Fish recruitment variability results from a complex mix of biological and physical processes, and their interactions, acting in the early life stages. In this study, we aim to investigate the environmental factors driving the recruitment success of blue whiting (Micromesistius poutassou) in the NW Mediterranean through reconstruction of early life history traits derived from otoliths microstructure analysis. To this purpose, the study characterizes the oceanographic conditions in winter-spring of two contrasted years, 2017 and 2018, and relates them to the onset and duration of the spawning, growth performance and condition of blue whiting recruits. Winter 2017 was mild, with a short period of cold temperatures and limited winter vertical mixing. In winter 2018, temperatures reached lower values and extended for a longer period with intense vertical mixing and dense water cascading down the continental slope at the end of February. These different conditions were mirrored in the subsequent phytoplanktonic bloom, which in 2018 occurred later and was more intense than in 2017, extending over a longer period and occupying a wider area. The reproductive period of blue whiting was linked to the duration of low winter temperatures (∼13 °C), shorter in 2017 than in 2018 (∼40 and ∼ 60 days respectively). While in 2017 all individuals were born in a relatively short period of time, and under similar environmental conditions, in 2018 the hatching period presented two differentiated peaks, separated by a period of relatively low hatchings at the end of February. This gap corresponded to dense water cascading and intense vertical mixing events, suggesting that these phenomena limited the survival of eggs and larvae. The few individuals hatched in this period showed the lowest growth rates (maximum values ∼ 1.5 mm TL day⁻¹), which would be related with the poor trophic environment during these events of intense mixing. Conversely, in both years, higher growth rates corresponded to the individuals born just before the phytoplankton bloom (attaining ∼ 2 mm TL day⁻¹). Recruits of 2018 showed better condition than those born the previous year which would be associated with the higher primary production detected in spring 2018. The recruitment strength in 2018, estimated from landings, was also much higher indicating that severe winter conditions translate into improved recruitment of a temperate water fish in the NW Mediterranean Sea.

鱼类补充变异性是生物和物理过程及其相互作用的复杂组合，在生命的早期阶段起作用。在这项研究中，我们旨在通过重建从耳石微观结构分析得出的早期生活史特征，研究推动蓝鳕 ( Micromesistius poutassou ) 在地中海西北地区成功招募的环境因素。为此，该研究描述了 2017 年和 2018 年两个对比年份冬春季的海洋学条件，并将它们与产卵的开始和持续时间、生长性能和蓝鳕新兵的状况联系起来。2017 年冬季气候温和，气温短暂，冬季垂直混合有限。2018年冬天， 2 月底，随着强烈的垂直混合和密集的水从大陆斜坡上倾泻而下，气温达到了较低的值并延长了较长时间。这些不同的条件反映在随后的浮游植物爆发中，2018 年发生的时间较晚，比 2017 年更强烈，延伸时间更长，面积更广。蓝鳕的繁殖期与冬季低温（~13°C）的持续时间有关，2017 年比 2018 年短（分别为~40 天和~60 天）。2017年所有个体出生时间较短，环境条件相近，2018年孵化期出现两个分化高峰，2月底孵化率相对较低。这个间隙对应于密集的水级联和强烈的垂直混合事件，表明这些现象限制了卵和幼虫的生存。在此期间孵化的少数个体显示出最低的生长速度（最大值 ∼ 1.5 mm TL day^-1），这与这些剧烈混合事件期间的不良营养环境有关。相反，在这两年中，较高的生长速率对应于在浮游植物开花之前出生的个体（达到 ∼ 2 mm TL day ^-1）。2018 年的新兵状况好于前一年出生的新兵，这与 2018 年春季检测到的较高初级产量有关。从登陆情况估计，2018 年的新兵强度也高得多，这表明严寒的冬季条件转化为改进的新兵招募地中海西北部的一种温带水鱼。