Browsing by Author "Schabuss, M."

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    Distribution and abundance of unexploited fish species in three Sri Lankan reservoirs
    (Asian Fisheries Science, 2009) Kumara, A.; Amarasinghe, U.S.; Schiemer, F.; Winkler, G.; Schabuss, M.
    In the reservoirs of Sri Lanka, two exotic cichlid species, Oreochromis mossambicus and O. niloticus are dominant. Small indigenous cyprinid species are abundant in reservoir fish communities, but they remain unexploited due to poor consumer preference. In the present paper, an attempt is made to investigate the spatial and temporal fluctuations of distribution of these unexploited small indigenous cyprinid species in three reservoirs of Sri Lanka. Experimental fishing with multi-mesh gillnets (12.5 mm to 37 mm stretched mesh) having the spread height of 1.5 m, was carried out in inshore and offshore areas of the three reservoirs during the seasons of high and low water levels. As cichlids exhibit depth preference with size, their juveniles were not caught in these gillnets which were set in offshore areas with depths greater than 1.5 m. Amblypharyngodon melettinus, Puntius chola and P. filamentosus were found to be the most abundant species in all three reservoirs. The species composition in the gillnet catches appears to be influenced by water level fluctuations in reservoirs perhaps due to inshore-offshore migration of individual fish species associated with water level fluctuations. Despite the site-specific differences in species distribution and abundance and their temporal variations, a small mesh (12.5 mm to 37 mm) gillnet fishery with the minimum panel height of 1.5 m can be introduced to exploit small indigenous cyprinids in Sri Lankan reservoirs without harming the existing fishery of exotic cichlids.
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    Gillnet selectivity of small cyprinids in three Sri Lankan reservoirs
    (Asian Fisheries Science, 2009) Kumara, P.A.D.A.; Amarasinghe, U.S.; Schiemer, F.; Winkler, G.; Schabuss, M.
    As it has been reported that there is a harvestable potential of presently unexploited small cyprinid species in Sri Lankan reservoirs, attempts were made to investigate the gillnet selectivity for small cyprinids in three reservoirs with a view to defining regulatory measures for the subsidiary gillnet fishery. As exotic cichlids support profitable fisheries in reservoirs of Sri Lanka, any strategy to exploit small cyprinids should not adversely affect the cichlid stocks. Possibly due to the depth preference, exotic cichlids are not caught in small mesh (12.5 to 37 mm) gillnets which are set in the areas with water depths of over 2 m. The effective mesh sizes (stretched) of gillnet which were set in these areas were 16 and 20 mm for Amblypharyngodon melettinus and 33 and 37 mm for Puntius chola and P. filamentosus. Although P. dorsalis is caught in significant numbers in 50 and 60 mm mesh gillnets, this species is unlikely to be exploited without harming exotic cichlids because sub-adults of exotic cichlids are also caught in these mesh sizes. The importance of gillnet selectivity studies of small indigenous cyprinids in Sri Lankan reservoirs is discussed.