Rainbow's, oh where do you come from?

Sunday morning was to be an epic Trico experience, air temp was 56, heavy river fog, gradual warm up usually equals a later Trico spinner fall. OK got to the BA at about 8:15 and still cold 62 then with fog blocking the sun, birds working the riffles, everything was looking just right. Started to see a few Trico duns and had an idea that today was to be just wonderful, some small rising fish, OK just a matter of time till it gets going, hold still and wait let the little guys alone, do not disturb the bigger fish. I just stood there taking in the sounds and the changing conditions, OK where are the bigger fish, oh maybe at the lower end of the pool, wade down there and watch- nothing but little guys (I did cast to them and caught them and they were little). Time passed and still no larger fish up, OK it should be going by now, still Trico's in the air but no brown's on top, it got to be 10:30 and nothing showing? Started to see tan caddis so I switched and began to catch a lot of fish- rainbows everywhere, I don't mean a few but a lot, on one inside seam I took 8, now these guys are not big 6-9" in length but healthy! Began fishing all the seams up stream and found larger browns in the shaded areas in water that averaged 12-18" in depth but the rainbows were everywhere. Total count was 37 little guys and 6 browns most all on the tan caddis bubble back. Yes there was a very brief spinner fall where I did cast to and catch more rainbows but the spinner fall was a total bust, can not figure out what was wrong but sometimes that happens and when you are handed apples when looking for oranges you become an apple eater or go hungry! I would love to know it the entire BA was the same or just where I was but I never did see a good number of spinners coming down the stream? I'm happy that we have town very important flies at this time of the year that we can count on if one of them takes a break, no I did not fish any ants or beetles, by 12:00 PM it got smoking hot, 85 and killer sun, too hot to fish!
  OK here's the question that no one seams to know the answer to, where do all the rainbows come from, natural reproduction or PFBC? If the BA or Spring Creek has the capacity of producing that many rainbows the water quality has to be just wonderful? What happens to them as the grow up or do they become food for the very larger browns that are found there, questions that I will ask the PFBC biologist the next time I see him at a Spring Creek TU project. Anyone have an idea what is going on there?