| 英文摘要 |
In this project, we trained scientific observers to collect otoliths of southern bluefin tuna (SBT, Thunnus maccoyii) on Taiwanese longline vessels and also estimated the age of 81 otoliths collected in 2009. The mean age of these otoliths was 4.64 !O 1.42 years (range: 2 - 10 years). The fork length of the SBT sampled for otoith was 111.4 !O 10.9 cm (range: 95 - 140 cm) and dressed weight was 24.7 !O 8.7 kg (range: 15 - 50 kg). We analyzed the stable C and O isotope of the otolith from 34 Pacific bluefin tuna (Thunnus orientalis) collected in Japanese coasts to determine their natal origins. The results suggested that 12 fish were hatched in the Japan Sea and 22 fish were hatched in the northwestern Pacific. The contribution of Pacific Ocean origin to the fish caught was 30% in Hagi Mishima, 34% in Tsushima, 90% in Sakaiminato and 100% in Goto Fukue. CaCO3 will re-mineralize on otolith core areas after the young stage and may lead to the wrong analytical data. We develop a method to remove the re-mineralized CaCO3 by etching the otolith core area with diluted HCl. The etching method can clear the re-mineralized CaCO3 and improve the accuracy of the analytical data.
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Keyword: Southern bluefin tuna, Pacific bluefin tuna, otol |