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UBC Theses and Dissertations

Survival and migration characteristics of juvenile Sockeye salmon (Oncorhynchus nerka) smolts through complex nearshore coastal migration corridors Johnston, Stephen D.


Telemetry tracking of Fraser River Sockeye salmon (Oncorhynchus nerka) smolts from Chilko Lake to the open ocean has revealed relatively high mortality through some coastal areas of British Columbia, and that coastal migratory routes may influence survival. Acoustic arrays were strategically deployed through the Discovery Islands region to track tagged smolts across all possible migratory routes, including three major entrances: Discovery Passage (DP), Sutil Channel (SC), and Desolation Sound (DS). A total of 465 smolts were tagged and released at Chilko Lake in 2017 (n = 315) and in the Northern Strait of Georgia in 2018 (n = 150) using a combination of VEMCO V4, V5 and V7 transmitters. Smolts were observed using all three routes with SC (n = 101), the most central, having the greatest proportion of use, followed by DP (n = 44) and DS (n = 13). Survival of the 2018 smolts was estimated using a Cormack Jolly Seber framework adjusted to account for variable distances of the major migratory routes. Highest survival was in DS (84% /100 km, 95% CI: 46 - 97%), followed by DP (71%, 95% CI: 39 - 90%), and lastly SC (48%, 95% CI: 37 - 60%). Each route presents variable environmental conditions that may influence smolt survival likely through variable exposure to predators. Smolts migrated through DP with mean travel rates of 36 km.d⁻¹ (SE ± 1.8) which was 1.7 times faster than through SC (mean travel rates of 21.5 km.d⁻¹ (SE ± 1.8) and 2.4 times faster than through DS (mean travel rates of 15 km.d⁻¹ (SE ± 2.9 ). Extreme tidal currents present with DP provide rapid transport of smolts through the route, while other routes provide beneficial currents further along their migration path. Survival and travel rates did not appear to be linked as survival was poorest through SC which had the ‘intermediate’ travel rate. This study provides the most detailed picture of behaviour and mortality of Pacific salmon smolt migrations in marine coastal areas to date and highlights the potential of spatiotemporal variability of migration to impact survival in early marine migrations of smolts.

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