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

太平洋鲑鱼，被认为是具有重大经济、社会和文化效益的哨兵物种。具体而言，在理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差距。从我过去对阿拉斯加红眼鱼系统的研究中，我们发现淡水湖泊中红眼鱼的生长和存活既受密度相关因素的影响，也受密度非密度因素的影响，迁徙到海洋中的红眼鱼的大小和年龄分布也是如此。然而，需要进行更深入的研究，以了解和量化导致特定湖泊系统红鱼鱼苗和黑潮鱼苗的大小和年龄结构不同的过程和机制。然而，沿海地区气候制度(降水和温度)的变化使实现这些目标变得更加复杂。更复杂的情况是因为在公元前的几个红眼湖引入了像鲈鱼和鲈鱼这样的物种，在幼年时期，它们可能与红眼鱼和刺鱼有显著的生态位重叠，而成年后，它们成为红眼鱼和刺鱼的捕食者。至关重要的是要确定这些不同的情景和相关过程如何影响红眼鱼鱼苗的大小和年龄分布、它们的食物和摄食习性、生态位变化及其与同居鱼类和无脊椎动物捕食者的营养相互作用，以及这些因素如何影响它们的生长和生存、向外迁徙的大小和年龄，以及它们在早期海洋生长期间的表现。同样，其他太平洋鲑鱼鱼种(如Coho和Chinook)在进入海洋时的幼体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。随着幼鲑鱼进入海洋，它们彼此之间以及与其他饲料鱼物种共享共同的觅食场所和生态位，我的研究兴趣也将是了解物种内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。根据我的长期研究目标，即观察水生系统的营养-食物网动态模式，以及它们与幼鲑鱼的营养相互作用和生长、沿水生食物网的能量和污染物转移、浮游生物多样性和水质的联系，我将在未来5年继续沿着同一主题进行研究。我提出了以下研究目标：1)测试可变密度如何改变低营养级的结构和基于大小的效率、红鱼鱼苗的生长以及迁出的黑鼬的大小和年龄结构；2)模拟红鱼鱼苗资源利用的空间模式(沿海和远洋)，以及在对比捕食-被捕食情景下与共生浮游动物的生态位重叠或缺失；3)测试引入的捕食性鱼类物种如何改变红鱼鱼苗的个体发育和相关的迁出黑鼬的人口学特征；4)描述和模拟太平洋鲑鱼幼鱼和其他两个太平洋鲑鱼品种(Coho和chinook)的食物网，作为进入海洋时和早期海洋生长期间大小的函数；以及5)模拟太平洋鲑鱼幼鱼营养位置、资源分配和个体发育生态位转移随大小的空间(陆上与近海)和时间(年际)变化。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，这些项目将产生基本的重要和新的知识，以了解与太平洋鲑鱼幼鱼高度可变的性能有关的过程。

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.