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

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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.