Preliminary study on the fishery biology of yellowfin tuna,Thunnus albacares,in the western central Indian Ocean

Based on the data of yellowfin tuna Thunnus albacares caught by tuna longline survey sponsored by Agriculture Department's Fishery Observer Programme in the western central Indian Ocean from January to June in 2003 and 2004,the basic biological characteristics of yellowfin tuna were studied.The results indicated that the dressed weight of yellowfin tuna varied between 7 and 81 kg in 2003 and 20 and 78 kg in 2004,respectively,and the dominant dressed weight varied between 20 and 50kg in 2003 and 30 and 60kg in 2004,respectively.The fork length of yellowfin tuna varied between 70 and 180 cm in 2003 and 110 and(170 cm) in 2004 respectively.Mean sex ratio remained 0.71 and 1.00 in all months of 2003 and 2004 respectively.There was no significant difference for monthly sex ratio in 2003.However,the monthly ratio varied remarkably during 2004.The monthly feeding fullness was dominated by grade 1 and grade 2 in 2003,but there was no significant difference between months.The monthly feeding grade for 2004 was dominated by grade 1 with significant differences between months.The relationship between dressed weight and fork length of yellowfin tuna was W=2.1890×10~(-5)L~(2.9269)