Abstract To clarify the reproductive activity of albacore, Thunnus alalunga, in the subtropical western North Pacific Ocean (WNPO) (13–25°N, 133°E–171°W), reproductive traits, such as the sex ratio, spawning season, batch fecundity, size at maturity and spawning fraction, were investigated. The sex ratio (5 cm intervals) was skewed towards females in each fork length class less than 95 cm and was skewed towards males in each fork length class larger than 95 cm. Spawning capable fish appeared throughout the year, except in January, and primarily occurred between April and September. The size at 50% maturity in females was estimated to be a fork length of 87.5 cm (approximately 5 years). The estimated total spawning fraction and spawning interval during the spawning season were 0.35 and 2.83 days, and the spawning fractions from May to August were larger than those in the other sampling months. The estimated batch fecundity and relative batch fecundity (mean ± SD) were 1.16 ± 0.67 million oocytes and 59.1 ± 31.5 oocytes/g, respectively (fork length range: 88.6–104.8 cm). There was a positive correlation between the fork length and batch fecundity (r2 = 0.27). These results suggest that albacore in the WNPO spawn year round, while peak spawning occurs between May and August (i.e., between boreal spring and summer).

中文翻译：

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北太平洋西部亚热带地区雌性长鳍金枪鱼产卵活动的繁殖性状和季节变化

摘要 为阐明长鳍金枪鱼（Thunnus alalunga）在北太平洋西部副热带（WNPO）（13-25°N, 133°E-171°W）的繁殖活动、性别比例、产卵季节、研究了批次繁殖力、成熟时的大小和产卵率。性别比（5 厘米间隔）在每个叉长度小于 95 厘米的等级中偏向女性，在每个叉长度大于 95 厘米的等级中偏向男性。除一月外，全年都有产卵能力的鱼出现，主要发生在四月和九月之间。雌性成熟 50% 时的大小估计为叉长 87.5 厘米（约 5 年）。产卵期估计的总产卵率和产卵间隔分别为 0.35 天和 2.83 天，5-8月产卵量大于其他采样月份。估计的批次繁殖力和相对批次繁殖力（平均值 ± SD）分别为 1.16 ± 67 万个卵母细胞和 59.1 ± 31.5 个卵母细胞/克（叉长度范围：88.6-104.8 厘米）。分叉长度和批次繁殖力之间呈正相关（r2 = 0.27）。这些结果表明 WNPO 中的长鳍金枪鱼全年产卵，而产卵高峰发生在 5 月和 8 月之间（即北方春季和夏季之间）。