The Potential of Mara River as Refugia for Indigenous Fish Species of Lake Victoria, East Africa: A Case Study for Labeo victorianus Abstract By A. P. Shoko, D. N. Oenga, Y. D. Mgaya and G. Mbahinzireki A study was conducted in August, 2006 on the Kenyan and Tanzanian side of Mara River to investigate the status of Labeo victorianus. During sampling a total of 150 Labeo fishes of a model lenth of 20 cm TL were caught. All labeo caught during this survey were spent. The results showed that the Mara river serves as refugia for protecting indigenous fish species such as Labeo victorianus. The study suggests that the rarity of fish species such as Labeo victorianus in the Lake Victoria and their possible extinction could be avoided by devising concrete and strategic conservation measures on the rivers such as Mara river. Introducing the indigenous fish species to aquaculture could serve as conservation strategy because it will reduce pressure from the wild since the fish will be made available to communities through aquaculture. Introduction Labeo victorianus Boulenger locally known as Ningu is endemic to Lake Victoria basin. This fish forms an important seasonal fishery on the lake and along many perennial and seasonal influent rivers (Lowe-McConnell, 1975). The population of Ningu has declined to alarming levels and the species is now under threat of extinction from the lake. L. victorianus is known to perform upstream migrations into the flood plains for the purpose of spawning (Whitehead 1959). This annual spawning migrations into rivers during rainy season predisposes them to be easily captured by waiting fishers (Garrod 1961; Cadwalladr 1965). This mode of fishing prevents most of the fishes from accessing the upstream spawning grounds and therefore depriving the Labeo population the chance to contributing to the future generations. In addition, there have been ecological changes in and around Lake Victoria in recent years (Hecky et al., 1993) that could have affected the life of many indigenous fish species of the lake. Rivers, satellite lakes, ponds, dams and flood plains in the catchment have been singled out as important faunal reservoirs for Lake Victoria endangered fish species (Katunzi, 2001). Such water bodies provide a subsistence fishery to the riparian communities. These water bodies also provide alternative habitats that act as temporary fish feeding habitats and breeding nurseries for a number of species. Apart from acting as shelter, rivers can be considered as natural conservation units that should be protected for scientific, cultural and recreational purposes. The primary objective of this study was to collect the broodstock of Labeo victorianus for aquaculture trials. Alongside with the primary objective the potential of Mara river in harbouring the indigenous fish species was also assessed. This article gives the scope of Mara River in terms of their potential for harbouring threatened fish species of Lake Victoria. 1
Materials and Methods Study sites The study was conducted in August 2006 on the Kenyan and Tanzanian side of Mara River in the Lake Victoria basin. Three sites were sampled which included Mulot bridge and Kaboson site in Amala and Nyangoresi rivers respectively, both of Bomet district. The two rivers are tributaries of Mara River on the Kenyan side. Another sampling site was Kichwa Tembo Bridge of Mara River in Maasai Mara district. A visual survey was conducted on the Tanzania side of Mara River especially at Kirumi wetland. Fish sampling was not conducted on the Tanzania side of Mara River. Methods Fishing of Labeo victorianus was done by using the electro fishing method (Fig. 1, 2 & 3) and kept in kept in a cage submerged in water (Fig. 4) for overnight before taken into the hatchery. For the purpose of this report the fish were measured in terms of total length (cm) and weight (g) to the nearest 0.1cm and g respectively. Female fishes were gently pressed at the lower part of the abdomen to find out whether they are ready for spawning. The identified broodstock were then transported to Kenya Marine and Fisheries Research Institute (KEMFRI) Sango ro hatchery. At Sang oro the fish were fed ad libitum on an artificial diet made out of dagaa/omena Restrineobola argettea to ripen for artificial spawning. The Microsoft Excel (MS Excel 2000) was used to determine the length frequency distribution curve of the sampled fish. During the survey discussions with fishers were conducted to explore the indigenous knowledge on the conservation options to be applied. Figure 1: Scientists, fishers and equipments for electro fishing 2
Figure 2: Collecting of Labeo victorianus after catching Figure 3: Sorting of Labeo victorianus 3
Frequency Figure 4: Putting Labeo victorianus in a cage immersed in water Results During the visits 68 fish were collected from Amala and Nyangoresi Rivers combined, whereas 80 fish were collected from Kichwa Tembo Bridge in Mara River; making a total of 150 fishes. Due to limited time only 41 fishes selected randomly in each sampling sites were measured for Weight and Total Length to the nearest 0.01g and 0.01 cm respectively. The length frequency distribution curve of the sampled fish is shown in Fig. 5 where most of the fishes were at 20 cm total length. 30 25 20 15 10 5 0 10 20 30 40 50 60 Total Length (cm) Figure 5: Length frequency distribution of Labeo victorianus In all sites sampled it was observed that most fishes were spent. There was no fishing encountered in the sampling sites on the Kenyan side probably because of the nature of the sampled areas. However fishing was observed on the Tanzania side 4
of Mara River at Kirumi wetlands. It was also noted with great concern that vegetation cover at Kirumi wetland on the Tanzania side of the Mara River during the time of study were subjected to a number of anthropogenic impacts such as clearing of vegetation cover in an attempt to procure space for agriculture where bananas and vegetable crops were observed at the wetlands (Fig. 6). Figure 6a: Clearing of vegetation for planting crops at Kirumi wetland. Figure 6b: Bananas and vegetables at Kirumi wetland 5
Figure 7: Reed fences at Simiyu River mouth (above) and upstream Simiyu River (From Benno, 2003) Discussion Fishing for Ningu is seasonal, although the fishers operate throughout the year. Ningu are caught in large quantities during the rainy season, but become very scarce during the dry season. The Labeo victorianus caught during the reported study were already spent. This was probably because Labeo spawns during February to May and November to December, which are the rainy seasons. In his study Benno (2003) reported that fish at spawning condition started to appear in the samples in November and reached the peak in May. It was initially expected to catch Labeo with ripe ovaries because during the period of sampling it was a raining season. It was thus decided to feed them at KEMFRI Sang oro aquaculture station until when they were ready for spawning. The breeding performance of this fish species held at Sang oro aquaculture station will be reported separately. This survey however noted the importance of rivers in the Lake Victoria basin as refugia for harbouring indigenous fish species. In all sites sampled it was exciting to observe quite a good number fish species swimming way from the area subjected to electric shock. This observation necessitated the authors to report and recommend on the urgency of having strategic conservation measures to be applied to these rivers. The importance of rivers for harbouring indigenous fish species was reported earlier (Katunzi, 2001). In his study (Katunzi, 2001) noted that several fish species currently known to be rare in the main lake are represented in the lake basin hence supporting fisheries of the riparian communities where they are exploited at various levels merely for subsistence. It was reported however that most fisheries in these smaller water bodies are not sustainable; and that certain threats such as over fishing, catching of juveniles by using illegal gears particularly undersized mesh net and destruction of breeding sites through clearing of vegetation for agricultural purposes were imminent to these areas (Kaufman 1992; Katunzi, 2001; Benno 2003). 6
From the reported results there was no fishing of L. victorianus observed in the Kenyan side probably because of the nature of the sampling areas. The sampling in Kenya was done in the protected areas such as National parks. This does not mean that fishing of Labeo and other indigenous fish species is not conducted in Kenyan rivers. Fishing was however observed in the Tanzania side especially at Kirumi wetlands. A study by Benno (2003) reported L. victorianus to be exploited at alarming rates. The types of gears commonly used to catch Ningu include basket traps, beach seines and reed impounding fences. Most fishers also use dug out canoes to fish in near shore waters and in rivers where Ningu recedes. The fish is caught from the near shore areas of the lake as well as in influent rivers. Some Ningu are trapped in flood plains during the rainy season (Lowe-McConnell 1975; Welcomme 1978) when the flooding conditions are right. Reed impounding fences are erected alongside the shoreline, across and alongside the river banks and in the flood plains (Fig. 7a & b from Benno, 2003) in anticipation of trapping the fishes that migrate laterally into the flood grounds. L. victorianus has suffered high mortalities and is considered as one of the several threatened fish species in the Lake Victoria. For example, fisheries catch data showed that L. victorianus catches contributed approximately 10%, 0.01%, 0.001% and 0% of the total fish landing in Tanzania sections of Lake Victoria in 1958, 1960/61, 1970, 1987 and 1995 respectively (Benno 2003). Fortunately the fishes are found in the small water bodies such as rivers which call for conservation strategies. The Mara River is shared between Kenya and Tanzania and thus any management options to be applied should involve the two countries. In addition the local people should be involved in any conservation strategies. Also management options for L. victorianus should consider other fish species as well since it is caught together with other fish species. In this study Ningu was caught together with Barbus altianulis, Schilbe mystus, Clarias gariepinus Mastecemberlus spp. and Oreochromis leucostictus. Other fish species reported to be caught together with the Ningu include Schilbe intermedius, Brycinus jacksonii and Synodontis spp. (Benno 2003). It was reported earlier (Benno 2003) that Labeo victorianus mature at smaller size (from <10.1 cm to 11.9 cm). The modal length of 20 cm TL was reported in this study and most fishes were spent. The fact that Ningu is very fecund (Benno 2003) suggests a great potential of recovery of this species provided there exists the right conditions for the survival of young and rational exploitation of the adults. According to FAO (1994) most indigenous fish species are preferred by consumers but have not yet been fully tested as candidate species for aquaculture. In his study Owori-Wadunde (2005) reported positive results in the attempt to fish farming trials of Labeo victorianus, such attempts should be encouraged. It has been recommended elsewhere (Jamu and Ayinla, 2003) that the development of production techniques for local fish species and their successful culture may help protect natural populations, which are threatened in many cases due to unsustainable fishing practices. It is therefore recommended that aquaculture research scientists should direct their efforts towards developing technologies for fish farming of the indigenous fish species such as Ningu. Efforts towards developing hatchery techniques for producing fish fingerlings of Labeo victorianus should be encouraged. It is hoped that once these fishes become available to consumers through aquaculture it will reduce pressure to the wild and limited stocks. 7
Conclusions and Recommendations The study concludes that rivers are important refugia for harbouring indigenous fish species such as Labeo victorianus and thus recommends that: i. Fishing activities in the rivers around Lake Victoria basin should be prohibited to give room for the resurging indigenous fish species to grow and reproduce. Fishing particularly in river mouths should be prohibited because it allows catching of gravid Ningu while moving upstream to breed. ii. A strategic plan to protect the wetlands from being cleared for agriculture activities should be put in place and implemented. iii. Introduction of indigenous fish species such as Labeo on aquaculture should be considered as important conservation measures as it will reduce the pressure from the wild. For those recommendations to be effective there should be full participation of local community including providing them with alternative livelihood strategies. Also the beneficiaries should be educated on the importance of conserving the indigenous fish species. Acknowledgements The authors express their sincere thanks to the Inter-University Council for East Africa (IUCEA) through Lake Victoria Research (VicRes) Initiative project for funding this study. The Heads of Tanzania Fisheries Research Institute (TAFIRI), Kenya Marine and Fisheries Research Institute (KEMFRI), Fisheries Resources Research Institute (FIRRI) of Uganda and the University of Dar Es Salaam, Tanzania are acknowledged for granting the authors with permission to participate in the study. We are grateful to the cooperation and hospitality we received from the communities in the studied areas. 8
References Benno, B.L.L. 2003. Movement, Reproduction, Habitat use, Trophic status and the fishery of Labeo victorianus in the Lake Victoria (Tanzania). PhD Thesis, Waterloo, Canada. 186pp. 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 Nzoia River, Kenya. East African Agricultural and Forestry journal. 30: 249-256. FAO. 1994. Aquaculture research and development in sub-saharan Africa. National News. In: Coche, A. G. (ed). FAO 23 supplementary, Rome, Italy. Garrod, D. J. 1961. A review of Lake Victoria fishery science records 1951-1956, Report for East African Fisheries Research Organization, Jinja, Uganda Hecky, R. E. 1993. The eutrophication of Lake Victoria. Internat. Ver. Theor. Ang. limnol. 25: 39-48 Jamu, D.M. and O.A. Ayinla. 2003. Potential for the development of aquaculture in Africa. World FishCentre Quarterly, 26(3): 9-13 Katunzi, E.F.B. 2001. Satellite Lakes, rivers and dams as refugia for the endangered fish species of Lake Victoria. Proceedings of the LVEMP-Tanzania 2001 Scientific Conference, 6-10 August, 2001, BOT Training Institute, Mwanza, Tanzania. pp. 44-53 Kaufman, L. 1992. Catastrophic change in species rich freshwater ecosystems: the lessons of Lake Victoria. Bio-Science: 42:846-858 Lowe-McConnell, R.H. 1975. Fish communities in tropical freshwaters: Their distribution, ecology and evolution. Longman, London and New York. Owori-Wadunde. 2005. The feeding habits and development of digestive system of Labeo victorianus Blgr (pisces: Cyprinidae). In: Knowledge and Experiences Gained from Managing the Lake Victoria ecosystem. LVEMP, Dar es Salaam, Colour Print (T) Ltd, pp. 479-494 Welcomme, R.L. 1978. Proceedings of the symposium on River and Flood plain Fisheries in Africa, 21-23 November 1977, Bujumbura, Burundi, CIFA Technical paper 5, 375p. Whitehead, P.J.P. 1959. The anadromous fishes of Lake Victoria. Rev. Zool. Bot. Afr. 59: 329-363 NB: The corresponding author Mr. Amon P. Shoko is a Senior Research Officer working with Tanzania Fisheries Research Institute (TAFIRI), Kigoma Centre, P. O. Box 90, Kigoma, Tanzania. His area of specialization is aquaculture research and development. Email: amon_shoko@yahoo.co.uk 9