Pacific salmon and the ecological importance of variability in their flowing stream environments : the influence of hydraulics on individual behaviour and hydrology on population dynamics

Lotic organisms experience and have adapted to a high degree of spatio-temporal variability in their flowing environments. Streams play a key role in the lifecycle of Pacific salmon (genus Oncorhynchus), a group of species of high ecological, cultural, and economic importance. Conservation of salmon habitat in streams often centers on the management and restoration of physical components, such as geomorphic features and instream flows. Recent technological developments and years of government-led monitoring programs have equipped us with the tools and knowledge to further our understanding of the relationship between salmon and their flowing environments. In this thesis, I investigate the importance of variability in stream environments through the lens of both ecohydraulics and ecohydrology. In Chapter 2 (ecohydraulics), I used an observational field-study to demonstrate the importance of fine-scale turbulence and velocity gradients in mediating microhabitat selection by drift-foraging juvenile steelhead, challenging the averaged metrics traditionally used to describe and quantify fish habitat. In Chapter 3 (ecohydrology), I compiled a database of historical records of stream discharge and salmon production across British Columbia, Washington State, and Oregon, in order to explore key drivers in the relationship between interannual variation in flow conditions and juvenile salmon production across broader spatio-temporal scales in the region. Together, both chapters highlight the ecological importance of variability in the flowing environment for Pacific salmon across spatio-temporal scales, highlighting potential mechanisms driving this relationship in both the context of individual behaviour and population dynamics. Such information is especially important given that climate change is causing shifts in the global hydrological cycle, potentially impacting Pacific salmon populations. By exploring this topic through different lenses, this document provides useful insights in the integration of scientific disciplines which allows us to move towards more system-based approaches in resource management and species conservation.Science, Faculty ofOceans and Fisheries, Institute for theGraduat