Identification of stock composition is essential for fish stock assessment and management. Previous studies have suggested that a mixed stock composition of Pacific saury Cololabis saira exists in the northwest Pacific Ocean, but the origins of the stock’s components are poorly understood. We analyze the otolith microstructure of Pacific saury collected in high-seas fishing grounds from June–November, 2016–2019, and estimate hatch date and reconstruct otolith growth trajectory before hyaline zone formation. Results confirm that Pacific saury recruiting to the high-seas fishing ground are mainly from a winter-spawned cohort, secondarily from an autumn-spawned cohort, but also with a small proportion from a spring-spawned cohort. Ages of medium (knob length 240–280 mm) and large (knob length > 280 mm) individuals are mainly 8–12 and 18–21 months, respectively. Two growth patterns are reported for individuals with different otolith growth axes in their early life stages. Each year, unsupervised random forest clustering analysis of otolith daily increment widths reveals two Pacific saury groups. One group, with younger age and a later hatching period, shows a consistently higher growth rate than the other, suggesting that the two groups have different hatch dates and locations. These findings permit more accurate prediction of Pacific saury recruitment, and improve the understanding of short-term stock fluctuations to enable more sustainable management of fisheries.

确定种群组成对于鱼类种群评估和管理至关重要。先前的研究表明，西北太平洋存在太平洋秋刀鱼Cololabis saira的混合种群成分，但对该种群成分的起源知之甚少。我们分析了2016年6月至2019年11月在公海渔场采集的秋刀鱼耳石微结构，估计孵化日期并重建透明带形成前的耳石生长轨迹。结果证实，进入公海渔场的秋刀鱼主要来自冬季产卵群体，其次是秋季产卵群体，但也有一小部分来自春季产卵群体。中型（旋钮长度240-280毫米）和大型（旋钮长度> 280毫米）个体的年龄分别主要为8-12个月和18-21个月。据报道，在生命早期阶段具有不同耳石生长轴的个体有两种生长模式。每年，耳石每日增量宽度的无监督随机森林聚类分析都会揭示两个太平洋秋刀鱼群体。一组的年龄较小，孵化期较晚，但其生长速度始终高于另一组，这表明这两组的孵化日期和地点不同。这些发现可以更准确地预测秋刀鱼补充量，并提高对短期种群波动的了解，从而实现更可持续的渔业管理。