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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13625

Differences in the reproductive status, spawning fraction, and batch fecundity of Pacific bluefin tuna Thunnus orientalis among three fishing grounds in the Sea of Japan

Hiroshi Ashida*, Yumi Okochi, Seiji Ohshimo, Takuya Sato, Yukio Ishihara, Shuuyo Watanabe, Ko Fujioka, Seishiro Furukawa, Tomonori Kuwahara, Yuko Hiraoka, Yosuke Tanaka

*Corresponding author:

ABSTRACT: Differences in the reproductive traits of Pacific bluefin tuna (PBF) in the Sea of Japan (SOJ) were investigated to evaluate the reproductive potential in three fishing grounds (i.e., northern, middle and southern areas). The size distribution of PBF differed among the fishing grounds, with smaller fish (100–130 cm in fork length) being caught in the middle and northern areas of the SOJ. Spawning capable females were found at sea surface temperatures (SSTs) between 17 and 25 °C, with most SSTs > 21 °C. Seasonal changes in SST differed among the fishing grounds, and the period when SST exceeded 21 °C differed in each fishing ground. Spawning capable females were found at different times among the fishing grounds, and were observed throughout the fishing season in the southern area of the SOJ. The mean relative batch fecundity (RBF) ± standard deviation was estimated to be 69.8 ± 45.3 and 92.7 ± 43.1 oocytes g-1 in the middle and southern areas of the SOJ, respectively. The total spawning fraction was 0.2, 0.38 and 0.73 in the northern, middle and southern areas of the SOJ, respectively. SST and fork length (FL) were positively correlated with the batch fecundity (BF). In addition, FL, SST and location affected the probability of occurrence of the spawning capable fish among mature fish. Therefore, the difference in the observed reproductive potential of PBF among fishing grounds in the SOJ can be linked to the differences in seasonal increases in SST and size distribution of adult fish.