There are two really good papers involving hook style mortality if you don't care is it's not fly fishing. The two papers are on Swedish Pike hooks, one by Wisconsin and the other done by I think South Dakota DNRs. The highest survival rate in Pike hooked and released using these hooks was something like 9 or 10%. They kill almost everything they catch. If you go to your local fisheries office you can likely get a copy of the papers. I have a copy of at least one of them somewhere around here, but finding it......
It used as comparison treble hooks and had about the opposite results with almost no mortality.
This also came up here on the forum recently. Some species can be held out of the water for a long time without much ill effect. I mentioned that Gar can be kept out of water for 24 hours or more without harm, as long as they are kept moist. They can breathe air so don't suffer the suffocation most fish do when kept out. Studies done by New York and Ontario show that as little as 30 seconds of air exposure causes delayed mortality of released trout. It has been shown that nearly 40 percent of exhausted trout that were kept out of
water for 30 seconds died. The death rate rises to almost 70 percent if they are kept out of the water for 60 seconds. In Trout, structures in the gills collapse when removed from the water almost completely stopping Oxygen transfer and a build up of CO2 in the fish's blood stream.
Then there are other contributing factors in a fish's survival. Depth it was hooked, where it was hooked, bleeding, how it was held, hook type, net type if any, time it took to land it (lactic acid buildup in the muscles), species, etc.
While I mentioned 'how it was held', I will give you a couple of dont's. Most species do not react well to being held vertically. They should be held parallel to the ground and supported if you take them out of the water. It's better for survival if you don't remove them from the water. I'm not sure if this was ever a common practice there, but here holding fish by the eyes, especially Pike and Musky was common. I still see it being done occasionally. I had an old guy here do it during Spring Pike fishing. I explained how bad it was for the fish after his first, second and third fish. On the fourth one I told him I would grab him by the eyes if he did it again. Then there is the jaw grab you see a lot of. Some guys swing the fish around by the jaw like it a handle on a suitcase. Jaws were not meant for that. You can break it. Treat a jaw like it can break. There are a lot of things you can do that reduce a fishes odds of making it. And as I tell people all the time, just because it swam away, it doesn't mean it survived.
You should take a trip to your local fisheries office to get a better idea of how your local fish species fare in catch and release.