To understand the population structure of the Japanese jack mackerel Trachurus japonicus in coastal areas adjacent to the Kuroshio Current (referred to as the “CAK”), we analyzed size composition and commercial landing data of juvenile fish in these areas for the period 2005–2015. Trachurus japonicus does not undergo population-scale spawning migration, and thus, the connectivity between the spawning and juvenile/adult habitat areas is important. Therefore, our primary aim was to assess the origin of juveniles landed in a number of subareas, including those spawned in local spawning grounds in January–May in the western part of the CAK (w-CAK), those spawned in May–July in the eastern part (e-CAK), and those spawned in February–March in the remote spawning ground in the southern East China Sea (s-ECS). Fishing periods starting in spring (spring onset) were commonly observed in the CAK, which involved relatively small size classes (50–100 mm fork length [FL]). Back estimates based on the growth rate of T. japonicus suggested that the contributions from the s-ECS probably dominated most of the spring onsets in April–June because the smallest size class (50–70 mm FL) occurred almost exclusively in April–May. In autumn, onset signals were associated with the landing of juveniles from the local spawning ground in an eastern subarea of the e-CAK. Despite the asymmetric transport and migration flows between the habitat areas of T. japonicus, its population levels may be sustained because the local and remote spawning grounds are used in different seasons.

中文翻译：

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黑潮沿岸地区日本鲭鱼幼鱼发生的时空变异性

为了解黑潮附近沿海地区日本鲭鱼Trachurus japonicus的种群结构，我们分析了这些地区 2005 年至 2015 年期间幼鱼的大小组成和商业上岸数据. 日本蜮不经历种群规模的产卵迁移，因此产卵和幼鱼/成鱼栖息地之间的连通性很重要。因此，我们的主要目的是评估降落在多个分区的幼鱼的来源，包括 1-5 月在 CAK 西部 (w-CAK) 的当地产卵场产卵的幼鱼，以及在 5-7 月产卵的幼鱼。东部（e-CAK），以及2-3月在东海南部偏远产卵场（s-ECS）产卵的。在 CAK 中通常观察到从春季（春季开始）开始的捕鱼期，其中涉及相对较小的尺寸等级（50-100 毫米的叉长 [FL]）。根据T的增长率反向估计。 粳稻表明来自 s-ECS 的贡献可能在 4 月至 6 月的大部分春季发病中占主导地位，因为最小的尺寸等级（50-70 毫米 FL）几乎完全发生在 4 月至 5 月。秋季，发病信号与来自 e-CAK 东部分区的当地产卵场的幼鱼着陆有关。尽管T的栖息地之间存在不对称的运输和迁移流动。 japonicus，其种群数量可能会持续下去，因为当地和偏远地区的产卵场在不同的季节使用。