A good starter are the hatchery information pages (state, federal or other). If you look at what fish they raise and then figure what months those fish typically return (i.e. Aug - Oct for Fall Chinook, Dec - Feb for Winter Steelhead, etc.), then cross reference that with a map of the hatchery so you can trace the rivers back out to the ocean, you'll have a pretty good idea. Regs for different bodies of water give you a good idea too (sometimes).