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Item Seasonal water-level fluctuations and changes in macro-benthic community structure in tropical reservoirs: A Sri Lankan case study(Lakes & Reserv, 2021) Weerakoon, S.N.; Chandrasekara, W.U.; Amarasinghe, U.S.Seasonal water-level fluctuations (WLFs) in reservoirs influence ecological processes, in turn affecting their benthic macroinvertebrate communities. The present study was carried out in 10 irrigation reservoirs of Sri Lanka to investigate the effects of seasonal WLFs on the benthic macroinvertebrate fauna. The study period was divided into two distinct phases: the drained period and the inundated period. Benthic macroinvertebrates were sampled during both periods and enumerated. Air temperature and soil quality parameters were also measured simultaneously, and hydrological data related to the Kala Oya River basin were obtained from irrigation authorities. Data analysis using non-metric multi-dimensional scaling revealed two distinct reservoir groups, namely, Hydrological Stress Group 1 (HSG1) and Hydrological Stress Group 2 (HSG2). A low hydrological residence time and low relative reservoir level fluctuations (RRLF) characterized HSG1, with the opposite describing HSG2. Temporal variations of macrobenthos indicated a high taxa richness and diversity in HSG1 reservoirs during the drained period, with scrapers and collector-gatherers being the dominant functional feeding groups. Reservoirs in the lower river basin (HSG1) exhibited a high taxa richness and diversity. During the inundated periods, insect taxa colonized, particularly, chironomids and ephemeropterans. Molluscan taxa were prominent during the drained periods. These observations highlight the influence of seasonal fluctuations of reservoir water levels on benthic macroinvertebrates. Benthic macroinvertebrate communities in reservoirs were significantly influenced by the RRLF, manifesting the importance of hydrological regimes in reservoirs to develop macroinvertebrate metrics for water-quality monitoring.Item Production trends and technical efficiencies of culture‐based fisheries in five tropical irrigation reservoirs: A case study from Sri Lanka(Fisheries Management and Ecology, 2020) Pushpalatha, K.B.C.; Kularatne, M.G.; Chandrasoma, J.; Amarasinghe, U.S.Culture‐based fisheries (CBF) are increasingly accepted as strategies for enhancing inland fisheries, especially in tropical Asia. In Sri Lanka, CBF development in irrigation reservoirs has gained momentum due to concerted efforts of government fisheries authorities for inland fisheries enhancement. In the present study, production trends of five irrigation reservoirs of Sri Lanka before and after the introduction of CBF were investigated and apparently optimal CBF yields were not realised. Hence, the stochastic frontier production function (SFPF) was employed to quantify technical efficiencies (TE) of CBF. For each reservoir, annual averages of input data from 2005 to 2018 (14 years) were used in the TE analysis. Hence, total sample size for estimation of SFPF was 70. Although CBF production gradually increased in all five reservoirs from 2005 to 2018, there were substantial variations of total fish production across the reservoirs. The SFPF indicated that CBF production could be further increased through more efficient management of inputs (i.e. number of fishers, mean number of fishing days per year and stocking density). https://onlinelibrary.wiley.com/doi/full/10.1111/fme.12460?af=RItem Life-History Strategies of Nile Tilapia, Oreochromis niloticus(Linnaeus, 1758) (Teleostei, Cichlidae), in Irrigation Reservoirs of Sri Lanka(Asian Fisheries Society, 2020) Bandara, K.V.S.N.; Ajith Kumara, P.A.D.; Amarasinghe, U.S.As in many tropical countries, reservoir fishery of Sri Lanka is dominated by the exotic cichlid, Oreochromis niloticus(Linnaeus, 1758). Oreochromis niloticuspopulations in irrigation reservoirs are expected to be under the influence of various disturbances such as changes in hydrological regimes, trophic conditions and fishing pressure. In the present study, an attempt was made to investigate the effect of biological productivity and fishing pressure on life history patterns of O. niloticuspopulations in 10 irrigation reservoirs of Sri Lanka. Oreochromis niloticuspopulations in environmentally stressed reservoirs, exhibited low age at maturity than those inhabiting reservoirs with relatively low biological productivity. Hydraulic retention time (HRT) in reservoirs also had negative influence on size and age at maturity of O. niloticus. As length at first capture of O. niloticusis positively related to mean length at maturity, these attributes have significant implications on the optimal fishing. Fishing intensity (FI) in O. niloticuspopulations also had negative influences on mean length and age at maturity. Hence, the present study supports the opinion that altricial or opportunistic traits having faster growth and achieving maturity early in the life dominate disturbed environments and that precocial or equilibrium traits exhibiting delayed maturity occur in more stable environments. Possible shifting of life history strategies of O. niloticusto opportunistic traits due to disturbance events could be manipulated by increasing FI for smaller individuals in the population.Item Population Dynamics of Nile Tilapia, Oreochromis niloticus(Linnaeus, 1758) (Teleostei, Cichlidae), in Some Irrigation Reservoirs of Sri Lanka(Asian Fisheries Society, 2020) Bandara, K.V.S.N.; Ajith Kumara, P.A.D.; Amarasinghe, U.S.Oreochromis niloticus(Linnaeus, 1758) exhibits differences in demographic parameters across the reservoirs, resulting in inconsistencies in optimal fishing strategies. This study aimed at investigating O. niloticuspopulations in 10 reservoirs. Length-frequency data of O. niloticusfrom fishlandings of 10 irrigation reservoirs in Sri Lanka were corrected for multi-mesh gillnet selection and were analysed by FiSAT II stock assessment software. Asymptotic total length ranged from 42.8 cm to 53.4 cm and growth constant ranged from 0.20 yr-1to 0.49 yr-1. As growth performance indices of 10 reservoir populations of O. niloticuswere within the range reported previously and as the estimated growth parameters fall within the “growth space” of the species, these estimates were consistent with those reported in the literature. Length-converted catch curves of 10 reservoir populations of O. niloticusalso gave reliable estimates of total mortality. Exploitation rates of the 10 populations ranged from very low (0.14) to very high (0.76) values. From the relative yield-per-recruit analyses, it was apparent that in some reservoirs, long-term fish yields can be optimised using gillnet mesh sizes of 7.6 cm. While optimal long-term fish yields of O. niloticusin other reservoirs could be achieved by increasing the permissible gillnet mesh size above the legal mesh size of 8.4 cm. Hence, the gillnet mesh regulations in the Sri Lankan reservoir fishery should not be uniform but reservoir-specific. Accordingly, site-specific management options, which are defined in consultation of resource users are necessary to be implemented in reservoir fisheries of the country.Item Institutional Robustness of Culture-based Fisheries in Perennial Reservoirs of Sri Lanka(Asian Fisheries Society, 2020) Pushpalatha, K.B.C.; Kularatne, M.G.; Amarasinghe, U.S.The utilisation of irrigation reservoirs for culture-based fisheries (CBF) development is a recent development in Sri Lanka. The trends in CBF development in five reservoirs were investigated, to identify the robustness of institutional arrangements in the rural fisheries organisations (RFOs) for the sustainability of CBF. Basic socio-economic characteristics of five fisher communities showed enabling features for implementing CBF through community participation. After the introduction of CBF, fish species composition in the landings changed with the occurrence of stocked species in the landings, resulting remarkablyelevated fishers’ income ranging from 194% to 2187% in Urusita and Ampara reservoirs respectively. The CBF management options of RFOs in two reservoirs, viz. Ampara and Jayanthi were at high compliance levels of Ostrom’s modified design principles, where fishers enjoyed increased mean annual income registering 2187% in Ampara and 409% in Jayanthi reservoirs after introduction of CBF. In Senanayake Samudra, where there was moderate compliance, there was 249% increase in CBF income. However, the lowest increase of income (194%) in Urusita reservoir was due to high annual fisheries income even during pre-CBF period. In Hambegamuwa reservoir, where levels of compliance of RFOs with design principles were relatively poor compared to other four fisher communities, increase of fishers’ CBF income, compared to that of pre-CBF period, was marginal (202%). Economic gains of RFOs due to increased levels of compliance with design principles through improving leadership qualities and empowering fishers for management decision-making would,therefore,ensure sustainability of CBF.Item Habitat related variations and comparison of fatty acid composition of muscle and stomach contents of secondarily colonized Malabar Sprat (Ehirava fluviatilis) in Sri Lanka(NeBIO, An International Journal of Environment and Biodiversity, Vol.10(3), pp.152-163, 2019) de Zoysa, H.K.S.; Amarasinghe, U.S.; Edirisinghe, E.M.R.K.B.; Sundarabarathy, T.V.Ehirava fluviatilis is a marine origin clupeid found in Southern India and Sri Lanka, also found in two freshwater lakes, namely Parakarama Samudraya and Rajanaganaya reservoir, and that places are identified as secondarily colonizedhabitats. The objectives of this study were carried toinvestigate the fatty acid (FA) profile in the flesh of E.fluviatilis, to investigate the FA profile in the food of E. fluviatilis, and identify the impactof the FA profiles for colonisation. The Bligh and Dyer extracting method was used to lipids extraction of flesh and stomach contents of E. fluviatilis and Gas Chromatography (GC) was used to identify the different types of FAs. Data were statistically analyzed to examine the differences in the quantities of different FAs using ANOVA and principal component analysis (PCA). The predominant FAs were recorded in two different habitats ofE. fluviatilis in both flesh) and stomach contents. The only recorded difference between FAs profile was the presence of C 18:2 (n-4) in the Rajanganaya reservoir. The difference in the FA profile may lead to colonization of marine origin E. fluviatilis in Rajanganaya reservoir as a freshwater lacustrine habitat due to the ability of modification of FAs. Further, this study also indicates that the presence of specific FAs could be used as biomarkers to identify species.Item Validation of logbook catch records in offshore fishing vessels of Sri Lanka using VMS data.(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Gunawardane, N.D.P.; De Croos, M. D. S. T.; Amarasinghe, U.S.Accurate information on fishing position is a timely need in the offshore fisheries, especially for preventing illegal, unregulated and unreported (IUU) fishing. Vessel monitoring system (VMS) is recognized as one of the effective mechanisms for validating the fishing positions of fishing vessels provided by logbook system. In the present study, an attempt is made for developing an approach to identify and validate the fishing locations of offshore vessels in Sri Lanka using VMS data. VMS data based on the speed, distance and angle filters were adopted to identify the fishing locations. Here, the best angle of the zig-zag shapes recorded in the cruise tracks of VMS was determined as < 15o using the flooding data of VMS. Similarly, speed level of <3 knots was identified as the possible speed of fishing. Distance gaps of fishing locations were recorded and converted to distance buffers. Data from 1291 multiday vessels, operated from 21 fisheries harbors of Sri Lanka from May 2017 to April 2018 were analyzed in the present study. Predicted fishing locations based on VMS data were compared with fishing data of log sheets reported by skippers were compared using paired t-test. Results of the analysis showed that fishing occasions predicted using the speed and course angle of VMS alerts had a good agreement (p<0.05) with the fishing locations reported by fishers. However, potential cruise occasions showed significant deviation from log-book records. Although the time differences of the locations of the two monitoring systems were > 4 hrs, most of the matched locations were recorded within 24 hrs. This may be due to the practice of skippers, who only record their fishing locations only once a day, which was found to be insufficient for reliable reporting. While the current manual logbook system is recognized as appropriate to comply with the enforcement and management needs, there is a need to adopt more appropriate method of reporting catch data by fishermen. Present analysis indicated that the use of VMS data provided an alternative approach for reporting fishing locations of offshore vessels with sufficient accuracy. Need for further improvement of the data recording system representing fishing duration, and species composition is discussed for preventing IUU fishing by offshore fishing vessels.Item Influence of hydrology on water quality and trophic state of irrigation reservoirs in Sri Lanka(Lakes & Reservoirs: Science, Policy and Management for Sustainable Use, 2019) Nadarajah, S.; Wijenayake, W.M.H.K.; Amarasinghe, U.S.Many reservoirs provide multiple benefits to people around the world, in addition to primary uses such as irrigation. Thus, reservoir management should address their multiple uses. The water quality of ten irrigation reservoirs in Sri Lanka was examined in the present study with the objective of better understanding the effects of hydrological regimes on reservoir water quality and trophic state. Basic limnological parameters pertinent to the nutrient loads to, and trophic state of, the reservoirs were collected from June 2013 to February 2016. The sampling period was arbitrarily divided into two periods of approximately similar duration (period 1 = June 2013–September 2014; period 2 = October 2014–February 2016) to investigate whether or not there was a seasonal variation in the water quality parameters. Although temporal and spatial variations were observed, most water quality parameters were within the levels acceptable for drinking water standards. The 10 reservoirs were also ordinated by principal component analysis (PCA) on the basis of the water quality parameters of the two sampling periods in a two‐dimensional score plot. Reservoirs in the first principal component (PC1) axis were represented by negative scores attributable to the dissolved oxygen concentration and pH and, to a lesser extent, by electrical conductivity and chlorophyll‐a concentration. Positive scores in PC1 were represented by reservoirs with a score loading attributable to alkalinity, nitrate concentration, Secchi depth, temperature and seston weight and, to a lesser extent, from the total phosphorus concentration. There was a significant negative correlation of PC1 scores with relative reservoir water‐level fluctuation (RRLF; the ratio of mean reservoir waterlevel amplitude to mean reservoir depth). Furthermore, Carlson's trophic index also were influenced by RRLF, although not by hydraulic retention time (HRT), indicating allochthonous nutrient inputs into the irrigation reservoirs were mainly governed by RRLF, but not by HRT. Thus, the results of the present study provide useful insights into achieving desirable reservoir water quality through the manipulation of the hydrological regime.Item Comparison of trophic structure of fish assemblages in two tropical steams in Sri Lanka: a seasonal dry zone stream and a perennial wet zone stream(International Review of Hydrobiology, 2019) Weliange, W.S.; Amarasinghe, U.S.; Vijverberg, J.; Leichtfried, M.; Füreder, L.Most tropical rivers especially in the Asian region, are severely impacted by various human perturbations, and the diverse habitats in streams support rich invertebrate and vertebrate communities. It is hypothesized that the fish assemblages and their dietary structure in two tropical streams differ because they flow through different terrains and are exposed to different climatic conditions. In the wet zone stream, which is geomorphological more complex, fish faunal diversity showed significant longitudinal variations, and sustains endemic fish species. In the diets of fish, taxonomic composition was different along the longitudinal gradients, but dietary taxa richness in the two streams was virtually similar having 32 dietary taxa in wet zone stream and 36 taxa in dry zone stream. In the wet zone stream, we observed a lower proportion of specialist feeding species than those in the dry zone stream. Trophic indices of individual species in fish assemblages ranging from herbivory to carnivory also indicate structuring of fish communities along the longitudinal gradients of the two streams based on dietary structure. The main differences between the fish assemblages in the wet zone compared to the dry zone were the higher number of endemic species and the lower percentage of specialist feeders with higher trophic indices. The outcome of this study hopefully contributes to plan future biodiversity conservation management schemes under various river basin development strategies.Item Dietary Guild Structure in Fish Assemblages and Trophic Position of Constituent Species in Brush Parks of a Tropical Estuary(Asian Fisheries Society, 2019) Gammanpila, M.; Amarasinghe, U.S.; Wijeyaratne, M.J.S.Trophic guild structure and dietary niche breadth in tropical fish communities are important to identify functional groups and to understand how trophic positions of constituent species help coexistence. Objective of the present study was to investigate whether the constituent species of fish assemblages in brush parks could be grouped into trophic guilds and how these species contribute to structure the fish community along trophic dimensions. Diets of 46 fish species caught in brush parks were analysed and the food items were categorised into 11 broad groups. Based on the composition of diets, fish were grouped into 8 trophic guilds. Levin’s index of niche breadth indicated that the constituent species in the trophic guilds for which food was abundant, were generalists, whereas the trophic guilds of higher trophic levels were specialists. Within each trophic guild, constituent species showed different trophic indices indicating low inter-specific competition resulting in optimum food resource utilisation.