Biological Features of Tuna Catch from Purse Seine of M.V. SEAFDEC Cruise No. 63-1/2001

Abstract

This preliminary result is concerning biological features of tuna catches from the first sampling onboard M.V. SEAFDEC. The data analysis of this part would certainly support for the study on by-catch composition of tuna purse seine fisheries within three years study. The length frequency distribution of skipjack and yellowfin tuna are evident as mode more than one cohorts. The relative length-weight was determined using allometric equation for skipjack tuna (W = 8.23185E-06 L^3.2319), yellowfin tuna (W = 2.36464E-05 L^2.9539), and bigeye tuna (W = 1.8E-05 L^3.0431). The skipjack tuna's mean weight was significant heavier than other species at the same length. The size at first maturation was occur at length 64.5 cm. for yellowfin tuna and 63.0 cm. for bigeye tuna and found mature all in skipjack tuna. The number of skipjack and yellowfin males is slightly higher than females but the number of bigeye females was out numbers the males. The female ratio was explain by equation; Rf(L) = 0.7407 - 0.006*L for skipjack tuna and Rf(L) = 1.3764 - 0.0105*L for yellowfin tuna. The largest gonad index was found about 67 in yellowfin tuna but low in number of samples same as bigeye tuna. The small number of samples was effected in some process of reproductive study. However, there was a significant correlation between the variables by the t-test statistic (t_0.05).