I have fish areas in the past that are 100% hatchery in origin (net pen fishery). The regs in this area allowed us to keep unclipped fish. Our catch rate of clipped vs unclipped was approx. 90% clipped to 10% unclipped. Of the 10% unclipped every single fish had a metal tag in its head, Yet, not one clipped fish had the tag. Thought that was pretty interesting.

I have heard that one reason for not clipping all hatchery fish was to allow for escapement.