Carrying capacity is not exactly fixed. First two years we trapped smolts on a creek we got 800 and 1200. BOTH were capacity as in the first brood year they only spawned about 2/3 of the anadromous zone.

Basically, the stream can produce as many smolts as it can overwinter. The better the habitat, the more smolts. For steelhead, the higher the productivity the younger the smolts. And younger smolts are more productive per unit area.

WDG made an estimate of steelhead capacity and WDF made a similar one for coho. Both were based on habitat. While it is easy to poke holes in what they did, the concept is sound and simply needs more data to fine-tune.

At the end of the day, there is a capacity but it changes annually depending on flows and area seeded. The idea that if we hit some magic number of spawners, or egg take, or release will give us an annually consistent fishery is simply foolish. There are too many variables beyond the freshwater that we don't know and that change almost faster than we can react.

Which is why terminal fisheries directed at maturing adults is the only way to consistently optimize escapement. Assuming you do in-season management and don't use auto-pilot.