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Abstract:

During period of 2016-2017, research on application of square mesh codens for the coastal trawl net was carried out in order to protection and development fishery resources. For seeking the suitable types of the square mesh codend which can be escape high ratio of juvenile and small fish, data on operating status of the coastal trawl net fleets (such as species composition, size of fishing individual, etc.,) was collected and heritage inherit previous studies including domestic and abroad studies. Combination of these elements, technical specifications of the square mesh codends were estimated. Then, the test trips were setup to collect the data on catching for analyzing and estimating to find out the suitable types of the codens which have the highest escaped ratio of juvenile and small fish and can be applied for the coastal trawl net.

The results of experiments showed that some high commercial species and the catch ratio in trial batches said that: Escaped ratio of juvenile fish calculated by individual of Saurida spp. (lizardfish) was 82.2%, with Mullidae (goatfish) was 86.3%, with Nemipterus spp. (Thread breams) was 92.5%, with Scolopsis taeniopterus (Lattice monocle bream) was 30.3% and Loligo chinensis (squid) was 80.5%. Average of escaped ratio calculated by total catch and individual were significal difference between types of the square mesh codends and these calculations were affected by size of square mesh (a = 15 mm; a = 17.5 mm and a =20 mm). The escaped ratio of the square mesh with a= 20mm was higher than other sizes. So that, application of square mesh codends for trawl net (a = 20mm) help escaping juvenile and reduce effect of trawl net and also protect and develop fishery resources.

Key words: juvenile, the square mesh codends, the coastal trawl fish, escaped ratio.