Wadge Bank trawl fishery studies. Pt. 1. The effect of the 1928 to 1935 commercial trawling on the demersal stock

The demersal fish stock of Wadge Bank is one of the important fish resources for both Sri Lanka and India. Sivalingam and Medcof (1957) have given an account of its history, general features and relative productivity. According to records the total fishing effort on the bank had been fluctuating and very recently the number of boats operating on the bank has suddenly increased, and there is a possibility that still more will begin operating on the bank in the near future (Mendis, 1965). The increased fishing effort with the possibility of still further increase calls for proper management practices by those concerned, in order to obtain the maximum sustained yield from the demersal stock. For this purpose a detailed study of the past performance of the fishery is essential. With this in view all records of commercial operations up to 1960 are being analysed by the present author and are to be published in a series. This is the first paper in the series and gives a detailed analysis of the first commercial trawling operations from 1928 to 1935. Since there had been a major break of about 10 years between this and the present fishery this data is being analysed separately.

Wadge Bank trawl fishery studies. Pt. 5. Rational exploitation of the resident demersal stock

The general history of the trawl fishery of the Wadge Bank off Cape Comorin, South India (Fig. 1), the nature and composition of its demersal fish population, and the present state of its fishery has been given by various authors (Malpas 1926, Pearson and Malpas 1926, Sivalingam and Medcof 1957, Medcof 1963, Mendis 1965a, 1965b, Sivalingam 1966a, 1966b, 1969a and 1969b). It has been shown earlier (Sivalingam and Medcof 1957, Sivalingam 1969a) that the Wadge Bank stock is made up of two groups. The resident stock which is present on the fishing grounds throughout the year and the migrant stock that appears on the fishing grounds only during the southwest monsoon months. The object of this paper is to discuss the effect of fishing on the resident stock between 1945 and 1962 and based on the information available; assess the maximum sustained yield of the resident stock. The "Bigfish" of the resident stock is the mainstay of the Wadge Bank trawl fishery (Sivalingam 1969a) and it will be shown that this stock has been overexploited from 1953 to 1957. The first sign of recovery was evident in 1960 and continued till 1962. The data since 1962 are not available to the author for analysis. It has been reported by Mendis (1965b) that considerable expansion of the trawler fleet was anticipated in 1966, and if so, the history of the fishery from 1953 to 1957 may be repeated. The assessment presented in this paper should form a rational basis for management programs.

Biology of the exploited stock of mackerel tuna E. affinis (Cantor) off the south-west region of Ceylon

According to the statistical data published annually in the Administration Report of the Director of Fisheries, the bloodfish production in 1967-68 showed about 100% increase over a period of five years and the production figures for none of the other groups of fishes have exhibited a parallel to this. Furthermore, the bloodfish group ranks first in the order of production, having displaced the herring and sardine group which had been in the lead for over a decade. This indicates that increasing attention was paid on the production of this group of fishes, in the coastal waters of Sri Lanka.

Biology, stock size and catch of small pelagic fish along the coast of Mozambique

A compilation of all the available information on the main small pelagic fish resources of Mozambican waters is presented. Resource data on distribution areas, reproduction, age, growth and stock size are described. Actual catch and catch per unit of effort of the commercially exploited stocks are also given. Results of the preliminary assessment of the stocks of scad and mackerel and the problems involving the assessment of Kelee shad stock at Maputo Bay are discussed.

An assessment of the stock of scad and mackerel at Sofala Bank and Boa Paz, Mozambique

The fishery for scad and mackerel along the coast of Mozambique began as a licensed fishery in 1977. In 1980, Mosopesca, a joint venture between Mozambique and the Soviet Union was formed and the licensed fishery ceased. Mosopesca started fishing with four vessels, but since 1984 the number of vessels has gradually been increased and at the end of 1985 a total of seven vessels was in operation. This report contains an updated assessment based mainly on information collected from July 1984 to May 1986.

Stock assessment of Haliporoides triarthrus (Fam. Solenoceridae) off Mozambique: a preliminary analysis

The pink shrimp, Haliporoides triarthrus, is an important species in the deep-water shrimp fishery in Mozambique. Total catches are in the range of 1,500 to 2,700 tons, with the pink shrimp accounting for 70-90%. Estimates of growth parameters and of natural mortality are used for a preliminary assessment of the fishery, based on length-structured virtual population analysis and yield-per-recruit analyses. With an arbitrarily chosen terminal fishing mortality F, the results indicate a situation of overfishing, but realistic parameters must be acquired in order to diagnose the state of the stock

Stock assessment of the deep-water spiny lobster Palinurus delagoae, off Mozambique

Preliminary estimates of growth parameters and mortality are presented for the deep-water spiny lobster Palinurus delagoae fished off Mozambique. The length-converted catch curve shows three levels of total mortality (year-1): Z=2.9 for the smaller sizes; Z=1.4 for intermediate, and Z=0.6 for the larger lobsters. These results are confirmed by a length-structured virtual population analysis. Yield-per-recruit analysis suggests that a long-term yield, at least 50% higher than the present one, could be obtained by increasing the mean size at first capture from about 6 cm (carapace length) to about 10 cm.

Cephalopod fishery at Kakinada along the east coast of India: Resource characteristics and stock assessment of Loligo duvauceli ·

At Kakinada along the east coast of India, cephalopods were exploited by trawls. Fishery occurred round the year with peak during August-October. Peak abundance and fishery of cuttlefishes coincides with this period, whereas for squids it is during March-May. Cephalopod production continued to increase initially with fishing effort, until 1995, but declined thereafter despite increased fishing effort and expansion of fishing to deeper waters. Fishery, growth, mortality, recruitment pattern and exploitation rates of Loligo duvauceli were studied. Nearly 97% of their catch was by zero year groups. They attain sexual maturity and spawn during the first year itself. Spawning occurred round the year with peak during December-February. Exploitation rate of the species is large, 0.741 compared to Emax (0.44). This indicated that their stock is under heavy fishing pressure and subjected to over-exploitation. Stock also exhibited declining trend over the years during 1995-'99. These necessitate immediate attention to avoid coHapse of the stock and fishery.

An empirical study on income and efficiency of pond fish and nursery fish production in some selected areas of Pabna, Bangladesh

The study was designed to determine the costs, returns and relative profitability of pond fish and nursery fish production. In order to attain this objective, a total of 70 producers: 35 producing pond fish and 35 producing nursery fish were selected on the basis of purposive random sampling technique from 6 villages under two Upazilas (Sujanagar and Santhia) of Pabna district. It was estimated that per hectare per year gross cost of pond fish production was Tk 65,918 while gross return and net return were Tk 91,707 and Tk 25,789 respectively. Per hectare per year gross cost of nursery fish production was Tk 87,489 while gross return and net return were Tk 1,39,272 and Tk 51,783 respectively. The findings revealed that nursery fish production was more profitable than pond fish production. Cobb-Douglas production function was applied to realize the specific effect of the factors on pond fish and nursery fish production. It was observed that most of the included variables had significant impact on pond fish and nursery fish production. Out of five variables included in the function, all the variables had positive impact on return from pond fish production but stock value of pond, material cost and pond area had positive impact on return from nursery fish production.

Fishery, population characteristics and stock assessment of cuttlefishes, Sepia aculeata and Sepia pharaonis at Kakinada along the east coast of India

Cuttlefishes were exploited exclusively by trawls along the coast. Growth, recruitment, mortality and exploitation rates of Sepia aculeata and Sepia pharaonis were studied. Fishery of the former was supported mainly by zero year and the latter by zero and one + age groups. Both attain sexual maturity during the first year itself and spawn during August-March with peak during November-December. Natural mortality of S.aculeata was 2.22, fishing mortality 2.34 and total mortality 4.56. It was 1.69, 1.97 and 3.66 respectively for S.pharaonis. Exploitation rate was 0.52 and Emax 0.72 for S.aculeata and it was 0.54 and 0.76 respectively for S.pharaonis. Their mortality and exploitation rates indicated that stock remains under-exploited and have considerable scope for improving the production. However, both stock and catch exhibited wide annual fluctuation with declining trend during the period. These necessitated immediate attention including measures to minimise juvenile exploitation for improving stock and fishery.

Factor intensity and economic returns of alternate shrimp crop and shrimp-salt farming in the coastal areas of Bangladesh

The paper examines the factor intensity and economic returns of alternate shrimp-crop and shrimp-salt farming in the coastal areas of Bangladesh. Data were collected from 30 shrimp-crop and 30 shrimp-salt farmers, 30 shrimp farmers and 30 rice farmers from three selected coastal districts of Bangladesh. Cobb-Douglas production function model was used to determine the effect of various factors on alternate shrimp-crop farming. The chosen variables were stocking of juveniles, paddy seed, labour, fertilizers, feed and farm size of respective type of farming. The results indicated that the production function exhibited increasing remrns to scale for alternate shrimp-rice, alternate shrimp-salt and year round shrimp farming while it indicated decreasing returns for year round rice farming. Economic analysis of same system of farming indicated that higher amount of input use produced higher level of yield, gross return and net return for each type of production system.

Standing stock of three species of demersal fishes from southwest coast of India

Standing stock of three principal demersal fishes of the inshore waters off Mangalore was assessed. The assessment was based on fortnightly samplings conducted in an area extending over ca 850 km². The data gathered was computed employing Alverson's methods. The standing stock of Nemipterus japonicus, Saurida tumbil and Grammoplites scaber indicates that this area supports good quantities of these fishes and if properly exploited, will sustain a profitable demersal fishery.

Stock assessment of the demersal offshore fishery resources off the Karnataka coast

The total biomass of the demersal stocks in the depth range of 30-200m between 12°401 and 15°N latitudes in the Indian Exclusive Economic Zone is estimated to be a:round 1,23,000 metric tons (t). There is scope for doubling the present catch of about 40,000 t from demersal resources by extending exploitation to 50-200m depth zone. About 78% of this increase is expected to come from four species, namely, Nemipterus japonicus, Priacanthus macracanthus, Saurida tumbil and Arius spp.

Effect of different sex ratios of ablated wild-stock Penaeus monodon Fabricius on maturation, fecundity and hatching rates

The study was conducted to determine other sex ratios of ablated wild-stock Penaeus monodon other than the most commonly practiced 1 male: 1 female. Four different sex ratios, 0:1, 1:1, 1:2, and 1:4 male: female were tested in four 4m diameter circular tanks for a period of 55 days. During the first run the 1 male: 2 females ratio gave: (a) the highest percentage of first (42.20%), second (30.00%) and third (33.33%) spawning; and (b) the highest total and average fecundity (3.9 million eggs and 300,692 eggs, respectively). The 1 male: 2 females ratio is recommended on the basis of highest percentage for the first, second and third spawners, total and average fecundity.

Population dynamics and stock assessment of the common carp (Cyprinus carpio) in Iranian waters of the Caspian Sea

In order to come up with the responsible fishing pattern of common carp, there was a need to identify some of the biological characteristics and stock assessment of carp in Iranian waters of the Caspian Sea .The fork length ,weight ,age ,growth parameters of von bertalanffy and mortality rates of common carp were estimated from oct 2006 to sept 2007.Based on the exponential relationship between length and weight in the size range 6.3-65.6 cm ,b was calculated 2.895, 2.843 and 2.925 respectively for combined sexes ,males and females. The mean condition factor was 1.9 which is close to the ideal condition.The results from measuring 3170 specimens ,were showed the first fork length of maturity was 30 cm for males and 32 cm for females. The results indicated that females were predominate and sex ratio was 0.66:1 (M:F) and chi-squares analysis showeda significant difference between males and females.(p<0.05).Length infinity and growth coefficient were calculated by three different methods as below: Length frequency analysis : k=0.17 L∞ =68.04 Age-Length Key k=0.15 L∞ =74.25 Back calculation : k=0.14 L∞ =68.4 The mortality parameters and exploitation rate were estimated as below : Z=0.73 per year M=0.31 per year F=0.42 per year E=0.56 Refer to amount of common carp catch in 2007 -08 ,biomass was calculated 9640.2 tones by jone's cohort analysis and MSY 2374.5 tones.According to analysis ,the number of common carp in the distribution area (Iranian part of the Caspian Sea ) was estimated 24 millions in the 2006-07.