by U. S. Amarasinghe, Department of Zoology, University of Kelaniya, Sri Lanka
and C.H. Fernando, Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
Reservoirs, not lakes, comprise the most widely distributed, large standing freshwaters globally today. Perhaps the highest concentration of reservoirs in the world is found in Sri Lanka, a country of 65,600 km2 with over 10,000 reservoirs (Fig. 1). The largest reservoir is circa 80 km2, about 40 are over 500 ha in surface area (FSL), but the majority (about 43% of the total reservoir area) are less than 250 ha (Table 1). While most of these reservoirs are in the low country, a few, especially the larger ones built recently, are at higher altitudes.
Reservoir building started about 600 BC and Sri Lanka has one of the most sophisticated irrigation systems ever constructed. Small reservoirs, often fed from large reservoirs, were constructed to form a cascading sequence within micro-catchments allowing a high efficiency of water use (Fig. 2). Rice cultivation using this system of reservoirs and channels supported a large population but this civilization collapsed about 500 years ago perhaps due to malaria, an accompaniment of irrigated rice cultivation even today. During the nineteenth century many ancient reservoirs were restored and, more recently, multipurpose reservoir systems were added.
Some of the earliest limnological studies on tropical reservoirs were done in Sri Lanka by Apstein (1907, 1910) on plankton ecology. Holsinger (1955) studied the phytoplankton of two reservoirs and zooplankton species and size composition were characterized by Fernando (1980a, b). Taxonomic studies covering all the zooplankton are available (see Costa, 1994; Fernando, 1990).
In Sri Lanka reservoirs have altered the landscape dramatically (Fernando, 1993). Together with a honeycomb of irrigation channels and streams, they have made the dry zone verdant and agriculturally productive. Fish have recently become an important additional biological resource. This started in the early fifties when an African cichlid fish, the tilapia Oreochromis mossambicus was introduced and in a few years became the basis of a commercial fishery. Most of the 30-40,000 tons of fish harvested annually now come from the larger, shallow low country reservoirs (Amarasinghe, 1995; De Silva, 1988; Fernando & Indrasena, 1969). Recently minor cyprinids have been assessed as a potential supplementary resource for harvesting commercially (Amarasinghe, 1985) but this fishery is still not operative.
Nevertheless, inland fish now provide a substantial food source at very low cost and the fishery provides employment to large numbers of people who otherwise may have sought employment in the already overcrowded towns.
Fish culture in small reservoirs (and ponds) has so far been a failure in spite of the investment of substantial funds, training of researchers and field workers, and the work of both local and foreign experts over 50 years. A study of the fisheries of reservoirs may provide clues to help reverse this failure. Oreochromis mossambicus and the more recently introduced O. niloticus have provided very profitable culture fisheries throughout the tropics and may do the same for fish culture in Sri Lanka.
Many scientists, with a strong indigenous component mostly from local universities, have studied a wide variety of limnological and fishery problems in reservoirs, including systematics of invertebrates and vertebrates (Fernando, 1990; Pethiyagoda, 1991), physico-chemical research (Costa, 1986; Gunatilleke, 1983), fish ecology and fisheries (De Silva, 1988; Amarasinghe, 1992) and the role of birds (Winkler, 1983). Over 150 research papers have been published (for reviews see Amarasinghe, 1992, 1995; Costa, 1994; De Silva, 1987, 1988; Fernando, 1993; Fernando & Indrasena, 1969). A volume that includes many aquatic studies (Fernando, 1984) and another devoted to a large shallow reservoir (Schiemer, 1983) also cover many aspects of reservoir limnology and fisheries. It is perhaps fitting that a theory to explain the extraordinary success of lacustrine compared to riverine fishes in lakes and reservoirs (Fernando and Holcik, 1991) drew its early inspiration from research in the country with the highest density of reservoirs.
The growing economic importance of reservoir fisheries has encouraged many studies in different parts of the country and a centre for these studies is now needed and the first steps have already been taken by the Zoology Department of University of Kelaniya. A library is being accumulated and funding is now available for field research from both national and foreign sources. Among the collaborative research activities centred at the University of Kelaniya are: A project on reservoir fishery with Deakin University, Victoria, Australia currently in progress under the auspices of The Australian Centre for International Research; Project funding under the INCO-DC program of The European Commission supports research in reservoir limnology and fisheries joinly with Royal Holloway, University of London, UK, the University of Vienna, Austria, Ecole National Superieure Agronomique, France, the University of the Philippines, Diliman and The National Inland Fisheries Institute, Bangkok, Thailand; Active research is also being carried out in cooperation with NARESA (National Aquatic Resources Research and Development Agency of Sri Lanka), Colombo and The Institute of Fundamental Studies, Kandy. These two local funding sources are for researchers in fisheries at the senior level and graduate students. Support is also provided for funding visiting researchers.
During the past two decades many students from The University of Kelaniya have proceeded to higher degrees in aquatic sciences at that University and abroad. A student completing his M. Phil. was recently awarded a Tonolli Fellowship by SIL to study tropical aquatic oligochaetes in Canada. Three projects in reservoir limnology and fisheries training M.Phil. and Ph.D. students are in progress at Kelaniya.
Sri Lanka offers a comprehensive base of literature on aquatic ecology including a manual on the fauna and fisheries (Fernando, 1990). Recent research activity in limnology and fisheries has attracted many researchers both local and foreign. It is hoped that courses in reservoir limnology and fisheries will be organised for postgraduate students using library and field facilities now available at the University of Kelaniya. We have compiled a selected bibliography of papers in reservoir limnology and fisheries in Sri Lanka which will be included in the Internet version of this SILNEWS.
We are making an appeal for literature and other support from SIL members and other well-wishers internationally. For those travelling through Sri Lanka, we encourage visits to the center. Those wishing to give talks on their speciality are encouraged to do so. If adequate notice is given local arrangements can be made.
References
Amarasinghe, U.S. 1985. Studies on the exploitation of minor cyprinids in Parakrama Samudra, a man-made lake in Sri Lanka. J. National Aquatic Resources Agency Sri Lanka 32: 11-23.
Amarasinghe, U.S. 1992. Recent trends in the inland fishery of Sri Lanka. pp.84-105. In E. Baluyut (ed.) FAO Fish. Tech. Rep. No.454 Suppl. Rome.
Amarasinghe U.S. 1995. Sustainable development of the inland fishery of Sri Lanka under environmental constraints. pp.160-176. In T. Petr and M. Morris (ed.). FAO Tech. Rep. No.512 Suppl. Rome.
Anon, 1991. Natural resources of Sri Lanka. Conditions and trends. NARESA, Colombo, 280pp.
Apstein, C. 1907. Das plankton in Colombo see auf Ceylon. Zool. Jb.(Abt.Syst) 25:201-224.
Apstein, C. 1910. Das plankton des Gregory see auf Ceylon. Zool. Jb. (Abt.Syst) 29:661-680.
Costa, H.H. 1986. The physical, chemical and biological characteristics of freshwater bodies of the lowlands of Sri Lanka. Spolia Zeylan. 33:43-99.
Costa, H.H. 1994. Status of the limnology of Sri Lanka. Mitt. Internat Verein. Limnol. 24:73-85.
De Silva, 1987. Impact of exotics on the inland fishery resources of Sri Lanka. Arch. Hydrobiol. 28:273-293.
De Silva, S.S. 1988. Reservoirs in Sri Lanka and their fisheries. FAO Fish. Tech. Pap. No.298, 128pp.
Fernando, C.H. 1980a. The freshwater zooplankton of Sri Lanka, with a discussion of tropical zooplankton composition. Int. Rev. ges. Hydrobiol. 65:85-125.
Fernando, C.H. 1980b. The species and size composition of tropical freshwater zooplankton, with special reference to the Oriental Region (South East Asia). Int. Rev. ges. Hydrobiol. 65:411-426.
Fernando, C.H. (ed.), 1984. Ecology and biogeography in Sri Lanka. Junk, The Hague, 550pp.
Fernando, C.H. 1990. The freshwater fauna and fisheries of Sri Lanka. NARESA, Colombo, 444pp.
Fernando, C.H. 1993. The impact of Sri Lankan reservoirs, their fisheries, management and conservation. pp.351-374. In W. Erdelen, C. Preu, N. Ishwaren and C.M. Madduma Bandara (ed.). Ecology and landscape management in Sri Lanka. Verlag Josef Margraf, Weikersheim.
Fernando, C.H. & J. Holcik, 1991. Fish in Reservoirs. Int. Rev. ges. Hydrobiol. 76:149-167.
Fernando, C.H. and H.H.A. Indrasena, 1969. The freshwater fisheries of Sri Lanka. Bull. Fish. Res. Stn. Ceylon 26:83-105.
Gunatilleke, A. 1983. Phosphorus and phosphatase dynamics in Parakrama Samudra based on diurnal observations. pp.35-47. In F. Schiemer (ed). Limnology of Parakrama, Samudra, Sri Lanka. Junk, The Hague.
Holsinger, E.C.T. 1955. The plankton algae of 3 Ceylon lakes. Hydrobiologia 7:8-24.
Pethiyagoda, R. 1991. Freshwater fishes of Sri Lanka. Wildlife Heritage Trust of Sri Lanka, 362pp.
Schiemer, F. (ed.), 1983. Limnology of Parakrama Samudra. Junk, The Hague, 236pp Winkler, H. 1983. The ecology of cormorants (Genus Phalocrocorax). pp.193-200. In F. Schiemer (ed.). Limnology of Parakrama Samudra, Sri Lanka. Junk, The Hague.
Dr. U.S. Amarasinghe
E-mail:Â zoousa@kln.ac.lk
Fax: 521385 and 521916
Telephone 521407, 521391,
521397 and 520164