Identifying mechanisms leading to size-selective mortality in the early marine phase of juvenile Pacific salmon

许多太平洋鲑鱼种群正在经历持续和严重的下降，尽管捕捞活动减少，并实施了养护和缓解举措。这种鲑鱼库存的长期下降在Chinook鲑鱼和Sockeye鲑鱼中特别普遍，在整个范围内都观察到了下降，但特别是在卑诗省南部。过去20年来，不列颠哥伦比亚省南部鲑鱼种群的收益率持续较低，归因于早期生命中不利的海洋条件，如气候变化、猎物可获得性的变化、捕食风险、疾病、栖息地退化或捕鱼以外的人类压力因素。虽然太平洋鲑鱼数量减少的原因可能是多因素的，但人们普遍认为，长期不利的海洋条件和糟糕的海洋生存状况是造成这些数量减少的主要原因。鲑鱼在其生命的海洋阶段的死亡率一般超过90%-95%。据认为，这种损失大部分发生在沿海环境中，原因要么是进入海洋时的大量捕食，要么是由于冬季饥饿。在这里，我们将采用多学科的方法来阐明海洋条件、生长、物候和生理表现对早期海洋幼体Chinook和红鲑鱼生存变化的交互影响。具体目标包括：1/通过评估早期海洋生长和状况对幼鲑鱼存活的作用，量化早期生长和死亡之间的联系；2/通过实验测试幼体鲑鱼如何应对气候和食物的多样性；3/测试冬季的严酷程度和饥饿的复原力对生长、存活和捕食的脆弱性的关系；4/通过温控实验确定鱼类耳石中氧同位素与温度的关系。通过评估幼年鲑鱼早期海洋死亡的程度和原因，该项目将提高我们对海洋环境中限制太平洋鲑鱼产量的因素的了解。

Many stocks of Pacific salmon are experiencing continued and severe declines despite reductions in fishing effort and the implementation of conservation and mitigation initiatives. This prolonged decline of salmon stocks is particularly prevalent in Chinook salmon and sockeye salmon, where declines have been observed range-wide, but especially in southern BC. The sustained low return rates of southern British Columbia salmon stocks over the last 20 years have been attributed to a combination of unfavorable marine conditions during early life such as climate change, variability in prey availability, predation risk, disease, habitat degradation, or human stressors other than fishing. While the causes of Pacific salmon declines are likely multifactorial, it is generally recognized that persistently unfavourable ocean conditions and poor marine survival played a major role in these declines. Salmon mortality rates generally exceed 90-95% during the marine stages of their life. Much of this loss is thought to occur in coastal environments as a consequence of either heavy predation upon ocean entry and/or due to winter starvation. Here, we will take a multidisciplinary approach to elucidate the interacting effects of ocean conditions, growth, phenology, and physiological performance on variation in survival of early ocean juvenile Chinook and sockeye salmon. Specific objectives include: 1/ Quantifying the links between early growth and mortality by assessing the role of early marine growth and condition to survival of juvenile salmon from otolith microstructure, length frequency analyses, energy dynamics and predator stomach contents; 2/ Experimentally testing how juvenile salmon respond to climate and food variability during early marine life; 3/ Testing the relationship between winter severity and resiliency to starvation on growth, survival, and vulnerability to predation; 4/ Determining the relationship between oxygen isotopes and temperature in otoliths from fish in temperature-controlled experiments. By assessing the extent and causes of early marine mortality in juvenile salmon, this project will improve our understanding of the factors limiting the production of Pacific salmon in the marine environment.