The Queets, Hoh, and Sol Duc (and possibly other rivers) have fresh run steelhead in April. Of course there are kelts and actively spawning fish in April as well. Ethical anglers don't target actively spawning fish; they are easy to avoid. Kelts may be found most anywhere in the river, so hooking some is part of the price of admission to fishing. I once caught a wild winter run kelt in the Humptulips in January, so the possibility exists through most of the season.
I hate being regulated out of fishing in April on the Skagit (not on the OP, but bear with me). There are more fresh fish than spawners or kelts, and many seasons I've fished through to April 30th without hooking a single spawner or kelt. Peak spawning is in May, so that helps, unlike the OP where the spawning season looks to be spread out over a longer period of time.
I've read posts claiming that we shouldn't fish for fish making their spawning run. Uh, OK, where do you draw the line? Because the reason steelhead (north of Rogue River, Oregon) enter fresh water rivers is because they are making a spawning run. So maybe no one should ever be allowed to fish for steelhead in rivers? Without going into a philosophical essay on recreational angling, I'll just say that doesn't work for me.
As the collective "we" work to recover wild steelhead, both their run timing and spawn timing will expand, forming a wide bell-shaped curve. If you choose to prohibit fishing when fish are actively spawning, you will have to close seasons before the peak of the run has even occurred. Is that the intent? Not for me. Instead, I prefer that we focus on management for healthy populations and not get ourselves wound around the axle of incidental hooking of kelts and actively spawning fish. I advocate spreading the word that it's unethical to target actively spawning fish; besides it's illegal anyway and has been for as long as I can remember, going back to the 1960s when I first became aware that such a thing as fishing regulations even existed. And incidentally hooking a few kelts isn't going to set back steelhead population recovery. How do I know this? Look at the Skagit for an example.
The Skagit has a good steelhead data set going back to 1978 spawning escapement estimates. Over that time period increasingly restrictive recreational fishing regulations have been imposed. But limited directed harvest of wild steelhead was allowed almost to the end of the 1990s. During the period of record (1978 - today) there is no evidence suggesting that recreational fishing has in any way limited the wild steelhead population run size. All indications point to the extent of the freshwater rearing environment and especially the marine/ocean environment as the factors limiting the adult wild steelhead population size. Recreational angling amounts to statistical background environmental noise, not threat to population health and abundance. Recreational fishing needs to have an eye kept on it, something WDFW has done quite a bit better than most things relating to anadromous fish management that it is responsible for.
Rebuttal enough?