About a year ago I read that there was a fatality rate of up to 30% for released fish. Some of the anti-fishing groups were pushing for folks to stop fishing, by law if they could, based on some of this research. And that got me curious about how one would go about doing a study of that type. I began tracking down as many of these studies as I could, and where possible looking at their study methods.
There wasn't one I could find that didn't have at least one fatal flaw in the study method, and most had more than a few flaws. Here are a few:
1. Not one study was performed on wild fish put back into their habitat by actually following that fish to see what happened to it. There were a couple where fish were tagged and released and then based on other fishermen reporting either catching a tagged fish or seeing a dead tagged fish a statistical analysis was attempted. Without having anything remotely resembling credible evidence they came up with mortality figures.
2. Most of the studies would take hatchery fish and put them in tanks, then stress them by "chasing" them around in the tank. They would compare mortality between the stressed fish and a control group. The dead stressed fish were analyzed for lactic acid. No autopsy was performed on the dead fish to determine cause of death. An assumption is being made that the stressed fish were killed by stress and the control fish died "natural" deaths.
3. A few studies set up tanks next to the fishing water and pumped the habitat water into the tanks, recirculating as necessary to maintain oxygen levels. Fish were caught and put into the tanks and observed. Fish that died were counted as death by exhaustion stress from having been caught.
4. There were some other miscellaneous methods, all of which had less chance of being accurate than the ones above.
The problem with trying to determine mortality of C&R fish is that it's impossible to track a significant number of fish released into their habitat. It's probably impossible to track even one. Putting a radio signal device into a fish would introduce a host of variables that would invalidate the study.
Wild fish are startled by movement above the water. We've all seen this. We appear and they flee. Put a wild fish in a tank and you've just introduced a world of stress on that fish, stress that the studies don't take into account. It's like putting any wild animal into a cage and then standing over it. Wild fish put into tanks, according to one study, begin to form ulcers at a rapid rate, have lowered resistance to infection. Hatchery fish just aren't wild fish and using them is a non-starter. Hatchery fish released into habitat begin to change right away.
The theory that a caught fish will be worn out, will have a high lactic acid (or other chemical response) and will die after being released as a result may sound okay if you say it real fast. But...what other animal dies from getting tired? Humans run marathons and some do die, but the deaths come from an underlying medical condition and not from the lactic acid build up.
Herd animals chased by predators get a ton of stress and get really tired, but if the predator doesn't get them they don't die a few hours later. My lab will run until he drops if you keep throwing sticks, then he rests and resumes. I can't think of one animal that dies from exhaustion unless it's a horse that was rode to death - and that may just be a hollywood myth (I like westerns), I don't know much about horses though. Even then, even then it's not the same situation. Can you fight a fish to death before you get him to you? I don't know, never seen that happen. Mostly they just quit fighting (if you caught them at long distance or in heavy current) and you drag them in, bass are really good at doing that. I have seen tired fish in very warm water that went belly up for a bit before swimming off, so maybe it's possible under the right circumstances.
I just don't believe the theory that a fish will die from the exhaustion of being caught. I do believe that an exhausted fish has a higher percentage of vulnerability to other predators until it has rested. I do know that a deep hooked fish has a high percentage of mortality if the hook is ripped out. I do believe that a deep hooked fish with the hook left in has a higher percentage of mortality than a lip hooked fish. Physical damage to a fish will lower its survivability, but hey, that's just common sense. Fishing is a blood sport, some of them get injured.
I know this for a certain guaranteed fact - every fish not released has a 100% mortality rate. Also from the best I can tell from the literature, studies, and my own experience, a lip hooked fish has at least a 99% survival rate after release. A gut hooked fish with the hook left in has about an 85% survival rate. A gut hooked fish with the hook removed has about a 50% survival rate.
If there's a study out there I haven't read yet that removed all the study flaws, I'd love to read it.
There are of course things we can do to improve the survival rate. Don't fight a fish to total exhaustion if you can help it. Take them out of the water for the minimum possible amount of time, or in other words put them back as soon as possible. I'm often able to leave them in the water and remove the hook without touching them by removing the hook with forceps. Handle them as little as possible, and wet your hands before handling. Don't remove deep hooks, snip the leader. Circle hooks are apparently better than J hooks, but I'm not sure by how much or how that would work with flys.