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Afr. 1. Trop. Hydrobiol. Fish. (1995) 6,1-10 The Potential for further proliferation of Water Hyacinth in Lakes Victoria, Kyoga and Kwania and some urgent aspects for research! T. TWONGO, EW.B. BUGENYI AND E WANDA Fisheries Research Institute P.O. Box 343, Jinja, Uganda ABSTRACT Shore environments of lakes Victoria and Kyoga with potential for the establishment and proliferation of water hyacinth were identified. They are characterised by: (i) shelter from violent off-shore and along-the-shore wind and wave action (ii) flat or gentle slope under relatively shallow water, and (iii) a muddy bottom rich in organic matter. Such environments are strongly associated with emergent macrophytes of papyrus, Vossia sp and, at times Typha sp where Pistia stratiotes, species of Ceratophyllum, Myriophylum and Nymphaea also occur. In Lake Kyoga association with Vossia sp facilitated establishment of water hyacinth even along wind-swept shores and promoted extension of mats of the two machrophytes into the open lake. Urgent research on water hyacinth is proposed in the areas of nutrient relations, weed biology and on its impact on the biodiversity resource, with particular emphasis on the fishery component. Findings from the research could facil- itate formulation of weed control options and alternative resource management strategies. A regional approach to address the water hyacinth menace is highly recommended. INTRODUCTION water supply. This trend is already apparent on Lake Kyoga; and large quantities of water In its native range In tropical South America, water hyacinth Eichhornia eras sipes (Mart) hyacinth biomass on Lake Victoria could also Solms occurs virtually harmlessly in seasonally eventually become a constraint on hydro-electric inundated environments rather than in permanent power generation at the Owen Falls plant, Jinja. water bodies like the large lakes of East Africa Secondly, the current trend towards eutrophication where the weed has appeared. Admirers of its of lakes Victoria and Kyoga is likely to sustain beautiful flower have translocated water hyacinth increased productivity of the weed. almost world-wide, and in the tropical and sub- In spite of the above concern and of the heavy tropical environments, the weed has reproduced dependence by the lakeside communities in East prolifically and spread rapidly to become one of Africa on lake resources especially water and fish, the most notorious freshwater weeds. In Uganda, and, although hydro-electricity and commercial where water hyacinth was first reported in Lake fisheries are regional economic assets, the Kyoga in 1988 and in Lake Victoria in 1989, potential danger posed by the proliferation of weed distribution around both lakes is almost water hyacinth to lake resources around Lake complete (TWONGO, 1991 a; THOMPSON, Victoria is not yet appreciated. This paper is firstly, 1991). There is therefore growing concern about to try and illustrate the impending danger to lake its proliferation potential from two perspectives. resources availability due to increased infestation First, the rapidly accumulating biomass would by the water weed. In this connection, the potential negatively impact the lake environment for fish- for further proliferation of water hyacinth on lakes eries production, maintenance of aquatic biodi- Victoria and Kyoga is highlighted. Secondly, versity, water transportation and for potable although the water hyacinth has been in the lower 1 This paper was presented at the Sixth Session of the CIFA Sub-Committee for management and development of the fish- eries of Lake Victoria, 10-13 February, 1992, and published as abstract (Twongo et al, 1992: FAO Fisheries Report No. 475). The full paper is given here for wider circulation in view of its baseline information content on water hyacinth. 2 T. TWONGO F.W.B. BUGENYI AND F. WANDA Pangani in Tanzania, and in the Sudan since the not common. Average dissolved oxygen level 1950s, scientific information about it in this was obtained from measurements taken at depth region is highly limited. Some urgent aspects for intervals of 50cm. research to improve knowledge on the biology and ecology of water hyacinth and on its environ- RESULTS mental impacts on various lake resources have Candidate habitats been identified. It is expected that the results of studies made on lakes Victoria and Kyoga would The survey of the shores of Lake Kyoga and Lake lead to options for control of water hyacinth and Victoria in Uganda revealed presence of estab- for lake resources management in the presence of lishing water hyacinth growing in habitats with the noxious weed. the following shoreline environmental features: METHODS OF STUDY 1. shelter from violent off-shore and along-the- shore wind and wave action; Surveys were made in a canoe powered by 25 hp outboard engine along the entire shoreline of 2. flat or gently sloping shores that are relatively lakes Kyoga and Victoria-Uganda portion, shallow (rarely deeper than five meters); including the major islands. Lake Kyoga where 3. a soft muddy bottom rich in organic matter. the weed was reported earlier (TWONGO, 1991a) was surveyed thrice between 1988 and 1991 Along the shores of Lakes Victoria and Kyoga, while Lake Victoria was surveyed once from 27 sites with the above characteristics supported an December 1991 to 17 January 1992. During the emergent macrophyte flora of papyrus - Cyperus survey the shoreline was carefully inspected and papyrus with patches of Vossia sp. A strong asso- the following environmental features were evalu- ciation was, therefore, established between shore ated in relation to presence of major infestations environments supporting the growth of C. of water hyacinth: papyrus or Vossia sp. and the presence of water hyacinth. This association which was established 1. slope of the shore landward (by ocular assess- early during the surveys, made it easier to locate ment) and lakeward (based on depth soundings water hyacinth infestations since the above along transects); emergent macrophytes could be seen from a long way off especially with the aid of binoculars. In 2. lake bottom type (whether rocky, firm soil or Lake Victoria, stands of Typha sp. were often muddy), based on Ponar grab samples; scattered among the papyrus or formed a back- 3. presence of emergent, floating and/or sub- ground to it, especially along the north eastern merged shore vegetation; shores of the lake but became rare towards the west. Typha sp. tended to grow on firmer clay 4. overall shelter situation: whether in a bay or soils. Shore zones with the features listed above along open shoreline, exposed to or on the lee almost always carried one or several of the follow- of prevailing winds. ing euhydrophytes in both lakes: Nile lettuce Pistia stratiotes, Ceratophyllum demersum, Some physical and chemical parameters (temper- Myriophylum sp., and Nymphaea sp. while ature, pH, conductivity, dissolved oxygen and Potamogeton spp. occurred at a few sites. redox potential) were measured in various bays on Lake Victoria using a Hydrolab Surveyor II to Spatial Spread compare the water environment in hyacinth mats with that off the edge of the water weed. The Water hyacinth occurred in almost all habitats parameters were measured about 10m away with environmental features already identified as from the edge of the mat and only five metres favouring weed establishment. In Lake Victoria inside it because larger water hyacinth mats were (Fig. 1) environments favouring establishment of WATER HYACINTH D1STRUBITION LAKES VICTORIA, KYOGA 3 water hyacinth were usually located at the tips of phytes. The small plants were clearly the product small bays and inlets within large bays such as of vegetative propagation from pieces of stolon Macdonald and Murchison. Water hyacinth broken up most probably by the waves. occurred in large well established mats already Water hyacinth mats were also found at unexpected breaking off to supply new invasion units. The locations such as exposed shores with hard rocky water weed was also frequently found as newly or sandy bottom not identified during the surveys established mats growing luxuriantly or in form as suitable for weed establishment and luxuriant of propagules consisting of one or several plants growth. Such mats usually showed poor growth cryptically perched among emergent macro- ~ Q ~ :z:.. ! ...'!! s • ...0 '"0 ~., fi .. '~ ct t; ., 0 .. ..... ...0 '" ... !!; :i: - ..J 0 0 a: ... « ;: z ;: '" 0 z .,~ a:.. ... .. ~ I!: ... ... l- => 0 I.> ... !: e 0 I \l I I I -> '0 o !AI o ~I ~ ...ct '0 o.. '0 .. o OJ'" '" '" Jo '".. o Fig. 1. Water hyacinth infestation (Jan. 1992) and potential for established prolification on lake Victoria Uganda 4 T. TWONGO, F.W.B. BUGENYI AND F. WANDA It :z: ____.. ). 0 -<,.. I n en IIII I :IE c.. r- I -c < Qi :z: - 0 ~ ;_, :z )0 :z: '" i: ...... -< "lI :z Q i: :z: I 0 ~ ,.. 1&1 '",. (I) 0 ~ ;:: - ~ -c ;- -c '" ~ ::I) "' -c c: ,.C (5 ~ (4 ..... :z: (4 .. ,. or (M N N ~ 0 0 "'0 (M (M 0 O. )10 ~ n () or or o o o \ "\ Fig. 2: Water hyacinth infestation on lakes Kyoga and Kwama - Nov. 1991 (From 1WONGO, 1991a) WATER HYACINTH DISTRUBITION LAKES VICTORIA. KYOGA 5 and were likely to have been stranded at the Hyacinth-macrophyte associations locations by onshore winds. It was noted that along the shores of the small nar- They would probably drift off as soon as the row and generally shallow Lake Kyoga (average winds ceased to blow or changed direction. This depth 3m), sheltered environments that supported type of "migratory" hyacinth was a constant establishment of water hyacinth were not con- problem at landing sites in heavily infested bays. fined to bays and inlets as was basically the case in Lake Victoria. Straight shores fringed by emergent In Lake Kyoga (Fig.2) water hyacinth had already macrophytes notably C. papyrus, Vossia sp. and at spread to cover most potential sites for infestation times, by Cyperus spp.

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