Some of this information is dated so it may not be entirely accurate but I think it's close enough to get the idea across.
The management plan was put together by WDFW, three tribes, and the Skagit River System Cooperative. The tribes were involved because that's what co-management means, and it's the law.

It's been reported that the tribes use most of their impacts during the Spring chinook fishery (June) which results in capturing steelhead kelts. This is not accounted for in a 1 for 1 manner, but something like 6 kelts being equal to 1 impact. Reason being that the fish have spawned already and there is reduced likelyhood that most of them will return again.

In the C&R fishery, impacts are calculated at 10% mortality; 10 released = 1 impact.

So what does it all mean?
Lets run some numbers. In the tiered impacts schedule a forecasted run of 5000 fish would allow for 10% impacts. That's 500 dead fish. The Tribes get half and we get half. So for us we are allowed 250 impacts. At a mortality rate of 10% we would have to release 2500 fish to max out the allowed impacts. It's a 12 week season...that means we would have to C&R 208.33 every single week for 12 weeks running. All this while 25% of the run never swims above the downstream fishing barrier!

If you can find a more conservative plan that still allows fishing for steelhead, I'd like to hear about it.