyanza Gulf of Lake Victoria there is usually a close relationship between gear distribution and species abundance. The relationship is in direct proportion: the more abundant the species, the more predominant is the fishing gear used in catching it. This means that the closer the ratio of the fish abundance (e.g., as represented by percentage contribution) to fishing gear dominance (also represented by percentage point dominance - see under Results) approaches 1:1, the more normal the exploitation rate. This means enough effort is being expended to catch an equivalent amount of fish, and hence for short-term purposes, the relationship should be seen as a healthy one. However, when there is an adverse imbalance in this ratio, an unusual relationship develops that needs to be rectified, for this situation indicates either underexploitation (ratio in favour of fish abundance) or overexploitation (ratio in favour of gear dominance). If this hypothesis is correct, then we can use data in Tables 1 and 2 to recommend the control of certain fishing gear, according to the abundance of their target species shown in Table 2. Similar conclusions were reached by the use of curvilinear regression analysis (Marten, 1979).

The dramatic decline in the catches of the potamodromous and other small sized species over the last two decades has been well documented (Whitehead, 1959; Cadwalladr, 1965; Lowe-McConnell, 1977), and as the present results suggest, the part that the above detrimental gears have played in bringing about this situation has been tremendous. This paper therefore proposes a total ban to be imposed by the authorities on the use of all the beach seines and the small-sized gillnets (3/4" – 5" mesh sizes), and to recommend a 0.6-fold increase in the use of medium (6" – 10" mesh sizes) to large size (11" – 14" mesh sizes) gillnets and longlines. Similarly this paper recommends a three-fold increase in the number of mosquito seines to be operative in the Lake. Apart from the last recommendation, all the others have been emphasized before (Wanjala and Marten, 1975; Marten, 1979).

I would like to conclude this topic by quoting Marten (1979a) on the same problem. He stated that “despite overfishing symptoms, it appears the total harvest of Lake Victoria can be increased by increasing the fishing effort, provided the additional effort is properly directed. This conclusion is fortunate, since the high human population pressure along the shoreline of the Lake, coupled with the difficulty of imposing certain restrictions on many fishermen, make more difficult the reduction of fishing efforts from a practical point of view”.

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

Butcher, D.A.P. and J.C.G. Colaris, 1975. Kenya, Tanzania and Uganda. A sociological survey of the fishermen population around Lake Victoria. A report prepared for the Lake Victoria regional fisheries project. Rome, FAO, FI:DP RAF/71/242/4:38 p. (mimeo)

Cadwalladr, D.A., 1965. The decline in the Labeo victorianus Blgr. (Pisces: Cyprinidae) fishery of Lake Victoria and an associated deterioration in some indigenous fishing methods in the Nzoia River, Kenya. E.Afr.Agric.For.J., 30:249–56

Fox, W.W., Jr., 1970. An exponential surplus-yield model of optimising exploited fish populations. Trans.Am.Fish.Soc., 99:80–8

Henderson, H.F. and R.L. Welcome, 1974. The relationship of yield to morphoedaphic index and numbers of fishermen in African inland fisheries. Relation entre la production l'indice morpho-edaphique et le nombre de pêcheurs des pêcheries des eaux continentales d'Afrique. CIFA Occas.Pap./Doc.Occas.CPCA, (1):19 p.

Kitaka, G., et al., 1971. Evaluation of fisheries resources in African fresh waters: Lake Victoria. Afr.J.Trop.Hydrobiol.Fish., 1:78–9

Lowe-McConnell, R.H., 1977. African Great Lakes, their fish and fisheries. In Ecology of fishes in tropical waters. London, Institute of Biology, Studies in biology, 76, pp. 50–2

Mainga, O.M., 1982. A comparative study of catch assessment surveys of 1972, 1978 and 1981 in Lake Victoria (Kenya). (Unpubl. MS)

Marten, G.G., 1979. Impact of fishing in the inshore fishery of Lake Victoria (East Africa). J.Fish Res.Board Can., 36(8):891–900

Marten, G.G., 1979a. Predator removal: effect on fisheries yields in Lake Victoria (East Africa). Science, Wash., 203:647–8

Muller, R.G., R.S. Benda and T.G. Powell, 1982. Exploitation of fish in the inner Kavirondo Gulf of Lake Victoria based on tag returns. J.Fish Biol., 20:667–71

Munro, J.L., 1979. Stock assessment models; applicability and utility in tropical small scale fisheries. In Stock assessment for tropical small-scale fisheries. Edited by S.B. Saila and P.M. Roedel. Kingston, R.I., University of Rhode Island, International Center for Marine Resource Development, pp. 35–47

Okedi, J., 1982. Standing crop and biomass estimates of Lake Victoria “dagaa” (Engraulicypris argentens Pelg.) Unpubl. MS Makerere University

Rinne, J.N., 1975. A preliminary observation on the age, growth and tagging of Bagrus, Clarias, and certain Tilapia spp. from Lake Victoria. Annu.Rep.E.Afr.Freshwat.Fish.Res.Org., (1974):25–48

Stevenson, D., R. Pollnac and P. Logann, 1982. A guide for the small-scale fishery administrator: information from the harvest sector. Kingston, R.I., International Center for Marine Resource Development, 124 p.

Wanjala, B. and G.G. Marten, 1975. Survey of Lake Victoria fishery in Kenya. Annu.Rep.E.Afr.Freshwat.Fish.Res.Org., (1974):84–5

Wetherall, J.A., 1974. On the catch assessment survey (CAS) of Lake Victoria. Occas.Pap.E.Afr.Freshwat.Fish.Res.Org., (14)

Whitehead, P.J.P., 1959. The river fishery of Kenya. l. Nyanza Province. E.Afr.Agric.J., 24(4):274

Table 1: Percentage fish species composition from selected beaches of the Kenya Sector of Lake Victoria, 1981

Table 2: Percentage contribution of various fish species to the total catch, allocated by gear types

Figure 1 Lake Victoria (Kenya) showing some of the major landing beaches

ANNEX 1.10
Principal Gaps in the Knowledge of Fisheries of the Kenyan Waters of Lake Victoria

by

E. Okemwa
Kenya Marine and Fisheries Research Institute
Mombasa, Kenya

INTRODUCTION

The importance of filling the gaps in the knowledge of fisheries of Lake Victoria and generally making possible awareness of information of the results is very necessary in Kenya, and elsewhere.

Formerly the East African Countries (Kenya, Tanzania and Uganda) undertook fisheries research together under the then East African Common Services Organization and earlier the East African High Commission. In 1977 the co-operation ceased, and some of these countries do not have access to all the past research accomplished. Take, for example, Lake Victoria which is shared by the three countries, any research on fisheries must take into account what has been done in the past.

The importance of retrieval of information, compilation of bibliographies and generally making possible awareness of information was realized in a symposium on “aquatic resources” held in 1981 at Mombasa in Kenya by the Kenya Marine and Fisheries Research Institute.

A BRIEF REVIEW OF FISHERIES RESEARCH

The need for research on problems connected with Lake Victoria was emphasized by the East African Common Services Organization after the Second World War. This led to the foundation of EAFFRO Station at Jinja, Uganda, in 1948. In 1972, two sub-stations were set up in both Kisumu and Mwanza to cater for Kenya and Tanzania, respectively. With the collapse of the East African Community, the laboratories were taken over by the respective states.

The important research on the fisheries of Lake Victoria have been made with respect to biology, ecology, fish production and stock assessment.

The fisheries research carried out during that period included among others, the life history (Fryer and Whitehead, 1959), taxonomy (Greenwood, 1966), ecology of Mormyridae fishes (Okedi, 1960), stock assessment of various fish genera (Bergstrand and Cordone, 1971; Kudhongania and Cordone, 1974) and the productivity of Lake Victoria (Talling, 1966). Most of the findings were compiled in EAFFRO Annual Reports (1951–74) and other journals. Okemwa (1983) prepared a bibliography of the East African Freshwater Fish.

Garrod (1960), Mann (1970) and Wanjala and Marten (1975) reviewed the history and assessed the condition of fish stocks in the heavily fished Kenya waters of Lake Victoria.

The inner Nyanza Gulf is being over-exploited, with Oreochromis esculentus, Mormyrus kannume and Barbus altianalis catch becoming scarce or non-existent (Muller and Benda, 1981). It must be acknowledged that the stocks in the inner gulf are overfished (Benda, 1979; Marten, 1979; Benda, 1981; Muller and Benda, 1981; Okemwa, 1981) and specific management goals should be developed by Kenya Fisheries. These goals should include supplying protein to the people, increasing employment and earnings in the artisanal fishing industry, while properly managing the inner gulf fishery for maximum sustainable yield.

Okemwa (1981) reported that the fish species composition of Nyanza Gulf changed drastically in the last five years. The haplochromines which used to dominate all other fish catch in this Gulf have disappeared. On the other hand, Lates has now colonized the whole of Nyanza Gulf and has got high potential fishery, Okemwa (1984).

PRESENT STATUS, FACILITIES AND MANPOWER

At present, fisheries research on Lake Victoria, Kenya waters are still underway. Four bottom trawl surveys carried out in Nyanza Gulf by Bergstrand and Cordone (1971), Marten, Wanjala and Gulaka (1976), Muller and Benda (1981) and Okemwa (1981) are compared in Table 1. This comparison shows:

1. A reduction in mean stock densities for Bagrus, Clarias, haplochromine cichlids, Labeo, Protopterus, Schilbe, Synodontis and T. zillii.

2. An increase in Lates niloticus and Oreochromis niloticus.

3. Apart from the 1967 survey, no Oreochromis esculentus was caught in the 1977 and 1981 surveys.

Facilities and manpower for carrying out research in Kenya are available.

Fisheries laboratories at Kisumu and Sangoro under KMFRI have been established. Small sub-stations will be established in Yala, Miriu and Gogo for aquaculture, fish biology of riverine species and general river ecology. The Kisumu laboratory is established and equipped with basically the essential tools to carry out fisheries research at Lake Victoria. The library contains a number of periodicals, books on fish biology, limnology and related subjects for references. A few Kenyan research officers and technicians have been trained locally and abroad in this field.

SUMMARY OF RESEARCH IN PROGRESS

Fisheries research in Kenya has gradually changed its character in recent years from a descriptive science to a more dynamic approach in which quantitative data and a certain number of interactions between hydrological/hydrographical and biological components of lakes are being studied.

The basic problem under study can be summarized in the following lines at the Kisumu KMFRI laboratory:

1. Fish stock assessment;

2. Catch effort assessment;

3. Fish Biology (Lates niloticus, and Rastrineobola argentea etc.);

4. Fish tagging experiments;

5. Environmental science (water chemistry);

6. Fish food technology;

7. Phytoplankton ecology and primary production;

8. Zooplankton ecology;

9. Benthic ecology.

PRINCIPAL GAPS IN KNOWLEDGE

The fish tagging project on Lake Victoria which was in operation during the time of the East African Community did not succeed when the community was dissolved. Therefore, studies on fish stocks mobility on Lake Victoria is lacking.

Sufficient information on the effect of fishing with small mesh size gillnets and beach seines during tilapia's peak spawning season is needed. The fisheries manager needs to know whether such regulations have sufficient effect on the fishery to justify the disturbance to the environment.

The Kenyan part of Lake Victoria is the most important single fishery resource of Kenya. A need to reactivate fisheries research in the deep waters is called for urgently, since the present results give a picture of the inshore fishery only.

Studies on benthic animal productivity and their relationship to energy flow in Nyanza Gulf is lacking. Knowledge of the factors controlling fish breeding and the affect of a flush of nutrients into the Lake during the rains is inadequate.

The nature of the pelagic community in the Lake is in need of investigation, not only to determine its magnitude but to define specific inter-actions such as those between the Lates, haplochromine and Rastrineobola stock.

The success of Lates in Lake Victoria is dependent on three species: Rastrineobola, Caridina and haplochromine species. The abundance and growth of Lates in Lake Victoria will be determined in time by the availability of these prey species. Knowledge on biology and ecology of Lates, Rastrineobola and Caridina is needed.

It seems that Lates niloticus and Oreochromis niloticus both introduced fish species, are doing well in Nyanza Gulf, the reverse is true with the indigenous fish species. Research is needed to ascertain the scientific reason behind this.

The catches of Labeo have declined over the last decade, therefore there should be further research into the breeding biology of this species and the effect of fishing methods upon the populations. Research on aquaculture of Labeo sp. is lacking.

There is still a need to find an efficient fishing method for Rastrineobola and a suitable processing technique for Lates caught in this Lake.

The rapidly increasing supply of Lates is causing marketing problems as consumers in the region are not familiar with this type of fish and do not appreciate it due to its high oil content. Work on product development should, therefore, be carried out in order to develop products which will suit domestic and export market requirements.

Fisheries research information is basic to decisions required for fishing management and biological problems. There is a need for long-term coordinated, regional research in Lake Victoria.

In order to have a proper interpretation of catch effort assessment data for Lake Victoria there is a need to give highest priority possible to the development and implementation of a unified system for the collection, compilation and analysis of various fisheries statistics for the Lake.

Studies in water movement in the Nyanza Gulf is lacking. Before the Mbita Channel in Lake Victoria was closed, no scientific research was carried out; and now that it is closed, there have been reports of mass fish mortality in the Nyanza Gulf-Misori area (pers.comm.). The effect of the closure of the Mbita Channel needs to be studied.

Historical data on the chemical composition of the Lake and its effluent river waters are meagre. Research to that effect is needed, with an eye on the continually increasing river discharge of agricultural and industrial wastes. Identification and quantitative analysis of the major chemical species, trace metals, nutrient elements and organic compounds of Lake Victoria is needed.

The principal reason for initiating fisheries research is to preserve and protect fish and freshwater systems. To achieve this, it is necessary first to have a better understanding of the Lake Victoria systems and the effects of various perturbations on these ecosystems. It is, therefore, important to develop a hard core of scientific information on Lake Victoria communities and their response to pollution so as to increase our ability to predict potential environmental impacts.

In the Symposium on Aquatic Resources of Kenya held in Mombasa by KMFRI in 1981 it was decided that future effort should be directed toward the evaluation and assessment of the fish in fresh waters. Recommendation on constraints and other necessities such as the need to publish research findings were summarized together with other general observations.

It appears from this paper that there is a large gap in our knowledge of fisheries of Lake Victoria which requires immediate attention as the freshwater ecosystems are gradually influenced more and more by man.

REFERENCES

Benda, R.S., 1979. Analysis of catch data from 1968–1976 from nine fish landings in the Kenya waters of Lake Victoria. J.Fish Biol., 15:385–7

Benda, R.S., 1981. A comparison of bottom trawl catch rates in the Kenya waters of Lake Victoria. J.Fish Biol., 18:609–13

Bergstrand, E. and A.J. Cordone, 1971. Exploratory bottom trawling in Lake Victoria. Afr.J.Trop.Hydrobiol.Fish., 1(1): 13–23

Fryer, G. and P.J.P. Whitehead, 1959. The breeding habits, embrology and larval development of Labeo victorianus Boulenger (Pisces: Cyprinidae). Rev.Zool.Bot.Afr., 59:33–49

Garrod, D.J., 1960. The history of the fishing industry of Lake Victoria, East Africa, in relation to the expansion of marketing facilities. E.Afr.Agric.For.J., 27:95–9

Greenwood, P.H., 1966. The fishes of Uganda. Kampala, The Uganda Society. 131 p.

Kudhongania, A.W. and A.J. Cordone, 1974. Bathospatial distribution patterns and biomass estimates of major demersal fishes in Lake Victoria. Afr.J.Trop.Hydrobiol.Fish., 3(1):15–31

Mann, M.J., 1970. A resume of the evolution of the tilapia fisheries of Lake Victoria up to the year 1960. Annu.Rep.E.Afr.Freshwat.Fish. Res.Org., (1969):21–7

Marten, G.G., B. Wanjala and L.T. Gulaka, 1976. Explanatory trawling of the Lake Victoria. Fishing in Kenya during 1975. E.Afr.Freshwat. Fish.Res.Org., 19 p. MS

Marten, G.G., 1979. Impact of fishing on the inshore fishing of Lake Victoria (East Africa), J.Fish.Res.Board.Can., 36(8):891–900

Muller, R.G. and R.S. Benda, 1981. Comparison of bottom trawl stock densities in the inner Kavirondo Gulf of Lake Victoria. J.Fish Biol., 19:399–401

Okedi, J., 1965. The biology and habitats of mormyrid fishes. Annu.Rep. E.Afr.Freshwat.Fish.Res.Org., (1964):58–66

Okemwa, E.N., 1981. Changes of fish species composition of Nyanza Gulf of Lake Victoria. In Proceedings of the Workshop, on Aquatic Resources of Kenya, July 1981. Mombasa, Kenya, Kenya Marine and Fisheries Research Institute, pp. 138–56

Okemwa, E.N., 1984. Potential fishery of Nile perch Lates niloticus Linne (Pisces: Centropomidae) in Nyanza Gulf of Lake Victoria, East Africa. Hydrobiologia, 108(2):121–6

Talling, J.F., 1966. The annual cycle of stratification and Phytoplankton in Lake Victoria, East Africa. Int.Rev.Gesamt.Hydrobiol., 51(4):545–621

Wanjala, B and G. Marten, 1975. Survey of the Lake Victoria fishery in Kenya. Annu.Rep.E.Afr.Freshwat.Fish.Res.Org., (1974):81–5

Table 1: Mean stock densities (kg ha^-1) from the Nyanza Gulf from UNDP, EAFFRO, TPRI and KMFRI bottom trawling surveys