The effect of mesh size on the fishing efficiency of sardine gill nets

The study deals with the effect of mesh size on the fishing power of gill nets. The authors have shown that there can be substantial difference in the out puts of sardine gill nets, of identical design and rigging, but of different mesh sizes, operated under the same conditions.

Trends in development in the prawn fishing technique in India: a review

The paper provides some background information about the developments in the prawn fishing technique. The important indigenous gear for prawns are the filtering type nets like the stake nets, boat seines and beach seines with bag. The only indigenous net, which can be compared in design with the modern bottom trawling gear, is the "Thuri Valai" of the Madras Coast. Prawns have also been reported from the catches of gill nets and cast nets. Dredges and beam trawls are simplest among the dragged gear. Even though several earlier attempts were made with the beam trawl, in 1959 season a detailed experiment was made to study the fishing features of this gear. The subsequent experiments conducted were for comparison with otter trawl, towing of 2 beam trawls one behind the other and the use of tickler chain. The initial experiments with otter trawls were mainly directed towards operational aspects. The experiments were to evaluate the effectiveness of fully mechanised and partially mechanised operation, the effect of extra buoyancy of floats and the use of tickler chain. Subsequent developments had been on the structure and design of prawn trawling gear. Effect of long wings and sweeps were tested. Catches of nylon and cotton nets were compared. The sizes of meshes of the cod-end have also been increased.

On the effect of tickler chain on the catches landed by a 55 ft. trawl net

The communication deals with the results of comparative tests conducted from Cochin base to study the effect of a tickler chain on the catches landed by a 55' shrimp otter trawl. The net was operated with and without chain and 82 hauls of 61 hours and 28 minutes total duration were made. The following are the conclusions: (a) the catch of shrimp per hour of trawling is increased by about 71% due to attachment of the chain to the ground rope; (b) the attachment of the tickler chain also increased the catch of fish by 25%. The increase in the catch of shrimps and fish is probably due to the disturbance caused by moving chain attached to the foot-rope.

On the selective action of the cod end meshes of a shrimp trawl

Selectivity studies using cod end and cover to determine the optimum cod end mesh size for commercial size groups of shrimps was carried out at Cochin during 1963-64 fishing season. The normality of the result was checked by trouser cod end method. Although the present investigation was mainly aimed to find out suitable cod end mesh size for commercial varieties of shrimps, five commonly occurring species of fishes were also taken. The 50% escape level, co-efficient of selectivity and selection factor for all the species were worked out. From the findings, the authors stress the necessity of increasing the cod end mesh size from the present condition (25.4 to 31.70 mm) to 41.65 mm fabricated mesh size to avoid depletion of the natural population.

An interpretation of the data from "The effect of mesh size on the fishing efficiency of sardine gill nets"

The paper "The effect of mesh size on the fishing efficiency of sardine gill nets" [K.M. Joseph and A.V. Sebastian, Fish. Tech; 1(2), 180-182 (1964)] marks an important step in the progress of fisheries technology and biology in India.

An experiment conducted with a floating trawl net off Cochin

The paper deals with an experiment with a floating trawl net off Cochin, using a pair of curved otter boards and a transducer mounted on the head rope of the net. 32 hauls were made with different towing speeds and warp length keeping one factor constant for varying parameters of the other factor. The working data for 32 hauls are presented and the effect in the fishing depth of the net due to the variation in one factor is mentioned. The 'fishing depth' is indicated in this paper as the distance between the head rope and the bottom. The usefulness of similar experiments with added information on the angle of leading warp at the stern for the exploitation of column fishes in Indian waters is indicated.

General features and productivity of the Wadge Bank trawl fishery

For several years one of the world's few successful tropical trawl fisheries has been carried on off the southern tip of India. Much of it has been under the auspices of the Government of Ceylon. Records covering the entire history of the fishery are remarkably complete and those of the last ten years are unusually detailed. The purpose of this paper is to summarize these records and relate them to information from other sources in such a way as to illustrate the principal features of the fishery and permit comparisons with other fisheries. This should provide a sound basis for clear thinking about the industry's present problems and prospects. This is important because the fishery is expanding.

General principles of the design of trawl net

The classification and the principles of design and construction of trawls in general are described. The method of calculating the length of rope required at each part for mounting the net and the requirements of floats and sinkers are given. The cutting rates to tailor machine made webbing are also indicated.

Nursery rearing of Macrobrachium rosenbergii (de Man) using hapa-nets: effects of stocking density

An experiment was conducted in two phases for 45 days each to study the effects of six stocking densities (phase-I: 100, 200 and 300 PL/m² and phase-II: 250, 500 and 750 PL/m²) on growth and survival of Macrobrachium rosenbergii postlarvae (PL) in nylon hapa-nets (1.8m x 1.8m x 1.4m) installed in a pond. Stocking densities of 100, 200 and 300 PL 10/m² resulted in similar (P<0.05) body length (47-48 mm) and survival rate (84-88%), while body weight (0.62g) in PL with 300/m² was significantly lower than that (0.70g) in PL with 100 and 200/m². The growth (body length 47mm and weight 0.64g) and survival (84%) of PL stocked at 250 PL/m² density were significantly higher (P<0.05) than that of PL at 500 and 750/m². Besides the variation in growth and survival in PL at six tests stocking densities, a sharp increase in body weight of PL was observed beginning at the 4th week of rearing.

On the relative utility of different methods to increase the vertical height in an otter trawl

Comparative fishing experiments to study the relative utility of different methods for increased vertical spread of bottom trawl and the availability of off bottom fishes in the region were made using gussets, kite, separate float line and side panels on a two seam net. The catch rates as well as composition of fish were studied. The opening of the trawl mouth, both horizontally and vertically, under different operating gears and towing tension on warps were measured and estimated for comparison purposes. Better catch rate with good quality fishes was obtained with the gear operated with separate float line. With kite, the vertical spread was increased with less catch indicating poor concentration of off bottom fishes.

Results of preliminary fishing trials with 15.8m six-seam otter trawl

The paper deals with the results of trawling operations conducted along the Saurashtra Coast of Gujarat State with 15.8 m six-seam otter trawl. Fishing operations carried out from Fishtech No. 8 with this new net were the first of their kind in the country and the results proved to be encouraging. The design in question is passed on to private agencies for commercial operations.

Some observations on the performance of 10.5 m mid-water trawl operated off Veraval

The communication presents the results of fishing trials conducted off Veraval with a 10.5 m four-seam unequal paneled mid-water trawl with vertically curved otter boards. The design and structural details of net and otter boards are described in detail. Particulars such as the fish caught during experimentation, horizontal spread of the net as well as towing resistance offered in action are also incorporated.

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. 2. The effect of trawling on the catch per hour from 1945 to 1960

The object of this series of papers has been given in Part 1 (see Additional informations for details) which deals with the first known commercial fishery on the Wadge Bank from 1928 to 1935. There is no recorded trawling on the Bank between 1936 and 1944. This paper deals with the changes in the total catch (i.e. all species combined) per hour of trawling in relation to the changes in fishing intensity from 1945, when the present trawling activities started, to 1960. The effect of trawling on individual categories or varieties will be presented later.

Bottom trawl codend mesh selectivity for Bagrus docmac (Forskahl) from Lake Victoria, with some remarks on the proposed trawl fishery

The methods of estimating codend selectivity for alternate hauls are briefly described and applied to Bagrus docmac (forskahl) data from Lake Victoria. Certain inconsistencies are noted and it is postulated that they may be due to differential escapement of larger Bagrus docmac through the trawl meshes when the different codends were fitted. The calculated 50% selection lengths yielded a fair regression on measured weigh give a fork length selection factor of 2.33, consistent with data from the smallest codend mesh size used. The implications of the findings are briefly discussed in relation to the proposed Haplochromis trawl fishery 1971.