• View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Aquatic Commons THE A leA JOU L OF (Afr. J Trop. Hydrobiol. Fish) Yo. 1 1994 ASPECTS OF THE BIOLOGY OF THE lAKE TANGANYIKA SARDINE, LIMNOTHRISSA n illustrated key to the flinji. (Mimeographed MIODON (BOULENGER), IN lAKE KARIBA ~as Development Ad­ ndon). R. HUDDART ision des Synodontis Kariba Research Unit, Private Bag 24 CX, CHOMA, Zambia. e Royal de I'Afrique 'en, Belgium. 500p. Present address:- ~). The ecology of the 4, Ingleside Grove, LONDON, S.B.3., U.K. is (Pisces; Siluoidea) Nigeria. (Unpublished ABSTRACT o the University of Juveniles of U11lnothrissa 11liodon (Boulenger) were introduced into the man-made Lake Kariba in ngland). 1967-1968. Thirty months of night-fishing for this species from Sinazongwe, near the centre of the Kariba North bank. from 1971 to 1974 are described. Biological studies were carried out on samples of the catch during most of these months. Limnological studies were carried out over a period of four months in 1973. Li11lnothrissa is breeding successfully and its number have greatly increased. [t has reached an equilibrium level of population size at a [ower density than that of Lake Tanganyika sardines, but nevertheless is an important factor in the ecology of Lake Kariba. The growth rate, size at maturity and maximum size are all less than those of Lake Tanganyika Li11lnothrissa. A marked disruption in the orderly progression of length frequency modes occurs in September, for which the present body of evidence cannot supply an explanation. INTRODUCTION light-attracted sardines in Lake Kariba were The absence of a specialised, plankti­ tested in 1970 and early 1971. Dip nets vorous, pelagic species of fish within the (lusenga nets), as used by Lake Tanganyika middle Zambezi fIsh fauna occupying the artisanal fisher-men, and lift nets caught new lake became obvious soon after the an average of less than 50 individuals per formation ofLake Kariba in 1963.Juvenile night. Afairly large (50m. by20m.) chiromila clupeid sardines were airlifted from Lake net caught an average of 23 kg. per haul. Tanganyika in 1967 and 1968 in order to Similar-sized catches were obtained fill this vacant niche. Sardines over 25 mm. throughout the lake from the dam wall to in lengthwere unable to survive the catching the Zambezigorge (Devil'sGorge) whether and transporta-tiorf process. Of the two from deep open wateror from shallowbays. species of Lake Tanganyika sardine, Thus Limnothrissa had become fIrmly Limnothrissa miodon (Boulenger) and established throughoutLake Karibaby 1970­ Stolothrissa tanganicae (Regan), the latter 71 and several catches of 0.5 tonnes per is the more pelagic while young. Hence, night1)ave more recently been taken in the only Limnothrissajuveniles could be found Sinazo:ngwe area. The study reported here near the shore and be driven into contain­ describes some investigations into the ers. biology of this species from 1971 to 1974 Unpublished data held by the Research in Lake Kariba. Division of the Fisheries Department of METHODS Zambia! show thatvarious methodsfor fishing Samplesofsardinewere obtainedby fish­ ing at night using lights and a chiromila 1. The Department ofWildlife, Fisheries and National Parks net, as described by COULTER AND of Zambia was split in January, 1974 the fisheries component ZNAMENSKY (1971), slightly modified to becoming the Department of Fisheries of Zambia. 32 RHUDDART suitlocal conditions. Unless othetwise stated, Samples of66 sardines with a roughly even RESULTS the net used measured 50m. by 20m. The length distribution were taken and their Polpulation lev buntwas of8 mm. mesh nylon. All samples lengths and weights measured. There were The total cat were obtained fromwithin 5 km. ofthe Sina­ 66 spaces on each of the cyclostyled data ably after April zongwe Fisheries Training Centre, itself160 sheets prepared for this study and it was km. from the dam wall and within basin III found that the size of sample dictated by ofthe lake as described by COCHE (1968). the fIlling-in of one of these sheets was These samples, unless otherwise stated,were adequate for the construc-tion ofa length/ soc taken within I km. from the shore in water weight curve. From each length/weight 15-20metres deep. Fishingstartedat2000hrs curve the weights at the arbitrarily-chosen local time and continued until the dawn of lengths of40mm., 55mm. and 70mm. were the following day. The sample for laboratory read off. These are shown plotted study was most often taken from those fish against calendt;r time in Fig. 6. K caughttoward the endofthe fishing period, A large, random sample of 400-1600 due to theirfresher condition, and therefore sardines was measured for length only, the a sample from, for instance, the night of llSualsamplesize beingbetween 700and 1000 IIthand 12thSeptemberis referred to below individuals. A length frequency histogram as a sampIe from September 12th. was prepared for each such large sample so As manyhauls as possiblewere made each that the mode or modes of the distribution night in order to render more accurate the could be distinguished. K calcul"ted catch per haul. A crew of10 men For the purpose ofthis analysis, the stages was originally necessary, using three boats of gonad development are distinguished llo,C and making amaximum ofonly 6-7 hauls per into only two groups, ripe and unripe. Ripe night, so thatmostofthe available research gonads occupied mostofthe body cavity and resources were expended in the routine the eggs were a deepmustard yellowin colour sc runningofthis commercial-scale operation.'TIlls and fully formed. Testes were opaque and situation gradually improved as con­ white. ELLIS (1970) separated female tinuous development of net-handling Limnothrissa into three stages of gonad • hydraulicmachinery made 24hauls pernight developmentand males into two. Samples of possible by early 1974 using only two boats 120-150 fish were taken for gonad examina­ andsix crewmembers. The number oflight­ tion. boatswas increasedinproportion to the number An all-glass displacement sampler was ofhauls per night (unmanned "light-buoys" used to obtain water s<lmples for primary serving the same function as manned light­ productivity studies. Otherwise, all water boatswere usedfrom early 1972) so thateach samples were obtained using a Nansen light-boat remained attracting sardines for sampler. Oxygen determinationswere made 1-2 hours before being fIshed. using the standard Winkler method as Fresh wet weight and fork length (the described by COLTERMAN (1968) and light distance from the tip ofthe snout to the end and dark bottle experiments followed the %1 ofthe median caudal rays) were measured. techniques described byVOLLENWEIDER Weight determinations were made using (l~). a torsion balance on which 0 to 1 gm. was A fleet of multifIlament gill nets with measured by the rotation of the torsion 50% mounting ratio and of various mesh spring and 0 to 10 gm., in 1 gm. steps, by sizes was regularly setovernight fur trapping Fig. 1 Limno adding or subtracting metal weights. speciespossibly predatoryupon Limnothnssa. night 33 BIOLOGYOFUMNOTHRISSAMIODONINLAKEKARIBA 'dines with a roughly even RESULTS in the number of hauls per night (Fig. 1). on were taken and their Polpulation level The catch per haul remained steady until tIts measured. There were The total catch per night rose consider­ Decem-ber, 1973 when replacement of h of the cyclostyled data ably after April, 1973 due to the increase paraffin pressure lampswith propane lamps for this study and it was ze of sample dictated by one of these sheets was :onstruc-tion ofa length/ SOO-r---------------------;("':":'1) om each length/weight A at the arbitrarily-chosen ,55mm. and 70mm. were e are shown plotted ime in Fig. 6. Kg am sample of 400-1600 ured for length only, the ~ingbetween700 and 1000 gth frequency histogram :ach such large sample so nodes ofthe distribution ihed. :ofthis analysis, the stages ,ment are distinguished ps, ripe and unripe. Ripe lostofthe body cavity and lmustard yellow in colour Testes were opaque and 500 170) separated female three stages of gonad lalesinto two. Samples of • lken forgonad examina- Kg )lacement sampler was er samples for primary s. Otherwise, all water I 0 I lined using a Nansen (B)\ terminationswere made 5 :1 Winkler method as ~RMAN (1968) and light Kg leriments followed the 0 0' 0 d by VOLLENWEIDER i'J100 filament gill nets with J and of various mesh t overnight for trapping Fig. 1 Limrwthissa catches from night fishing. A: total catch per night B: average catch reI' haul for that ltoryupon Limnothrissa. night C: proportion of full moonlight occurring. dependent on the lunar cycle and cloud. 34 RHUDDART andmuch heavierweightingofthechiromila The considerable detrimental effect of revealed. Somt net to suit its faster operation resulted in moonlightonsardine catches (Fig. 1) follows sampIingatthirl an increase. Adverse weather conditions thesituation inLake Tanganyikawhere com­ in Fig. 2. caused much late starting and early aban­ mercialfishing is suspendedduringfull moon, According t< donment of fishing trips inJanuary, 1974, buttherearenoseasonal fluctuationsinsardine is nearest to tlH preventing an associat-ed increase in total landed like those in Lake Tanga-nyika: the ofdawnanddm catch. records of the CENTRAL STATISTICAL 4 metres durin OFFICE (1971) show that sardine landings through thewatl increased markedly in Lake Tanganyika of the sardine: duringAugust-Novemberin 1969 and 1970 4 metres ofwat andwere associatedwith minimainJune:July Proportion of in 1969andApril-May in 1970. The catch per Therewas al haul ofintroduced sardine in Lake Kariba 1000l 2.00 in deepoflShon 18 Oct -1 10 Noy (which is, in this-case, a closeapproximation chiromilasamp to catch peruniteffort) has beensteadysince within 1 kIn oft atleast 1971. There have beenno detectable 1. A year-by-yt changessince, apartfrom those induced by jj II steadily falliI j improvedfishing technique. Fishing continued although this .. I over all phases of the moon in the present monthly avera! LJI study, resulting in a lower average catch per The length 0 0 haul thanin 1970,when fishingwas suspend­ lOOO 100 ed duringfull moon.