||This project aims to train the scientific observers to collect otoliths of southern bluefin tuna (SBT, Thunnus maccoyii) from Taiwan longline fishery. The age of each SBT whose otolith was collected will be estimated by examining the otolith annuli. These data together with length and weight data will be used to evaluate the growth rate parameters of the SBT caught by Taiwanese longliners. Length and weight data of all SBT caught will be transformed into age data to develop the age composition via the age-length (weight) key. Pacific bluefin tuna (PBT, Thunnus orientalis) has two spawning grounds, one in the northwestern Pacific Ocean and the other in the Sea of Japan. We will examine the PBT otolith collected by the observers to estimate the age structure of the PBT spawners in northwestern Pacific Ocean.