Habitat effects on stream productive capacity, energy flow, and adaptive tradeoffs among juvenile salmonids

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The ability of fish to successfully exploit stream habitats depends on physical habitat structure, prey production, and the abundance of predators and competitors. These features form the adaptive landscape for drift-feeding fish like salmon and trout, while simultaneously constraining energy transfer to the fish trophic level. Along with water chemistry and temperature, physical habitat structure (e.g. channel form, velocity, substrate) remains the most fundamental determinant of stream productive capacity, and understanding physical constraints on fish production is key to predicting the effects of habitat change on fish populations. The objectives of this proposal are i) to develop a general process model relating production of invertebrate drift and juvenile drift-feeding salmonids (i.e. Pacific salmon and trout) to stream habitat structure and discharge, as a quantitative framework for modeling habitat and flow effects on juvenile salmonid production in streams; ii) to experimentally determine the adaptive tradeoffs differentiating juvenile salmonids at different taxonomic levels, with a particular emphasis on understanding the role of growth differentiation; and iii) to evaluate whether latitudinal constraints on herbivorous fish distribution affect energy flow and production of other functional feeding groups of fish, particularly drift-feeding fish (e.g., juvenile salmonids). This research will provide i) a novel synthesis of habitat effects on production and modeling of invertebrate drift and juvenile salmonid carrying capacity; ii) significant advances in instream flow science, both in terms of model development, validation, and identification of empirical flow thresholds; iii) improved understanding of the physiological basis of adaptive tradeoffs that allow habitat partitioning and co-existence along environmental gradients; and iv) an assessment of the generality, underlying causation, and consequences of large-scale latitudinal clines in stream (herbivore) trophic structure. These represent important contributions to fundamental issues in stream, organismal, and community ecology, and will provide direct application to improving management of endangered fish species, instream flows, and habitat restoration in Canada, with potential impacts ranging from local (endangered species) to global (improved instream flow modeling techniques).