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.

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 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.

Experiments on preservation and weathering of net twines

Koura (1963) reporting the results of the comparative studies on different preservation methods of cotton twines stated that "by the difference of rotting in the different waters, not ever one method may be the most economical one". The observations were simultaneously made at Alexandria in Egypt in the sub-tropical region and Cuxhaven in the estuary of the River Elbe in the temperate zone. The course of weathering and effect of immersion in water of man-made fibres have also been mentioned in this communication. Subsequently work on similar lines were extended to Cochin in the tropical region with Cuxhaven and Hamburg as the other places of observation and the results of these studies are presented in this paper.

Effect of stocking density on the growth of Thai pangas, Pangasius sutchi (Fowler) in net cage fed on formulated diet

A three month long experiment was conducted to observe the effect of stocking density on the growth of Pangasius sutchi in net cages. The size of each cage was 1m³.The three stocking densities used were 40, 50 and 60 fishes/m³ and designated as treatment T1, T2 and T3 respectively. Each treatment had three replicates. All the fishes were of same age group having mean length and weight of 7.13 ± 1.37 cm and 2.46 ± 0.12 g respectively. The fish in all the net cages were fed a diet containing 34% protein. The result of the study showed that fish in the treatment T1 stocked at the rate of 40 fish/m³ resulted the best individual weight gain followed by T2 and T3 respectively. The specific growth rate (SGR) ranged between 3.51 and 3.09, the food conversion ratio (FCR) values ranged between 1.73 and 2.04 with treatment T1 resulting the lowest FCR. The protein efficiency ratios (PER) values were 1.69, 1.16 and 1.43 for treatment T1, T2 and T3 respectively. There was no significant (P>0.05) variation among the survival rates of fish which ranged between 92 and 95%. The net productions in different treatments were 2189, 2343, and 2283g for treatment T1, T2 and T3 respectively. The result of the present study indicated that the best individual growth of P. sutchi was obtained at a density of 40 fish/m³ but the highest total production was obtained at a stocking density of 50 fish/m³ in net cages.

Drift-net fishing in Ceylon waters

Fishing with drift-nets beyond the continental shelf was more profitable than fishing within the continental shelf. Fishing operations conducted over the year beyond the shelf yielded an average catch approximately 1000 lbs. per operation while fishing within the shelf yielded an average catch of 400 lbs. per operation. The seas off the south-west and south coasts were found to be much richer in pelagic fish than the seas off the east coasts. There was a seasonal abundance of fish off the south-west, south and east coasts of Ceylon. On the south-west and south coast fish were more abundant during the months of the south-west monsoon while on the east coast fish were more abundant during the months of the north-east monsoon. Drift-net fishing proved to be a more lucrative method of capturing fish than trolling, longlining and trawling in the seas off Ceylon, and has contributed to an increase in the gross catch in Ceylon waters.

Status of the gill net fishery for the small pelagic fish species in western, south-western and southern coastal waters of Sri Lanka during 1995-1997

Small pelagic fish species are mainly caught by gill nets operated by fibre reinforced plastic boats fitted with 8-25hp out board engines, traditional crafts fitted with 8-1hp out board engines and non mechanised traditional crafts. Around 28 to 55% of the small pelagic catch in the study area consisted of trenched sardine Amblygaster sirm during 1995-1997 period. Another 26-36% of the catch composed of other Sardinella species such as Sardinella gibbosa, S. albella, S. sindensis and S. longiceps. Engraulids such as Encrasicholina heteroloba, Stolephorus insularis and Stolephorus indicus and Thryssa spp formed around 3-5% of the catch. The major component of this fishery consisted of Clupeids and Engrauhds and over 65 species ranged between smaller Engraulids to incidental rock fish, sail fish, seer fish, sharks, skates and rays. Around 1.4 to 1.9% of the catch consisted of Chirocentrus dorab, Sphyraenaspp, Scomberomorus spp, Lepturcanthus sp and Megalaspis cordyla. Around 1-11% of the catch consisted of incidentally catches of sharks, rays, skates and sail fish. Another 1.6 to 6% of the catch consisted of Selar crumenophthalamus and Rastrelliger kanagurta. The best fishing season appeared to be from June to October in the west coast and August to December in the south coast. The major components of Amblygaster sirm, Sardinella albella and Sardinella gibbosa were caught within the size ranges of 10.0-22.5 cm, 11.0-13.0 cm and 11.0-15.0 cm respectively. However, smaller sized fish of above species of sizes between 6.9 cm to 9.7 cm total length were incidentally caught in the gill nets operated for small Engraulids with a stretched mesh size of 1.6cm. The overall catch rate for the major fish landing centre at Negombo indicated an increase from 38.5 kg/boat trip during 1984-1990 period to 49.5 kg/boat trip during 1995-1997 period. The catch rate for the dominant species Amblygaster sirm has decreased from 28.17 kg/boat trip during 1983-1990 period to 17.47 kg/boat trip during 1995-1997 period at Negombo. The paper also discusses the changing overall catch rates, change in species abundance and possible management consequences that should be considered.