Route-specific movements and survival during early marine migration of hatchery steelhead Oncorhynchus mykiss smolts in coastal British Columbia

摘要

For migratory species, spatiotemporal variability in movement patterns, such as routes, has the potential to influence survival, but this aspect of movement ecology is poorly understood. For anadromous steelhead Oncorhynchus mykiss smolts, little is known about important migratory corridors used during early marine migration. To investigate route-specific movements and survival during outmigration, we implanted acoustic tags into 243 hatchery steelhead smolts, released them at 2 different points along their migration route, and tracked their migration through coastal British Columbia for up to similar to 400 km. Poorest survival was in the river and the marine inlet first encountered by smolts. Releasing smolts beyond this inlet increased survival to the first marine subarray by more than 2-fold relative to fish released in freshwater. Total survival to the final subarray was 9.1% and 27.3% for river-and marine-release fish, respectively. Survival rates in all other migratory segments were similar between release groups, suggesting that the near-shore environment after ocean entry is a region of particularly low survival for outmigrant steelhead. Route-specific survival was detected through a series of channels similar to 200 km from release, with the westernmost route being associated with significantly higher survival for smolts. This westernmost passage was also more travelled, with 77% of smolts using this route. Migration rates were higher and more variable through these islands, potentially due to tidal-driven currents in this region. Approximately 11% of tagged smolts exhibited ` milling patterns', including reversals in migration direction or lateral movements along subarrays. Our results demonstrate rare evidence of route-specific survival of a migrant organism and identify potentially important, yet understudied corridors for juvenile salmonids along the British Columbian coast.