Browsing by Author "Amarasinghe, U.S."

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A comparative assessment of the fisheries in lacustrine inland waters in three Asian countries based on catch and effort data
(Fisheries Research, 1991) de Silva, S.S.; Moreau, J.; Amarasinghe, U.S.; Chookajorn, T.; Guerrero, R.D.
The catch and effort data of the artisanal fisheries of the natural lakes and reservoirs in the Philippines, and reservoirs in Sri Lanka and Thailand are evaluated. The yield (kg ha?1 year?1) to effort relationship of the Philippines lakes and Thai reservoirs conformed to a second-order curve, and that of Sri Lankan reservoirs was linear. Similarly, the catch per unit effort (CPUE) to effort per unit area relationships for the Philippines and Thai fisheries were similar and conformed to the Fox model. The relationship of the mean annual yield (kg ha?1) to mean effort in the Sri Lankan reservoirs when considered as a whole, on a yearly basis, conformed to the Schaefer model. On the basis of these relationships the effort which gave the maximum yield per annum was computed for each fishery. The yields were 515, 256 and 93 kg ha?1 for efforts of 20, 6.4 and 10 fishermen for the fisheries of the Philippines, Sri Lanka and Thailand, respectively. An attempt is made to explain the reasons for the apparent differences in these three artisanal fisheries, and the importance of the models in the management of the respective fisheries are discussed. 1 Present address: Deakin University, Warrnambool Faculty of Applied Science and Environmental Technology, P.O. Box 423, Warrnambool 3280, Australia.
A note on the occurrence of a Branchial parasite, Epipenaeon ingens Nobili in Penaeus semisulcatus De haan in Puttalam lagoon, Sri Lanka
(J. Nat. Res. Ag. Sri Lan., 1986) Rajapakse, T.A.; Amarasinghe, U.S.
A synthesis on the management of the capture fisheries of Sri Lankan reservoirs
(Vidyodaya Journal of Science, 1994) Amarasinghe, U.S.
Sri Lankan reservoir fishery is one of the best documented in the South East Asian region. It is very productive and the average fish yield in reservoirs of the country is about 300 kg ha-I, yr". Nevertheless the Sri Lankan reservoir fishery is not managed scientifically and in some reservoirs, fish stocks are over-exploited. Since recently, some studies have been carried out on the aspects of management of the capture fisheries in perennial reservoirs of the country. Empirical yield prediction models are found to be useful for setting limits to the size of the fishery. Also by employing surplus yield predictive models, maximum sustainable yield and optimal fishing intensity have been estimated to be 256 kg ha'" yr-I and 3.2 boats km? respectively. Dynamic pool models are also reliably applicable for the reservoir fisheries of Sri Lanka. Fish yields in reservoirs could further be increased by introducing a subsidiary gillnet fishery for minor cyprinids. Socioeconomics of fishing communities should be better understood for effective implementation of fisheries manage- ment strategies in Sri Lankan reservoirs.
Abundance and diversity of freshwater molluscs in some selected reservoirs of the Kala Oya river basin, Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Weerakoon, S.N.; Chandrasekera, L.W.H.U.; Amarasinghe, U.S.
Benthic macroinvertebrates such as molluscs are known to be possible bioindicators of aquatic ecosystems. We carried out a study to investigate how the abiotic factors affect the abundance and diversity of molluscan fauna at 10 irrigation reservoirs in the Kala Oya river basin during the dry season from August to November 2014. In each reservoir, three sampling sites were selected where at each site, a 50 m long perpendicular line transect was established running from its maximum water supply level towards the center of the reservoir. Three soil samples were collected at 10 m intervals each along each transect using a 0.5 dm3 soil corer. These samples were sieved in situ through a 1 mm sieve and the remains were preserved in 10% formalin solution containing Rose Bengal. Later the molluscs and other associated macrofauna were identified to the nearest possible taxonomic category using standard taxonomic keys and the fauna belonging to each taxon were enumerated separately. In addition, data related to vegetation cover, intensity of human disturbances, intensity of pollution, agrochemical inputs, soil texture and human settlements based on a modified scoring system were also collected. Altogether 4328 molluscs belonging to 11 genera were recorded. Molluscan genera such as Bellamya (45.9%), Melanoides (26.7 %) and Thiara (16.9 %) dominated the samples while the remainder (10.5%) belonged to less dominant genera consisting of Planorbis, Gyraulus, Indoplanorbis, Lamellidans, Planorbella, Lymnaea and Pila. The abundance of the molluscan genera varied significantly between the reservoirs (MANOVA; F (99, 899) = 4.300, P = 0.000; Wilk’s λ = 0.06515) and along the transect distances (MANOVA; F (44, 483) = 0.901, P = 0.654; Wilk’s λ = 0.73988). High diversity measures of molluscs were observed at Angamuwa wewa, Katiyawa wewa, Rajanganaya reservoir and Usgala-siyambalangamuwa wewa. Principal Component Analysis (PCA) for the mollusc abundance and the relationship between PC1 scores and Shannon–Wiener diversity index endorsed that Bellamya, Melanoides and Thiara were the highly contributing genera to the high diversity of the molluscs in the above reservoirs. Results of the PCA for abiotic factors revealed that both the abundance and species diversities were high at moderately sandy bottoms with high vegetation cover and agrochemical inputs. In contrast, the intensity of human disturbances, pollution, human settlement and shadiness showed a negative effect on the abundance and diversity of these molluscs. This study was carried out as part of a comprehensive study which investigates how the aspects related to biotic integrity and multiple uses of reservoirs could be used to develop effective management options for reservoir fisheries in Sri Lanka.
Accounting for Diel Feeding Periodicity in Quantifying Food Resource Partitioning in Fish Assemblages in Three Reservoirs of Sri Lanka
(Asian Fisheries Society, 2003) Weliange, W.S.; Amarasinghe, U.S.
Most investigations on food resource partitioning in fish along the temporal dimension are based on the diet composition of constituent species in fish assemblages, pooled over a longer time lapse, but variation within 24-hour cycle is not considered. In the present study, an attempt was made to account for diel feeding periodicity in fish species in quantifying dietary overlaps among constituent species in fish assemblages in three reservoirs of Sri Lanka. The dietary overlap of fish species estimated as a mean for short time intervals in three reservoirs is significantly lower than that is based on the sum of all time intervals, especially for pairs with moderate and high overlaps. Furthermore, the dietary overlaps estimated for short time intervals, which indicate moderate and high dietary overlaps between pairs, exhibit negligible overlaps of peak feeding period indicating the necessity to account for diel feeding periodicity in quantification of food resource partitioning.
Activity Pattern and Environmental Variation of Micro Habitats of Six-Toed Green Frog Euphlyctis hexadactylus Lesson 1834(Anura:Ranidae)in Sri Lanka
(The Herpetology of Sri Lanka, 2004) Weerawardhena, S.R.; Amarasinghe, U.S.; Kotagama, S.W.
Alien Species in Aquaculture and Biodiversity: A Paradox in Food Production
(AMBIO: A Journal of the Human Environment, 2009) de Silva, S.S.; Nguyen, T.T.T.; Turchini, G.M.; Amarasinghe, U.S.; Abery, N.W.
Aquaculture is seen as an alternative to meeting the widening gap in global rising demand and decreasing supply for aquatic food products. Asia, the epicenter of the global aquaculture industry, accounts for over 90% of the global aquaculture production quantity and about 80% of the value. Asian aquaculture, as with global aquaculture, is dependent to a significant extent on alien species, as is the case for all the major food crops and husbanded terrestrial animals. However, voluntary and or accidental introduction of exotic aquatic species (alien species) is known to negatively impact local biodiversity. In this relatively young food production industry, mitigating the dependence on alien species, and thereby minimizing potential negative impacts on biodiversity, is an imperative for a sustainable future. In this context an attempt is made in this synthesis to understand such phenomena, especially with reference to Asian inland finfish, the mainstay of global aquaculture production. It is pointed out that there is potential for aquaculture, which is becoming an increasingly important food production process, not to follow the past path of terrestrial food crops and husbanded animals in regard to their negative influences on biodiversity.
Allochthonus inputs into seasonal reservoirs: "Ornithological eutrophication" as a source of nutrient enrichment
(Sri Lanka Association for Fisheries and Aquatic Resources, 2010) Gunaratne, A.M.; Jayakody, S.; Amarasinghe, U.S.
The current study evaluates a lesser known allochthonus nutrient input into water sources, i.e. accumulation of bird faecal matter. Asian Open bill (An8stomus oscit8ns) population is increasing in Sri Lanka and due to mass breeding within reservoirs and higher population densities. Faecal matter could be a potential input of nutrients. Field investigations were carried out in Anavilundawa Ramsar sanctuary during 2007/08, where the reservoir was divided into four strata; inlet, breeding ground, centre and outlet. Surface and bottom water samples were analyzed for NO;, NH:, PO.... K+, hardness and dissolved oxygen (DO). Total depth, Secchi depth, temperature, turbidity and water pH were also recorded. In surface layers, the highest amount of NO; was recorded for breeding ground (0.55 mgr') followed by reservoir centre. The highest levels of PO... (0.93 mgr'), alkalinity (142 mgr') and NH: (1.9 mgr') were also recorded in breeding grounds. In the bottom layers. the highest level of NO; was recorded in breeding ground (0.49 m r') followed by reservoir centre. Similarly, the highest levels of PO."- (0.83 mgr ), alkalinity (147 mgr') and NH: (2.16 mgr') were recorded from the breeding ground. The lowest level of DO was recorded for breeding grounds 'both in surface layers (2.03 mgr') and bottom layers (0.84 mgr'). The lowest levels of pH were recorded for breeding grounds in surface layers (5.90) and bottom layers (5.93). The highest level of turbidity was recorded at the centre of reservoir for both surface water (30.95 NTU) and bottom water (2.76 NTU). Canonical variate analysis indicated the influence of ornithological eutrophication in water with four strata being significantly distinct for surface layer whilst, similarities in water quality in inlet and outlet for bottom layer. Hence bird faecal matter could be a constraint for maintaining water quality; however the results also suggest evidence for self regulation of water quality within the system. a character which needs to be retained.
An Analysis of Fish Species Richness in Natural Lakes
(Environmental Biology of Fishes, 2002) Amarasinghe, U.S.; Welcomme, R.L.
There is a growing recognition of the need to conserve biodiversity that has been conceptualised in the Convention of Biological Diversity. Maintenance of fish species richness is particularly important, because habitat degradation in inland waters continues to accelerate on a global scale. Here we develop empirical models for predicting fish species richness in natural lakes in various geographical regions of the world. In tropical lakes where fish biodiversity is richer than in temperate lakes, fish species richness can be predicted by a few variables such as lake area and altitude. Low fish species richness in most temperate lakes might be due to the effect of glaciation on colonisation and speciation of fishes. In US, Canadian and northern European lakes, lake acidification is one of the important factors influencing fish species richness. Although limnological characteristics influence fish species richness in temperate lakes, lake area and altitude have greater predictive power. This is in contrast to fish species richness in rivers, which can be reliably predicted by basin area. In the power curves, which describe the relationship between fish species richness and habitat size in lakes and rivers, the exponent is always greater in tropical regions than in temperate regions. Because fish biodiversity is greater in the tropics threats to fish biodiversity through habitat degradation are greater than those in temperate inland waters.
An evaluation of the role and impacts of alien finfish in Asian inland aquaculture
(Aquaculture Research, 2006) de Silva, S.S.; Nguyen, T.T.T.; Abery, N.W.; Amarasinghe, U.S.
Asia dominates global aquaculture production accounting for over 80% of the total and the mainstay in Asian aquaculture is finfish. Over the years, Asia has experienced a number of inter-continental and intra-continental transfers/introductions/translocation of finfish species, between nations and watersheds, beyond their natural range of distribution, primarily for aquaculture development. In this article all such species are referred to as alien species. An attempt is made to evaluate the importance of the production of alien species in selected Asian nations, using statistics of the Food and Agriculture Organization. Also, negative effects, if any, based on literature surveys, of alien species in relation to displacement of indigenous species, and on biodiversity and/or genetic diversity together with associated pathogen transfers are evaluated. The major alien species, based on their significance to Asian inland aquaculture considered, are the tilapias, catfish, Chinese and Indian major carps and common carp. It is estimated that currently alien species account for nearly 12% of the cultured finfish production (2.6 million tonnes) in Asia, valued at US$ 2.59 billion, and the contribution exceeds 40% when Asian countries excluding China are taken into consideration. Inland finfish aquaculture in some Asian nations, such as Indonesia and the Philippines, is predominated by alien species, and in some others, e.g. Bangladesh and India, the contribution from alien species has been increasing steadily. It is suggested that overall alien finfish species have done little ecological harm to native flora and fauna. However, in the wake of increasing anthropogenic development taking place in watersheds the resulting environments are often made unconducive to indigenous species but not to some alien species, thereby potentially and indirectly making the latter invasive.
An appeal to redefine stunning in Oreochromis mossambicus (Cichlidae)
(Asian Fisheries Forum, 1998) Amarasinghe, U.S.; de Silva, S.S.
Application of a Multiple-criteria decision making approach for selecting non-perennial reservoirs for culture-based fishery development: Case study from Sri Lanka
(Elsevier, 2016) Wijenayake, W.M.H.K.; Amarasinghe, U.S.; de Silva, S.S.
In Sri Lanka, small non-perennial reservoirs (mostly < 50 ha) are numerous in the dry zone receiving less than 185 cm annual precipitation. These are irrigational and are not traditionally used for inland fisheries, due to inadequate natural recruitment, but have the potential for utilization for the development of culture-based fisheries (CBFs), a form of extensive aquaculture. However, the suitability of water bodies for CBF is wide ranging because of the seasonal water retention period and fingerling availability for stocking, variable biological productivity, and community willingness to adopt CBF. In such circumstances multi-criteria decision making (MCDM) approaches are useful for selection of water bodies for CBF. Analytic hierarchy process (AHP), a MCDM approach was employed in this study where, three main criteria (reservoir productivity, catchment characteristics and socio-economic factors) that influence CBF yield were considered. There were two, five and three sub-criteria under each, respectively. As most of the sub-criteria in the analysis are essentially spatial data, it was possible to quantify the influence of each of these on CBF yield using geographical information systems (GIS) and remote sensing (RS) techniques, which were subsequently weighted. Based on the total scores from the weighted linear combinations of the AHP for various sub-categories, the reservoirs were categorized for their suitability for CBF in to four levels as excellent, good, fair and poor. As there was a positive significant relationship between the total AHP score and CBF yield, it was concluded that use of AHP based weighted linear combination would be a feasible approach for selection for CBF development, and that this methodology would be applicable to comparable situations in the tropical region.
An approach to classify seasonal reservoirs of Sri Lanka using Carlson’s Trophic State Index
(Sri Lanka Association for Fisheries and Aquatic Resources, 2003) Jayasinghe, U.A.D.; Amarasinghe, U.S.; de Silva, S.S.
Aspects of the biology and fishery of Malabar Sprat, Ehirava fluviatilis (Osteichthyes: Clupeidae) in the outflow canal of Left Bank sluice of Rajanganaya reservoir, Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 2012) Mihindukulasooriya, L.D.; Amarasinghe, U.S.
Ehirava f/uviatilis is of marine origin and has colonized some freshwater habitats of Sri Lanka. A small scale fishery of E. f/uviatilis exists in the outflow canal of Rajanganaya reservoir in the North Central province of Sri Lanka. This study was carried out to investigate the biological aspects and the status of the fishery of E. f/uviatilis in this location to document preliminary information on these aspects. Sampling was done fortnightly from the landings. The theoretical weight of SO mm fish calculated from length weight relationship (928 mg) was higher than that of the population in Parakrama Samudra (540 mg). E. f/uviatilis in Rajanganaya reservoir feeds mainly on diatoms and copepods unlike the populations in Parakrama Samudra and 80lgoda Lake which feed on rotifers and copepods respectively. The male to female sex ratio was 1:1.4. Size at first maturity was 24.4 mm for males and 34 mm for females and was lower than that of estuarine population in Bolgoda Lake. Mean fecundity of female fish body weight of 0.26 g (SE 0.01 g) was 263.3 (:I: 14.9). Mean diameter of an egg was 270.8 (:I: 4.1) m. The fishery of E. f/uviatilis at the left bank sluice of Rajanganaya reservoir is essentially small scale. Small meshed encircling nets are used to catch fish. There were 4-5 fishers engaged in the fishery during sampling period. Catch per net per day was estimated to vary from 0.01 kg to 2.84 kg per day and the total annual catch was 3720 kg. The fish catch seems to increase two to seven days after the closure of sluice gate. From the length frequency data collected, growth parameters were estimated using the FiSAT software package. Asymptotic total length (48.9 mm), the growth constant (2.9 year') and natural mortality (5.94 year') indicated that the E. fluviatilis population in the fishing site has a high turnover rate.
Aspects of the Biology and Fishery of Malabar Sprat, Ehirava Fluviatilis (Osteichthyes:Clupeidae) in Bolgoda, Sri Lanka
(Asian Fisheries Society, 2002) Amarasinghe, U.S.; Sriya, I.D.P.
A seasonal fishery from December to May each year exists for a small-sized clupeid, Ehirava fluviatilis in an estuary on the West coast of Sri Lanka. Two kinds of lift nets are used for catching this species. The theoretical weight of 50 mm fish, as calculated from length-weight relationship that was used as an index of body condition (942 mg) is considerably higher than that of a reservoir population (540 mg). In contrast to feeding habits reported from the reservoir population in which rotifers were the major food items, E. fluviatilis in the estuary feeds mainly on copepods. Size at first maturity of this species is also higher in the estuarine population than that reported from the reservoir population. From the length frequency samples collected approximately in bi-weekly intervals, growth and mortality parameters were estimated using FiSAT software package. Total mortality coefficient (5.73) calculated on the basis of asymptotic total length (54.3 mm) and growth constant (2.00 yr-1) indicates that E. fluviatilis population in the estuary has a high turnover rate. Relative yield-per-recruit analysis performed by incorporating probabilities of capture indicates that the fish stock is underexploited and that the fishing strategy can be optimized by decreasing size at first capture from the present value of 45.8 mm to about 26 mm at an exploitation rate of about three times higher than the present level. The high total annual production of E. fluviatilis of 15.9 tons that is equivalent to an annual yield of 23.2 kg�ha-1 could be due to its ability to withstand heavy fishing mortalities through high turnover rates.
Assessment and Management of Irrigation Impacts on Tropical Inland Fisheries: A Case Study from Sri Lanka
(2003) Khoa, S.N.; Smith, L.; Lorenzen, K.; Garaway, C.; Perera, L.R.; de Silva, S.; Kumara, M.M.C.; Amarasinghe, U.S.; Kularatne, M.G.; Bandara, H.M.S.C.
Assessment of fishing effort in Parakrama Samudra, an ancient man-made lake in Sri Lanka. Fisheries Research
(Fisheries Research, 1986) Amarasinghe, U.S.; Pitcher, T.J.
As in most artisanal fisheries, assessment of fishing effort is crucial to the management of the artisanal fishery of Parakrama Samudra, an ancient man-made tropical lake in Sri Lanka. Since there were few similarities between alternative ways of expressing effort for the gill-net cichlid fishery is the lake, this study aimed to find the most effective formulation of catch per unit effort (CPUE). The variability of preliminary estimates showed that, before analysis, the data needed to be stratified for different seasons with low and high water levels, and for three geographically distinct areas of the lake. Standardised catch per man was higher in boats operated by smaller numbers of fishermen, but catch per net did not change with the number of nets per boat, and is therefore recommended as the best measure of CPUE. The measure of fishing effort also needs to take account of fishermen who increased their catch by a water-beating technique. The incidence of beating varied with season and area, but could account for a significant portion of the catch. The highest catch efficiencies derived from one-man boats using this technique. Using this method of assessing effort, total annual yield from Parakrama Samudra was estimated at about 120 kg ha?1, a lower value than previously reported.
Assessment of water poverty of agricultural farming communities adjacent to Kala Wewa and Siyambalangamuwa reservoirs
(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Wimalasena, S.S.; Kularatne, M.G.; Amarasinghe, U.S.; Jayasinghe-Mudalige, U.K.
Provision of safe water in sufficient quantities has become a major upcoming issue globally, because water is considered as one of the most critically stressed natural resources and act as a major livelihood capital. Lack of access to water is directly associated with the nature and state of poverty; thus, it becomes a necessity that water is allocated in more equitable manner at every level, i.e. from individual household to the national. The root causes associated with water poverty and reservoir water management and the areas of greatest need to facilitate the prioritization of action towards integrated water management aiming equity and transparency in the Kala Wewa (2,914 ha) and Siyambalangamuwa reservoirs (788 ha) in the North-Western Province of Sri Lanka were investigated using the Water Poverty Index (WPI) – a multifaceted index with its values range from ‘0’ (minimum) to ‘100’ (maximum) and is estimated by taking the weighted sum of scores provided by respondents to five major components, including: (1) Resources; (2) Access; (3) Capacity; (4) Use, and (5) Environment, and each is characterized by several sub components. The data were collected from agricultural farming communities adjacent to these reservoirs by means of a series of in-depth personal interviews supported by a pre-tested structured questionnaire. Principal Component Analysis was employed to select the components with a large variance and to discard those with a smaller variance, and those indicators retained (i.e. the 1st Principal Components associated with Eigenvalues greater than 0.7) were combined using an additive aggregation. The estimated WPI was 76.24 to which the contribution of each component was, in their order: Capacity (17.79), Access (17.75), Use (15.47), Resources (12.93), and Environment (12.30). It was revealed that the severe drought condition prevailed in 2013 and 2014; chronic kidney disease, and the low rate of water quality assessment have led into low contribution from Environment component. The outcome of analysis implies that the information generated through WPI can be used effectively at the ‘ground level’ to assess the relationships between water and poverty that enables implementation of new strategies aiming integrated water management in reservoir-based communities in Sri Lanka.
Better-practice approaches for culture-based fisheries development in Asia
(Australian Centre for International Agricultural Research, 2006) de Silva, S.S.; Amarasinghe, U.S.; Nguyen, T.T.T.
Buffaloes in favour of culture-based fisheries in Sri Lanka
(NETWORK OF AQUACULTURE CENTERS, 2007) Amarasinghe, U.S.; Jayasinghe, A.