Ben questions - I am always curious about how many adults are left from each year class to return to their stocking location. Between smolt mortality, predation and being caught and kept for a couple of years what percentage of stocked fish are left to return?
Good question. It's hard to say exactly, because we can't really measure it the way you've phrased it. We essentially can measure *relative* survival - comparing what proportion of the catch in open waters came from what stocking tag lot, for example. The units would be say number of fish caught per 100,000 stocked. But that doesn't measure how many adults existed but weren't caught. Which, you might imagine could vary quite a bit from year to year based on any number of factors such as fishing effort, movement patterns, survival rates of year classes, catchability of the fish themselves (if there's a ton of bait, in general harder to catch fish, whereas less bait - hungry fish and your lure might stand out more), and other factors.
We can also measure the number of fish "returning to creel" via our surveys, but that doesn't account for fish that did return and weren't caught, or fish that survived to adulthood but did not return for whatever reason - maybe the water was too hot, maybe they strayed into another system, tried to spawn in the harbor instead of going up into the stream, etc. Catchability of returning adult fish can vary tremendously based on water temps, how fast they get upstream, how much angling pressure there is, how long they remain in areas vulnerable to anglers, and so forth.
As a general rule of thumb though, we see returns to creel between 0% and 5% for most trout and salmon. Lower end of that for coho and kings, higher end for steelhead.
I would say if you really wanted to put a very general number to it, 3% of kings might survive until adulthood. And it varies from year to year, and regionally through the lake. So I wouldn't be very confident in that number.