Freshwater Life History, Habitat, and the Production of Chinook Salmon from the Upper Yukon Basin
Michael J. Bradford, Alan von Finster, and Patrick A. Milligan
Abstract.—Potential yield and escapement goals for salmon populations are often determined with stock-recruit relations, but for many Chinook salmon Oncorhynchus tshawytscha populations, this information is lacking or is uninformative. One alternative is a habitat-based approach, but the complex early life history of Chinook salmon presents challenges to biologists and managers wishing to use this method. Published fry and smolt data from other populations is summarizd, which show that habitat limitation in the freshwater rearing stage is common and may limit production. The freshwater life history of Chinook salmon from the Canadian portion of the Yukon basin is then reviewed to evaluate the potential link between habitat, migration and density-dependent mortality that leads to population regulation. There is a significant downstream redistribution of age-0 fish from spawning areas in June and July that results in juveniles being distributed throughout a variety of habitats, at great distances from natal streams. DNA analysis of the population of origin of migrants showed significant inter-populational variation in dispersal behaviour. Spatially extensive sampling is required to determine the full range of juvenile habitat for the Canadian populations, and to quantify relations between the number of parent spawners and juvenile abundance and distribution. This fuller understanding is needed to determine if freshwater rearing habitat limits the productivity of this population complex.