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Home , Lake Kyoga, Lake Nabugabo, Lake Victoria

Nabugabo: a potential reservoir for mukene (Rastrineobola argentea)

Item Type book_section

Authors Wandera, S.B.

Publisher Wetlands Inspection Division

Download date 01/10/2021 14:16:17

Link to Item http://hdl.handle.net/1834/35580 A compilation of

Scientific Information on

Nabugabo Ramsar Site,

Proceedings ofthe Scientific Conference held at Nabugabo in January, 2001

.;n'. ~ .~~.: ~"ST~ Tl1E REPUBLIC OF UGANDA (0

Edited by:

Busulwa H., P. G. Mafabi and L. M. Ndawula

2005

The Nabugabo Ramsar Site : A POTENTIAL RESERVOIR In the lake itself, Muk FOR MUKENE (Rastrineobola Argentea) value' to the country. Wandera Sylvester Bwaku nights lighted pressure Resources Research Institute (FIRRI), P.O. Box 343, Jinja, Uganda. e-mail: [email protected] thus attracted are colle was introduced into lal Abstract well developed for tht ofMukene in Tanzani, "Mukene" Rastrineobola argentea occurs in Victoria, Kyoga, Nabugabo and the Victoria This was intro . On lakes Victoria and Kyoga the commercial fishery is well developed. While some Lake Nabugabo has p< fishing occurs at isolated places on the Victoria Nile, the species is yet to be exploited on lake to have negative effeci Nabugabo although the potential exists. Experimental fishing (light fishing and beach seining) was conducted on Lake Nabugabo based at the Lake Nabugabo Holiday and Conference Center. ofother species th, Specimens obtained were analyzed for biological and fisheries parameters. Mukcne on Lake outlines biological ane Nabugabo still grows to a large adult size compared to the populations. Size at possible mukene fisher first maturity at 42 mm SL is close to that observed on Lake Victoria. Peak breeding occurred between August and January. Unlike on Lake Victoria, R. argentea in Lake Nabugabo is not infested by the cestode Ligula intestinalis that is common in these . Catch rates of 9.8 kg/lamp/hr by the lampara net on this lake compare favorably with ma~ parts ofLake Victoria and on where a commercial fishery exists. The amount of by-catch species in Samples of fresh Mul the catches however is high and does not therefore favour the establishment of the fishery on a small 10 mm mesh 1 this lake. Human exploitation of mukene on Lake Nabugabo would also affect the Nabugabo Holiday and fishery which depends on the species as a source offood. taken. Later light fishin and Keywords Size Stmcture, Predation, Exploitation. Kyoga was also c ampsite and out in tl Introduction :Tilapiines, Schilbe etc.j shes (Mukene, Barbu ere mixed up and a n "Mukene" Rastrineobola argentea occurs in lake Victoria, Lake Nabugabo, the d preserved for labor Victoria Nile and Lake Kyoga. On lakes Victoria and Kyoga the commercial fishery is well developed. While some fishing occurs at isolated places on the the laboratory differ Victoria Nile, the species is not yet exploited on Lake Nabugabo. Because rted, counted weighe there is still plenty ofNile perch and Nile and other native fish species easured (Standard Ie such as Schilbe intermedius and afrofischeri in Lake Nabugabo, amples were collecte fishing for Mukene has not begun. But with greater demand for fish both for January and April t local consumption and for export, it is just a matter of time before commercial 001. exploitation of mukene on Lake Nabugabo starts. This has been the trend in all the waters where the fishery exists. On Lake Victoria the fishery never existed until the early eighties when the traditional fishery had been depleted. On Lake Kyoga, fishing for Mukene started in 1995 after the Nile perch and boom. The species is exploited for both human consumption and animal feeds production. .ength frequency dist] dicated a range from 46 The Nabugabo Ramsar Site Nabugabo Ramsar Site 10IR In the lake itself, Mukene is food to the Nilc perch, a fish of now great export value to the country. Fishing for mukene takes place at night. On moonless nights lighted pressure lamps are floated on the lake to attract Mukene. The fish ~firi.go.ug .thus attracted are collected by scoop, ring lift or beach seine nets. Light fishing . was introduced into lake Victoria from where the method was well developed for the clupeids. The Swahili name "dagaa" is the equivalent ofMukene in and is the same name for the lake Tanganyika clupeids. Ithe Victoria This fishery was introduced into Ugandan waters in the early 1980's. While While some Lake Nabugabo has potential for the Mukene fishery, its exploitation is likely Dited on lake to have negative effect both on its populations in the lake and on populations ~ach seining) of other fish species that live with or depend on the species for food. This paper rence Center. :ene on Lake outlines biological and fisheries parameters useful for the management of the tions. Size at possible mukene fishery on Lake Nabugabo. ling occurred )ugabo is not Materials and methods h rates of 9.8 Lake Victoria ch species in Samples of fresh Mukene were obtained by experimental fishing. Initially the fishery on a small 10 mm mesh beach seine net was used at the Campsite of the Lakc he Nile perch Nabugabo Holiday and Confcrcnce Center. Each time, two to three hauls were taken. Later light fishing as done by the commercial fishermen on Lake Victoria and Kyoga was also conducted. Lamps were set both near the shore at the Campsite and out in the open water. On retrieval large sized species (, Tilapiines, Schilbe etc.) were picked out, counted and weighed. The rest of the fishes (Mukene, magdalene and juveniles of the above large species) were mixed up and a random sample of approximately 0.5kg was scooped off bugabo, the and preserved for laboratory analysis. commercial laces on the In the laboratory different by-catch species still remaining in the samples were )0. Because sorted, counted weighed and their lengths takcn. Specimens ofR. argentea were fish species measured (Standard length in mm) and gonad maturity state was determined. Nabugabo, Samples were collected bi-monthly between August and June 1991/1992 and ish both for in January and April to June in 1993. Sampling was also done in December commercial 2001. ~ trend in all ever existed ~d. On Lake Nile tilapia Size structure mimal feeds

Length frequency distribution ofMukene in Lake Nabugabo in December 2001 indicated a range from 23 to 63 (mean 36) mm Standard Length (Figure 1). The

~bo Ramsar Site The Nabugabo Ral1lsar Site 47 1991 mean length was 50.2 mm and in 1993 was 45.4 mm SL. (Figure 2). The maximum size to which Mukene has been growing has consistently remained large, at over 60 mm SL.

15 30

20 ~ 10 i 10 ~ ~ 5 A. o

30

o '-,.,.,.,',',',.,',',',.,',.,',',',.,',',',',',',.,.,.,-,-,',',',.,',',.,',',., ,', ~ 23 25 27 29 31 33 35 37 39 41 43 45 47 49 20 Standard length (mm) i

j 10 Figure 1. Length frequency distribution ofMukene in Lake Nabugabo 2001

Maturity and Breeding Periodicity o

Size at first maturity for both sexes ofMukene in Lake Nabugabo was calculated 30 at 42 mm SL. Just like on other lakes where it occurs, Mukene breeds throughout the year in Lake Nabugabo. The species however shows peak breeding activity between the months ofAugust and January (Figure 3). 20

Thefishery 10 Fishing rates of Mukene on the lake stood at an average weight of 9.8 kg per lamp-hour. Five fish species were recovered as by-catch in this fishery. These o were in order of importance (numbers) Lates niloticus, Barbus magdalene, niloticus, Brycinus sadleri and Schilbe intermedius. Fishing inshore yielded a higher percentage (7.7%) ofby-catch species than in the open water (3%). The number ofby-catch species was likewise higher inshore (5) as gure 2. Lengl compared to the open water (2). 2001

48 The Nabugabo Ramsar Site J. (Figure 2). The istently remained

30 1991

20

10

0

1993 30

~ III••••• c: ii' I i I Iii I- I II :J 20 I 55 57 59 61 63 :u

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,'abo was calculated 30 2001 ~ breeds throughout Lk breeding activity 20

reight of 9.8 kg per l this fishery. These

Barbus magdalene, 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 ~termedius. Fishing Standard Length (mm) ~ies than in the open ligher inshore (5) as re 2. Length frequency distribution of R. argentea from Lake Nabugabo in 1991, 1993 and 2001

"he Nabugabo Ramsar Site eNabugabo Ramsar Site 49

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1999). 1999).

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argentea argentea R. R. breeding breeding of of percentage percentage Monthly Monthly 3. 3.

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T: T: ------======::~~~-~- Table 1. Catch rates of Mukene from different fishing grounds

Lake Site Catch rates (kg/lamp/hr) Victoria Lambu 20.7 Kikondo 13.2 Lingira 10.0 Kyoga Bukungu 6.2 Nabugabo CoU Campsite 9.8

Table 2. Relative abundance of Mukene by-catch species from Lake Nabugabo

Fish taxon % Contribution Lates niloticus 1.6 Oreochromis niloticus 0.2 Schilbe intermedius 6.2 Brycinus sadleri 5.1 Barbus magdalenae 2.0

Despite the presence in Lake Nabugabo of the hosts to various stages of life cycle ofthe parasite Ligula intestinalis, the parasite is absent from these fishes. Aug Oct Dec It is not only 1. intestinalis that has been observed absent in Lake Nabugabo despite its presence in the nearby Lake Victoria. Schistosome parasites have Nabugabo been reported absent from this lake (Cambridge Expedition). Another organism not encountered is Caridina nilotica and the few gastropods found in the lake show undeveloped shells (Ndawula-Mwebaza et al., 2002). The absence or the poor state of these organisms in the lake could possibly be traced to the lize structure of R. argent chemistry of the lake. Lake Nabugabo is very poor in salts (low conductivity ecline in the mean length values) and shows low pH (Mugidde & Magezi, 2002). The water is very soft . 2). Large individuals (ov and may not support these organisms. •Nabugabo unlike on Lak ICploitation exists (Wande Conclusions and recommendation ~ Nabugabo is similar to t (Wandera, 1999). At 9.8k Information available indicates that R. argentea in Lake Nabugabo shows very bo compare well with tho similar biological and fishery characteristics to the Lake Victoria population. 1). The amount of by-cat The potential for the fishery on Nabugabo exists. Commercial exploitation of on. Other than the introduc the species might howeverprove harmful to the already existing table fish (Nile 11 harbors over twenty nati perch and tilapia) fishery since many juveniles of these species will be caught these species co-exist wi as by-catch. The lake's fish biodiversity will likewise be reduced by the capture ofthe Mukene fishery (Tab of this by-catch species. Considering that Mukene is already being exploited ) tend to be attracted to Ii in the other water bodies where it occurs and may in future suffer over-fishing,

The Nabugabo Ramsar Site 51

The Nabugabo Ramsar R. argentea in Lake Nabugabo should be left as a reserve source in the event that the species is depleted in those lakes. The Nile perch in Lake Nabugabo THJ currently depends on R. argentea for the bulk of its food requirement. Human THE exploitation of Mukene in a small and shallow Lake Nabugabo is likely to deprive the Nile perch of its food source and may lead to the collapse of the perch fishery. Commercial exploitation should therefore be discouraged on Lake Nabugabo in order to preserve the existing biodiversity and the Nile perch II fishery. Abstract Acknowledgement The wide-spread together with ave The 1991 Mukene data were collected using funds from IDRC, Ottawa, Canada. caused endemic i Recent data are through funding by the World Bank/GEF, Fish Biology and become virtually Biodiversity Sub-component of the Lake Victoria Environment Management native species in i Project (LVEMP). I also wish to acknowledge all colleagues at the Fisheries Victoria basin (Na Resources Research Institute (FIRRI) whom I have worked with in the course an objective ofass (Mburo and Kach( of data collection, analysis and the preparation ofthis paper. basin, were sampll

References Among the Nabug total fish catch by Mugidde, R. and G. Magezi, (2002). Physico-chemical and algal dynamics ofNabugabo Lakes. A paper cm TL) was caugh presented at the Nabugabo lakes workshop 16th to 19 th January 2002. smallest (6.6 cm T Namulemo, G., Ogutu-Ohwayo R., S.B. Wandera ,and D. Mbabazi, (2001). Conservation of fish factor K (1.89± O.C species diversity in the Victoria and Kyoga lake basins through protection of satellite lakes and (compared with otl refugia. Paper presented at thc Lake Victoria Environment Management Project (LVEMP) I" th National Scientific Conference, 17 - 21" September 2001. Mukono, . Diatoms, especiall: esculentus in Lake Mwebaza-Ndawula, L., V. Kiggundu and P. Gandhi, (2002). communities of Nabugabo Kayugi. In Lake K lakes: A vital support resource for fisheries and diversity. A paper presented at the Nabugabo lakes workshop 16th - 19th January 2002. while Microcystis v more male than ferr Wandera, S.B., (1999). The reproductive biology of Rastrineobola argentea in the northern waters of This is comparable Lake Victoria. In: Report of the Fourth FJDA WOG Workshop held in , , 16th ­ mean fecundity Wl 20th August 1999. Technical Document no.7, Lake Victoria Fisheries Research Project LVFRP/ (399±143). Based Tech/99/07. esculentus and Whl be a most valuable Wandera, S.B., (2001). The potential ofMukene (Rastrineobola argentea) fishery in Lake Victoria with restocking and for c suggestions for its management. Paper presented at the Lake Victoria Environment Management over exploitation ar Project (LVEMP) I" National Scientific Conference. 17 th to 21" September 200 I. Mukono, Kampala.

Key"

The Nabugabo Ramsar Site 52 The Nabugabo Rams~

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