Trophic interactions, foodweb dynamics and ontogeny in juvenile Pacific salmon in lakes and coastal marine ecosystems

太平洋鲑鱼，被视为具有显著经济、社会和文化效益的哨兵物种。具体而言，在了解淡水和海洋生态系统中太平洋鲑鱼幼鱼的资源分配、营养相互作用和食物网动态方面存在重大空白。从我过去对阿拉斯加红鱼系统的研究中，我们发现淡水湖中红鱼鱼苗的生长和生存受到密度依赖和密度独立因素的影响，小鲑鱼洄游到海洋的大小和年龄分布也受到密度依赖和密度独立因素的影响。然而，需要进一步的研究来了解和量化导致特定湖泊系统中红鱼鱼苗和幼鱼大小和年龄结构变化的过程和机制。然而，沿海地区不断变化的气候（降水和温度）使实现这些目标变得更加复杂。进一步的复杂情况是由于在不列颠哥伦比亚省的几个红湖中引入了鲈鱼和鲈鱼等物种，它们在幼年时可能与红鱼苗和刺鱼有显著的生态位重叠，而成年后它们成为红鱼苗和刺鱼的捕食者。确定这些可变情景和相关过程如何影响红鳉鱼苗的大小和年龄分布，它们的食物和摄食习性，生态位变化以及它们与同居鱼和无脊椎捕食者的营养相互作用，以及这些如何影响它们的生长和生存，幼鱼的外移大小和年龄，以及它们在早期海洋生长期间的表现，将是至关重要的。同样，其他太平洋鲑鱼物种（如银鳕和支努克鲑鱼）的幼体在入海时的大小在不同年份和不同种群之间也有很大差异，这可能对它们在沿海海洋生态系统早期生长期间的表现产生重大影响。当鲑鱼幼鱼进入海洋时，它们之间以及与其他饲料鱼类共享共同的取食地和生态位，我的研究兴趣也将是了解物种内部的个体发生生态位变化，物种之间的生态位重叠及其对海洋生长和生存的影响。我的长期研究目标是观察水生系统的营养-食物网动态模式，以及它们与营养相互作用和幼鲑鱼生长、水生食物网中的能量和污染物转移、浮游生物多样性和水质的联系，在接下来的5年里，我将继续沿着同一主题进行研究。我提出以下研究目标：1)检验不同密度的红鱼鱼苗对低营养层结构和尺寸效率、红鱼鱼苗生长和外迁幼鱼鱼苗尺寸和年龄结构的影响；2)在不同捕食-被捕食情景下，模拟与同居浮游生物重叠或缺乏生态位的红鳉鱼苗和生态位资源利用的空间（沿海与远洋）格局；3)检验引进的掠食性鱼类如何改变红鱼鱼苗的个体发育和与外迁幼鱼相关的种群统计；4)描述和模拟幼年红鲑和其他两种太平洋鲑鱼（银鲑和支努克鲑）的食物网在进入海洋和海洋生长早期的大小函数；5)太平洋鲑鱼幼鱼营养位置、资源分配和个体发生生态位变化的空间（陆上与海上）和时间（年际）变化模型。大约6-8名研究生和10-12名本科生将通过拟议的研究项目接受培训，这些研究项目将为理解与太平洋鲑鱼幼鱼高度变化的性能相关的过程产生重要的新知识。

Pacific salmon, regarded as sentinel species with significant economic, social and cultural benefits. Specifically, there are major gaps in understanding resource partitioning, trophic interactions and foodweb dynamics of juvenile Pacific salmon in freshwater and marine ecosystems. From my past research on sockeye systems in Alaska, we found that the growth and survival of sockeye fry in freshwater lakes are affected by both density dependent and density independent factors, as do the size and age distribution of smolts migrating to ocean. However, significant further research is needed to understand and quantify the processes and mechanisms leading to variable size- and age-structure of sockeye fry and smolts for specific lake systems. However, achieving these is further complicated by the shifting climate regimes (precipitation and temperature) in coastal region. Further complications are be due to introduced species like perch and bass to several of the sockeye lakes in BC, which as juveniles may have significant niche overlaps with sockeye fry as well as stickleback, while as adults they become predators of sockeye fry and stickleback. It would be fundamentally importance to determine how these variable scenarios and the associated processes influence the size- and age-distribution of sockeye fry, their food and feeding habits, niche shifts and their trophic interactions with cohabiting fish and invertebrate predators, and how these affect their growth and survival, out-migrating size and ages of smolt, and their performance during early marine growth. Similarly, the sizes of the juveniles of other Pacific salmon species (e.g., coho and Chinook) at ocean entry also vary greatly between years and among stocks, which may have significant implications for their performance during their early growth in the coastal marine ecosystems. As the juvenile salmon enter the ocean, they share common feeding grounds and niches among themselves and with other forage fish species, my research interest will also be to understand the ontogenetic niche shifts within species, niche overlaps among species, and their implications for ocean growth and survival. In line with my long-term research goals of looking at the patterns of nutrient-foodweb dynamics of aquatic systems, and their links with trophic interactions and growth of juvenile salmon, energy and contaminant transfer along aquatic foodweb, planktonic biodiversity and water quality, I will continue along the same theme during the next 5 years. I propose the following research objectives: 1) test how the variable density of sockeye fry modifies the structure and size-based efficiency of lower trophic levels, growth of sockeye fry and size and age structure of out-migrating smolts; 2) model spatial (littoral versus pelagic) patterns of resource utilization by sockeye fry and niche overlaps or lack there of with cohabiting planktivores under contrasting predator-prey scenarios; 3) test how the introduced predatory fish species shift ontogeny of sockeye fry and associated demography of out-migrating smolts; 4) characterize and model the foodwebs of juvenile sockeye and two other Pacific salmon species (coho and chinook) as a function of size at ocean entry and during early marine growth; and 5) model spatial (onshore vs. offshore) and temporal (inter-annual) variation in trophic position, resource allocation and ontogenetic niche shifts in juvenile Pacific salmon as a function of size. About 6-8 graduate students and 10-12 undergraduate students will be trained through proposed research projects that will generate fundamentally important and new knowledge towards understanding of the processes linked with highly variable performances of juvenile Pacific salmon.