Zoology
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Item Promotion of sustainable capture fisheries and aquaculture in Asian reservoirs and lakes(Hydrobiologia, Springer Netherlands, 2001) Amarasingha, U.S.; Dancun, A.; Moreau, J.; Schiemer, F.; Simon, D.; Vijverberg, J.A collaborative international project funded by the European Union’s INCO-DC programme is undertaking limnological, fish biological, environmental and socio-economic research in five tropical lakes and reservoirs in Sri Lanka, Thailand and the Philippines over the period 1998–2001. The aim is to determine their trophic structure and their capacity to sustain both their existing fisheries and present and future aquaculture. In some cases, these activities could potentially be expanded for the benefit of rural communities and of the local market within the bounds of social and environmental sustainability. This paper describes the concepts and methods involved in this innovative multidisciplinary project which aims to integrate limnological, fisheries and socio-economic issues in a comparative approach involving Asian and European research teams.Item Use of geographical information system and remote sensing techniques for planning culture‐based fisheries in non‐perennial reservoirs of Sri Lanka(Journal of Lakes & Reservoirs: Research & Management, 2014) Wijenayake, W.M.; Gunaratne, A.B.; de Silva, S.S.; Amarasinghe, U.S.The presence of a wide areal extent of small-sized village reservoirs offers a considerable potential for the development of culture-based fisheries (CBFs) in Sri Lanka. To this end, this study uses geographical information systems (GISs) and remote sensing (RS) techniques to determine the morphometric and biological characteristics most useful for classifying non-perennial reservoirs for CBF development and for assessing the influence of catchment land-use patterns on potential CBF yields. The reservoir shorelines at full water supply level were mapped with a Global Positioning System to determine shoreline length and reservoir areal extent. The ratio of shoreline length to reservoir extent, which was reported to be a powerful predictor variable of CBF yields, could be reliably quantified using RS techniques. The areal extent of reservoirs, quantified with RS techniques (RS extent), was used to estimate the ratio of forest cover plus scrubland cover to RS extent and was found to be significantly related to the CBF yield (R2 = 0.400; P < 0.05). The results of this study indicated that morphometric characteristics and catchment land-use patterns, which might be viewed as indices of biological productivity, can be quantified using RS and GIS techniques.Item Limnology and culture-based fisheries in non-perennial reservoirs in Sri Lanka(Lakes & Reservoirs: Research & Management, 2005) Jayasinghe, U.A.D.; Amarasinghe, U.S.; de Silva, S.S.This study was carried out to investigate the possibility of using the limnological characteristics of non-perennial reservoirs in Sri Lanka for the future management of culture-based fisheries. Forty-five reservoirs were randomly selected to study their limnology, out of which 32 were stocked with fish fingerlings of Chinese and Indian carps, tilapia and freshwater prawn at stocking densities ranging from 218?4372 fingerlings ha?1. Of these, 23 reservoirs were harvested at the end of the culture period (6?10 months). Thirteen limnological parameters were measured during the water retention period of each of the 45 reservoirs between November 2001 and January 2004. The mean values of the limnological parameters were used to ordinate the reservoirs through principal component analysis. Ordination showed a productivity gradient among reservoirs where Secchi disc depth, total phosphorus, chlorophyll-a, inorganic turbidity and organic turbidity were identified as key factors. The total fish yield of culture-based fisheries was positively correlated to the scores of the first principal component axis. This study reveals that it is possible to classify non-perennial reservoirs in Sri Lanka based on the above limnological parameters in order to develop culture-based fisheries and that they could be applicable in comparable water bodies elsewhere in the tropics.Item Use of geographical information systems as a tool for predicting fish yield in tropical reservoirs: case study on Sri Lankan reservoirs(Fisheries Management and Ecology, 2001) de Silva, S.S.; Amarasinghe, U.S.; Nissanka, C.; Wijesooriya, W.A.D.D.; Fernando, M.J.J.Use of geographical information systems (GIS) in inland fisheries has hitherto been essentially restricted to site evaluation for aquaculture development and assessment of limnological changes in time and space in individual water bodies. The present GIS study was conducted on the land-use pattern of the catchments of nine reservoirs in Sri Lanka, for which detailed fishery data, viz. yield, fishing intensity, landing size of major constituent species, together with selected limnological data such as conductivity and chlorophyll-a, were available. Potential statistical relationships (linear, curvilinear, exponential and second-order polynomial) of fish yield (FY, in kg ha?1 yr?1) to different land-use patterns, such as forest cover (FC, in km2) and shrub-land (SL, in km2), either singly, or in combination, and/or the ratio of each land type to reservoir area (RA in km2) and reservoir capacity (RC in km3), were explored. Highly significant relationships were evident between FY to the ratio of SL and/or FC+SL to RA and/or RC. Similarly, the above land-use types to RA and RC ratios were significantly related to limnological features of the reservoirs. The relationships of FY to various parameters obtained in this study were much better correlated than those relationships of FY to limnological and biological parameters used in yield prediction in tropical and temperate lacustrine waters previously.Item Sri Lankan reservoir fishery: a case for introduction of a co-management strategy(Sri Lankan reservoir fishery: a case for introduction of a co-management strategy, 1999) Amarasinghe, U.S.; de Silva, S.S.The inland fisheries of Sri Lanka are essentially artisanal on most of the reservoirs in the country. The annual inland fish production declined dramatically after 1990, when state patronage for the development of the inland fisheries was discontinued for 4 years. This decline was shown to be a result of growth overfishing of the two dominant cichlid species which accounted for over 90% of landings. This was a result of using small mesh (?Item Impact of Oreochromis mossambicus ? O. niloticus (Pisces: Cichlidae) hybridization on population reproductive potential and long-term influence on a reservoir fishery(Fisheries Management and Ecology, 1996) Amarasinghe, U.S.; de Silva, S.S.Exotic cichlids, introduced to Asia during the second half of the twentieth century, contribute significantly to the reservoir fisheries in the region. The two major cichlid species, Oreochromis mossambicus (Peters) and O. niloticus (L.), tend to interbreed easily. In Sri Lankan reservoirs, introgressive hybridization of these two cichlids takes place. The reproductive biology of O. mossambicus, O. niloticus and their hybrids in three reservoirs in Sri Lanka was evaluated. An imbalance in sex ratio with male dominance was evident. The estimated fecundity for 20-cm fish, using fecundity-total length relationships for various populations, indicated that there was a decline in fecundity in hybrid forms. It is hypothesized that the long-term effect of crosshybridization between the two cichlids might lead to a decline in fish yields in perennial reservoirs of Sri Lanka. The importance of the findings of the present study for the management of the reservoir fisheries in Asia is highlighted.