Science
Permanent URI for this communityhttp://repository.kln.ac.lk/handle/123456789/1
Browse
14 results
Search Results
Item Extent of the catchment of reservoirs of Sri Lanka: an important aspect in the management of their capture fisheries(Asian Fisheries Forum, 1998) Nissanka, C.; Amarasinghe, U.S.; de Silva, S.S.Item Influence of catchment characteristics on fish yields in reservoirs of Sri Lanka(Sri Lanka Association for Fisheries and Aquatic Resources, 1999) Nissanka, C.; de Silva, S.S.; Amarasinghe, U.S.; Wijesuriya, W.A.D.D.; Fernando, M.J.J.Item Population dynamics of Penaeus indicus (Crustacea: Penaeidae) in Rekawa Lagoon, Sri Lanka(Sri Lanka Association for Fisheries and Aquatic Resources, 1997) Nissanka, C.Item Fisheries in perennial reservoirs of Sri Lanka: Strategies for management(Sri Lanka Association for Fisheries and Aquatic Resources, 2008) Amarasinghe, U.S.; Nissanka, C.The inland capture fishery in Sri Lanka is essentially based on the multitude of perennial reservoirs in the country. It was developed after the introduction of the exotic cichlid species, Oreochromis mossambicus into Sri Lankan freshwaters in 1952. O. niloticus introduced in 1975 is also well-established in the reservoirs of the island. These two cichlid species, which form over 90% of total landings in the perennial reservoirs of Sri Lanka, are sources of high quality, affordable sources of animal protein for rural communities. The other unique characteristics of the reservoir fishery of Sri Lanka include, (a) the use of non-mechanized fibreglass canoes, approximately 6 m in length manned by two persons; and (b) the exclusive use of gillnets as the fishing gear (6-20 net pieces per craft), range of mesh size of which is from 7.5 cm to 12.7 cm, and each net piece being of a standard length and height of 60 m and 1.5 m, respectively. Small sized cyprinids are also abundant in Sri Lankan reservoirs. They can be differentially exploited using small-mesh (15-52 mm stretched mesh size) gillnets without catching juvenile cichlids because juvenile O. mossambicus and O. niloticus are only found in shallow (<1.5 m in depth), littoral areas of reservoirs and their adult counterparts, which are targeted by the fisheries, are found in deeper waters. These small cyprinid species (i.e., Amblypharyngodon melettinus, Puntius chola, P. dorsalis and P. filamentosus) can be utilized to make fishmeal or dried fish. Resource-based approaches such as length-based fish stock assessment methodologies have been employed to determine the optimal fishing strategies in the perennial reservoirs of Sri Lanka. Empirical models have also been developed to estimate potential fish production based on catchment land-use characteristics, which can be quantified by GIS methodologies. However, these resource-oriented approaches are inadequate for effective management of fisheries in perennial reservoirs of Sri Lanka. For this purpose, it is imperative that fishing communities be made active partners in decision-making process. A co-management procedure in which the centralized fisheries administration authority and fishing community share the responsibilities of making decisions for fishery resource management should be introduced for effective management of the reservoir fishery of Sri LankaItem Recruitment of Penaeus indicus (Crustacea : Penaeidae) to the fishery of Rekawa lagoon Sri Lanka: Is artificial enhancement possible?(Sri Lanka Association for Fisheries and Aquatic Resources, 1996) Nissanka, C.; Amarasinghe, U.S.; Jayakody, D.S.Item Land-Water Linkages in Rural Watersheds Electronic Workshop(2002) de Silva, S.S.; Amarasinghe, U.S.; Nissanka, C.Item Fish yield prediction based on catchment features , quantified using Geographical Information Systems, in lowland reservoirs of Sri Lanka(GIS/Spacial Analysis in Fishery and Aquatic Sciences, 2004) Amarasinghe, U.S.; de Silva, S.S.; Nissanka, C.Item Effect of hydrological regimes on fish yields in Sri Lankan reservoirs(Reservoir and Culture-based Fisheries: Biology and Management, 2001) Nissanka, C.; Amarasinghe, U.S.The need for empirical models for predicting fish yields in lakes and reservoirs, both in tropical and temperate regions, has long been recognised because investigation of the fisheries of individual water bodies for management purposes is prohibitive. In a previous study, morphological and edaphic factors, including extents of catchment areas in reservoirs of Sri Lanka, were found to influence fish yields. Hydraulic retention time is reported to be another factor influencing fish yields in tropical reservoirs. This paper attempts to investigate the effect of hydrological regimes on fish yields in irrigation reservoirs of Sri Lanka. Daily catch and effort data were collected from 10 shallow irrigation reservoirs from December 1997 to September 1999. Nitrate, phosphate and chlorophyll-a content in each reservoir were determined once in two months. Hypsographic curves (i.e. area-water depth relationships) and monthly mean data on reservoir capacity, water level, reservoir area and total outflow volume were obtained from the Department of Irrigation. Flushing rate (outflow/reservoir capacity) had little influence on water nutrients, chlorophyll-a and fish yields in reservoirs. As irrigation authorities control the hydrological regimes of these reservoirs, strong co-ordination between fisheries and irrigation authorities is useful for augmenting fish yields in the reservoirs of Sri Lanka.Item Fluctuations in Water Level in Shallow Irrigation Reservoirs: Implications for Fish Yield Estimates and Fisheries Management(Reservoir and Culture-based Fisheries: Biology and Management, 2000) Amarasinghe, U.S.; de Silva, S.S.; Nissanka, C.Due to fluctuations in water level, reservoir surface area changes considerably. Despite this effect, fish yields (Y) and fishing intensities (FI) in these reservoirs are often estimated for the reservoir area at full supply level (FSL). This paper compares the estimate of optimal fishing strategies according to this conventional method with those based on Y and FI calculated for actual mean monthly reservoir area. Catch and effort data, collected at least for 20 days a month from 10 individual reservoirs in Sri Lanka, were analysed to estimate mean annual fish yields (kg/ha/yr) and total FI (boat-days/ha/yr). Reservoir areas at FSL were used to estimate these values. Using the hypsographic curves and mean monthly water levels in individual reservoirs, actual mean reservoir area in each month in each reservoir was determined. Annual fish yields (kg/ha/yr) and total FI (boat-days/ha/yr) in individual reservoirs were then estimated, based on these actual reservoir areas. In both estimates, Y was linearly related to FI, indicating that the fish stocks were perhaps exploited at suboptimal levels. The results appear to indicate that the conventional method of using reservoir area at FSL to estimate Y and FI in multi-purpose reservoirs, instead of actual reservoir area, may have serious implications for fisheries management. An alternative method for estimating fish yields and FI is suggested for reservoirs with heavy draw-down.Item Yield predictive models for Sri Lankan reservoir fisheries(Fisheries Management and Ecology, 2000) Nissanka, C.; Amarasinghe, U.S.; de Silva, S.S.Tropical reservoirs are primarily constructed for irrigation, generation of hydroelectricity and water supply schemes. Development of inland fisheries is a secondary use of most reservoirs. In Sri Lanka, most reservoirs are scattered in the rural areas of the country so that investigation of the fisheries of individual reservoirs with a view to developing management plans is prohibitive. The present study was instigated to explore the possibilities of developing suitable yield predictive models, which can be used in developing management strategies for the Sri Lankan reservoirs. The study was carried out in 11 perennial reservoirs of Sri Lanka. Basic limnological parameters (conductivity, dissolved phosphorus, total phosphorus, chlorophyll a [chl a] content and alkalinity) were determined in each of these reservoirs. Daily data on fish catch and fishing effort were collected in each reservoir. Data on catchment areas (CA), reservoir area (RA) and reservoir capacity (RC) were obtained from the irrigation and survey departments. It is evident that chl a is positively influenced by nutrients (dissolved phosphorus and total phosphorus), morphoedaphic indices derived as alkalinity to mean depth (MEIa) and conductivity to mean depth (MEIc) ratios and CA/RC ratios. MEIa and MEIc are also positively influenced by CA/RC ratios. All these morphological and edaphic parameters were found to positively influence fish yield in reservoirs. As fishing intensity (FI) is also a major determinant of fish yields, fish yield was better accounted by multiple regression models in which FI and individual morphological and edaphic parameters were used as independent variables. Of these multiple regression relationships, the best predictive power for fish yield (Y in kg ha?1 yr?1) was found by Y=18.9+6.78 FI+0.0073 CA/RC where FI is expressed as boat-days ha?1 yr?1 and CA and RC are in km2 and km3, respectively. In this relationship, FI and CA/RC account for about 68% of the variation in fish yield.