Its not when the fish enter the system, but when they spawn, which is during the fall for spring, summer, and fall varieties. So the springers would have to hang out in the river until then. Given the success that summer-run steelhead have in the sky, I would think, river temperature and flows would be suitable for springers.

However, studies have shown that specific genetic varieties of chinook are found in specific geographical areas; mixing varieties (i.e., wild and hatchery fish spawning together) reduce the fitness of the particular wild stock in the river. This is even moreso a detriment to chinook salmon than for steelhead.

Given we're already dealing with an ESA stock, mixing varieties is not a good idea.