We analyzed distribution and differences in body length, age, and maturation rate of Pacific saury Cololabis saira in the western North Pacific Ocean, during the main spawning season (winter), to locate its spawning ground. Sampling was conducted in the coastal area north of the Kuroshio axis (CA), the offshore area of the southern Japanese archipelago (SA), and the area east of the Honshu Island (EA) from 1996 to 2017. Higher densities of Pacific saury were widely observed on or just north (within 100–200 km) of the axis of the Kuroshio and the Kuroshio Extension currents. Body length, age composition, and sea-surface temperature (SST) differed across the studied areas, with larger fish (>250 mm knob length, mainly age-1) dominating at higher SST (16–21°C) in the SA and smaller fish (<250 mm knob length, age-0) dominating at lower SST (14–16°C) in the EA. In the CA, both SST and body length values were in between those in the SA and EA. The area where matured Pacific saury were collected was broadly distributed in the study area, except for the CA and a part of the Transition zone where the SST was low and mean body length was short. This study suggests that the main spawning ground during winter, where the area of high density and high maturation rate overlap, is formed on or just north of the Kuroshio and the Kuroshio Extension axis.

中文翻译：

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利用主要产卵期成鱼成熟状态的分布和地理变异估算秋刀鱼的产卵地

我们分析了秋刀鱼Cololabis saira 的体长、年龄和成熟率的分布和差异在北太平洋西部，在主要产卵季节（冬季），以定位其产卵地。1996 年至 2017 年在黑潮轴线 (CA) 以北的沿海地区、日本南部群岛 (SA) 的近海地区和本州岛 (EA) 以东的地区进行了采样。在黑潮和黑潮延伸流的轴线的北部（100-200 公里内）上或就在其北面（100-200 公里内）广泛观察到。不同研究区域的体长、年龄组成和海面温度 (SST) 不同，在南澳和南半球，较大的鱼（>250 毫米的节长，主要是 1 岁）在较高的 SST（16-21°C）下占主导地位。较小的鱼（<250 毫米旋钮长度，0 岁）在 EA 中以较低的 SST（14-16°C）占主导地位。在 CA 中，SST 和体长值都介于 SA 和 EA 之间。除CA和部分过渡带海温低、平均体长短外，研究区广泛分布了成熟的秋刀鱼采集区域。这项研究表明，冬季的主要产卵场，即高密度和高成熟率区域重叠的地方，形成于黑潮和黑潮延伸轴上或刚好以北。