Winter survival of stream salmonid fishes and implications for population dynamics

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Winter is perceived as a critical period of survival for freshwater fishes in north temperate latitudes. Relatively little work has focused on direct estimates of survival and especially the influence on recruitment and fish population dynamics. To estimate winter survival, three graduate projects are planned. First, I address the question "Is egg survival a function of winter severity?" In various New Brunswick streams, wild egg/alevin survival will be determined in response to physico-chemical disturbance (ice, dissolved oxygen concentration) of the incubation environment (redd). To answer the question "Is winter a population survival bottleneck?" the focus of the second project will be on wild juvenile Atlantic salmon (parr). Based on successful modifications for tracking small fishes using passive integrated transponder (PIT) technology, the specific objective will be to distinguish between winter mortality and emigration of parr by tracking PIT-tagged parr in large river reaches throughout winter and spring and in response to disturbance events like freeze-up and flooding. These results will form the basis for modeling inter-stage survival and the relative importance of environmental and biological factors for driving salmon population dynamics. Climate change scenarios for Atlantic Canada predict increased winter precipitation, and a higher probability of mid-winter break-up events. Such changes may affect parr survival. However, no experimental studies have investigated the relationship between winter discharge events and body condition (and survival) of salmon parr. This is the focus of the third project. Using outdoor tanks and simulated 'flood' events over winter, the condition, energy content, ability to complete smoltification, and survival of three age-classes of immature and mature parr will be determined. The proposed research has a strong conservation focus and attempts to identify the effect of natural environmental stressors (ice, variable flows) especially as these stressors may be exacerbated by climate change scenarios (e.g., mid-winter break-ups). Results should improve understanding of the relationships between environmental factors and biota, and our ability to protect populations at risk.