Migration patterns and energetics of adult chinook salmon Oncorhynchus tshawystcha in Alaska rivers

Abstract

Adult Chinook Salmon Oncorhynchus tshawytscha undertake extensive and energetically costly migrations between food resources in the ocean and their freshwater spawning habitats, requiring them to adapt behavioral and physiological traits that allow them to successfully reach their spawning streams and reproduce. Such adaptations may be shaped by physical factors in the environment and individual- and population-specific biological characteristics. Chinook Salmon in North America are important resources for both United States and Canadian stakeholders, but relatively little is known about their freshwater migration patterns and energetic status in many rivers across their range. This research explored variation in migration timing and migration rates of Chinook Salmon in two Southeast Alaska transboundary rivers (Taku River, Stikine River), examined energetic status at multiple sampling locations in Alaska, and created and tested a predictive model for energetic status using bioelectrical impedance analysis (BIA). Migration timing was earlier for fish that spawned in more distant tributaries in both transboundary systems and the Taku River was earlier compared to the Stikine River. Migration rates decreased during periods of high flows, were slower for fish in the Taku River, and were slower in both systems in 2016 compared to 2015. Migration rates were faster for fish with spawning sites farther upstream when compared to those that spawned closer to the river mouth, but these rates decreased over time as fish swam farther upriver. Chinook Salmon (N = 129) sampled for energetic status at the beginning of their freshwater spawning migration had higher total percent lipid than those near the spawning grounds (ANOVA: F = 202.1, df = 3, P < 0.001), and total percent lipid and water were precisely predicted based on BIA measurements (R² = 0.82, RMSE = 5.33; R² = 0.78, RMSE = 2.43 respectively). The BIA model was tested to determine if it could be generalized between similar species, but this was found to be less precise than species-specific models. The BIA measurement technique was also easily implemented into an existing study on a remote Chinook Salmon population. Given threats from climate change and mining activities, this information will be useful for fisheries researchers as a benchmark for understanding migration behaviors in these Chinook Salmon populations, and indicates that integration of BIA into population monitoring may be a useful tool for creating management practices targeted at facilitating successful migration behaviors and increasing or maintaining energetic status for these fish.