ABSTRACT: The growth-survival paradigm predicts that year-class strength is determined by growth-dependent mortality during the larval stage. In Atlantic mackerel Scomber scombrus, the possibility that strong growth-dependent mortality extends into the early juvenile stage has not previously been tested because of the difficulty in sampling young-of-the-year (YOY) juveniles. The present study determined the timing of the ‘endpoint’ during the early ontogeny, when growth-selective mortality decreases and recruitment is set. We relied on regurgitations from one of the main predators of mackerel, the northern gannet Morus bassanus, as a source of YOY juveniles. Early growth trajectories of YOY mackerel were reconstructed from the otolith microstructure and were compared to those of 1-yr-old (OYO) juveniles from the same cohort for the year classes of 2015 and 2017. In both cohorts, the early growth trajectory of OYO fish was faster than that of YOY juveniles, indicating that growth-selective mortality extended beyond the larval stage. For the 2017 cohort, the comparison of larval growth trajectories between 2-mo-old YOY, 3mo-old YOY and OYO juveniles indicated that strong selection for fast growth persisted until the pre-wintering period, but that winter mortality likely did not play an important role in shaping year-class strength. These findings suggest that in Atlantic mackerel, the endpoint when the relative strength of cohorts is fixed occurs at the age of 3 mo. These results highlight the importance of considering growth-dependent mortality processes occurring beyond the larval stage to obtain a better understanding of causes of recruitment variability.

中文翻译：

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北部mac鱼摄食的年幼幼体揭示了大西洋鲭鱼幼体后生长选择性死亡的证据。

摘要：生长生存模式可预测年级强度由幼虫期的依赖生长的死亡率决定。在大西洋鲭鱼Scomber sbrbrus中，由于难以对年幼（YOY）幼鱼进行取样，因此尚未测试过依赖于生长的强死亡率一直延伸到幼年早期的可能性。本研究确定了个体发育早期“终点”的时机，即选择性生长死亡率降低并确定了募集的时间。我们依靠鲭鱼的主要捕食者之一北鱼桑us桑Mor的反流，作为YOY青少年的来源。从耳石的显微结构重建了鲭鱼的早期生长轨迹，并将其与2015年和2017年同一班级的1岁（OYO）幼鱼进行了比较。在这两个队列中，OYO的早期生长轨迹鱼类比幼年快，表明生长选择性死亡率超过了幼虫期。对于2017年的队列研究，比较2月龄，3月龄和OYO幼虫的幼虫生长轨迹，直到冬季前，对快速生长的强烈选择一直持续，但是冬季死亡率可能没有发挥作用。在塑造年级实力中起重要作用。这些发现表明，在大西洋鲭鱼中，当队列的相对强度固定时的终点出现在3 mo岁。