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

尽管减少了捕捞努力并实施了保护和缓解举措，许多太平洋鲑鱼种群仍在经历持续和严重的下降。这种鲑鱼种群的长期减少在奇努克鲑鱼和红鲑鱼中尤为普遍，在整个范围内都观察到这种减少，但在不列颠哥伦比亚省南部尤其明显。在过去的20年里，不列颠哥伦比亚省南部鲑鱼种群的持续低回报率归因于生命早期不利的海洋条件，如气候变化、猎物数量的变化、捕食风险、疾病、栖息地退化或捕捞以外的人类压力因素。虽然太平洋鲑鱼数量下降的原因可能是多方面的，但人们普遍认为，持续不利的海洋条件和海洋生存能力差在这些下降中起了主要作用。在它们生命的海洋阶段，鲑鱼的死亡率通常超过90-95%。据认为，这种损失大部分发生在沿海环境中，这是由于入海时遭到大量捕食和/或由于冬季饥饿造成的。在这里，我们将采取多学科的方法来阐明海洋条件、生长、物候和生理性能对早期海洋幼鱼奇努克和红鲑鱼生存变异的相互作用。具体目标包括：1/通过评估早期海洋生长和条件对幼年鲑鱼生存的作用，从耳石微观结构、长度频率分析、能量动力学和捕食者胃内容物中量化早期生长和死亡率之间的联系；2/通过实验测试幼年鲑鱼在早期海洋生物中对气候和食物变化的反应；3/测试冬季严重度与生长、生存和捕食脆弱性之间的关系；4/在温度控制实验中确定鱼耳石中氧同位素与温度之间的关系。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理解。

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.