Migration ecology of juvenile Pacific salmon smolts : the role of fish condition and behaviour across landscapes

Migrations are utilized across taxa to exploit spatiotemporal variability across landscapes. The benefits of migrations are balanced with costs, and understanding the factors that limit migratory success is needed for proper management and conservation. Sockeye salmon (Oncorhynchus nerka) are of economic, cultural, and ecological importance and undergo downstream migrations from natal freshwater systems through rivers to the ocean as juvenile smolts. In this thesis, I describe a series of studies investigating the migration behaviour and survival of sockeye smolts emigrating from Chilko Lake, British Columbia, a large population that experiences poor survival in the Chilko River. First, field sampling and bioenergetics models were used to find that short-term feeding on smolts by bull trout (Salvelinus confluentus) in the Chilko River was extreme, not limited by cold temperatures, and resulted in greater exploitation of smolts than expected using traditional bioenergetic assumptions. Examining bull trout stomach contents revealed that consumed smolts had higher rates of infection by hematopoietic necrosis virus and Flavobacterium psychrophilum and were smaller than non-predated smolts. Through acoustic telemetry, I found that smolts traversing the upper Chilko River with higher densities of conspecifics experienced improved survival relative to smolts travelling at times when few smolts were migrating. Thus swamping predators can maximize survival. It is more difficult to conduct field studies in the coastal marine environment such as the Strait of Georgia, and even knowledge on migration routes and behaviour is limited. Aggregating telemetry data collected over ~10 years of research on sockeye and steelhead (Oncorhynchus mykiss) populations determined that contingents of both species exhibited westward lateral movements within the strait, consistent with predicted currents. Steelhead using the eastern migratory route experienced improved survival through the Strait to a location ~250 km further along the migratory corridor - a rare example of migration route impacting fitness. Individually, chapters advanced the fields of migration and feeding ecology and tested long-held ecological hypotheses. Important links were identified between smolt migration behaviour and/or survival and components of the movement ecology framework. This thesis has expanded our understanding of the factors influencing the migration of one of the largest sockeye populations in Canada.Forestry, Faculty ofGraduat