Early Marine Ecology of Juvenile Chinook Salmon

Under this project, salmon sampling within the lower Yukon River was designed to replicate and expand on the work of Martin et al. (1987). Salmon were sampled in 2014 and 2015 from all three of the lower Yukon River tributaries using a surface trawl net. Sampling began shortly after ice-out in May and continued until the end of July, and stations were sampled three times per week. Additionally, salmon were sampled along the delta front in June, July and August of 2014 and 2015 using surface- and mid-water trawls. Sampling locations were selected to maximize spatial coverage around the delta, allow sampling across the freshwater/marine transition of the Yukon River plume, and to maintain project cost. Captured fish were identified to species, and a minimum of 30 fish (distributary) and 50 fish (front) of each species were measured. Chinook, coho, and chum salmon specimens were preserved for laboratory analysis. Genetic samples were collected from Chinook and coho salmon. Fish that could not be identified to species in the field were photographed, vouchered, and returned to the laboratory for identification. In the laboratory, each salmon was weighed and sagittal otoliths and stomach contents collected for analysis. A total of 381 juvenile Chinook salmon were analyzed for energy content: 155 distributary and 7 front for 2014 and 204 distributary and 15 front for 2015. A total of 949 juvenile Chinook salmon were evaluated for stomach fullness; 337 tributary and 17 front specimens from 2014, and 555 and 40 from 2015. Diet analyses were also conducted on a total of 388 juvenile coho salmon.

This research will update juvenile life-history data on the timing and size of marine entry under current climate conditions. This research will augment existing data on the marine ecology of juvenile Chinook salmon in the northern Bering Sea by providing seasonal distribution, size, and condition information prior to their capture in eastern Bering shelf (BASIS) surveys. This research investigates a period in the life of juvenile Yukon Chinook salmon that is expected to be highly influential to cohort return strength.