Reproductive biology of female Pacific bluefin tuna Thunnus orientalis from south-western North Pacific Ocean |
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| Authors: | Kuo-Shu Chen Paul Crone Chien-Chung Hsu |
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| Institution: | (1) Institute of Oceanography, National Taiwan University, PO Box 23-13, 106 Taipei, Taiwan;(2) South-west Fisheries Science Center, National Marine Fisheries Service, 8604 La Jolla Shore Drive, 93027 La Jolla, CA, USA |
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| Abstract: | Pacific bluefin is a highly valuable pelagic species that inhabits a broad range in the North Pacific Ocean. The reproductive
biology, especially for the spawning aggregation in the south-western North Pacific Ocean, is not well understood. Thus, a
total of 119 paired ovary specimens were collected from the Taiwanese longline fleet during the 1999 fishing season (late
April through June) to gain a better understanding of important reproductivity-related stock parameters associated with this
species. The following conclusions were made: (i) condition factor decreased from late May to early June; (ii) the sex ratio
might be 1∶1 for spawners; (iii) the gonadosomatic index stayed at a relatively high level and markedly increased from late
May to early June; (iv) histological examination of oocytes indicated that all specimens were sexually mature; (v) spawning
activity appeared to start in May and peak in late May to early June; (vi) batch fecundity incre ased with fork length; and
(vii) preliminary estimates of spawning frequency between batches ranged 2–4.5 days based on analysis of postovulatory follicles. |
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| Keywords: | batch fecundity oocyte stage Pacific bluefin tuna sex ratio spawning frequency spawning season Thunnus orientalis |
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