Looks like some folks have doing some thinking- Very Good!!
Rich G -
The huge "excessive numbers" of fish in populations is the Mother Nature's safety net so that they can survive the worst of times (low point of survival cycle) or colonize new habitats (example would be the opening of rivers as the glaciers receded). If your concern is that we need all the populations productive to survive the worst of times then we should never place any mortality on the them. However if survival trends can be monitored I don't see why most populations can't support some mortality when survival is in the up portion the cycle. How much mortality could depend on how good your information is and how risk avoidance one wants.
Is 20 years enough? I doubt we will ever understand these complex systems prefectly (actually I hope we never do as part of the mystic of steelhead is the unknown) however 20 years is better than 10 and 50 will be better. Somehow I doubt that folks would be willing to wait 50 or 100 years w/o fishing just so the managers have better info upon which to make decisions.
My real concern is that at least in Puget Sound rivers management options such as hatchery only seasons and no targeting of wild stocks (no CnR) doesn't seem to be "protecting" the fish. In the early 1980s when under-escaped rivers where managed with wild steelhead release and early closures the populations repsonded immedialely; escaped doubled. In the last 4 years on the same rivers with management under wild steelehad release and no CnR our escapements have fallen by more than 50% from when some harvest was allowed!
Like the way you have approached this problem. You clearly would be setting up a system that recognizes the impacts that catch and release has on a population. In a post last spring (Feb/March?) I suggested some guidelines for steelhead managment. It that I suggested a 1 wild fish a year limit where the fish could be taken from a river that had been met criteria that indicate a "healthy" population however I had an additional kicker that if I wished to fish those various spring CnR seasons the angler had to have an used "wild fish tag" - the angler had to choose whether use their impact by "bonk" their one fish or with hooking mortality during CnR. Those interested in such ideas may wish to visit that old disussion.
Actually Boater's 1/10 comparison may be right on the money. Bob Hooten, fisheries biologist from BC who was the source of the 3 to 5%, has recent put forth a paper recapping hooking mortality information and fishing impact concerns recommends that because of the way that 3-5% information was collected and the differences between having highly skilled and caring anglers verus the average angler CnR fish that the 3-5% hooking mortality be doubled.
If one wishes to error on the side of the resource then it would seem that assessing a CnR hooking mortality of 10% would be appropriate.