Chinook come in two flavors... stream type and ocean type.
Ocean type refers to expeditious migration to the ocean at just a few months post-emergence from the gravel.... in other words sub-yearling smolts.
Stream type spend at least a year in freshwater before dawning their silver coats for their outmigration to the big blue pond.
Not all fall chinook smolt-up as sub-yearlings. I was told by one of the OR policy dudes that URB's smolt both ways.
FishDoc has the best answer to eddie's question. In general, fall Chinook are ocean type, in which the juveniles migrate as sub-yearlings. The adults are usually mainstem spawners (e.g., Hanford Reach). The juveniles leave the redds in early to late spring. When the water starts to warm up in early to mid summer, they leave for the estuary or the open ocean.
But it's not a "hard and fast rule". Some fall Chinook, especially on the Snake River hold over for a year before migrating to the salt. But the water has to be cool enough in the mainstem for this to happen. If it gets too warm (e.g., the summer of 2015), they're cooked. Salmon can't survive long in 70F water, and they're dead at 75F.
So the ocean-type life history pattern is a response to increasing water temperature. Which, in light of climate change, means that our salmon resources in the future are likely to favor the ocean type life history pattern.
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