Of the last few hatchery steelies my buddy and I have caught on the N. Fork Stilly, two had healed scars where their dorsal fin should've been. Their dorsals were entirely missing. I've worked in aquaculture and not observed rubbing or nipping to this degree, but it's not unfeasible if one were to cram too many smolts into too little water. Still, I'm more likely to believe the adipose fin-clipping apparatus is to blame...