Studies showed that with the bigger bulls being killed by hunters, much of the breeding was being done by younger bulls, so the DFWP (Dept. of Fish, Wildlife, & Parks) changed some hunting units to be 'spike' bull ONLY for regular hunters, and in those areas you can only kill a larger branch-antlered bull if you are drawn for a permit.

I haven't seen data from any follow-up studies, but the theory is that changing the hunting regulations would allow more bulls to reach maturity and re-introduce more natural selection where the biggest, strongest bulls are doing most of the breeding.

My brother got lucky and drew that limited-entry tag a few years ago and shot a nice bull.