Browsing by Author "Jayasinghe, R.P.P.K."

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    Effect of lunar rhythms on fish yields in three reservoirs of Sri Lanka
    (Sri Lanka Association for Fisheries and Aquatic Resources, 1999) Jayasinghe, R.P.P.K.; Amarasinghe, U.S.
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    Evaluation of marine subareas of Europe using life history parameters and trophic levels of selected fish populations
    (Journal of Marine Environmental Research, 2015) Jayasinghe, R.P.P.K.; Amarasinghe, U.S.; Newton, A.
    European marine waters include four regional seas that provide valuable ecosystem services to humans, including fish and other seafood. However, these marine environments are threatened by pressures from multiple anthropogenic activities and climate change. The European Marine Strategy Framework Directive (MSFD) was adopted in 2008 to achieve good environmental status (GEnS) in European Seas by year 2020, using an Ecosystem Approach. GEnS is to be assessed using 11 descriptors and up to 56 indicators. In the present analysis two descriptors namely “commercially exploited fish and shellfish populations” and “food webs” were used to evaluate the status of subareas of FAO 27 area. Data on life history parameters, trophic levels and fisheries related data of cod, haddock, saithe, herring, plaice, whiting, hake and sprat were obtained from the FishBase online database and advisory reports of International Council for the Exploration of the Sea (ICES). Subareas inhabited by r and K strategists were identified using interrelationships of life history parameters of commercially important fish stocks. Mean trophic level (MTL) of fish community each subarea was calculated and subareas with species of high and low trophic level were identified. The Fish in Balance (FiB) index was computed for each subarea and recent trends of FiB indices were analysed. The overall environmental status of each subarea was evaluated considering life history trends, MTL and FiB Index. The analysis showed that subareas I, II, V, VIII and IX were assessed as “good” whereas subareas III, IV, VI and VII were assessed as “poor”. The subareas assessed as “good” were subject to lower environmental pressures, (less fishing pressure, less eutrophication and more water circulation), while the areas with “poor” environment experienced excessive fishing pressure, eutrophication and disturbed seabed. The evaluation was based on two qualitative descriptors (“commercially exploited fish and shellfish populations” and “food webs”) is therefore more robust.
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    Evaluation of status of commercial fish stocks in European marine subareas using mean trophic levels of fish landings and spawning stock biomass
    (Ocean and Coastal Management, 2016) Jayasinghe, R.P.P.K.; Amarasinghe, U.S.; Newton, A.
    Most of the fish stocks in the world, including European fish stocks, are threatened by overfishing and/or degraded environmental conditions. Although the Common Fisheries Policy (CFP) is the main policy instrument managing fish stocks in Europe, there is continued concern as to whether commercial fish stocks will achieve Good Environmental Status (GEnS) in 2020 in accordance with the Marine Strategy Framework Directive (MSFD). In this context, the evaluation of the status of fish stocks in the subareas of FAO fishing area 27 was carried out using mean trophic levels (MTL) in fish landings and spawning stock biomass (SSB). Comparisons were made before and after 2008 to establish whether the trend is positive or negative. The main data sources for landings and SSB were the International Council for the Exploration of the Sea (ICES) advisory reports. MTLs in landing and SSB were determined for each subarea and the subareas were categorized into four groups, according to MTLs after 2008. The first group (subareas I + II, V) had higher MTL in landings and higher MTL in SSB after 2008. Therefore, fisheries in these subareas appear sustainable. The second group was subareas VIII + IX, for which the fish stocks have higher MTL in landings but low MTL in SSB, indicating that SSB was being overfished. The third was subarea (VI), where fish stocks have lower MTL in landings than those in SSB after 2008, which may indicate that fish stocks are recovering. Fish stocks in the fourth group (subareas III, IV and VII) had low MTL in landings and the MTL in SSB was lower than that of landings before 2008. This may be due to heavy fishing. In addition, we estimated the harvest rate (HR) of the fish stocks before and after 2008. The results showed that most of the fish stocks have lower HR after 2008, indicating that the status has improved, perhaps due to improvements in the implementation of CFP. However, some fish stocks showed high HR even after 2008, so that new management options are still needed. Other factors such as eutrophication, seafloor disturbances, marine pollution, invasive species etc., influence SSB ecosystem health options and should also be incorporated in the management criteria. Most of these environmental pressures are of high priority in the MSFD, and therefore the findings of this study will be useful for both CFP and MSFD.
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    Length-based stock assessment of Oreochromis mossambicus and O. niloticus (Actinopterygii: Perciformes: Cichlidae) in multi-mesh gillnet fisheries in reservoirs of Sri Lanka. Acta Ichthyologica et Pischatoria
    (An International Journal for Ichthyology and Fisheries, 2017) Amarasinghe, U.S.; Jayasinghe, R.P.P.K.; Moreau, J.
    Background. Gillnets of mesh sizes (6.9 to 12.7 cm) are used in individual boats in Sri Lankan reservoirs targeting exotic cichlid species, Oreochromis mossambicus (Peters, 1852) and Oreochromis niloticus (Linnaeus, 1758), which dominate the fisheries. The mesh composition of gillnets varies from boat to boat and from season to season making catch samples in individual boats are under the influence of different selectivity patterns. As such, the conventional procedure of correcting length frequency samples using the overall mean selectivity pattern in the fishery is not precise in estimating growth parameters. The presently reported study aimed at assessing cichlid stocks in three tropical reservoirs accounting for gillnet selectivity of individual sampled boats. Materials and methods. Length frequency data obtained from each boat were corrected for the combined selectivity of the fleet of gillnets of different mesh sizes used in the boat during the sampling occasion. For predicting optimal fishing strategies using a yield-per-recruit approach, probabilities of capture determined from the array of fishing mortality in the length-structured virtual population analysis was incorporated. Results. Length frequency data corrected for overall gillnet selectivity in sampled boats gave reliable estimates of von Bertalanffy growth parameters. Based on these estimates, mortality parameters were determined and the overall gear selection pattern was deduced from the array of fishing mortality in the length-structured virtual population analysis. Optimal fishing strategies were determined incorporating overall probabilities of capture in the relative yield-per-recruit (Y′ × R–1) analysis. Conclusion. The overall gillnet selection pattern of a sampled boat offers a methodology for reliable estimation of growth parameters. Although both cichlid species are caught in gillnets simultaneously, Y′ × R–1 analyses predicted increase of exploitation rate for one species while its decrease for the other species perhaps due to influence of other factors such as fish behaviour and fishers’ choice of specific areas for fishing. This analysis provides a methodology of a more precise length-based stock assessment in future research.
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    Microfractionation-based approach to screen potential specialized anti-microbial metabolites of Sri Lankan marine sponges
    (Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Gamage, J.B.; Kosgahakumbura, L.N.; Cárdenas, P.; Jayasinghe, R.P.P.K.; Hettiarachchi, C.M.; Gunasekera, S.
    The discovery of bioactive specialized metabolites from marine invertebrates has increased significantly during the last two decades. Marine sponges (phylum Porifera) are the existing oldest metazoan group that host rich microbial communities, and are considered as potential sources of future drugs in pharmacological and biomedical industry as they produce an impressive array of anti-inflammatory, immunosuppressive, neurosuppressive, antitumor, antiviral, and antimicrobial compounds. Of the few studies that have been carried out on such products in Sri Lankan marine sponges, the discovery of bioactive peptides has been largely overlooked. Therefore, a study was carried out to screen potential specialized anti-microbial metabolites especially peptides and sterols in Sri Lankan marine sponges with the intention of large scale isolation of targeted bioactive molecules. Bioassay-guided micro fractionation is an efficient method for the rapid screening of a large number of samples using only a small amount of starting material. Aqueous extracts (60% methanol) and organic extracts (Dichloromethane: methanol 9:1) of 20 different sponge species collected in coastal waters in Sri Lanka were micro fractionated into 48 fractions in deep well plates (1 mL per well), using reversed-phase HPLC. A volume of 100 µL from each fraction was tested for antimicrobial activities and the wells with antimicrobial activity were analyzed by LC-MS coupled to a PDA detector to identify the molecular ions of the bioactive compounds. Of all the 40 extracts, 18 extracts produced by Rhabdastrella globostellata, Aciculites sp., Rhabderemia sp., Erylus sp, Aulospongus sp., Manihinea sp., Agelas sp., Phakellia sp., Topsentia sp., four species belonging to order Haplosclerida and one species belonging to order Suberitida showed bioactivity against Staphylococcus aureus (ATCC 25928). Stylissa massa showed bioactivity against Escherichia coli (ATCC 35218) while Aulospongus sp., showed bioactivity against Candida albicans (ATCC 90028). Sponge species were identified using their morphology, spicule arrangement and DNA barcoding. The 5’ end of CO1 and 28S rRNA genes were sequenced for both forward and reverse direction. Sequences were compared using the BLASTn tool with the NCBI database in order to narrow down and identify the possible lowest taxonomic level. The wells that indicated bioactivity contained fractionated extract at ≤ 0.2 mg/mL concentration. Organic extracts of Aciculites sp., Topsentia sp. and the aqueous extract of Erylus sp. were the most active at ≤ 0.05 mg/mL. The targeted masses obtained from LC-MS will be isolated in large scale and the structural characterization of isolated specialized anti-microbial metabolites will be determined using LC-MS and NMR. Furthermore, these micro fractions will be subjected to lymphoma cell toxicity assay to identify potential anticancer compounds.
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    Multi-mesh gillnet selectivity of Oreochromis mossambicus and O. niloticus (Cichlidae) in the fishery of three large perennial reservoirs in Sri Lanka
    (Sri Lanka Journal of Aquatic Sciences, 2017) Jayasinghe, R.P.P.K.; Amarasinghe, U.S.; Moreau, J.
    As in many tropical reservoir fisheries, the major fishing gear in the reservoirs of Sri Lanka is gillnet. Gillnets of a wide range of stretched mesh sizes (6.9 - 11.4 cm) are used in individual boats in Sri Lankan reservoirs targeting mainly two exotic cichlid species, Oreochromis mossambicus and O. niloticus, which dominate the fisheries accounting for over 80% of the landings. Although the filament characteristics and dimensions of gillnets of different mesh sizes are uniform, their mesh composition varies from boat to boat making catch samples in individual boats are under the influence of different selectivity patterns. As such, an approach is presented for constructing the overall selection curves in the sampled boats during different sampling occasions for the two cichlid fish species in the three reservoirs. For this purpose, gillnet selectivity of each mesh size was determined using Baranov-Holt method. Probabilities of capture of mesh-wise gillnet selection curves were then summed up giving weight to the contribution of each mesh size to the total number of net pieces in the sampled boat, to determine the overall gillnet selection from gillnets of all mesh sizes. The importance of the findings of the present study for length-based stock assessment methods and for imposing mesh regulations to the gillnet fisheries in reservoirs of Sri Lanka is discussed.