Preliminary Results on By Catch from Tuna Purse Seine Fishery in the Eastern Indian Ocean
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The exploitation of tuna resources in the East Indian Ocean is now enhancing by many countries. From 1994 to 1999 (March), sampling tuna were collected from purse seine operation of the Training and Research vessel, MV SEAFDEC. The length distributions of skipjack yellowfin and bigeye tunas were observed ranging between 36-70, 34-94 and 35-125 cm. respectively. The catch was consisted of tuna in difference ages, the age between 1-2 year are the dominant catch. About 50% and 31% of total catch were young bigeye and yellowfin tunas. The bigeye, length between 34-100 cm and yellowfin, length 35-110 cm were in the recruitment phase or it can be said that more than 90% of bigeye and yellowfin tunas were in the pre-exploited stage. The seine net using mesh size of 90 mm at bunt part and 105 mm at upper body part, can measure the nominal mesh perimeter of 180 mm and 210 mm, respectively. From the relationship between fish length and dorsal girth, the tuna greater than 25 cm will be captured and the main target of tuna purse seiner is skipjack. It's difficult to avoid captures of young of young tuna due to the overlapping between size of adult skipjack and young bigeye and yellowfin tuna. For reduce by catch of young skipjack and some of young bigeye and yellowfin tunas from seine net, the mesh size (strrtched) bunt part is expected to increase from 90 mm to 130 mm, then the young skipjack would be escape 100% and some of young bigeye 5.56% and yellowfin 4.17%.