The adipose fin on a steelhead is not the only thing that determines whether it came from a hatchery or not. Every steelhead has scales, and scales from a hatchery fish are markedly different from scales on a wild fish because of their radically early life history and growth rates. Pretty sure WDFW is reading scales to determine wild steelhead return rates, if for no other reason than any effort to do 100% of anything 100% of the time is physically impossible and doomed to failure, marking steelhead smolts included. So I would say they probably know what the wild steelhead return is in those rivers.

Salmo said it once for you guys, they can't allow unrestricted harvest of hatchery steelhead in the upper Columbia because even the hatchery fish are endangered up there, due to the extremely sorry state of the habitat from damming, diverting, denuding, and destroying the landscape (maybe that's why it's called the 4d rule ). So they leave a significant amount unmarked to ensure that enough hatchery and wild fish show up to keep things going, they close the rivers that have perennially poor returns because they need all the fish for hatchery and wild broodstock, and they hope for the day when things change, like perhaps when the dams exceed their engineered life and will cost so many billions to replace that it will never get done, and they will either be taken out or fall down, or perhaps when enough political will is generated to change the way we treat the landscape for the betterment of the fish. Like that's ever going to happen - I'll bet on the dams falling down first