Pelagic fishery resources of Sri Lanka and its present level of exploitation with special reference to off-shore and deep-sea waters

Pelagic resources around Sri Lanka may be categorized into three major groups: (1) the small pelagic varieties such as the sprats, halmessa, sardines (salaya, soodaya), and herrings (hurulla). (2) the medium size pelagic species such as the mackerel (kumbala and bolla), barracuda (jeela), seer Spanish mackerel (thora), frigate mackeral (alagoduwa), mackerel tuna (atawalla) and the skipjack (balaya). (3) the large size fishes such as yellow fin tuna (kelawalla), big eye tuna, marlins (koppora and gappara), sail fish (thalapath), sharks (mora) and rays (maduwa). Production levels of exploited resources are noted, and seasonal patterns and annual in their abundance are considered. On the basis of observations and estimations of the existing fisheries, and the results of experimental fishing, figures are presented of the potential yield of those species already exploited. The development of that potential depends on the development of modern techniques of pole and line fishing, application of tuna longline and shark longline, increasing the number of units of drift nets and the introduction of a bait fishery for the longline and pole line fishery. Some features upon which the successes of any venture to exploit such resources are noted, particularly those which relate to the nature of the fishing vessels used.

Fishing gear and methods for off-shore fishing in Sri Lanka

The author describes the commercial viable off-shore fishing methods for catching known commercial resources available around Sri Lanka. He also describes the in-shore fishing methods such as bait fishery which are related and of prime importance for carrying out certain off-shore methods. The paper is intended as a background for the description of fishing methods. The methods discussed are: (1) Longlining for large pelagic species such as large tuna (yellow fin, big eye), shark, spearfish and others; (2) Drift-netting for small and large tuna species (skipjack, yellow fin and others), shark, spearfish, etc.; (3) Pole and line for all deep-sea pelagic species such as skipjack, yellow fin, frigate mackerel, etc.; and (4) Purse seining (small scale) for small pelagic species suitable as bait fish for pole and line and longline fisheries.

The freshwater zooplankton of Sri Lanka, with a discussion of tropical freshwater zooplankton composition

Based on the study of over 500 zooplankton samples collected in Sri Lanka during 1965-1974, the species composition from different habitats is analysed. The zooplankton assemblage is typically tropical with relatively few species of Cladocera and Copepoda. The Rotifera include a large number of species of the genus Brachionus. The limnetic zooplankton resembles the pond zooplankton closely in that all the eurytopic species found in the different types of habitats, including ponds; also occur in the limnetic zooplankton. The large Cladocera belonging to the genus Daphnia are very rare. In general, large zooplankters are absent. The size composition of the zooplankton has a smaller range than in temperate regions. This is due to the absence of large-sized zooplankton species. The reasons for the differences in species variety and size composition between zooplankton of temperate and tropical regions is perhaps due to a number of factors. These include the effects of high and uniform temperatures, food availability and predation by fish and invertebrates.

Induced spawning of two major species of Chinese carps, Ctenopharyngodon idellus and Aristychthys nobilis in Sri Lanka

Induced spawning of grass carp (Ctenopharyngodon idellus) and bighead carp (Aristychthys nobilis) was carried out successfully in Sri Lanka for the first time in 1977 and 1978, respectively. This article describes the techniques involved in induced spawning in Sri Lanka at the Freshwater Fish Breeding and Experimental Station in Udawalawa.

Results of the Austrian-Ceylonese hydrobiological mission 1970 of the Institute of Zoology of the University of Vienna (Austria) and the Department of Zoology of the University of Sri Lanka, Vidyalankara Campus, Kelaniya. Pt. 19. Aquatic and semiaquatic Hemiptera of Sri Lanka from the Austrian Indo-Pacific expedition, 1970-71

This report concerns the aquatic and semiaquatic Hemiptera collected in Sri Lanka by Prof. Starmühlner and Prof. Costa during November and December 1970. A surprising number of new species have been found in the Starmühlner-Costa material, even in groups for which comprehensive revisions exist. Seven new species are described here.

The National Aquatic Resources Agency of Sri Lanka

A general discussion on the establishment of the National Aquatic Resource Agency, its functions and activities, is presented under the following major headings: objects and functions; the institutional framework: policy-making and interaction and coordination, and implementation; the Agency; and the activities of the Agency.

Sri Lanka: is it a mid-plate platelet?

Two observations suggest the possibility that Sri Lanka is acting as a small-mid-plate platelet moving very slowly within and relative to the larger Indian plate. First, sediments of the Bengal Deep-Sea Fan off the SSE continental margin are folded and uplifted in a manner similar to the deformation from front of accretionary prisms where thick sediment columns are passing into subduction zones. And second, subsidence rates in the area of presumed spreading or continuing stretching of continental crust, the Cauvery-Palk Strait-Gulf of Mannar Basin, have not decreased during the Cenozoic as would be predicted by an aborted rift or aulacogen model, but instead appear to have accelerated during the Neogene. Information available on other phenomena which re predicted by the model is at the present time inadequate for evaluation.

200 mile Exclusive Economic Zone and fishery development in Sri Lanka

Following details of the marine fishery resources of Sri Lanka, prospects for fishery development with respect to the 200-mile Economic Zone are examined, outlining also the 5-year fisheries development plan (1979-83).

Estimations of maximum sustainable fish yields and stocking densities of inland reservoirs of Sri Lanka

The Maximum Sustainable Yields of all fish species for 9 man-made reservoirs in Sri Lanka were calculated by the simplified version of Schaefer Model. The relationship between the Maximum Sustainable Yield (MSY) and Morpho-edaphic Index, (MEI) for Sri Lankan reservoirs was found to be: Log sub(e) MSY = 0.9005 log sub(e) MEI + 1.9220. MSY for these reservoirs were estimated using this relationship. The number of Tilapia) juveniles needed to be recruited to the fisheries of some reservoirs in addition to the present recruitment to increase the fish production to the level estimated by MEI relationship were calculated mathematically.

The morphometrics and the proximate composition of the edible fresh water mussel Lamellidens lamellatus (Lea) from Bathalagoda tank, a man made reservoir in Sri Lanka

Morphometric characteristics of Lamellidens lamellatus were studied using a random sample of 138 individuals collected from Bathalagoda reservoir in Kurunegala district. The largest number of individuals in the collection was between 40-50 mm in length. They had a body weight between 60-80 gm. The most abundant bio-chemical component in the adductor and in the foot was protein. Carbohydrate and lipid quantities were almost equal while ash showed the least value. The total protein content ranged from 48.8% to 73.4%; the carbohydrate content from 12.64% to 23.8%; and lipid content from 12.0% to 28.1% of their dry weight. It was found that there were significant relationships between the length and the body weight; and between length and volume.

Note on the occurrence of Artemia in Sri Lanka

A brief account is given of the Artemia populations occurring in Sri Lanka with respect to inland and brackishwater aquaculture activities.

Restricted water exchange in the Negombo Lagoon on the west coast of Sri Lanka

Salinity, fresh water and sea level data from the Negombo Lagoon with respect to oceanic sea level and salinity data were considered. The open ocean spring tidal range was 0.57 m, whereas the neap tidal range was 0.10 m. In lagoon, the corresponding spring tidal range was 0.13 m and neap tidal range is 0.05 m. The lagoon tide was strongly choked because of the restricted inlet channel, through which only a limited water exchange could take place over a tidal cycle. Mean water exchange and the residence times for variable fresh water supplies were calculated. These calculations were based on fortnightly measurements of salinity and river discharges in 1993. During this year, salinity varied from 30-5‰ depending on the river inputs which were 20-225 m³ sˉ¹. Corresponding residence times varied from 11-2 days and the tide is dominated the exchange during low discharges of freshwater.

Nutritional evaluation of some small coastal fish in Sri Lanka

Small pelagic fish play a very important role in human nutrition and health. Lipids of these fish differ remarkably from plant and other animal lipids. The aim of the study was to describe the proximate composition of thirty-three small pelagic fish species commonly available in Sri Lanka. Fish species were collected from Negombo and Chillaw fish landing sites and subjected to analysis for moisture, ash, protein and total lipid content. Tiger tooth croaker (Otolithus ruber) was found to have the highest moisture percentage (80.0%) followed by Clarias sp. (78.9%), Indian anchovy (Steloporus indicus) and Comerson's anchovy (Stelophorus commersonii), (78%). The lowest percentage of moisture, 69.4%, was recorded in white sardinella (Sardinella albella). Indian ilisha (Ilisha melastoma) was found to have the highest amount of ash (10.1%) followed by Otolithus sp. (8%) and big-eye barracuda contained the least amount (2.5%). Carassius Carassius, pick handle barracuda (Sphyraena jello) and Indian mackerel (Rastrelliger kanagurta) contained higher amounts of protein, 24.3, 20.6 and 19.2% respectively. The lowest protein content (10.1%) was found in Indian scad (Decapterus russelli). The protein content of the fish was in the range of 13-15%. The results revealed that the small fish are moderate protein sources. The total lipid content varied between 0.6-8%. White sardinella recorded the highest percentage of lipid (8%) where tiger tooth croaker contained the lowest percentage (0.6 %). The study showed high fatty species to contain low amount of moisture and vice versa establishing an inverse relation between fat and moisture quantitatively.

Antibacterial properties of some marine algae of Sri Lanka

The authors report on the antibacterial activity of 11 algae, green, brown and red. Prepared extracts were tested, and varying degrees of activity were exhibited. Most activity was shown by Ulva fasciata, Sargassum cervicone and Halimeda macroloba.

Vertical temperature structure of 250 m. water layer around Sri Lanka at the tail-end of the north-east monsoon

Data collected during cruises of the Hoyo Maru in Jan-Mar 1975 are analysed. Data is tabulated to show vertical temp profile, surface water temp and temp gradient. Each of these features is discussed. Thermoclines are shown to be established off the coast of India, their depth varying according to time of year. Upwelling off the Cochin coast is discussed. This occurs during Oct-Nov. Surface temp is considerably influenced by the north-east monsoon. The 'clockwise current' (or 'transparent current) characterised by high salinity, high transparency, and rich nutrient conchs, and which prevails in Jan-May brings oceanic water into the Bay of Bengal and sweeps along the Ceylon coast.