I went to Deadwood 6 times last year. The most I ever bagged was 23 kokanee. The fish seemed a lot larger this past year and after my experience fishing there after the spawn, I have an idea. My last trip, after the spawn, I couldn't catch a kokanee larger than 8-10 inches. This kind of leads me to believe that I was catching 1 year old kokanee.
Where did the 2 year old kokes go? If you all recall, the Pioneer Fire ripped through that area late 2017. Back in 2012, the mustang fire burned above Anderson Ranch and fish and game estimated that they had an 80% loss of kokanee population due to pH level changing from ash and fire retardant washing down stream to Anderson. Could the Pioneer Fire have wiped out close to a year's spawn from the tributaries getting too hot or pH changes?
As I said before, the size of the kokanee from this past summer were much larger than previous years. If 1 year's spawn didn't make it, that would have reduced the population and the competition for food explaining the size difference.
I'm planning on hitting Deadwood this coming summer just to see the size of the fish. Might not be a good koke year this year, but if I'm right, the 2020 matured adults will again be large.