Reproductive biology of blue marlin <Emphasis Type="Italic">Makaira nigricans</Emphasis> around Yonaguni Island,southwestern Japan |
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Authors: | Tamaki Shimose Maki Fujita Kotaro Yokawa Hirokazu Saito Katsunori Tachihara |
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Institution: | (1) Laboratory of Fisheries Biology and Coral Reef Studies, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan;(2) National Research Institute of Far Seas Fisheries, Fisheries Research Agency, 5-7-1 Orido, Shimizu, Shizuoka 424-8633, Japan;(3) Present address: National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Shizuoka, Japan |
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Abstract: | We studied the spawning seasonality and gonadal development of blue marlin Makaira nigricans using specimens captured around Yonaguni Island in southwestern Japan between February 2003 and February 2006. The mean (±SD)
lower jaw–fork length of females (234 ± 24 cm) was greater than that of males (191 ± 12 cm). The smallest mature female and
male were 183 and 160 cm, respectively. Most of the 717 females had immature ovaries. However, in March and from May to September,
the ovaries of 26 females contained oocytes with yolk globules, hydrated oocytes, or postovulatory follicles. Most males had
testes with a large amount of spermatozoa throughout the year. The occurrence of mature blue marlin at Yonaguni Island suggests
that spawning occurs here. The mean condition factors (fatness of the fish) of both sexes decreased from March to June or
July, presumably as they expended energy to reproduce. We discuss our results in the context of migration theory for blue
marlin in the western North Pacific Ocean. |
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Keywords: | Blue marlin Condition factor Makaira nigricans Migration North Pacific Ocean Spawning season |
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