The origin, age and growth of Pacific bluefin tuna (Thunnus orientalis) inferred from otolith isotopic composition
Date Issued
2015
Date
2015
Author(s)
Lu, Han-Bo
Abstract
Pacific bluefin tuna (Thunnus orientalis, PBF) is an important target species of Taiwanese neritic fisheries, but their stock has been declining in recent years. Age, growth and the natal origin of PBF are important life history characters for effective management. This study aimed to reconstruct the age composition of the PBF landed in Taiwan by reading their otolith annuli. In addition, we evaluated the natal origin of PBF by the analysis of otolith stable isotopic composition. A total of 688 otoliths were collected form Tungkang and Nanfang-ao ports from 2011 to 2014. The estimated ages ranged from 4-28 years and different readings on the samples were consistent with, the mean APE and CV of 0.74 % and 1.05 %, respectively. The generated von Bertalanffy growth equation of PBF had L∞ = 249.0 cm, k = 0.179 year-1, and t0 = -1.383 years. The mean age of PBF landed in Taiwan were 10-12 years old in 2002-2007 then the values gradually increase to 16-17 years old between 2008-2013. The change of age composition of the spawning stock might due to overfishing of young PBF by Japanese neritic fisheries. In addition, most (83.3 %) PBF analyzed (n = 30) were hatched in the northwestern Pacific Ocean indicated by the otolith δ18O profiles. This result suggested that PBF have high fidelity of natal origin. A small group (16.7 %) of PBF caught by Taiwanese longliners might hatch in the Japan Sea. Therefore, genetic flow of PBF shall exist between the two spawning grounds and this species shall be managed as a single population.
Subjects
Pacific bluefin tuna (Thunnus orientalis, PBF)
Otolith
Age determination
Stable isotopes
Natal origin
SDGs
Type
thesis
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