You are referring to the practice of the PFBC publishing the number of approximate fish that each stream got, right? I remember this well and used to find it a fascinating bit of info. This was long before I cared about trout, wild trout, their habitats, etc but Kish Creek reportedly used to get close to 10,000 fish. I would say that streams that are still stocked have declined by at least 20%. There are obviously many small streams that only saw minimal stockings that are no longer stocked, too.
The slow decline in stocking is a blessing.