Stock-specific marine distribution patterns of juvenile Chinook Salmon reveal a gradient of migratory strategies during their first year at sea

Knowing where and when juvenile Pacific Salmon use marine habitats is key to better understanding survival after ocean entry, particularly given stock-specific migration routes and behaviour. Using geostatistical models, we combined catch and genetic stock composition data from 30 years of surveys in British Columbia and southeastern Alaska waters to quantify the juvenile marine distributions of 11 Chinook Salmon Oncorhynchus tshawytscha stock groupings. We found strong evidence of diverse migration strategies of juvenile Chinook Salmon during their first year at sea, ranging from nearshore resident to fast migrating individuals. There was also variability in both timing and migration routes within some stock groupings, suggesting migratory behaviour also varies at finer ecological scales. These findings highlight that juvenile Chinook Salmon from separate populations interact with disparate environmental conditions and ecological communities, which in turn can drive divergent patterns in juvenile survival. Our approach can be adapted to elucidate fine-scale patterns of habitat use, which can be useful for identifying the mechanistic drivers of survival variability and adapting habitat-based management interventions for at-risk stocks.