UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Physiological and environmental factors influencing migration survival and behaviour of hatchery Seymour River steelhead smolts (Oncorhynchus mykiss) in coastal British Columbia Healy, Stephen James


For anadromous steelhead smolts (Oncorhynchus mykiss), physiological condition and spatiotemporal variability in movement patterns, such as routes, have the potential to influence survival, but these aspects of the migration are poorly understood. To investigate route-specific movements and survival during outmigration, I implanted acoustic tags into 243 hatchery steelhead smolts and tracked their migration through coastal British Columbia for up to ~400 km. Two release groups (marine and freshwater) were used to assess survival through the first marine inlet. To better understand how smolt condition influences migration fate, I combined acoustic telemetry with non-lethal gill biopsies and used high-throughput quantitative polymerase chain reaction to assess how infectious agents and host gene expression profiles influence smolt migration fate. Poorest survival was in the river and marine inlet first encountered by smolts. Survival rates in all other migratory segments did not differ between release groups, suggesting the near-shore marine environment is associated with particularly poor survival for outmigrant steelhead. I present rare evidence of route-specific survival for a migratory species, which was detected though a series of channels ~200 km from release. The westernmost route here was associated with significantly higher survival and was more travelled. A portion of smolts exhibited ‘milling patterns’ including reversals in migration direction or lateral movements along acoustic subarrays. Redundancy analyses of gene expression, infectious agent loads, and body condition highlighted gene expression profiles indicative of migratory fate. Smolts that were never detected in the river clustered together, far from other groups in ordination space. Smolts that did not make it from the river to the estuary had significantly elevated expression of the immune genes Il-17D and RPL6, and lower expression of the osmoregulatory gene NKA α1b relative to other individuals. Two infectious agents were detected in tagged smolts (Flavobacterium psychrophilum and 'Candidatus Branchiomonas cysticola'), neither of which had an influence on survival. My results identify potentially important, yet understudied regions affecting survival of salmonids smolts. I also demonstrate some of the first evidence of gene expression profiles predicting individual migration fate in juvenile salmonids, and highlight potential mechanisms influencing freshwater and early marine survival for steelhead smolts.

Item Citations and Data


Attribution-NonCommercial-NoDerivatives 4.0 International