Studies on juveniles and Size selection of Threadfin bream (Nemipterusjaponicus) in bottom trawling off Mangalore

Size selection studies for threadfin breams were carried out with square shape meshed cod-ends of 20, 30 and 40 mm mesh size at high opening bottom trawl (HOBT). Results were compared with conventional HOBT. Experiments were conducted at depth of 40-90 meter off Mangalore from September 2003 to May 2004. Results revealed that fish measuring more than 15 cm contributed to the highest percentage of total catch (40%) followed by 10-15 cm group (33.2%) and 15.3% of the size group of 5-10 cm. Fish measuring less than 5 cm contributed to an average of 11.5% to the total catch. Size selectivity of threadfin breams showed that the high peak frequencies in HOBT with diamond-meshed codend than that of square meshed cod ends. When compare the catches, the bigger sized are more valued fishes which are retained in the square mesh cod-end.