Ecosystem structure and dynamics: a management basis for Asian reservoirs and lakes.

Abstract

INCO-DC FISHSTRAT Project, funded by the European Commission, is an ongoing multidisciplinary research program undertaken over the period 1998–2001. Three reservoirs in Sri Lanka (Victoria, Minneriya and Udawalawe) of different morphology, age and geographic location, Ubolratana reservoir, in Thailand, and Lake Taal, in the Philippines, are the object of this study. The scope of the project encompasses a comparison of the limnology, fisheries and socioeconomic aspects of local communities in order to determine whether the trophic characteristics and key ecosystem processes sustain the available fisheries, and to examine the ecological potential for increased fish production by intensive cage culture. The paper first presents integrated results on trophic state, trophic structure and food web relationships of different water bodies. The results demonstrate the importance of ecosystem-orientated analysis in order to optimise management strategies. The broad spectrum of Asian water bodies studied allows testing of a set of hypotheses on: 1) the control of the trophic state of lakes and reservoirs by geographic, climatic and morphometric conditions; 2) the significance of the structure of the fish assemblages (biogeography, exotic species) on ecosystem processes; 3) bottom up versus top down control under Asian reservoir and lake conditions (in comparison to established concepts for water bodies in the temperate zone); and 4) the human impact and resilience of ecosystem processes and trophic conditions towards human impact. A COLLABORATIVE international project funded by the European Union’s INCO-DC Program is undertaking research in five water bodies (four reservoirs and one lake) in Sri Lanka, Thailand and the Philippines over the period 1998–2001. The partner institutions within this Project are from the three Asian countries, the United Kingdom, Austria, France, the Netherlands and the Czech Republic. The program combines three main research fields: 1. Ecosystem orientated limnological studies; 2. Fisheries and fish communities; 3. Socio-economics of the riparian fishing communities. The aim of the program is to integrate the results from the three fields and to define their interdependencies. The ecology of the reservoir ecosystems determines the habitat quality and the carrying capacity for fish and provides the basis for its fisheries and local socio-economics. On the other hand, there are top-down influences on the aquatic ecosystems by fisheries management via exploitation, stocking practices, cage culture etc. and by the socio-economics of the local communities via landuse practices. Also the regulation of the hydraulic regime for irrigation and hydroelectric power generation, have profound impacts on the ecology of the aquatic resources (Figure 1). 1Department of Limnology, Institute of Ecology and Conservation Biology, Althanstr. 14, PO Box 285, A-1091 Vienna, Austria. E-mail: friedrich.schiemer@univie.ac.at 2Department of Zoology, University of Kelaniya, Kelaniya 11600, Sri Lanka. E-mail: zoousa@kln.ac.lk 3Hydrobiological Institute AS CR, Na sadkach 7, 370 05 Ceske Budejovice, Czech Republic. E-mail: frouzova@ hbu.cas.cz 4Department of Fisheries, National Inland Fisheries Institute, Pholyothin Road, Jatujak, Bangkok, 10900, Thailand. E-mail: boonsosr@fisheries.go.th 5Institute of Fundamental Studies, Hantana Road, Kandy, Sri Lanka. E-mail: sil@ifs.ac.lk