Juvenile Chinook salmon early ecology, prey and condition on the Yukon Delta, AK

Juvenile Chinook salmon on the Yukon River undertake one of the longest fish migrations in the world, travelling over 3000 kilometers from spawning grounds in Canada to the marine waters of the Bering Sea. Evidence suggests that much of the variability in Yukon River Chinook salmon production occurs prior to the end of the first summer at sea, either during freshwater rearing, downstream migration, or entry into the marine environment. Prey availability and prey quality are important factors in juvenile Chinook salmon growth and condition. This research investigated spatial and temporal patterns in prey consumption and availability on the Yukon River Delta. Results suggest that while there are limited spatial differences in availability, prey varies seasonally and juvenile Chinook exhibit prey selectivity. Comparisons of the results of this study with data from prior sampling years indicates that juvenile Chinook salmon in 2016 had lower stomach fullness and lower energy density than Chinook from prior years. Additional years of prey sampling is needed to identify factors that affect prey availability.

The general patterns investigated in this research provide insight into factors that may affect juvenile Chinook salmon growth and condition prior to their first marine summer. However, additional tools are needed to tease out factors contributing to variation in diets and energetic content. This survey samples several migrating populations of Chinook, some of which have travelled up to 3,000 km and some that originated from tributaries in the Lower Yukon. It is reasonable to expect that there may be differences in growth and condition based on distance traveled and habitats encountered. New tools, such as advanced genomic methods or otolith chemistry, need to be evaluated for their potential to identify groups or clusters within the outmigration that can provide insight into factors affecting juvenile Chinook salmon health.