RESERVOlR FlSHERIES 1N SOUTH EAST ASIA : PAST, PK13SEN'14 AN11 FUTURE C. H. Fernando Ilcpmtment of Biolog.~, Uniuersifg. of Wntwloo Waterloo, Onturio, Canuda Abstract Reservoirs are being constructd at :in accelerating pace in S*)uthEast Asia adding vastly to ancient and more recently built reservoir systems. At present ihc reservoir area for the region is 5.0 million hmn and the figure will itlcreasc to I 5 million hm2 before the turn of the ccntury. Natural lakes in South East Ash are few and some of theare atypical (flood lakes). Fisheries it1 South East Asian reservoirs arc of very recent origin ;ind poorly developed. Fish yields :ire low in most areas. Indigenous fish species in South East Asia are mostly riverine. Introduced African cichlid fish (mainly T, mossambicaj have increased spectaculai~lgfish, yields in some areas. This can bc attributed to their more efficeint exploitation ofthe lacustrine h.shitat. It is suggested that introduction of lacustrine species is necessary if fish yields from reservoirs in South '\ktAsia :Ire to he increased to levels comparable to those founc! in tropical Africn. Some adverse effects due directly or indirectly to the introduction of T. rnossambicn have been re.ported. Thesc include interference with culture in fishponcls and the spread of parasites. The effect of introduced fish on fish yields in deep and up-country reservoirs has so far been small. It is suggested that deep water African cichlids be introduced into deep reservoirs and cold water tolerant species into reservoirs at high a1tit~1d.e~.It is suggested tlut iutroduc-d foreign lacustrjne fish may not take easily in areas like the Mekong where thc indigenous fish fallria is rich in species. Cooperation between the different countries in South East Asia is desirable in developing reservoir fisheries. The shartng of expertise nntl hcilities will enable a more realistic and vlakle approach to research on and management of reservoir::. The potentla1 5 r ~ncreasedfish yields from South East Asian reservoirs is high. A rough estimate of rhc total reservoir yield hy the end of this century is 1.25 million tons. This fish yteld wrll also be avail:hle at: relat~velylou-=?st, on a sustainalde basis and in rc@ons where protein shortage is greatest. CONTENTS r. INTRODUCTIOK 2. RESERVOIRS : AREAS AND DIS'rRlBUTI( IN 3. THE FTSI-1 FAUNA 3.1 Tnd~gcnousfis'i fauna 3.2 Inti c ductlon OF foreign iisb speclcs Into reservoirs 3.3 'The irnpnct of tntlocluced fish species 4. PRESENT 1X5II PRODUCTION IN KESERVOlRS 5. FUTUKE 1WH INTR0DUCTIC)KS 6. BIOLOGICAI, STUDIES ON KESERVOIRS 7. hlANAGLMEN?' OF RESORVOIR FlSIIIXlES 8. ACKNC>WLEDGHMENNIS 9, RFTER13NCIiS I. INTRODUCTION If the age of reservoirs is of any significance, South East Asia has the oldest. Reservoir building is suppwed to have c mrn~nc-dab?ut 4 ooo years apand they are being built at an accelerating pace in many parts of the world. This is true of S mth Elst Asia where the present reservoir area of about j million hm2 will increase to about 15 million hm3 by the turn of this century. S nth Iht Asia is conspicuously poor in natural lakes compared to any other region except arid areas and S )uth Americ?. H~wever,both South America and Smth East Asia are rich in running waters; hence they possess a high potential f.)r reservoir construction. Fisheries in reservoirs of any magnitude date back only a vcry short time 111 Sw~thEast Asia and the potential for fish production has been rcali .ed only to a very limited cxtent. The failure of indigenous fish species to give high yields In reservoirs is due to the lack of a lacustrine component among Snuth East Asian fishes. The plucky of natural lakes jn the region is certainly a major cause for this lack. Hqwever, in the last 20 years or so, reservoir fi jheries have assumed considerable importance in limited areas ltke Sri Lanka, and this tend-ncy is spre-ding thrmghout the region. Marked increases in fish yields from reservoirs havc been noted in areas where Tilnpia spp. (mainly T. mssambica) have been introduced. In the prcsent paper I shall discuss thc extent of reservoirs in South Jhst Asia in relation to other standing waters and the fish production from tkse reservoirs in the past, present and future. The composition of the indigenous fi;h fauna a~dthe role of intr?ducecl fish species on fish prod~ictionin reservoirs in S~thEast Asia will be evaluated. Rased on past experience, and the present situation, an attempt will be made to assess future fish yields. The data I have used are drawn mainly from Sri Lanka, but I have included the available published and unpublished dxta from other parts of Smth East Asia. The reservoir fisheries of India have been ~~~~~~~~~d by J1lingran (1975). Fernando (1965, 1971, 1973) and Fernand,) and Indrasena (1969) ]lave deaIt in dctail with the reservoir fisheries of Srl Lanka. Achmad (1970) gives some data on an lnd~nesianreservoir. Yap (1974) gives fish prodwtion data for a Malaysian res-rvoir and Oopatham Pawaputonon (1976) gives dlta on fish production in Thai reservoirs. The earlier dm on reservoir fisheries in South East Asia have been summariz~dby Hickling (1961). Fernando and Furtado (1976) havc summarizzd the more recent data. 2. RESERVOIRS : AREAS AND DISTRIBUTION In 195 t the reservoir area of S ~thEast Asia was estimated at less than I million hma (IPFC report quoted hy Dassart, 1974). The total area of standing watcr in the region was estimated in the same report as 3.2 million hm2. Th~sincluded rice fi-lds, estuaries, natural lakes, brackishwaters and fishponds. The present extent of reservoirs in the region is abmt 3.0 million hm2 (Table I). At the turn of the century this fi~ureis expected to Increase to 15 million hm"Tab1e I). The total area of natural l-tk-s in the reg-ion amounts to only 1.8 million hm2. Hwwux, this fi ;ure in- clude~the f1oc.d 1, k~ of Camb :dia and I<dirnantan a~dthe high al-itude lak-s in India and Pakistan. The first type is not typical and the sec?nd group not tropicd. Only Ind3nesia and The PhiIippines have siz~ble areas of natur~llakes. A gmd p-irtion of lndonesian 1~kes is l~atcdin S ~luwesi(Tabl: 2) which is on the wrong side of Wallace's line for Cyprinidae and Siluroid-a-fishes which are the mainstay of Asian freshwaters. Reservoirs are by no means evenly d;stributecl in Swth E%st Asia (Table I, Fig. I). The highest con- centration of ancient reservoirs is found. in Sri Lark? (Fig. 2). Recently constructed (mainly llrge) reservoirs are cmccntrated in Tnclia ard the Mekong region (FI~.I). Active reservoir construction at an accelerated pace is going on in Indonesia, S.:i Laaka, l.t~diaancl the Mckong region. Details of reservoir areas in the region are available for somc countries only. Jhingran (1975) has given a list of rnaj~~rlndlan reservoirs and their areas. Fernando (1973) has ;:iven a clerailec! list of all reservnirs over 300 hm in S -i Lwka. Data from 'I'hailand and Indmesia are given in Tables 2 and j. Fcrnandf) and Purt~do(1976) have m2.d.: estimates wherc p-)ssible of reservoir areas in th.e region ('Table I), but there is a gap in our knowledge of reservoir areas in Burma, Bangladesh, Victnam, Laos adCambodia. 3. THE FISH FAUNA 3.1 Indigenous fish fauna The tropics f-rm three widely separated, faunally distinct arcas, as far as freshwater fiih are c~nc-,rned. Lqwe McCmnell (196~)has reviewed this subject in detail and has discussed the re;ls-ms for this diIference and its implications. Of the three areas, only Africa has a lacustrine component in its fi;h fauna. The number of indigenou~freshwater fishes in each country of Smth East Asia is shown in Fig. 3. They vary from the very rich fauna of Thailand to the very poor fauna in Sri Lanka. Lowe McConnell(1969) gives fi:ur$s fxAfrican lakes, the Am2 :on Central America, Argentina and Smth Africa. S2me African lakes have over zoo species and the majw Africm rivers are rich in species too. The Amazon has over I ooo species. Althouph riverine fish are numerous, b9th S mth (and Central) America and Swth East Asia have few l~custrinefreshwater fi;hes, although Myers (1960) found a species flock of Cyprinidae in Lake Lanao, The Philippines. Tropical Asian and Ssuth American freshwater fish faunas ate dominated. by Cyprinoidea and Characoidea respectively. Fishes of these families often breed only during high water following fl~ods.Lqwe McCmnell (1969) points out that the lacustrine cichlids of Africa breed throughout the year giving mqre stabl.: p3pu- lations of all siz-s. S-asonal fluctuations in food occur to a lesser extent in lacustrine than in riverine c3n- ditions. Plarktonivorous species can be expected in lacustrine conditions but hardly in riverine cmd'tions. The net result of these adqptations is that when reservoirs are built in Sonth East Asia the fish recruits available are orly poorly adapted for lakes. The indigenous fi;hes that colonized reservoirs in Sri Lanlia include practically the whole spectrum of available species except torrent dwellers and some small stream fi;hes. A similar situation probably exists in other parts of South East Asia. The d~minantfish in the catch were the larger carps and large predltors. However, in no reservoir in the whole of S mth East Asia was the fi;h yield of indigenous species c3mparable to the high yields recorded in African reservoirs stocked with African cichlids (Hickling, 1961).