Humic acids in sediments of North-Central Arabian Sea, west coast of India

Sediment samples (28) collected during the ORV Sagar Kanya cruise-29, were analysed for humic acid (HA) concentration from the North-Central Arabian Sea. Generally oceanic samples had more HA concentration than the continental shelf (< 200 m depth) samples. The photo-acoustic infrared spectra of shelf sediment HA indicated the presence of more C-H saturated aliphatic chains, while oceanic HA had few peaks for the above groups. Both the IR spectra indicated the absence of aromatic C = C, carbonyl, ketonic groups. Clayey-silt sediment generally had higher concentration of HA compared to sandy-silt type of sediment.

On the use of different natural baits for sea-fishing in India

Rod and line, hand-line, trolling line and fish-traps are the different types of fishing gears wherein suitable fish baits are employed with a view to luring the catch. The coastal fishermen of India mostly use different types of natural fish-baits to catch fishes like Perches, Carangids, Sciaenids, Scombroids and Elasmobranchs. The reactions of the fishes caught to the different baits used are quite varied. Successful line fishing operations very much depend on the fish-baits. A detailed record of the variety of fishes caught, types of fishing and different baits used by the coastal fishermen of India has been made.

Trawling pull exerted by a trawler: a method of estimation from propeller dimensions and its comparison with sea measurements

The proper matching of the pull exerted by a trawler and the size of trawl is important for maximizing the catching efficiency. The available pull is more dependent on the propeller and its working conditions than the installed engine power. The normal practice is to directly connect net size to the installed power in the boat by formulae without reference to the prope1ler dimensions or the available trawling pull and this is not adequate to find out the optimum combination. By the method outlined in this paper, the accurate calculation of trawling pull is possible by taking into account only the propeller diameter, pitch and r. p. m. The predictions by the method are compared for trawlers with powers between 30 and 60 hp and agreement is found to be within + 5%. The power absorbed by the propeller in trawling condition can also be calculated by this method for checking whether the engine is being overloaded.

Bothid larvae (Pleuronectiformes-pisces) of the Gulf od Thailand and South China Sea

The larvae of bothids were found to be sparsely distributed in the Gulf of Thailand and South China Sea being only 11.9% in the Naga Expedition Collections. They were confined mostly to the coastal waters and were found in near shore stations situated between Bangkok and Saigon. Their density was high in the Gulf of Thailand. The larvae seem to prefer darkness with greater incidence during April 16 to October 15 period, with a peak in the collections taken during April. This report includes the occurrence of 17 species belonging to 6 genera collected from the Gulf of Thailand and South China Sea, along with their regional, seasonal as well as diurnal variations

Studies on the seasonal cycle of sea surface temperatures, salinities and phytoplankton in Puttalam Lagoon, Dutch Bay and Portugal Bay along the west coast of Ceylon.

The monthly average temperatures at Puttalam Lagoon, Dutch Bay, Portugal Bay towards Kovilmunai and Portugal Bay towards Pallugaturai showed a distinct annual cycle. The peak was in April and values gradually fell till September. There was a further gradual fall in temperature from October to January. The highest temperatures in all four stations were in April. The highest salinities in all the stations were from May to October i.e., during the south-west monsoon. The salinities at Dutch Bay and Portugal Bay were high in March and April corresponding to the highest temperatures reached during these months. Two maxima have been observed in phytoplankton production. A primary maximum in May-June and a secondary maximum in October. The primary and secondary maxima are due to the influx of nutrient laden waters from the rivers Kal Aru and Pomparippu Aru. The phytoplankton producing blooms were Rhizosolenia alata. Rhizosolenia imbricata, Chaetoceros lascinosus, Chaetoceros pervianus, Ch,aetoceros diversus, Coscinodiscus gigas, Thallasionema nitzschioides, Thalassiosira subtilis, Thallassiothrix frauenfeldii, Asterionella japonica, Sceletonema costatum, Bacteriastrum varians and Biddulphia sinensis. Sudden outbursts of a single species were common. These diatoms were species of Chaetoceros and Rhizosolenia, and Thallassiothrix frauenfeldii. Wide fluctuations have been observed in the distribution of phytoplankton but no definite conclusions can be drawn as the period of observation was only one year.

Marine bacteria as indicators of upwelling in the Sea

The “oxidase reaction” (using p-amino-dimethyl-aniline oxalate as the reagent) has been used to distinguish oxidase-negative from oxidase-positive bacteria from the sea, when grown on membrane filters. By this means, it has been shown (a) that under conditions of stable stratification of the sea as in the tropics, a relationship exists between the percentage incidence of oxidase negative bacteria in the flora and the depth of the water; (b) that the maximum value for this percentage incidence (100) is reached at or immediately below the upper limit of the oxygen minimum layer; (c) that this percentage value (expressed as Oxⁿvalues) may be used to demonstrate the movements of water masses during upwelling. Such upwelling as indicated by theoretical findings and by temperature determinations along two transects off the west coast of Ceylon during the north east monsoon, has been confirmed by the distribution of Oxⁿvalues at these transects.

A Comparison of the bacterial flora of surface and sub-surface water of the sea off Ceylon

Under stable conditions of stratification of the sea, evidence of generic differences of the associated bacterial flora of the water masses has been obtained, between surface and sub-surface water. Gram negative rods, especially pseudomonads and achromobacters were more frequent at the surface. The fermentative and oxidase negative flora was more frequent in sub-surface water. The surface water in general had a greater variety of bacterial types while the sub-surface water had a flora with a greater range of biochemical activity. These results are discussed in relation to the hydrological condition of the water masses and the bacterial flora of freshly caught fish.

The Development of Ceylon's fisheries (a symposium)

In July, 1964, it was decided that a Government Fisheries Corporation be set up. At the request of the Directors-designate of this Corporation a series of lectures on the development of Ceylon's fisheries was organised by the Fisheries Research Station, all except two being delivered at a seminar on 15th September, 1964. The speakers were asked to prepare and submit their texts and these are presented in the sequence in which the talks themselves were delivered: 1. Ceylon's fisheries: past and future (A.C.J. Weerekoon) 2. Fisheries by-products (C.St.E. Gunesekara) 3. The role of technology in fisheries development in Ceylon (N.N. De Silva) 4. Seaweeds (M. Durairatnam) 5. Coastal fisheries (T.P. Goonewardente) 6. The trawler fishery (A.S. Mendis) 7. A review of Japan's tuna long-line fishery in the Indian Ocean (K. Sivasubramaniam) 8. Off shore and deep sea fishery for larger scombroids in the Indian Ocean (K. Sivasubramaniam) 9. The development of fresh water fisheries in Ceylon (H.H.A. Indrasena) 10. Brackish-water fish farming in Ceylon (T.G. Pillai) 11. The role of inland waters in relation to the development of Ceylon's fisheries and a note on the pearl oyster fishery (C.H. Fernando) 12. The mechanization of the inshore fisheries and the relationship to fisheries development in Ceylon (E. Kvaran)

Coastal fisheries

The coastal zone of Sri Lanka is the most important area of fish production at present. This coastal zone is limited seawards to the edge of our relatively narrow continental shelf. The fishing methods employed are such that only a fraction of the shelf area is exploited. The extent to which the coastal zone is exploited depends on the craft and gear used in the fishing operations. The non-mechanized traditional crafts such as the teppams and orus generally operate within about five miles from shore. The mechanized traditional crafts and the small mechanized boats introduced around 1957 carry out fishing operations up to the continental shelf or beyond. The gear used by these fishing crafts is determined by the habits of the type of fish to be caught, the nature of the sea bed and other related conditions. For the pelagic fishes they use trolling lines or float long lines or drift nets. For the demersal fishes hand lines, bottom long lines, bottom set nets or drag nets are used. However, the net is the preferred fishing gear. The beach seines or madels, the traditional crafts such as orus, teppams and vallams and the small mechanized boats are the important contributors in the coastal fishery. Of these the madels are considered the most important since a high percentage (25-35%) of the Island's landings are produced by the operation of these nets.

Wadge Bank trawl fishery studies. Pt. 4. An analysis of the length frequency measurements of the sea bream (Lethrinus nebulosus) made in 1949 and 1953 to 1958

Length frequency distributions of the sea bream collected during the period 1953 to 1958 have been analysed. The increase in average sizes of the sea bream with depth suggests a movement to deeper waters with increase in size. By numbers, the sea bream is more abundant between 21 and 30 fathoms than in deeper areas. The recruitment was continuous and regular. There is no sign of entry or progression of a dominant brood throughout the period under study. Length frequency distribution shows three distinct modes. The first mode occurs regularly but does not progress beyond 40cm, recruitment being balanced by natural and fishing mortality. The other two which are not regular are probably the result of fishing outside regular areas. Short sections of “growth” lines which fit into one another when extrapolated, are evident. The larger lines obtained by extrapolation are parallel to one another. These tentative "growth lines" indicate that this species which enters the fishing grounds, when 15 cm or larger in length are exploited by the trawl fishery for a period of three to four years. This species appears to be six months old when it enters the fishing grounds and increases in length by about 37.5 cm in the next 30 months. Later growth slows down. The average size of the specimens sampled continued to get smaller from 1953 till 1957. It is shown that this reduction in size is due to increased fishing effort.

Studies on the seasonal cycle of sea surface temperatures, salinities, oxygen and phytoplankton in Koddiyar Bay, Trincomalee in relation to the shore seine fishery

In Sri Lanka waters, Durairatnam (1963, 1969) had reported on the seasonal variation of plankton at Puttalam lagoon, Dutch Bay, Portugal Bay and in the inshore and off shore waters off Colombo. Similar investigations were carried out at Koddiyar Bay especially in the estuarine waters where the three tributaries of the river Mahaveli empty their waters into the bay. The estuary is perennial. The fishes constituting the estuarine fisheries are mostly shallow water marine species which can tolerate considerable variations of salinities. Prawns and crabs also constitute a very valuable fishery in estuarine waters.

Development of off-shore and deep-sea fishing in Sri Lanka

Since 1950 onwards, a practice has grown in Sri Lanka of dividing the marine fisheries into three different classes depending on the location of the resource to be exploited viz. coastal fishing, off-shore fishing and deep-sea fishing. The author describes commercial fishing activities, paying attention to changes emerged and future prospectives.

Problems facing the deep-sea fishing industry in Sri Lanka

Fishing in Sri Lanka has been carried on largely with the use of traditional methods and in recent years there has been a marked increase in the use of mechanized craft for fishing. Although some effort has been made in the sphere of deep-sea fishing both by trawlers and long line tuna boats, such efforts have not made a significant contribution towards improving the industry. The progress of deep-sea fishing in Sri Lanka has been hindered due to a number of reasons described by the author.

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

Following a brief review of development of demersal fishing off Sri Lanka, the author reviews the fishing grounds of the Wadge Bank, the Pedro Bank, and the Mannar Bank. He reviews the deepwater trawling fisheries particularly in relation to the 1972 survey conducted by the 'Optimist' and also small boat trawling in coastal waters. Lastly he considers handlining for groundfish, which is principally conducted by fishermen operating traditional craft.