Lake 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, Uganda 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 LAKE NABUGABO: A POTENTIAL RESERVOIR In the lake itself, Muk FOR MUKENE (Rastrineobola Argentea) value' to the country. Wandera Sylvester Bwaku nights lighted pressure Fisheries 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 lakes Victoria, Kyoga, Nabugabo and the Victoria This fishery was intro Nile. 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 fish 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 Lake Victoria 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 fishes. Catch rates of 9.8 kg/lamp/hr by the lampara net on this lake compare favorably with ma~ parts ofLake Victoria and on Lake Kyoga 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 Nile perch 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 tilapia and other native fish species easured (Standard Ie such as Schilbe intermedius and Synodontis 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 Nile tilapia 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 lake Tanganyika where the method was well developed for the clupeids. The Swahili name "dagaa" is the equivalent ofMukene in Tanzania 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 (Lates, Tilapiines, Schilbe etc.) were picked out, counted and weighed. The rest of the fishes (Mukene, Barbus 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, Oreochromis 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 cGI U ai Q. 10 1 0 ,'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 ------------==========::~~~-~- T: ,I 100 1< l' 75 Ta OJ c '6 <D F ....<D 50 CO L ~ 0 C S, 25 B B D{ o cy Jan Feb Apr May Jun Aug Oct Dec It de: Figure 3. Monthly percentage of breeding R. argentea in Lake Nabugabo bel no Discussion sh< the The effect of predation by the Nile perch on the size structure of R. argentea chI is already apparent as shown by the progressive decline in the mean length, val . Mukene populations between 1991 and 2001 (Fig. 2). Large individuals (ov anI .60 mm SL) of Mukene are still available in Lake Nabugabo unlike on Lak, Victoria and Kyoga where in addition, human exploitation exists (Wander Co 2001). At 42 mm SL, size at first maturity on Lake Nabugabo is similar to th observed in the inshore waters of Lake Victoria (Wandera, 1999). At 9.8k Int lamp/hr., catch rates of Mukene in Lake Nabugabo compare well with tho SlIT in areas where a commercial fishery exists (Table 1).