Assessment of impact of trawling in Gulf of Mannar Biosphere Trust Region

• Recruitment over fishing( fishing of brooders) was found to be the major problem due to trawling along the coast of Gulf of Mannar
• Out of the 25 species examined, recruitment overfishing was reported in 11 species such as Scomberomorus commerson, Lethrinus lentjan, Lethrinus olivaceus, Alectis indicus, Decapterus macarells, Selaroides leptolepis,Stolephorus indicus ,Parupeneus indicus,Lutjanus quinoquelineatus ,Saurida tumbil,Lepturacanthus savala, Leiognathus dussumieri and was found to occur from March to May.
• Three species such as Decapterus russelli, Nemipterus japonicas, Nebiea maculate were found to suffer both due to recruitment overfishing and growth overfishing. These species were found to be highly affected as both brooders and juveniles are captured heavily due to trawling
• Square mesh cod panel of 30 mm at 30% of the cod end has to be fixed in the cod end of trawl nets of Thoothukudi.

Nemipterus japonicas

Nebiea maculate

Decapterus russelli

Studies on bycatch reduction in trawl fishing of Gulf of Mannar coast for biodiversity conservation

• Bycatch from bottom trawls of Thoothukudi coast was found to range between 80 and 90%, of which, 20- 40% were found to be discards. Bycatch from mid-water trawls of Thoothukudi coast was found to range between 70 and 85%, of which 10- 30% were found to be discards. Discards were recorded up to 70% in catches of trawls, which were operated below the depth of 50m and this was less than 50% beyond 50m depth.
• Juveniles of commercial fishes were recorded up to 40% of the fish catches of trawl net. More than 60% of semisculcatus were found captured before attaining first maturity in mini trawls nets of Thoothukudi coast. Square mesh panel with 40 mm size was found to facilitate escapement of juveniles through square mesh of mini trawl.

Study on the performance of mini trawling in Thirumoorthy reservoir of Tamil Nadu

• A 38m two seam trawl with the head rope length of 38 m was designed and fabricated. The net was designed suitable for trawling from two boats each powered with a 25 hp out board engine. Topographic survey carried out using portable echo sounder revealed that there are trawlable fishing grounds in Thirumoorthy reservoir.
• During the survey, the depth of trawlable grounds of the reservoir varied from 9.5 to 12 m. Apart from this marked site, the remaining areas of the reservoir were found unsuitable for trawling as there were rocks, trees and trenches.
• The mean catch rate of trawl was found to be 9.5 kg per haul. Among the four species that contributed to the catch, rohu was found to be the dominant species followed by catla, mrigal and common carp.

Waypoints to trawlable fishing grounds of Thirumoorthy reservoir

Optimization of mesh size of gillnet for barracuda fishing in Thoothukudi coast

• Synthetic hormone viz., wova-FH was injected intramuscularly to the brooders at the rate of 0.1ml/kg for male and 0.15 ml/kg for female. Induction of triplody was done by giving heat shock (39⁰C, 40⁰C and 41⁰C) for 1 min and cold shock at    (0-4⁰C) for 30 min, 45 min and 1 h after 9 min post fertilization.
• Fertilization rate ranged from 72.0-86.5%. Induction of triploidy using heat shock and cold shock was successful. The percentage of hatching of heat shock treated group was 63.5% at 39⁰C, 58.0% at 40⁰C and 50.0% at 41⁰C. The percentage of hatching of cold shock treated group was 53.0% at 0-4⁰C for        30 min, 44.0% for 45 min and 36.0% for 1 h.

• Four species of barracudas form the commercial fishery in the small and big meshed gillnets of Thoothukudi coast viz. Sphyraena obtustata, S. forsteri, jello and S. picuta.
• Barracudas could migrate and are available for fishing in shallow waters during the South-West monsoon (June to August).
• Selection factors derived for obtustata, S. forsteri, S. jello and S. picuta were 5.70, 7.04, 8.27 and 9 .47, respectively. Optimum mesh sizes for the commercial exploitation of S. obtustata, S. forsteri, S. jello and S. picuta were estimated to be 4.21, 5.82, 5.92 and 8.87 cm, respectively. Commercially significant length group of S. obtustata, S. forsteri, S. jello and S. picuta was estimated to be 24, 41, 49 and 84 cm, respectively.