Animal mortality is difficult to observe in marine systems, preventing a mechanistic understanding of major drivers of fish population dynamics. In particular, starvation is known to be a major cause of mortality at larval stages, but adult mortality is often unknown. In this study, we used a laboratory food-deprivation experiment, on wild caught sardine Sardina pilchardus from the Gulf of Lions. This population is interesting because mean individual phenotype shifted around 2008, becoming dominated by small, young individuals in poor body condition, a phenomenon that may result from declines in energy availability. Continuous monitoring of body mass loss and metabolic rate in 78 captive food-deprived individuals revealed that sardines could survive for up to 57 days on body reserves. Sardines submitted to long-term caloric restriction prior to food-deprivation displayed adaptive phenotypic plasticity, reducing metabolic energy expenditure and enduring starvation for longer than sardines that had not been calorie-restricted. Overall, entry into critical fasting phase 3 occurred at a body condition of 0.72. Such a degree of leanness has rarely been observed over 34 years of wild population monitoring. Still, the proportion of sardines below this threshold has doubled since 2008 and is maximal in January and February (the peak of the reproductive season), now reaching almost 10 % of the population at that time. These results indicate that the demographic changes observed in the wild may result in part from starvation-related adult mortality at the end of the winter reproductive period, despite adaptive plastic responses.

在海洋系统中很难观察到动物死亡率，这阻碍了对鱼类种群动态主要驱动因素的机械理解。特别是，已知饥饿是幼虫阶段死亡的一个主要原因，但成虫死亡率通常是未知的。在这项研究中，我们对野生捕获的沙丁鱼Sardina pilchardus 进行了实验室食物剥夺实验来自狮子湾。这个群体很有趣，因为平均个体表型在 2008 年左右发生了变化，变得以身体状况不佳的年轻小个体为主，这种现象可能是由于能量可用性下降造成的。对 78 名被圈养的缺乏食物的个体的体重损失和代谢率的持续监测表明，沙丁鱼可以在身体储备的情况下存活长达 57 天。在食物剥夺之前接受长期热量限制的沙丁鱼表现出适应性表型可塑性，与没有热量限制的沙丁鱼相比，可以减少代谢能量消耗和忍受更长时间的饥饿。总体而言，进入临界禁食阶段 3 的身体状况为 0.72。在 34 年的野生种群监测中很少观察到这种程度的瘦身。仍然，低于这一阈值的沙丁鱼比例自 2008 年以来翻了一番，并在 1 月和 2 月（繁殖季节的高峰期）达到最高，当时达到了近 10% 的人口。这些结果表明，尽管具有适应性塑料反应，但在野外观察到的人口变化可能部分是由于冬季繁殖期结束时与饥饿相关的成年死亡率。