Migration can result in considerable exposure to both natural and anthropogenic stressors that can impact the ability of an anadromous fish to complete this critical component of their life-history. In this thesis I use a range of physiological and behavioural measures to evaluate natural and anthropogenic factors influencing the migration of wild adult migrating steelhead in the Bulkley River, British Columbia, including pathogens and fisheries captures. Steelhead appeared to be relatively resilient to pathogens and capture within fisheries, though I observed changes to their physiology, behaviour, and survival in relation to these stressors. A key finding throughout this thesis work was the influence that water temperature had on steelhead physiology and behaviour, suggesting steelhead may be vulnerable to increases in water temperature with climate change. This work provided novel insight on the pathogens influencing wild steelhead and has provided mortality estimates that fisheries managers can incorporate into their management models.