Accuracy of species identification of yellowfin and bigeye in three canneries of Kingdom of Thailand

In WCPFC area and Indian Ocean the catch of four tuna species (skipjack, yellowfin, bigeye and albacore) was over 3400 thousand metric ton in 2008. Around 750 thousand tons (22 %) of these were landed at Kingdom of Thailand. Accuracy of species identification of yellowfin and bigeye in three canneries of Kingdom of Thailand was investigated in April 2010. In these factories yellowfin and bigeye are sorted to five market categories according to their sizes (1.4 kg down, 1.4 1.8 kg, 1.8 3.4 kg, 3.4 9.0 kg and 9.0 kg up) for each species. We conducted species identification for 2,572 individuals of total 25 market categories except for the largest category (9.0 kg up), and measured body lengths and weighed up to 20 individuals for each category, and then calculated the mixture rates of species (% of BET (or YFT) / (YFT+BET)) by market category and cannery (and in some cases by each fishing boat). For the smallest categories the mixture rates were relatively high, 12.6% on average which ranged from 0.0% to 21.7% (% weight) varying among factories. The mixture rates for the larger three categories represented relatively-accurate values, 2.8% on average (0.0 to 6.8 %). The estimated accuracy of amount of catch in market report (corrected catch / market report) were from 98.7 % to 113.3 % for bigeye, and from 98.0% to 105.1 % for yellowfin. The accuracy of amount of catch by species in market report of the three Thai canneries investigated seems to be reliable, although the accuracy is depend on the amount of catch in smallest market categories, where the species mixture rates are relatively high.