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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 Harmonizing water allocation for multiple uses in irrigation reservoirs of the Kala Oya river basin, Sri Lanka(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Wimalasena, S.S.; Kularatne, M.G.; Jayasinghe-Mudalige, U.K.; Amarasinghe, U.S.The primary use of many lowland reservoirs in Sri Lanka is to supply of water for irrigation, and inland fishery has become a secondary use. In the present study, four irrigation reservoirs in the Kala Oya river basin, namely: Dewahuwa, Kala Wewa, Siyambalangamuwa and Usgala-Siyambalangamuwa were selected to investigate the optimum water requirements for irrigation, fisheries and other small-scale economic activities such as livestock farming and brick making. A cross section (from year 2014 to 2015) of household heads (n=756) adjacent to the four reservoirs were interviewed to gather information on their degree of dependence on reservoir water for those multiple uses. General Stochastic Production Frontier Model was employed to evaluate the technical efficiency of water uses for various economic activities, and to quantify the volume of water that can be saved through more efficient uses. Water poverty index (WPI) was estimated to investigate accessibility and availability of water for multiple uses. Water valuation and optimum level of water allocation between uses were then calculated based on Marginal Value Product (MVP). The results indicated that the highest technical efficiency of water uses was for fisheries followed by livestock farming, rice farming and brick making, mainly due to nonconsumptive use of reservoir water for fisheries. The lowest WPI was in Dewahuwa reservoir situated in the upper region of Kala Oya river basin followed by Kalawewa, Usgla-Siyambanagamuwa and Siyambalangamuwa, which were located in the lower regions of the river basin where water uses for irrigation and other consumptive uses are much higher. In terms of MVP, the value of product for a unit of water use was higher for livestock farming and brick making. However, these economic activities are less significant compared to agriculture and fisheries. As such, this analysis highlights the need for concerted action of reservoir water management through cooperation between irrigation and fisheries authorities.Item Impact of irrigation on reservoir fisheries: Antagonistic or supportive?(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Nadarajah, S.; Amarasinghe, U.S.; Wijenayake, W.M.H.K.Although reservoirs represent lacustrine ecosystems, they are drastically different from natural lakes for the main reason of prominence of anthropogenic perturbations, which affect ecosystem functioning. Many reservoirs in Sri Lanka are primarily used for irrigation of agricultural lands and are secondarily utilized for inland fisheries production. Effects of hydrological regimes on the biological productivity in reservoirs are therefore expected to have a significant bearing on the fish yield. Aim of this study is to investigate the influence of hydrological regimes on fish yield. In the present study, twelve limnological characteristics of 10 irrigation reservoirs in the Kala Oya river basin of Sri Lanka were investigated from June 2013 to February 2016. Fish yield data in these reservoirs were obtained from the log-book records of fisheries societies. Hydrological data were obtained from the irrigation authorities. Relative water level fluctuation (RWLF), defined as the ratio of amplitude of mean water level fluctuation to mean depth, showed a third order polynomial relationship with chlorophyll-a content (Chl-a) according to, Chl-a = -2.4046 RWLF 3 + 18.732 RWLF 2 - 39.487 RWLF + 44.052 (R² = 0.4351). There was also significant third order polynomial relationship of Chl-a, with fish yield (FY) as: FY = -0.047 Chl-a 3 + 2.689 Chl-a 2 - 45.186 Chl-a + 328.54 (R² = 0.410). As some of the reservoirs in the Kala Oya river basin are terminal reservoirs (e.g., Rajanganaya, Angamuwa, Siyambalangamuwa) from which water is released mainly for irrigation while some are, in addition to irrigation water supply, feeder reservoirs of several downstream reservoirs (e.g., Ibbankatuwa, Kalawewa), effect of hydrological regimes on the biological productivity were possibly represented by polynomial relationships. There was a positive linear relationship between RWLF and FY according to the equation, FY = 27.222 RWLF + 66.729 (R² = 0.586). This indicates that through manipulation of hydrological regimes, reservoir fish yield can be optimized. As such, an effective dialogue should be in place between irrigation authorities responsible for controlling hydrological regimes and authorities responsible for inland fisheries development.Item Trophic ecology and resource partitioning of fish assemblages in brush-parks of Negombo estuary, Sri Lanka(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Gammanpila, M.; Amarasinghe, U.S.; Wijeyaratne, M.J.S.three major brush park fishing areas (Munnakkaraya, Katunayake and Dungalpitiya) in Negombo estuary, Sri Lanka were investigated during April 2014 - April 2016 to classify diet composition, evaluate trophic guilds structure, dietary breadths, interspecific dietary overlap and to determine the degree of food resource partitioning of the community. Fraction of food (proportion by volume) consumed by species was used to establish trophic guilds, applying dietary niche breadth, and the inter-specific food niche competition among species was evaluated using Horn’s index. A cluster analysis, based on Euclidean distance resulted in six trophic guilds on the basis of feeding preferences. Although many fishes fed on a diverse range of food items, diets of 15.2% of fish species, which were included in ‘omnivore’ trophic guild, were dominated by algae/macrophytes with less amount of animal matter (omnivores), 23.9% were detritivores, 2.2% were molluscivores, 2.2% were zooplantivores, 17.4% were macro-crustacean predators and 39.1% were piscivores. The trophic levels of the constituent species varied between 1.0 and 3.0 and the both extremes were occupied by about 60% of the species in the fish assemblage. Standardized dietary niche breadth was highly variable. Species in the omnivorous feeding guild (e.g., Gerres oblongus) and those in the detritivorous feeding guild (e.g., Liza subviridis) showed higher dietary niche breadths (>0.82) showing occurrence of wide choices of food categories for them. The species of intermediate trophic class such as Carangoides talamparoides in macro-crustacean feeding guild and those which fed on macro-crustaceans and fish such as Epinephelus sp. and Lutjanus fulviflamma also had broader (>0.88) dietary breadths. The piscivores Sphyraena jello and Terapon puta with highly specialized feeding habits had the narrowest (0.0) dietary breadth. Species which primarily fed on phytoplankton/macrophytes and detritus such as Mugilids and Siganids, and species such as Acanthurus gahhm, Monodactylus argenteus, Scatophagus argus, Etroplus suratensis, Oreochromis mossambicus and Oreochromis niloticus indicated high dietary overlap ranging from 0.50 to 0.97. It was also evident that even majority of the species in the feeding guilds of macrocrustacean predators and piscivores exhibited relatively high dietary overlaps (range 0.1 - 1.0). The present study therefore illustrated that the fish assemblage in brush parks show both food resource partitioning and dietary competition, the former characterizing divergence of resource use to minimize competition for limited food resources and the latter reflecting resource abundance.