There are many layers to it. The fish stocks enter at different times. To make numbers up for purely discussion purposes, steelhead tagged in the Fall could be primarily summers bound for Idaho and the upper river. A different group of summers from those that enter in May and June. If they ran the net later in the Fall, when chum are the target, you would probably be in winters, none of which would go above McNary.

They have, or should have, a pretty good idea of which stocks would be encounters at any given time. It is likely, too, that an experienced person can identify stock (summer/winter, spring fall, tule/bright) and age only the stocks of interest.