I'm 65 and I've fished lake Michigan since the late 60s and started fishing for salmon in early 70s. I typically put anything over a pound in my box when it comes to Coho. Why, because most of the time there mouth is torn up by the treble hook.
I think most people who have caught these small Coho know if the fish has been hurt bad enough that they wont make it.
I wasn't always this way! In my early days we'd hook these small fish and release them and it wasn't long and a couple seagulls were fighting over it that when I decided it's better to put them in my box. They still are excellent eating, just not much to eat!
I'm definitely not here to give someone a bunch of BS about what they do or don't do but if I'm able to suggest a better way I'll do that depending on the situation.
I will say something about putting perch back. I've caught perch in 65 plus foot of water and put them back and never had an issue. It very visible if there swim bladder has push out their mouth! But this happens when they are pulled to the surface quickly. I've never used anything other than a light to ultra light rod to catch perch. I've had browns and steelhead hit my line and that's a bonus and I've lost them as well but using light tackle I dont normally have the swim bladder pop out but if it does, it goes in my box unless its undersize. I use to put anything that had the swim bladder pop out in my box even if it was under the size limit until I got checked by the DNR and got a warning for keeping under size fish. I was young and thought I was doing the right thing plus I was trying to get my limit so size didn't matter.
The South End provides useful resources and discussion forums for those that fish The South End of Lake Michigan for Salmon, Steelhead, Perch, and Bass as well as elsewhere in the Region and Chicago area.