While there is no empirical indication that CNR steelhead seasons in WA (which is virtually all wild steelhead in WA) is reducing the productivity of any steelhead population, it surprises me that conservationists who are also anglers embrace such extreme restriction of angling. Of course, if conservation is the only objective, then closing all the water all the time to all the fishing will achieve that. However, that isn't conservation so much as it's altruism. And that's not a bad thing; just not my thing.
I don't support petitions of this sort. Mainly because the evidence isn't presented. There is a whole world of sub-lethal effects that might be negative. But we can't or haven't measured them. I don't agree that the "cautionary principle" means we should simply not fish because we might have a negative impact. Fishing does have a negative impact. I can't prove it, but I'm fairly certain that the fish don't approve of it. I'm more interested in preventing the negative impacts that include killing so many fish that the spawning population is reduced such that the carrying capacity of the habitat cannot be used.