Evaluation of Growth, Survival, and Recruitment of Chinook Salmon in Southeast Alaska Rivers

Recent declines in the spawning runs of Chinook Salmon Oncorhynchus tshawytscha have caused social and economic hardships throughout Alaska. Previous research suggests that salmon abundance is mediated by size-dependent mortality, with the time period during freshwater and early marine residence being critical for influencing survival patterns and, ultimately, recruitment to the spawning stock. Therefore, growth is thought to be a crucial determinant of recruitment. However, the relative importance of freshwater versus marine growth in determining recruitment success remains uncertain. We conducted a scale-based retrospective analysis of the effects of freshwater and marine growth on survival to the age of reproduction for female Chinook Salmon by brood year in the Taku and Unuk rivers (southeastern Alaska). In both rivers, Chinook Salmon marine survival was significantly and positively related to growth during the first year at sea. Our results also indicate that Chinook Salmon smolts from both systems may experience size-selective mortality soon after entering the marine environment. These evaluations will allow for a more complete understanding of the factors that influence Chinook Salmon returns and inform the development of more accurate and reliable forecasts for making management decisions on Chinook Salmon stock status and escapement goals in southeastern Alaska rivers.