Abstract In the Bay of Biscay, mean body length and weight of sardines (Sardina pilchardus) have been decreasing since the early 2000s and could severely impact the fishing and seafood industry sector. These trends have no apparent link with fishing pressure, although the latter has been increasing since the late 2000s. As part of an effort to develop suitable assessment and management tools for this stock, we investigated the life-history traits of sardine and analyze its seasonal and inter-annual variations. Based on 14 years of morphometric data from both scientific surveys and professional samples, we analyzed the variability in sardine body condition and its responses to environmental changes. Generalized Additive Models revealed an age-sex specific decreasing trend in body length over the study period, with most of the variability explained by the age class. Linear Mixed Effect Models applied to the body condition evidenced its strong seasonality and an age class specific decreasing trend. Regardless of age class, maximal body condition is reached at the end summer, after the spawning and plankton productive periods. Overall, annual trends in body condition-at-age showed remarkable coherence, with a significant decrease since 2007 for all age classes, suggesting that factors influencing body condition operate at population level. The shift in sardine body condition towards lower values could be broken down into three periods, with a high dependence on surface Chlorophyll-a and sea surface temperature. However, this study highlights that the period supporting the main decrease in body condition is characterized by high Chlorophyll-a, the available proxy for food, which is counterintuitive. Such a result suggests more complex trophic responses involving secondary production, with potential shift in the timing of the production and/or the quality of the food. At the population level, those changes may have a long-term negative effect, with a decrease in body length and important changes in phenology (length at first maturity, reproductive phenology) and potential consequences on sardine population dynamics in the Bay of Biscay.

中文翻译：

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2003 年至 2016 年比斯开湾沙丁鱼生长和身体状况的主要变化：时间趋势和驱动因素

摘要 在比斯开湾，沙丁鱼 (Sardina pilchardus) 的平均体长和重量自 2000 年代初以来一直在下降，并可能严重影响渔业和海产品业。这些趋势与捕捞压力没有明显的联系，尽管后者自 2000 年代后期以来一直在增加。作为为该种群开发合适的评估和管理工具的努力的一部分，我们调查了沙丁鱼的生活史特征并分析了其季节性和年际变化。基于来自科学调查和专业样本的 14 年形态测量数据，我们分析了沙丁鱼身体状况的变异性及其对环境变化的反应。广义加法模型揭示了研究期间身体长度的年龄-性别特异性下降趋势，大多数变异性由年龄等级解释。应用于身体状况的线性混合效应模型证明了其强烈的季节性和特定年龄段的下降趋势。无论年龄等级如何，在产卵期和浮游生物生产期之后的夏末达到最佳身体状况。总体而言，年龄身体状况的年度趋势显示出显着的一致性，自 2007 年以来所有年龄段的身体状况均显着下降，这表明影响身体状况的因素在人口水平上起作用。沙丁鱼身体状况向较低值的转变可以分为三个时期，高度依赖于表面叶绿素 a 和海面温度。然而，这项研究强调，支持身体状况主要下降的时期的特点是叶绿素-a 高，食物的可用代理，这是违反直觉的。这样的结果表明更复杂的营养反应涉及二次生产，生产时间和/或食物质量可能会发生变化。在种群水平上，这些变化可能会产生长期的负面影响，包括体长的减少和物候的重要变化（首次成熟时的长度、繁殖物候）以及对比斯开湾沙丁鱼种群动态的潜在影响。